Hsg28 - Safety Advice for Bulk Chlorine Installations

© Crown copyright material is produced with the permission of the Controller of HMSO and Queen's Printer for Scotland.

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Safety advice

for bulk chlorine installations HSG28(rev) HSE BOOKS

© Crown copyright 1999 Applications for reproduction shouldhe madein writing to: Copyright Unit, Her Majesty 's Stationery Office. St Clenienis House, 2-16 Colegate, Norwich NR3 JBQ First published1987 Second edition 1999 ISBN 0717616452 rights reserved. No part ofthis publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means All

(electronic, mechanical, photocopying. recording

or otherwise) without the prior written permission

ofthe copyright owner.

This guidance is issued by the Health and Safety Executive (HSE). Following the guidance is not compulsory and you are free to takeother action. But ifyou do follow the guidance you will normally be doing enough to comply with the law. HSE Inspectors seek to secure compliancewiththe law and may referto this guidance as illustrating good practice.

Safetyadvice for bulkchlorineinstallations

Foreword vii Introduction

I

Managementofhealth and safety and risk assessment Risk assessment 5

3

Design and location ofinstallations 7 Potential incidents 7 Siting ofinstallations 8 Unloading area 10 Design cincl locatin /0 Delii'crie.c ofliquidc'hlori ie hi' road tankeror ISO tank container interlocks 3 Delii'eric',', ofliquidchlorine hi' rail tanker /4

/

/2

Connections between thetankerand the fixedlinesto the storage installation Ti'pes (?t c'0n1icC'tiofl 15 Flexiblec'ouplingv (seoii—rigid loading arms) 15

14

Flexiblehoses /6 Articulated arms /6 Pipework for liquid chlorine 17 Permanentpipeworkat the iozloaclingpoint /7 Designcriteria for pipework transferring liquidchlorineto storage tanks' or from storagetopoint of use 7 Protectionofpipeu'or/c 19

/

Marking 20 Protection ofliquidchlorine pipework againstoverpressure 20 Proi'ision ofrelief si'stems' 20 Valves 22 T'pe.v of ia/ic 22 Vertical globe vali'es 23 Conicalplug vali'e,r (PTFE-s'leeved) 23 Ball i'alve.s 24 Remote/i controlled vcili'es' 24 Storage vessels 24 Design criteria 26 Connecting pipc'work cmii ,necmn,s' for isolation of storage tc,nk.s' 27 Liquid chlorineinlet 25 Liquid chlorineoutlc'i 25

Safety advice forbulkchlorineinstallations

III

tent ciiicl comprc'sseddirgas hues

30

Relic! svsteni 30

andchlorinedetectorsystems30 Chlorine detectorsand alarms 32 Protection ofstorage vessels against ovcrpressure 33 Reliefsystem 33 B,,rstint' discs 34 Arrcoigcmentsfoi' ic//cf systems 34 Expansion vessels 37 Pressurealcirnis 37 Arrangements for unloading ofliquidchlorine from road tankers to storage 38 lJnloaclmg usingdcv conipressecic/jr Oc/ct' nitrogen 38 Suppli ofcirt'pcidcliog gas to ti/c system 39 lJn/oad/iog usingchlorinegas pm ssure 39 Useofre—compressed chlorinevapour 39 Chlorine \'aporisers40 Instro,neotation

T'pes 40 Regulcilion of throughput 41 Methods ofheating 41 Generalinstallation 42 HaarcIs 42 Routineand emergency isolcition 45 Pressure control vc,hi'e 46 Corrosion 46 Chlorine absorptionsystem 47 tent collectwn system 47 1bsorptionequipoient 48 Jnstrionentcution 48 Disposalofeffluentfroumu ti/c chlorine absorptionplant 49 Operating and maintenanceprocedures, trainingand PPE 51 Operating instructions5 1 Maintenance, inspection and installation 52 Generalouainteoance rec/uirements52 Mc,intencunceofconnections 52 Insjcc'tion coid conioussioniog ofchlorine tank installations 53 inspection procea'ioe 54 Testing 55 Modification ofthechlorinesystem and clearance procedures 55 Unloading ofliquidchlorinefromroadtankers to storage 56 Use of ISO (demountable) tank containers 57 Transferofchlorine to the consuming units 58 Trcmnsfcrofgcmseouschlorine 58 Trcmnsfer of liquidchlorine using vapourpressure 59 Transfer ofhcjiocl chlorine hrpadding with dry conipressech gas 59 Transferofh/c/u/cl chlorine using asepclrate pionping tcmnk 59 Precceutions 59

iv

Safety advice forbulkchlorineinstallations

Training 61

Competence (10(1(Ilk/it 62 Personal Protective Equipment (PPE) 62 Seleciinç' sintallc respiratort'protectiveequipment(RPE) 63

Emergencyarrangements 67 Emergency equipment 68 Control of leakages 68 Releases insideliuildins 69 Appendices 71 I Toxicologicalproperties and first aid 71 2 Characteristics ofchlorine 73 3 Relevantlegislationand HSE guidance 79

4 Useful

contacts and standards 91

5 Outside installations and inside installations 95 6 Procedures for discharging road tankers of chlorine 99 7 Types of vaporiser 103 8 Emergency plans 107 References 111

List ofacronyms and abbresiations

119

Safety advice forbulkchlorineinstallations

V

I ::ulIulllutuIIi!::

7'

T

he aim ofthis gLildance note is to help those responsible for ihe safe ue ol chlorinehum bulk containers to meet their oliligatlons under health and salely law.

itli

This guidance. like the document that preceded it. was prepared the help of the chlorine producers, users, trade unions, the WaterServices Association (WSA), and the Chemical Industries Association (CIA). We are grateful to those whocontributedfor their assistanceand co—operation in preparing this advice, and to Shaw Valvesand to Descote Ltd for permission to usethe photographs linked to paragraph 74, to Weston Point Studios for permission to use the photographs linkedto paragraph 216 and to Zeneca plc for pernhission to takethe remainingphotographs. The guidelines maybe appliedto any bulk chlorineinstallationbut they are not intended to be a detailed design code. Sonic existinginstallations maynot at present meetall the recommendations and, in sonic cases, not all the recommendations may be appropriate. It is for the occupier, usually in consultation with the chlorine supplierand/orspecialistadvisers, to judge the need for further risk control measures,following an assessment ofthe actual risks. If improvements are shown to be needed, a responsible decisionis required from the operating company on the nature and timing of changes sothat they can be made safely. Where reference to British. European and otherstandards is made in this document equivalent standardsare equally acceptable alternatives.

You mayneed helpbeyondthat given in this guidance.

If

you do, trade and employer associations, such as the Chemical Industries Association and Euro Chlor, or your chlorine suppliercan offera range ofadvice and support. These and othersources of informationare

given in Appendix 4.

Safety advice forbulkchlorineinstallations

Vii

This publicationgies guidance on the sal handlingorhtlll\ liquid chlorineat chlorineby road or rail tanker,or by I tank container. The guidance is aimedprimarily at managersofthese installations, but it is also relevant for plant supervisors, design and maintenance engineers, and safty professionals. Application of the guidance ill help to ensure that the risksto people on—site and off—site are niimisedso far asis reasonably practicable. I

()

Sites which recei C liquid

The risks arise because chloriiie is a highlytoxiC (see Appendix I ) and reactie substance (see Appendix2). It forms flammable and explosixe niixtures

2

ithsonic organicandinorganicsubstances.Whenreleasedfroni coiltainmentit gas cloud that is hea\ icr thanair and hich maintains contact withthe ground as it disperses, possihl endangering people in its path.

\

l'orms a

Despite theserioustoxic and reacti'e ha,ards, and the potential to harm people oft—site,the chlorme industry has established a ver' good safty record. This has been achieved through the (Ie elopment and practice of eliective procedures for handling chlorine sa Fely. This gL!idance, likethe document it replaces. is issued to help maintain and enhance that record. Guidance on thesafi handling ofchlorine supplied m drums and Iinders is given else here. 3

c

The guidanceis based on the conibmed experience of'the Ibur 1 K manuftcturersof'chlorine, their customers, trade Unions and associations and HSF. It co ers the safity and health requirements at all stages. from the receipt of'the liqLiid chlorine to the point of use, including the location, design. testing. operation and maintenance of'equipment. Procedures for dealing ith eniei'gencies are also 4

outlined.

Safety advice forbulk chlorine installations

1

I

Employers havea legal responsibility under Sections 2 and 3 ofthe Health and Safety at Work etc Act 1974 (HSW Act)2 to ensure, so )aras is reasonably practicable. the health and safety oftheir employees and others who may be affected by their activities. Other people. such as designers, installers and suppliers, also havesimilardutiesunderthe HSW Act with respect to products. Since 1 974various regulations have been maderequiring specific controls for particular hazards leg pressure systems), oractivities(eg manual handling). A list ofthese and other current health and safety legislation, codes ofpractice and guidance is published annually.3 This list also covers amendments to the regulations. References in this docunient are to the base regulations. Appendix 3 gives au overview of the main legislation and regulations relating tothe safe handling ofchlorine. 5

You must obtain planning permission for new installations in the usualway from the 6 Local Planning Authority, who will,when appropriate, referto HSEfor advice. If you store, or plan to store. morethan 10 tonnesol chlorine. your site will be subject to a numberof specific regulations. 7 The Notification of Installations Handling Hazardous Substances Regulations l982 require you to notify your activity to HSE ifmore than 10 tonnesofchlorine is liable to be must alsonotify subsequent changesto your activity. New installations over 10 kept. tonnes chlorine capacity, or proposals to increase the notified capacityto morethan three times the original capacity, must be notified threemonths in advance. Theform ofthe notification is in the Regulations.

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The Control of Industrial MajorAccident Hazards Regulations 1984 (CIMAH )5 also apply to sites storing or processing chlorine. These regulations apply at two levels. The lower level requirements apply to sites which store 10 or more tonnes. They also apply at sites where chlorine is involved in a process in any quantity. unless the process operation is incapable ofproducing a major accident hazard. You needto comply withtwo general requirements: 8

(a)

to demonstrate to HSE, at any time, that major accidenthazardshave been identified and adequately controlled; and

(h)

to reportany majoraccidents to 1-ISE.

Safety advice forbulk chlorineinstallations

3

For sites which store 75 or more tonnes,or which process chlorine and haveinventories of 25 ormore tonnes, unless the process operation is incapable of producing a major accident hazard, niore stringent regulations apply. These require the preparation of a safety report. the preparation of oil—site and off—site emergency plans and the provision of information to members ofthe public likely tobe affected by a major accident. CIMAH will be replaced in February 1999 by the Control of MajorAccident Hazard Regulations (COMAH) which implement the requirenients oftile Seveso II Directive6 on the control ofmajoraccident hazards tile thresilold for the lowertier requirements is 10 tonnes, and 25 tonnes for the top tier. 9 The Planning(hazardous Substances) Regulations I992 apply to sites with 10 or more tonnesofchlorine. lJnderthese regulations tile consent'of the local Hazardous Substances Authority (I-ISA) is needed for the presence ofclllorine in sucil quantities. The HSA must consult HSE on the associated risk levels. To quantify the off-site risks HSE mayrequest technical intornlation about the installation.8 10 In addition, any process wilicil involves the manufacture or useofclllorine or any process wilicil is likely to result in the release ofclllorinc into tile air or water, is a prescribed process undertile Environmental Protection (Prescribed Processes and Substances) Regulations l99i. Otiler processes arealso prescribed in tile Regulations. Undertile Environmental Protection Act 1990 no person shall carry on a prescribed except underan autllorisatioil granted by the enforcingautllontyand in accordance witil the conditions in the authorisation. Applications for the authorisation ofa prescribed process in England and Wales must be made to the Environment Agency ([A) and in Scotland to tile Seottisll Environnlental Protection Agency (SEPA). In addition in Scotland wilere tile Alkali and Works Regulation Act 1906,11 as anlended by tile Health and Safety (Emissions into Atmosphere) Regulations 1983,12 is still in force, suell processes are listed as Scheduled works and must be registered amuiaiiy witll SEPA.

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II If you fill containers from your bulk installation and transport themoff—site.you will needto comply with the Carriage of Dangerous Goods(Classification. Packaging and Labelling) and Use ofTransportable Pressure Receptacles Regulations 1996,13 aild the Carriage of Dangerous Goods By Road Regulations 199614 (in the case of transportatioll by road). The relevant legislation is outhned in an NSF booklet.15 Note: The (legal) ternl for gas cylinders is now transportahlepressure receptacles'. 12 Although you must comply with health and safety legislation, regulatorycontrol cannot compensate for deficiencies inthe way that safetyis nlanaged. Effective health and safety managenlent is mainlyabout management (at all levels)taking a proacti\e approach to minimise the chance of incidents occurringratilertllan putting tilings right after they havegonewrong . Guidance on effective healtil and safety management is given eisewllere' 7 which advocates and elaborates Oil tile following general principles of good nlailagelllentpractice:

4

(a)

set your policy and demonstrate commitment to it;

(b)

organise and train your staff to ensure effective communications, co—operation, and their competence to control risks;

Safetyadvice for bulk chlorineinstallations

(c)

plan what you need to do, set perfomianccstandards, and establish systems and procedures for controlling risks;

(d)

measure your performance to assess whetherthe risks are being adequately controlled;

(e)

conductsafetyaudits to ensure that yoursystemsare working as intended; review your findings and take any corrective action.

A risk assessment isessentialto this proactive approach to safetymanagement and is a statutory requirement ofthe Management ofHealth and Safety at Work (MHSW) Regulations 1992.18 Guidance on these Regulations and risk assessment is contained in an Approved Code ofPractice.19

RISKASSESSMENT The M1-ISW Regulations require you to conducta full risk assessment to identify all the hazards and assess the associated risks. Therisk assessment needsto include all sources ofhazards, including thoseassociated with transportaroundthe site, accessto plant and security. The needfor risk assessment is also a requirement ofother regulations (eg The Control ofSubstances Hazardous to Health Reulations 1994 (COSHH)20 and the Fire Precautions (Workplace) Regulations 1997.2! 13

14

In outline, a risk assessment for your chlorine operations requires you to:

(a)

look for the hazards ic potential sources ofchlorine releases;

(b)

decidehow serious each ofthese loss-of-containment events could be, ie who could be hannedand how seriously;

(c)

decidethe likelyfrequency ofeach ofthese hazardous events;

(d)

evaluatethe associated risksand consider whetherthe precautionsto prevent releasesofchlorine and to mitigate theireffectsare adequate, or ifmore shouldbe done (this guidance and the sources ofadvice listedin Appendix 4 is relevant here; particularly the publications ofEuro Chlor;22

(e)

recordyour significant findings; this is a statutory requirement ifyou have five or more employees; and

(f)

updateyour risk assessment at least every threeyears.and before making significantmodifications. Check that your operational experience accords with any significant assumptions you madeto carry out your risk assessment. Safetyaudits, as well as day-to-day management arrangements. should address the need to check assumptions.

Safety advice for bulkchlorineinstallations

5

15 Each site will have its own special featuresand you need to takethese into account when conducting your risk assessment. A properrisk assessment will helpyou to:

(a)

decidewhetherthe risks are being controlled so far as is reasonably practicable; and, if not,to:

(b)

establish adequate controls and safeworkingprocedures based on the advice in this note.

16 Your risk assessment will needto consider the mainpotential causes ofreleasesof chlorine. For bulk chlorine installations these are (see paragraph 20):

(a)

plant damage causedby external sources (vehicles, hoists,flying debris from nearby accidents, fires etc);

(b)

incorrect operation; and

(c)

inadequate inspection and maintenance.

17 The people conducting your risk assessment must have relevant experience and knowledge. Ifnecessary, you niust18 seek assistance from experienced and knowledgeable people. Your chlorine supplier will be able to identify competent people able to conductthe risk assessment on your belialiland supplyinformation to help youcarry out your risk assessment and to manage safety. 18 The remaining sectionsofthis booklet provideguidance on the arrangements for prevention and mitigation ofchlorine leaks and spillages through good design,operation (including emergency procedures) and maintenance. The guidanceappliesonly to installations storing liquid chlorine underpressure in bulktanks or tank containers. You should therefore pay particularattention to the requirements ofthe Pressure System and Transportable Gas Container Regulations 1989 (PSTGC).23 Precautions for the storage ofliquid chlorine in refrigerated tanksat low pressure are outside the scopeofthis guidance. Additional sources of advice and information are listed in Appendix 4.

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Safety advice for bulk chlorineinstallations

19 Bulk chlorine installations operate under pressure. Consequently, the design, installationand operation (includingperiodicexaminationand maintenance) of these pressuresystemswill need to meetthe requirements of PSTGC.23 Pipework, equipmentand protective devices for liquid chlorine are part ofthe system. The regulations do not apply to systems operating at or below pressures of 0.5 bar gauge, except for steam systems. Guidance on PSTGC is contained in an Approved CodeofPractice24 and the publication A guide to the Pressure Systems and Transportable Gas Containers Regulations I 989;25 see Appendix3 for brief

details.

POTENTIALINCIDENTS 20 When designing or modifying your installation,you should include provisions to prevent the following potentialincidents whichcould result in a release of chlorine: (a)

Damage to chlorine linesfrom external sources eg by hoists or vehicles while it is toor from the the road tanker unloadingpoint. including moving When the tanker is positioned for unloadingyou need to provideadequate clearance for the valve dome when it is open. You also need to make allowancefor movement ofthe delivery vehicleduring thc transferoperation, eg the normal upwardmovementofthe tankeron its suspension can cause damage thereis inadequate flexibility in the connection, or movement caused by inadequate brakingor wheel chockingor careless operation by the driver.

if

(b)

Damage to the liquid chlorinedelivery vehicle,storage tank or connecting pipeworkcausedby impact from other vehicles.

(c)

Joint and gasket failures due to failure to tighten joints, over-tightening of joints, incorrectly fitted or the use ofunsuitablejoint rings, or the use of hydrocarbon based lubricants which mayburn whenattacked by chlorine(see Appendix2).

Safety advice for bulk chlorine installations

7

(d)

ElTors in operating procedures, including over-filling ofthe storage tank and

(e)

Plant and equipment failure due to inadequate maintenance. eg 'passing' valves, or leaks causedby corrosion or erosion, or use ofplant and equipment beyond the recommended

overloading ofthe vent scrubber, failure to closevalveswhenremovingcontainers, or breaking into the system for maintenance.

Iife.

(f

Damage caused by fire or explosion.

SITING OF INSTALLATIONS The guidance in this section relates to general features which affectthe location of the installation. More specific factors arc reviewed in the detailedsections dealingwith offloading (see paragraphs 134-147) and eniergency procedures (seeparagraphs 247-263). When deciding the location of your installation an important consideration is the potential risksto people and the environment. Theserisks decrease as the separation distance increases. The site of such separation distances will depend upon a nuniberoffactors, including: 21

(a)

the numberand size ofstorage tanks:

(b)

whetherthe storage is indoors oroutside

(c)

the operational conditions and the type of process:

(d)

the frequency ofchlorine deliveries;

(e)

the design ofthe installation, eg length and diameter ofliquid and vapour lines; and

(f)

the size,distribution, and type (eg sensitive groups) ofthe surrounding population.

You should carefullyconsider these factors whendesigning and deciding the location of installation and when conducting your risk assessment (seeparagraphs 13-17). You your should involve your chlorine supplierat an earlystage. Consideration should be given to maximising the distance between the site boundary and the chlorine installation. It should be emphasised that your risk assessment and individual circumstances (see paragraph 21) will determine the separation distances. The same considerations alsoapplywhen making significant changes to an existinginstallation within a site. 22

When choosing the location for your chlorine area,you needto consider the location of other on—sitebuildings in relation tothe prevailing wind direction. It is recommended that the chlorine area should be located downwind ofbuildings thatare regularly occupied. Ventilation intakes to occupied rooms should be at least25 m from the chlorine installation, and preferably at a high level. 23

24 You alsoneed to take account ofthe prevailing wind direction whendecidingthe locations ofemergency assembly points. Two assembly points are recommended; these should be located so that at least one will be available regardless ofthewind direction when a release occurs. For complex sites, indoor assembly points are recommended; open air assemblypoints may be suitable for simple sites.

8

Safety advice for bulk chlorine installations

For a new installation, full account will have tobe takenofany requirements attached to the planning permission granted by the Planning Authority. In addition the local Planning Authority needsto ensure that theoverall planwill avoid problems arising in thefuture from developments leading to a high density of population near the installation, or from the introduction of other potential hazards in an adiacent area (see Appendix 3: Planning (Hazardous Substances) Regulations 1992). For sites which maypresent such hazards HSF. may recommend that the highest standards are applied, before consent can be granted by the HSA. In some casesthe consideration of'off-siterisk levels by HSE may requirc control measures in addition to those recommended in this guidance. 25

For existinginstallations, control of neighbouring population densities is not possible in the shortterm. However, proposed developments nearbywhich would increase the number of peopleare controllable and would he permitted by the local Planning Authority only after detailed consideration. Suchconsideration will include the advice received from HSEon the risks from chlorine releasesto those who mayoccupy or use the proposed development. 26

27 The location ofa new chlorine installation within a site shouldbe decided following a risk assessment. In making your decisionyou should takeinto account possible damage from flooding or subsidence, and the possible damage to the installation if neighbouring plant or factories suffer a catastrophe by fireor explosion. Installations shouldbe sited at a sufficient distance (25 iii minimum) from public roads or main railway lines to reduce the riskof damage to the installation ifthere is an accident. Protective haiTiersshouldbe installed where necessary. In all cases, suitable fences, together with adequatesecurity supervision, should he provided to minimise the possibility of unauthorised access. 28

29 Hazards arismg from aircraft maynormally he regarded as minimal with probabilities below the level ofsignificance required for any special consideration. Flowever.attention may be necessary in exceptional circumstances, eg ifthe installation is at the end ofan airport runway or close to a busy airfield. In such circumstances liaisonwith the airfield operatoron suitable risk reduction measures is essential. 30 The installation is preferably located in the open air:but undersome circumstances an indoor installation maybe appropriate. In decidingthis, it is important that a risk assessment is made, taking into accountthe factors listed in Appendix 5. Youneed to consider the following possible risk reduction measures at an earlystage: (a)

the scopefor reducing the chlorine inventory, eg rescheduling of deIiveries

(b)

interlocking arrangements (see alsoparagraphs 35, 39-41) for the automatic isolation ofleaks and to prevent the delivery vehicle moving during transfer operations:

Safety advice forbulkchlorineinstallations

9

(c)

minimising the length and diameter ofpipework carrying liquid chlorine and ensuring overpressure protection;

(d)

mechanically ventilating chlorine buildings and discharge through a fume scrubbing system; the associated air inlet ductsshouldbe at a low level;

(e)

improving the leak-tightness ofany chlorine building against major leaks; and

(f')

restricting transfersofchlorine to daylight hours or normal working hours (8.00am to 5.0() pm) as the weatherconditions are likely to be more favourable for the dilution of chlorine concentrations ifthere is a release.

UNLOADiNGAREA Design and location

Youshouldaim to minimise the possibility ofchlorine escape during the transferof liquid chlorine from the delivery vehicles to the storage tank. Detailed attention to the siting, design and layout ofthe unloadingequipment and operating procedureis essential. 31

32 The unloading area should be on reasonably level ground with adequate surrounding space providing goodaccess from different directions. The location should minimise the risk ofimpact damage from vehicles, mobileequipment or fallingobjects from lifting equipment. 33 The unloading point shouldbe reasonably close tothe storage installation. To avoid impact damage a protective barrierbetween the tankerbay and the storage installation is recommended. The unloading point shouldalso be sitedat a safedistance from drains, rivers, drainage collection points and any plantor equipment which might give rise to fire or explosion. 34 Satisfactory accessshouldbe provided tothe permanent pipework for dischargeofthe chlorine tankers and to ensure that connections tothe tankers can be madesafely. Wherethis involves working from a place abovegroundlevel,a permanentstructure should be provided. This should be designed so that, in case ofemergency, escape is possible with minimum risk. You canachievethis by installing a substantial and non-flammable (eg steel) structure and ensuringthat platforms are free ofobstructions and have non-slip surfaces, adequate toeboards and guard-rails. Alternative escapeways shouldbe providedwith stairways ofstandard slope. Vertical ladders or steep stairways should be avoided. If vertical ladders are unavoidable, ensure that safety hoops, etc. do not impede access for peoplewearingbreathing apparatus. The design ofmoveable platforms givingaccesstothe top ofthe tankers needsto minimise the possibility ofaccidents due to collision with thetankers. Interlock systemsmay be used for this purpose, see paragraphs 39-41.

10 Safety advice for bulkchlorineinstallations

A welldesigned unloading area

35 You needto provide for the safe isolation ofany leaks that may arise, particularly from pipework carrying liquid chlorine, It is recommended that remotely or automatically controlled valves should be installed on thetransfer line to the storage tanks. When automatic isolation is employed, operated by chlorine sensors in the unloading area, the detector systemneeds to closeboththe storage tank isolation valveand that on the tanker. The possibility ofliquid chlorine being trapped between closed valvesand the needfor pressure relief (seeparagraphs 6167) needs to be considered, 36

It is also goodpracticeto provide:

(a)

protection against theweatheron fixed gantriesat unloading points, eg by windbreaks or overhead canopies;

(b)

storage space for connectors used for transferoperations so that they can be kept dry and protected from dirtand moisture gettingin, and possible impact damage;

(c)

storage space for emergency equipment (eg filter respirators, breathing apparatus, protective clothing and spareequipment) in a safe location so that theequipmentis readily available in an emergency;

(d)

adequatelighting and emergency lighting covering the unloading area, and all escape routes;

(e)

sufficient manuallyoperatedalarmstationsto enable warning to be given in the eventofa chlorine escape. Furtherdetails on emergency procedures are given in paragraphs 247-263.

Safety advice for bulkchlorineinstallations

11

Deliveriesofliquid chlorine by road tankeror ISO tank container The Carriage ofDangerous Goods(CDG)by Road Regulations 199614 and the CDG (DriverTraining) Regulations 199626apply. For safetyreasons all UK road tankers are fitted with air-operated shut-offvalves for the paddingair (see paragraphs 134-141) and the chlorine delivery connections. Itis also strongly recommended that the following meansof minimising potential risksare adoptedwhereverpossible: 37

(a)

Provision of a separate and protected unloading areafor the sole use of chlorine tankers (eg by erecting sideprotection ofthe motorway-type crash barrier).

(b)

Restriction by suitable means of the speedoftraffic on adjacent roads.

(c)

Unauthorised access ofvehicles and personnel tothe unloading area shoLild be prevented, egby placing warning barriers, notices, moveable barriersor road cones, or closing gates when the chlorine tankers are in position.

(d)

Provision ofan interlock (see paragraphs 39-41)systemto preventcoupling of liquid chlorine lines to the tankers and openingofthe dischargevalveuntil the tanker is immobilised. In addition, the air-operated tankervalves should be interlocked withthe chlorinedetectionand shut-downsystem, orbe remotelyoperable from the emergencystop points.

(e)

A systemofwork wherebyone person (the driverfor road deliveries) is present throughout the unloading (seeparagraphs 214-215, and Appendix 6), and a second is present during connection and disconnection. The second person shouldbe nearbyand available throughout unloading to providehelp on request.

(f)

Routing ofchlorine pipework in thearea to minimise the risk ofdamage from impact by thetanker,other vehicles or mobileequipment.

r

12 Safety advice for bulk chlorine installations

38

Where a separate unloading area cannot be provided, and the unloading point

is on a factory through road, such roads should be physically closed (seeparagraph 37c) to other traffic duringthe transferofliquid chlorine. Yourrisk assessment will determine whetheradditional measures are needed. Interlocks

39 Interlocks should be used to prevent seriousincidents. For example, interlocks can be used to ensure that the vehicle brakes are fully applied befoi-e the unloading pipe is finally connected Ll and the tanker valve opened or, a barrieron the unloading platform can be interlocked to the loading connector, so preventing inadvertent movement ofa tanker still connected up. Alternatively the pressurein the unloading pipecan activate a flashing sign to remind the driverthat the tankeris —--- still connected (the latter system may be appropriate at a producerplantor a consumer plant with a large throughput).

The manoeuvring necessary to locate a road tankerprecisely in relation to a solid pipeconnector may make it more difficult to devise an interlock to the highest standard ofsecurity. In such cases, an illterlock to prevent access ofother tankers is strongly recommended, and specialattention musthe paid to the 40

The airsupplyto the iruek's h,ukesIllS to be dth oune(tc'd he/ire 1/u'tnstume,,( 00 (,uehs/ 100/X'IY11I the IaO/u'i pa(kIu0' Wt00(1(h/allot' discharge ;'a1re) i(iit hi-

system ofwork which effectively prevents accidental movement ofthe tanker, and to drivertraining. Alternatively movement detectors ofthe light beam and reflector typecan be Ll5ed and interlocked to close the isolation valvesand soundtheaudiblealarm.

Interlocks may he used to prevent somereleases due to operator error.For example to ensure that liquid chlorine is not transfi'rred to the ventabsorber, in addition to a procedure (step 9 of Appendix 6) 41

Safety advice for bulkchlorineinstallations 13

requiring the closure ofthe manual vent valve on the liquid chlorine delivery line before starting thetanker discharge procedure, the vent valve shouldbe interlocked with the delivery point or thetanker off-loading valve.

Deliveriesofliquidchlorine by rail tanker 42 The Carriage of Dangerous Goods by Rail Regulations 199627apply. it is strongly recommended that you adopt the following nieans ofminimising potential risks. Your risk assessment will determine whetheradditional measuresare needed. (a)

Closethe sidings to other traffic duringtransferofchlorine from tankers to storage. by locking the points. Alternatively, friction buffers or a de-railermay be used.

(h)

Control by suitable means the volume and speedofadjacent traffic.

(c)

Close warning barriersand/orplace warning notices when the chlorine tankers are in position.

(d)

Provide an interlock (see paragraphs 39-41) systemto prevent coupling or uncoupling of the liquid chlorine lines, unless barriers or warning notices are in position. it is recommended thatthe interlock system extendsto ensure that appropriate points on the rail sidings arc locked and wheelstops raised before transfer of liquid chlorine can start.

(e)

Establish a system of work whereby one person is responsible for the whole operation of unloading, and a second is within call during connection and disconnection. The second person should be in the area and available throughout unloading. Route chlorine pipelines in the area to minimisethe risk ofdamagefrom collision by thetanker, other vehicles or mobileequipment.

Owingto the very limited use of rail transport. the rest ofthis guidance focuses on chlorine delivery by road tanker. When rail transportis used, the sanie generalprinciples forthe safe handling of bulk deliveries ofchlorine apply. CONNECTIONSBETWEENTHE TANKERAND THEFIXED LINES TO THESTORAGE INSTALLATION(see also paragraphs 134 -147) Flexiblecouplings to thetanker forhquul chiorineondpadding

the.swo'elJolt?! (toil iur.\otiee •

the Jti1ngloaded pipeirork uvpeo ton forthepwklingcar •

li,

((lid liquid (JiloflOc

To transferliquid chlorine to storage, it is necessary to couplethe liquid chlorine outlet line on the tankerto the inlet line to storage. It is alsonecessary to increase thetanker pressure by about I .7. bar abovethat in the storage tank by connecting a . supplyof dry compressed air, nitrogen or chlorine vapourto the tanker. The associated pipework (seeparagraphs 53-79)should be as simple as possible to minimise the risk ofpotential loss-of43

containment accidents.

14 Safety advice for bulk chlorine installations

44 Connections For the transferofliquid chlorine require very careful consideration, as theyare a potential source ofloss—of—containmentleading to a releaseofchlorine to the environment. Failure ofthe unloading connections can result From inadequate design, poor weather protection, incorrect materials of' construction, inadequate pipework support, improper use, or inadequate inspection and maintenance. Therefrire. you need to ensure that the design standards are adequate. that testing and inspection procedures are regularly carriedout andthat the equipment is satisfactorilymaintained. Types of connection 45

Three types of'connection are available:

(a)

Flexible couplings (sometimes called semi—rigid loading arnis)have:

(if

a solid connection pipe with swivel joints to flicilitate connectionto the tanker and

(ii)

a degree offlexibility built into the supports and hangerto allow movement when coupledup, ie a crankedfree length ofpipe or a coiled pipe.

(b)

Flexible hoses.

(e)

Articulated arms.

Flexible couplings are normally used,but flexible hoses or articulated arms may be used by agreement with, or recommendation of. the chlorine supplier.

Flexiblecouplings (semi-rigid loadingarnis) 46 Flexible couplings arc normally constructed from steel pipe. However, Hastelloy C (not B) pipe is recommended up to the firstisolation valve. This offers greater life in situationswhere the pipe is repeatedly exposed to very small amounts of atmospheric moisture by the connection/disconnection process. Flexibility is provided by a crankedfree length ofpipe(less usually by a coil) to allow for vertical movement of thetanker during discharge. Screwed connections are used for the connections to the road tanker screwed connections to BS2128 are commonly used at eitherend of the flexible coupling. 'Swivel' joints in the paddinggas line and the liquid chlorine line facilitate connection to the tanker. These joints are tightened oncethe connections are made. Flanged connections are used fi)r connecting to rail tankers. Piping local to the tankerberth should not hefixed forthe first 5-7 m but it needsto be supported. Thesystemofsupport used should ensure that the pipework is keptabovethe headroom required by the tankerwhen it is being put in position. The support should alsoallowthe pipework sufficient vertical movement to accommodate that in the delivery vehicle's suspension system during the unloading operation typically about 150 mm. A minimum internal pipediameterof 25 mm is 47

—

recommended.

Safety advice forbulkchlorineinstallations 15

48 The desitzn criteria for flexible couplingsconstructedfrom pipeworkare similarto those for fixed pipework (see paragraphs 56—60). Where the connections arc screwed connections, the gasket should he a trapped joint ring, which is renewed at every connection (see also paragraph 215). Flexible hoses The designofflexible Iioses2' should he agreed with your chlorine supplier. They require more frequent testing than flexible couplings and their life is shorter,but position rig of tankers is easier. FlexibleMonel braided hose connections are normally constructed up to 50 mm (2 in) size for the liquid chlorine discharge, and 25 mm (1 in) size for the compressed gas connection to the tanker.

49

50 The operating instructions coveringunloadingshould ensure that visual inspection and leak testing of theflexible hoses iscarried out before commenciilgtransferof liquid chlorine (see also pL1i'agi'ipl1 2 I5).

Articulatedarms Articulated arms, with swivelledjoints (knuckles). are Lisually used on high volume installations. They should be designed to meetthe requirements specified in the Euro C'hlor publication (lEST 75/44 and certilied as nleetmg this or an equivalent standard. They shouldbe operated and niaintained as advised by the manulicturer. Arms shouldbe visually inspected for dellcts and tested tor gas tightnessevery time they are Lised. Suspect arms shouldbe immediately withdrawn from service fOr maintenance. 51

52

Where the seals at knuckle joints are purgedby a flovv of dry (dew point less than —40°C) air or nitrogen. this gas should he continuously sampled by a chlorine detectorsystem with an alarm. An isolation valve suitable for use with articulated arms should be attached to the dischargeend of thearm to prczei1t air entering the arm after operation. It should: (a)

ensure a gas tight seal when the arm is not in use to prevent moisture getting in an end cap shouldalso be used and

(b)

permit the venting down of'the arm and depressurisation of'any connection adapter. The arm should he ventedafter each operatioil and purged with a suitable dry gas.

—

Whenan arm is oLit of service the purge gas shoLild be maintained under a small pressure (eg 0.5 bar gauge).

t

You need to keep a register showing each operation and the quailtity (eg tonnes) of chlorine trans rred

16

Safety advice for bulkchlorineinstallations

PIPEWORKFOR LiQUID CHLORINE In designing your pipework you shouldtake stepsto guardagainstthe following caises offailure: 53

(a)

impact:

(ii)

heatino.

(c)

severe internal

(d)

overpressure(see paragraphs 61—67); and

(c)

erosion due to relatively high liquid velocities and inadequate inspection and maintenance procedures. Liquid velocities less than 2 m's are recommended.

cc fire (resulting in a reaction between (lie steel and chlorine): or external corrosion;

54 Routing ofpipcvork fir liquid chlorine should normally heabove ground and should he sLich as to maximise protection from mechanical damage,corrosion and fire. A minimum internal diameter of 25 mm (I in) is recommended to ensure adequate mechanical strength.

Permanentpipework at the unloadingpoint 55

The permanent pipework at the unloading point usually consists ofthe

lollowing lines: (a)

pipework fi)r pressurisiigthe tanker with dry air, nitrogen or chlorine (see alsoparagraph 1 34—I47);

(h)

pipework for the transferofliquid chlorine to storage; and

(c)

instrument air lines. eg to operate the remotelycontrol lcd valves pipework on the tanker.

br

The source ofcompressed 'padding' air needs to be independent from that supplying other services. Detailed design reqLnrementsfor the pipework and fittings aredescribedin paragraphs 56—79. The system for off—loading ofliquid chlorine is described in paragraphs 134-147. Design criteriaforpipeworktransferringliquid chlorine to storage tanks or from storage topointofuse

Your pipework will be part ofa pressure system and subject to (lie requirements of the PSTGC RegLilations.232 It therefore needs tobe properly designed. fabricated, inspected and tested in accordance with a recognised Code, eg ANSI/ASME B3 1.332, and shouldhe sufficiently robust for all friresecable conditions of work. 56

Safety advice forbulk chlorine installations 17

(a)

Design pressure. Should not be less than 12 bar gauge (174 psig).corresponding to a design temperature of+45 O( Any part ofthe system which may operateat a higher temperature shouldbe designed to withstand the corresponding vapourpressure (see Appendix 2. Figure A2.l).

(b)

Design temperature. Should be lessthan the minimum at which the pipe is intended to operate. or the temperature to which it will be cooled Lf liquid chlorine boils offat atmospheric pressure (—35°C). Thenormal designrangeis —35°C to +45°C. In certain uncommon situations lowertemperatures are possible due to chlorine cooling below its boilingpoint,eg when purging systems with dry gas — locations where liquid chlorine has collected maycool to temperatures as low -50°C due to evaporative cooling. Your chlorine supplier should be able to provide advice on the needto design for such low tei1peratures.

(c)

Materials of construction. Care is needed in selecting suitable materials (see Appendix 2). Seamless carbonsteel tubing is recommended thr pipework. All components ofpipes,valvesand fittings shouldbe resistant tothe action ofchlorine between the extremes ofoperating temperatures and pressures.. Original material certificates shouldbe kept throughout the plant's life.

(d)

Corrosion allowance. 1 mm.

(e)

Radius of curvature ofany formed bends. Three pipe diameters minimum (weldelbows must be used where tighterbends are necessary). Elbows, tees and reducing pieces should be forged or hot-formed without reduction in wall thickness.

(f)

Bolting. Should be designed to the requirements ofBS 4S82.

(g)

Flanges. The numberofflanges shouldbe limited as far as possible and thoseused or shouldbe to the requirements of a recognised design codeeg BS ASME/ANSI Bl65.36 Steel used for fabrication of flanges or welded connections to the pipe must be compatible with that ofthe pipe itself.

(h)

Gaskets. Theuse ofincoiTectmaterials for gasketscan be dangerous; if in doubtyou shouldseek the advice ofyour chlorine supplier. Rubber gaskets should never be used for liquidchlorine service. All packings. gaskets and diaphragms shouldbe resistant to the action of chlorine between theextremesofoperating temperatures and pressures. Proven materials such as spiral wound Monel, Kel-F or Aramid fibreare suitable. Compressed asbestosfibre(CAF) gaskets to BS I grade A or 0, preferably graphite-treated on each face to facilitate dismantling, are suitable forjoints that are expectedto remain in service for several years without being disturbed. Any used asbestoscomponents shouldbe collected and disposed ofsafely. Where joints are made and remaderelatively frequently CAF is not recommended for environmental reasons. Alternative jointing material such as ararnid fibre shouldbe used. Polytetrafluoroethylene (PTFE) to BS 656438 grade CA I/I may be suitable provided thejoint is ofan encapsulated type (eg a spigotted joint) to preventthe PTFE 'creeping'. Some users havefound lead tobe suitable on smalldiameterpipework (less than 25 mm). Where a varietyofgasketmaterials arc used joints should be tabbed for easy identification.

l560

832,

18 Safety advice forbulk chlorine installations

(i)

Manufacturers' instructions needto be strictlyadheredto. Avoid overtightening fittings asthis can result in leaks due to the subsequent failure of the fixing nuts or packing.

(j)

Lubrication. Normally in assembling pipe flanges, boltsand gaskets, no lubricants are required. Where lubrication is needed, onlyfully inert oils and greases recommended for chlorine duty shouldbe used. On no account must hydrocarbon-based lubricants be used as they react with chlorine and may ignite. The heat generated may be sufficient to cause a chlorine-iron fire (see Appendix 2) which\vould result in a pipework failure and a release of chlorine.

57

The following controls should be applied during construction:

(a)

Stress relief All fabricated items and butt welds should be stress-relieved before final inspection and testing.

(b)

Inspection and pressuretesting. All weld spatter, scale and other foreign matter should be removed. All butt welds should be fully radiographed or ultrasonically examined. All pipework should be pressure-tested in accordance with the design code. Where hydrostatic tests are made it is essential thatthe complete piping system is thoroughly cleanedand dried to a dew point less than -40°Cbefore introducing chlorine. All traces of oil,greaseand solvents mustbe removed (eg with steam or aqueous detergents or both) for the reasons stated under 'Lubrication' in paragraph 56. Ifa hydrostatic test is madeafter installation it will be necessary to change all gaskets to ensure dryness. Appropriate leak tests will then be required to cheekthe newlymade joints.

(e)

Modifications. Any extension, modification or repairs to pipework should be carriedout to a standard at least equivalent to the original design and construction codeincluding stress relief,inspection and testing.

Protection ofpipework 58

You should install pipework conveying chlorine so that it is:

(a)

protected from impact by vehicles by distance or with barriers;

(b)

protected from falling objects eg no overhead hoists.Canopyroofsfor weather protection should be constructed oflightweight materials;

(e)

separated from pipework carrying corrosive or flammable materials or other sources ofheat,eg steani - the separation will depend on the natureofthe other material and anestimateofthe hazard;

(d)

adequately supported;

(e)

accessible for maintenance and inspection; Safety advice forbulkchlorineinstallations 19

(f) preferably unlagged; and (g)

regularly inspected under any lagging to detect corrosion due to failure ofweathersealing.

Marking 59 The chlorine areaneedstobe clearlyidentified, marked3941 - see also the Dangerous Substances Regulations in Appendix 3 - and secured against unauthorised entry. It is recommended that chlorine pipework should be clearly labelledand paintedyellow in accordance with BS 171042 to 08E5l-BS4800). The Health and Safety (Safety Signs and Signals) Regulations require clear labelling whenever risks to employees cannot be avoidedor adequately reduced by other mcans advice is given in the associated guidance.45

(e l996

It is good practiceto markvalves which are required to operate in an emergency. They shouldbe marked with a clear indication oftheir function and thedirectionin which they open and close. These markings needto be consistent with the markings on any flow diagrams or operational nistructions. Valve keys for operating the emergency valvesshouldbe located near to the valve.

60

PROTECTIONOF LIQUID CHLORINEPiPEWORKAGAiNST OVERPRESSURE Trapping of liquid chlorine between closed valves, followed by a rise in temperature. increases the risk ofoverpressure. Even a small temperature rise cancausea very high hydraulic pressure, becauseofthe high coefficient ofexpansion ofliquid chlorine (see Appendix 2). 61

62 Therisk of liquid chlorine being trapped between closed valves is increased by the following factors: (a)

Isolation valves that are controlled by differentoperators. This may be a special risk where there are long linesor complex pipework between units.

(b)

The simultaneous closure of automatically operated valves that have been installed for plant isolation. This risk shouldbe assessed. In somecircumstances it may be preferable to employ at least one manuallyinitiated remotely controlled valve.

You shoulddesign your system and operating procedures to minimise the risks of overpressurisation. Whenappropriate, pressure reliefdevices should be fitted. 63

Provisionofreliefsystems 64 Reliefsystenis complicate pipework and introduce other potential hazards, and should in general be avoided. However, ifthe capacity ofyour system is such thatrelease ofthe chlorine present could lead to a serious incident, automatic means of releasing excessive pressure in the pipework needs tobe provided. It follows that the configuration ofthe pipework, positioning ofvalves, and valve-closing methods (see paragraph 62) haveto be studied to see whether the hazardcan occur.

20

Safety advice forbulk chlorine installations

Pressure reliefsystemsshould be designedto meet your operating conditions. It is recommended that the needfor, and thedesign of, relief systems is fully 65

discussedwith your chlorine supplier.

66 A common method ofpressurerelieffor protection ofliquid chlorine lines is viaa bursting disc installed in a vertical tee on thepipework, discharging to a

suitable collecting system (see Figure 1) The relief volume ofthe pressure vessel shouldbe at least 20% ofthe line volume. Anyexpansion vessel should be registered as a pressure vessel for examination and recordingpurposes.23

Figure 1 Pressure relief system for chlorine pipelines Note: Valve A should be secured open and valve 13 closed. Locking mechanisms should be defeatable if the valve position needs to be changed under emergency conditions. Pressure alarm gauge

V Locked open valve

Lockedshutvalve

Vent line toprocess ortoabsorption plant

Pressure vessel

Bursting disc assembly

Chlorine pipeline

67 The pressure vessel should be fitted with a suitable alarmwhichoperatesas a result oftherise in pressure in the vessel, ifthe bursting disc leaks or ruptures. The vesseland line can then be vented to process, orto the chlorine absorption system via a normally locked-closed valve. The heated bottle' system originally used on older installations is now obsolete and not recommended.

Safety advice forbulk chlorine installations

21

VALVES It is strongly recommended that Euro Chlorapproved valves are used on new installations. Care isessentialin the choiceofvalves (eg see the publications on valves in reference 22) as theyhave tobe resistantto chlorine and able to copewith the stresses to whichthey may be subjected. The valve bodyshouldpreferablybe madeofforged steel: cast ironis not acceptable. Ifthe valvedesign is such that liquid chlorine could be trapped within the body when the valve is closed, provision should be madeto avoid excess pressurewhichmay developwith temperature rise. Inothersituationsthe evaporation of liquid chlorine may cause operating temperatures to fall below 350( (see paragraph 56(b)): the valves shouldbe selected so as not to fail ifthis occurs. Problems whichare specific to coldor to liquid chlorine limit the application ofcertain designs of valve. 68

69 The selection ofthe appropriate type ofvalve for each application should be reviewed with your chlorine supplierwho will be able to suggest manufacturers ofvalves whose equipment has given satisfactory service with liquid chlorine.This will reduce the possibility ofunsatisfactory valves being used \vhich will require replacement after a short period and could he a potential source of hazard. 70 Valves which are 'permanently'open (eg to prevent inadvertent isolationofpressure alarms), or 'permanently'closed(eg emergency vent lines) shouldbe securedin these positions. The locking mechanisms should be capable ofbeing broken in the event of an emergency, eg the lead or plastic seal type.

It is emphasised that, during maintenance operations, reliance on valves ofwhatever for type isolation is insufficient. The design ofthe system shouldbe suchthat complete isolationofthe section concerned is possible. Suitable methods for achieving this include the installation of spool pieces in the lines which can be removed and substituted by blanks,or the insertion ofslip plates.46 71

Types of valve 72 Valvesofthe following types have beendeveloped for use with liquid chlorine or dry chlorine gas under pressure: (a)

vertical globe valves;

(b)

conical plug valves;

(c)

ball valves.

73 Valveshave tobe degreased using steam or detergents and thencompletely dried before use. All traces ofany solvent usedshouldbe removed as it could react with chlorine (seeparagraph 57(b)). It is recommended thatafterthis treatment the valves should be stored in individual gas-tight plastic bags ready for installation when required.

22

Safety advice for bulkchlorineinstallations

Verticalglobe valves 74 This typeofvalveis preferred to other types and is used for isolation of liquid chlorine stocktanksor for large flows ofchlorine gas. The billet-globe valve is recommended for installation on the liquid chlorine outlet line from chlorine storage tanks(see paragraph 96). The gas seal aroundthe valve spindle in globe valvesmay be formed by a packedgland (preferably usingringsor chevrons of PTFE) or by a bellows seal. The bellows shouldbe backedup by a secondary gland seal. Globe valves may, with advantage, be fittedwith a back seating arrangement which isolates the gland from line pressure when the valve is fullyopen.

Glandpackedglobevalve (('pica! si:e.s(0,01101)/c I5nim

In250mm)

Be/lows sealed globevalve with pneu,na/lcactualor. Hydraulic and electricalactuatorsare also available

Conicalplug valves (PTFE-sleeved) Conicalplug valves, PTFE-sleeved, are satisfactory for isolation of liquid chlorine lines, particularly when quick isolation maybe required, but the primary valveon the storage tank is preferably a globe valve. Rapidisolation can cause pressure surges and you needto consider these whendesigning your installation (seealso paragraph 79). 75

76 Conical plug valves for use with liquid chlorine require provision for the avoidance ofproblemsarising from liquid chlorine trapped in the bore when the valve is closed. If this makes the valves uni-directional, they needto be marked with an indication ofthe required directionof liquid flow to ensurecorrect installation. Gas-tightness is providedby a PTFE sleeve inserted into the bodyof thevalveand by a supplementary seal along the length ofthe spindle between the valve bodyand head. Careshouldbe takento avoid the application ofside thrustto thespindles ofplug valves. Safety advice for bulkchlorineinstallations 23

Ball valves 77 This typeofvalvecan be used for isolation in liquid chlorine linesand should incorporate the following: (a)

spherical turning limited to a quarter-turn:

(b)

straight-through flanging:

(c)

PTFE seals.

78 Ball valves shouldbe avoidedwhenoperating conditions involve large and frequent temperature changes. If used with liquid chlorine, you shouldmakeprovision for avoiding problems arising from liquid chlorine trappedinthe borewhenthe valve is closed. Liquid trapped in the ball shouldbe released downstream via a small hole in the ball. Ifthis makes the valve uni-directional it needsto be marked with an indication ofthe required direction of liquid flow to ensure correctinstallation. (Ball valves may not seal whenthe sealing pressure and the system pressure are in opposite directions). The reniarks about pressure surges in paragraphs 75 and 79 also apply. Remotely controlled valves 79 The rate ofclosure ofany actuatedvalveshouldnot be so rapid that it causes undue pressure surgesin the system. The standard rate of closure shouldbe satisfactory for pipework up to 50 mm diameter. Longruns of larger diameter pipework may require lowerrates of closure to prevent liquid hammer. You should seek advice from your valve supplier.

STORAGEVESSELS(seealso paragraphs 190-229) 80

To minimise the dangerofover-filling your storage vessel, its capacity needs to be

significantly greaterthan that ofthe largest delivery vehicle. The chosencapacitywill depend on therate ofconsumption and the frequency ofdeliveries. Installation ofbulk storage facilities shouldbe considered only ifthe annual consumption ofchlorine is sufficient to justify bulk supplies ratherthanpurchaseof liquid chlorine in drums or ISO containers (see paragraphs 216-221). An installation consisting ofsmallertankswhichwould require split loads is not recommended. New sites should involve HSE at an early stage. 81 In considering the number of individual storage tanksfor a required total storage capacity, take the following pointsinto account:

(a)

The minimum workingcapacityofthe tankshouldbe adequate to safelyaccommodate the working stockresidue and the maximum foreseen unit delivery.

(b)

Ifcontinuity ofsupplyis essential, at least two tankswill be requiredto allow time for necessary inspections and to facilitate maintenance. Thisalso providesgreater flexibility

ofoperation. (c)

24

Increasing the numberofstorage tanks leads toan increase inthe ancillary plant and equipment witha corresponding increase in complexity of operation.

Safety advice forbulkchlorineinstallations

82 The distance between adjacentstorage tanksshouldbe adequateto provide good access tothe tanksunderall circumstances. This includes those in which bulky protective equipment(suchas self-contained breathing apparatus) is being

used.

83 All chlorine storage tanks should be installed in a bund which is impervious to liquid chlorine. The bund shouldbe capableof taking the contents ofthe largest storage tank with adequatefreeboard and a sump. Ifthere is a sub-division to givea separate section under each tank, each section shouldhave a sloping floor leading to a sump, whichmay servemore than one tank. Sumps shouldnot be connected to the drain. Provision shouldbe included for removal of rain water over the bund wall, not viathe drain or through valvesin thebund. 84 Leaksofliquid chlorine are potentially much more dangerous than leaks ofgaseous several) attheedge ofthebund. chlorine. Your systemtherefore needsto be designedso that sources ofleakageofliquidare reducedto a minimum, eg by avoiding joints which are continuously exposed to liquid chlorine such as bottom outlets, see paragraph 88. Chlorine storagevesselandbund. Note theemergencystopbutton(oneof

85 The severityofa leak is reducedby loweringthe pressurewithinthe system and therefore it is important that facilities for transferring gaseouschlorine to a consuming processor to a waste-chlorine absorptionplantare available. You should also consider in your risk assessment the need for arrangements to transferliquid chlorine from a leaking tank to anothertank whichcan be isolated.

86 Layout ofthe chlorine areashouldbe plannedto provide all facilities necessary for good housekeeping and emergency response. Chlorine storage tanks shouldtherefore be erectedaboveground level.Installation in deeppits is not recommended becauseit increases the difficulties oftreatment and dispersal ofa chlorine escapeand ofaccess for maintenance or repair. Ample storage space is needed for maintenance and safetyequipment, which has to be readilyaccessible in an emergency. Thermal insulation ofthe storage tanks is not normally required. However, if your vessel is relatively close to a firehazardand lagging is required, the material should be fire-resistant, chemically inert to liquid or gaseouschlorine and resistant to atmospheric moisture getting in. Periodic inspection beneath the lagging is essential whenchecking for corrosion. 87

Safety advice forbulk chlorine installations

25

Designcriteria 88

Design criteriafor new liquid chlorine storage and expansion vessels are outlined below.

(a)

Design pressure. 12 bar gauge (174 psig) minimum.

(b)

Design temperature. When liquid chlorine evaporates at atmospheric pressureits temperature fallsto -35°Cand therefore the minimum design temperature should not be any higher, but lowertemperatures are possible ifevaporative cooling of liquid chlorine occurs, see paragraph 56(b). Thenormaldesign range is -35°C to +45°C.

(c)

Filling ratio. Filling ratios fortransportable liquid chlorine containers are detailed in BS 535547 for various size ranges ofmobilecontainers and for differenttemperatures. Although there is no equivalent standard for fixed tanks, for simplicity a figure of 1 .25 kg ofliquid chlorine/litre capacity is normally used to fix the maximum level to which thetank may be filledand the settingchosenfor the high level alarm. This ensures that the volume of liquid chlorine does not exceed95% ofthetotal volume of the vessel, even for a maximum temperature of 50°C.

(d)

Design code. New vessels shouldbe designedand manufactured Category I (or an equivalent standard).

(e)

Corrosion allowance. Minimum 1 mm.

(f)

Supports and load cells. The vessel supports should be designed in accordance with the design code to permit thermal expansion or contraction overthe design temperature range. Special consideration may be necessary (checkwith your supplier) where load cellsare used for determining the contents ofthe tank.eg certain types of weighing device require secondary supports.

(g)

Branches. Dimensions shouldbe limited to the minimum required, particularlyfor the liquid lines. All branchesshould be mounted, wherepossible, on the manholecover or covers. Manhole accessshouldbe providedon top ofthe vessel. The opening should preferably be 600 mm diameter, but in no case should it be lessthan 460 mm diameter. Bottom outlets should not be providedexcept where required for chlorine transferby pumping. Any bottom outlet should have an internal valve, preferably remotelyoperable, plus a back-up isolating valve (seeparagraph 97).

(h)

Bolting. Should meet the requirements ofBS 4882.

(i)

Gaskets. Use ofincorrect materials for gaskets can be dangerous, see paragraph 56(h) for suitable materials.

(j)

Documentation. Regulation 5 ofPSTGC2325

to BS 550048

requiresdesigners, manufacturers and

suppliers ofpressure systems to provide sufficient written information concerning the

design, construction, examination, operation and maintenance to enable the regulations to he complied with. You must retain this information togetherwith any Certificate of Compliance (eg BS 5500' or similardocumentation ifother standards are being used).

26

Safety advice forbulk chlorine installations

(k)

Marking. The vessel must bemarkedwiththe details specified in Schedule 4 ofthe PSTGC Regulations. All valvesand pipework associated with chlorine storage tanks should be labelledand colour coded(see alsoparagraphs59 and 60).

89 Paragraph 88 applies to new systems designed and constructed in accordance with a current standard. Wherean existingtank has beenprovidedin accordance with a different standard, the systemsshouldbe assessed according to the requirements of thoseoriginal standards. In particular, ifthe vessel'ssafe working pressureis less than 12 bar gauge(174 psig),then the air system pressure, relief devices etc all have to he altered to suit, and the delivery system has tobe arranged so as to be capable ofworkingwithin the storage tank conditions. It is recommended that such tanks are replaced withtanks meeting the requirements of paragraph 88. The timingofthe replacement shouldbe agreedwith your chlorine supplierand the competent person who examines your vessels.

Connectingpipeworkandmeansforisolation ofstorage tanks 90

The main connections tothe storage tanks are:

(a)

liquid chlorine inlet

(b)

liquid chlorine outlet;

(c)

vent linesand compressed dry gas lines;

(d)

reliefsystem;

(e)

instrumentation and pressure gauges.

You need to keep the numberofconnections to a minimum to reducethe 91

Connections atthetop ofthechlorine storagetank. .ate thepressuresreliefsystem with interlocked valves

potential sources ofleakage. The arrangements ofvalves and pipework shouldbe made as simple as possible to mm imise errors in operation. Pipework isolation valves should be fitted directly to the branches on the manlidor the tank itself. The system should be designed and operated so that, ifthejoints between the valvesand the storage tanksfail, gaseous chlorine only will be released (seeparagraphs 94-96).

(seeparagraphs120 to 127)

Safety advice for bulk chlorineinstallations

27

92 Whenevertwo valvesare installed in series for isolation, it is recommended that the system ofoperation is plannedso that each valve is used exclusively for a defined period during normal operation. This ensures that both valvesare kept in operable condition at all times. 93 An application ofthe principles in this sectionis shown diagrammatically in Figure 2. Notall installations will beto this pattern, and variations (some ofwhich are described in the text) maybe appropriate.

Liquidchlorine inlet 94 The liquid chlorine inlet should not normally extendfurther into the tank than the maximum liquid level. Some older installations use a dip-pipe on the inlet line. To avoid liquid chlorine flowing back ifthe fillingline fails, holesare drilled in the top ofthe dip-pipe so that liquid will not siphon back. A full dip-pipe maybe provided as an inlet to a vessel used for both importation and exportation. Suchvesselsneedto be fittedwith the additional controls appropriate to a liquid chlorine outlet. Youshould discuss the controls neededwith your proposed chlorine supplierat an early stage. 95 The isolation valve on the chlorine inlet line, directlybolted to the flangeon the storage tank,should preferably be a billetor high integrity globe valve. A back-upvalveshouldbe provided, which maybe remotelyoperated. Ifa manualback-upvalve is used, the isolation valveat the delivery point end of the pipework should be remotely operablefrom the emergency stop points.

Liquid chlorine outlet 96 The removal ofliquid chlorine from the storage tank is by meansofa dip-pipe. You therefore needto makearrangements to prevent chlorine releasescaused by the joint between the isolation valve and storage tank failing. This ismost satisfactorily achievedon new plant by use of a billet-type globe valve, bolted to the flanged branch on thestorage tank, with the dip-pipescrewed into the bottom of the valve. 97

You needto back up the main isolation valvewith anadditionalvalveto enable isolation

ifone valve fails to seat effectively. Depending on thelocal pipingarrangement, provision of

one or more remotelycontrolled valvesis recommended for emergency control. A remotely operated valvewhichis designed to give positive isolation and which is suitably positioned mayalso serveasone ofthetwo isolation valvesrequired.

In addition, it is strongly recommended that you incorporate a restricting orifice in the line tothe consuming plant.The objectofthis is to reducethe size ofa releasefrom a major failure to as low as reasonably practicable, ie appreciably lessthan the full-bore flow through the pipe.The size and location ofthe orifice needscareful consideration. The orifice should not be so small asto lead to problems, such as proneness ofthe orifice to blocking, etc. In somecases it may be practicable to limitthe flow in the line tothe maximum requiredby the process. The orifice shouldnot be located within the dip-pipe becauseofthe problem of removing the liquid chlorine fromthe tankin theeventofa blockage oftheorifice.In some 98

28

Safety advice for bulkchlorineinstallations

I

0

—

poets(rriu9o)

need

pools Ipara

37d

lobe inkedinto the automaticgas detect on and shut down system (parall3etseq) and Or

Whtblth

—

-

vesse poras 128 133

H

2

:

Eopanniee

Valve A or B shOu Ire rereotely operab e Iron emergency slop

0..

0

hi b'< read tuoker ira

stop

LPata

Dry air ordry N sapply Systeer at 000trettedpte080re t34 t4t)

1

Storage vessel

—

be rvmvtely operab e from emergeevystop P0 nts (Peru 97)

01ev) these valves shov

—0--

Liqu dcl to vvrsvirerg plan (peru 98)

seapara

96

il rage vesse

bilage pipe (pares 07 and tb8(

000 paId PA

—J!

v<

- Vent absorber (para t7t t89)

It there is any risk vi iqu rem the vent being sucked huk this ne should nvlvde a preventive device (107 174)

The parirwthiothe dotted Inc are repeated00 every

H

i:ri

Restrictingoritice

plants, the flow restriction can be replaced by the remotely operable shut-offvalves(see paragraph Ill) controlled by a suitable flow or pressuresensor. Excessflow valvesmay be advisable for linesnormally taking a flow ofchlorine much lessthan the flow which could passthrough in fault conditions. They arenot suitable for lines in which the normal flow rate is high, and for which other means of fault detection and flow isolation shouldbe used.

Vent and compressed drygas lines 99 Vent linesand compressed dry gas lines can be connected to the storage tank either through separate inlets or through a combined single inlet. In eithercase, the valvedirectly connected tothe storage tank shouldbe backed up by a second valve.

The prevention ofsuck-back of aqueous liquor into the vent line requires similar precautions to those described for vaporisers (see paragraph 161). The prevention ofbackdiffusion ofmoisture is describedin paragraphs 1 78-181. The inlet tothe scrubbing system should include a lute pipe(barometric leg) to prevent liquid from the scrubbing system entering the chlorine system. 100

The procedure for transferring liquid chlorine to the storage tanksshouldprovide for the vent valve to be opened slightly at the end of discharge for about a minute(see Appendix 6, paragraph 17) to confirm that thetank has not been significantly over-filled. ie abovethe extra-high level alarm(see paragraph 104). Overfilling is indicated by frosting on the vent line, in which casepressurerelief maybe necessary (seeparagraphs 102-132). 101

Reliefsystem 102 The special requirements for the isolationvalveson the pressure relief system on the storage tanksarecoveredin paragraphs 123-133.

Instrumentation and chlorine detector systems 103 Control instrumentation on storage tanksand elsewhere in the installation should,

whereverpossible, be designedto fail safe. Electrical and electronic equipment. unless specially protected against corrosion. should not be placedin areas where itcould be affected by gas leaks. 104 Storage tank contents. The quantity ofliquid chlorine in each storage tank is preferably determined by installing the tankon loadcells or on a weighbridge. Load cells should be recalibrated whenever the vessel is inspected and pressure-tested with water. Accuracy checks caii alsobe madeagainst the weight ofchlorine supplied whenever a delivery is made, provided the plant is off-line. Itis recommended that load cells are recalibrated at intervals not exceeding three years. The weight of liquid chlorine in each tank shouldbe indicated locally and maybe repeated in the plant control room. The contents-measuring devices needto operate a high—contents alarm in the control room (and on complexplants,possiblyan extrahigh contents alarm) for safety reasons. The extra-high level alarmneeds to be run independently ofthe systemgivingthe high-contents alarm, for reliability reasons.When fitted, it is recommended that the extra-high level alarm is used to automatically closethe tank inletvalveand thetanker oLitlet valve, see paragraph 105.

30 Safety advice for bulkchlorineinstallations

105 Asan alternative to the measurement ofthe quantityof liquid chlorine by weight, measurement by liquid level in the tanksis alsoacceptable. However, selection of suitable equipment is difficult and you shoulddiscuss ii with your chlorine supplier. Such devices are preferred as themeansoftriggering the extra— high level alarm.

106 To limitthe liquid volume in the storage tank to that permitted by the filling ratio (seeparacraph88(c)). an ullage pipecan be screwed into the bottom ofthe valve on the vent line. The length ofthis ullage pipeneedsto he consistent withthe filling ratioso that, if liquid chlorine rises abovethe correctlevel, it will flow through the ullage pipewhenthe vent valveis opened at the end of a delivery (see Appendix 6) or in response to an alarm. The ullage pipe shouldbe checked when the routine Inspection ofthe storage installation is made. A low temperature or other alarm(see paragraph 107) shouldbe fittedon the vent line from the storage tanks to warn if liquid chlorine is entering the ullagepipe on the vent line. 107 On a simpleinstallation, with good staffing and attendance at the tanks, an ullage pipe (see paragraph 106) may serveasthe extra—high level alarm. You need to he awarethat this method requires the vent line to be left open, which is not necessarily thecase for alternative methods, see Appendix 6. Ifa high contents alarm is ignored during filling ofthe tank, the liquid reaches the bottom of the ullage pipeand evaporates in the vent—lineabovethevent control valve, producing frostiig ofthe pipe. An ullage pipe therefore presents the risk ofliquid chlorine being passed to the scrubber unless the line contains a knock—out device fitted with a high level alarm. A knock—out pot in thevent line with level alarmsis also recommended for other reasons (see paragraph 157). The minimum protection fitted should be a restriction orifice plate (seeparagraph 98) and a low temperature alarm. 108 Ullage pipes arenot recommended for contents indication on new installations: instead an extra—high level alarm on thetank should be installed, see also paragraph 105. 109 A low contents alarm ma be usefLil for operational reasons and may have safety implications if, eg therecould be process upsets on thilure ofchlorine supply or passage ofpadding air (seeparagraph 226) into a downstream vessel. 110 Storage tank pressure. The pressLirein the chlorine storage tanksis usLially measured by gaugesspecially developed for use with liquid chlorine these have silver or tantalum diaphragms. Before use, the gauges needto he completely degreased (eg with steam and/ora detergent), dried and all traces of solvent removed, and be pressure—tested using only clean, dry. oil-treecompressed air. The pressuregauges may be tOtedwith switches to give analarm ifthe pressure exceeds, or tOlls below, a pre-set value. Alternatively, pressure switches maybe used to give an independent signal for the high and low pressure alarms.

Ill Where reference is made to flow or pressure sensors 'operating' valves(see paragraph 98) there isa choice whetherthe operation is automatic or via manual intervention (seeparagraph 62(h)). At the extremes, operation should be automatic

Safety advice forbulk chlorine installations 31

in an unstaffed plant, and maybe indirectin a well-instrumented plant with a continuously staffed control room. 112 Equipment associated with the automatic pressurerelief systemis describedin paragraphs 120 and 128-133.

Chlorine detectorsand alarms 113 The air in a buildinghousingchlorine storage tanksshouldbe continuously monitored using proprietary chlorine detector systemsto givewarning of chlorine leakage. Detectorsare strongly recommended in buildings which are not continuously staffed to provide early warning of leaks, allowing promptremedial action. For outdoor installations, the value of detector systems needs to be assessed by considering factors such as the size ofthe installation, the staffing levels and the response timesachievable. On detecting a leak, the detector should:

(a)

raise an audible alarm in a continuously staffed area or control centre;

(b)

activate audible alarms in the affected area;

(c)

operate the automatic isolation valves; and

(d)

control the mechanical ventilation, if fitted.

114 Audible alarms need to havea distincttone. In addition, warning lights ofthe amber

flashing ortraffic light type maybe fittedoutside each chlorine building. Whereappropriate, eg at large, remote or sensitive sites, alarmsshouldbe connected to a telemetry systemto providewarning at a staffed control point. The control point shouldbe able to isolate the chlorine supply, preferably via a remotelyoperable valvefitted to the outletofthe tank.

II 5 Chlorinedetectorsmay be placedin storage and plant areas. The manufacturer or supplier ofthe system should advise on the best location for the sensors; typically sensors are mountedbetween 0.3 iii and 0.5 m abovegroundlevel,and at the outletfromfume scrubbers. For indoor installations, sensors mayneedto be located inor near the entrance to ducts carrying chlorine pipework,and the air intakes to extractorfans.Where forced ventilation systems havebeeninstalled,the detector should be located at theoutlet ofthe system; where this is not reasonably practicable the detector should be placednear the storage and use areas. 116 Detection systems shouldprovide a continuous monitoring function whenchlorine is in

storage or in use. Chlorine gas sensors should be tested regularlyin accordance with the manufacturer's instructions to denionstrate that the detector and its associated circuits are functioning correctly. A record ofsuch tests is recommended. The detection system should operate thealarm circuits in the event ofpower loss, sensor failure,or low condition ofthe standby batteries.All alarm relayoperations shouldbe protectedby a battery back-up facility. The detector system should activate the low level alarmat a chlorine concentration of 1-5 ppm. Lower settingsare liable to activate the systemat every tank-fillingoperation, unless

I 17

32

Safety advice forbulk chlorine installations

a duration requirement is alsoimposed. For example,some companies set the low

level alarmat 0.5 ppm, but require the sensorto register this concentration for at least30 seconds, to avoid spurious trips ofthe alarmsystemduringfilling operations. For indoor installations, the lowalarmlevelshouldactivate the ventilation fan, open the intake louvers, and activate local audio alarms and any remotetelemetry alarm.

118 Multi-stage detectorsystems are sometimes used to give an indication ofthe severityofthe malfunction to personnel outside a chlorine room. It is suggested that the high level alarm operates at aboutthreetimes thelevel ofthe first-stage alarm, ic 3-15 ppm, depending on the durationthat the sensorneedsto register this level. However, some companies set the high level alarm at 2 ppm with a 30 second

duration requirement.

On activation ofa high level alarmthe ventilation system should be shut off, the auto-shutdown systemactivated (where fitted ) and the high level alarmsounded. Thetone ofthe alarm at lowand high levelsshouldbe differentand operators trained to recognise the difference and how to respondin eachcase. Local alarms may be supplemented by telemetry links to control rooms, where appropriate. The response to alarmsis coveredin paragraphs 247-263. Some sensors can be damaged by high chlorine concentrations; detector systems should therefore be checked after any high level alarm. PROTECTIONOF STORAGEVESSELSAGAINST OVERPRESSURE Highpressure on the liquid chlorine storage tank is indicated by a high pressure alarm (paragraph 110). Overpressure in the liquid chlorine storage tanks can result from over-filling or excessive paddingpressure. Over-filling with liquid chlorine is indicated by alarmson the weigh systemused to determine the liquid chlorine content ofthe storage tanks (paragraphs 104-109). Overpressure on the compressed air or nitrogen supplyto the storage tank is prevented by the installation ofa reliefvalveon thesupply source of the compressed gas. The supply source should be wellupstream ofthe tank and separated from it by isolationvalves 119

(paragraph 139).

Reliefsystem 120 The storage tanksneedtobe protectedagainstoverpressure by a suitable automatic pressurerelief system which is set to operate at a pressurebelow the design value. The preferred pressurerelief systemconsistsoftwo bursting discs placed back to back. A bursting disc followed by a relief valve may alsobe used, but is always subject to the risk of corrosion ofthe reliefvalve. Protection ofthe relief valve from corrosion mustbe carefully considered ifthe bursting discrelief valvesystem isused. The use of reliefvalvesaloneis not recommended because of the corrosion or blockage whichcould occur ifa reliefvalve were left continuously exposed to chlorine. Whichever system is used, you should provide a pressure alarm/indicator between the two discs or between the disc and reliefvalve(see paragraph 133). Inthe latter arrangement it is good practiceto remove and overhaul the relieF valvewhenever the bursting disc is replaced.

Safety advice for bulkchlorineinstallations 33

121 The dischargeline from the pressurerelief system normally entersa closed expansion vessel (except in a few specialised arrangements). Anypressure iii the expansion vessel or between components in the relief system reducesthe protection given to the storage vessel (seeparagraphs 85, 128-133). Special relief arrangements are usually requiredwhenthere is a significant risk of overpressure from continuous pressure sources such as radiant heat oi by pumping chlorine. Underthese circumstances relief into a closed expansion vessel may be inadequate. Reliefarrangements based on relief valves into an 'open' system (cg a vent scrubber) may be preferable to bursting discs,as the valves reseat once the source of overpressure hasbeen removed. This arrangement is normallyonly found on larger installationsyou shouldconsult your chlorine supplier.

Burstingdiscs 122 Bursting discs (which are designed to fail at or below the design pressure of storage tanks) are commonly made ofnickel, although tantalum, silver or other compatible materials may be used. Uncoated graphite is not recommended. Discs should coniply with BS 291 549 (or equivalent standard) and should he carefully selected for the operating temperature range, as the rupture pressure is temperature-dependent.

ArrangementsJbr reliefsystems 123 On simple installations, such asthose with a single storage vessel and associated expansion vessel, a single bursting discsystem without any isolating valves, installed directly on the storage vessel, may be acceptable. In practice, however, it is more convenient to install a valvedsystemto allow replacement ofdiscs undera controlled system ofwork, without needingto completely empty and purge the system. Wheretwo or more storage vesselsshare an expansion vessel, the relief arrangements should allow prompt replacement ofdiscs and venting 012111 excess pressureout ol the expansion vessel. 124 The preferred arrangements are shown in Figures 3 and 4 and shouldbe used on all new installations. The kolatingvalvesmay be mechanically mterlocked (recommended for new installations) so that one pair of discs is alwaysoperative, or the isolatingvalves may be individually locked. To he cffi,ctive the bursting discs needtobeol the sLmple domed unsupported type with the concave sidefacing in the directions shown in Figures 3. 4. and 5. The identifying tags should be lefi attached to each disc so that they can be identified as having been installed correctly. Existing older installations usingthe arrangement shown iii Figure 5 should replace it with a prefi.rred arrangement (Figure 3 or 4) when major modifications lire in hand. 125 The valves which remain open must permit the operational devices to discharge at the required rate toan expansion vessel. Pipework before the isolating valves should beas short and simple as possible to minimise the risk ofchlorine leakage fromjoints and pipework the isolation using valves before the bursting discs should preferably be fitted directly on flanged connections on thenianlid of the storage tanks.

34

Safety advice for bulk chlorine installations

Figure 3 Pressure relief system (preferred arrangement). Double stream with interlocked valves

Toexparsior vessel

Pressure alarmgauge

Pressure aart gauge

xx

Borstieg

::

ds S

Bursting dscs

TestCurrentOfl forpros Crc gaugeroroboes)

Figure 4 Pressure relief system. Double stream with locked-open

valves

Pressure alarmgauge

(

Toexpansion vesse

fl

Ptessuealarmgauoe

Looked vane

at eastoneline needstobe —

B i uring discs

_i__(

onkedoper

____ Bursi

—

i pdsos

— Loused ualves

Testnornedonslvi nressure gauge trotsrotor)

Safety advice forbulk chlorineinstallations

35

Figure 5 Pressure relief system Single stream ith locked—open

Toexpansion vessel

\ alves

Lockedopen valve

Barsting discs

Looked open colon

126 Your procedures for dealingwith a failure ofa bursting disc shouldbe clearly defined. Base themon the principlethat at no timeshouldpressuresbeyondthe design range beallowedto develop(see alsoparagraph 127). 127 At any installation where a 'locked'-open isolating valveprecedes a bursting disc, a safe system ofwork should be defined to preventunacceptable pressures from any source occurring in the vessel while the isolatingvalveis closed. The procedures needto cover the safe removal ofthe vessel from normal service, stabilising the pressure, changing the bursting disc, venting the expansion tank and returning the vessel to normal use. Such safe systemswill vary with plantdesign hut should:

(a)

be in a written form, unambiguous and readilyavailable

(b)

include a permit-to-work system:

(c)

be included in plant personnel training programmes;

(d)

be properly supervised with responsibilities clearly allocated;

(e)

be regularly updated and periodically subjected to HAZOP 50 review, particularly whenplant design, operating procedures or management systemsare modified; and

(f)

be rigidly adheredto.

36

Safety advice forbulkchlorineinstallations

Expansion vessels 128 The design requirements for the construction of the expansion vessel aresimilarto thosefor the storage tanks;the capacity of the expansion vessel shouldbe at least 10% ofthe largeststorage vessel.

The expansion vessel should be capable of vented being manually toan absorption system;the ventvalve is normally lockedclosed. Controlled venting shouldbe through a suitable flow restriction device, eg an orifice plate to prevent overload ofthe absorption system. 129

The expansion vessel should be providedwith a pressure-sensing device which gives an alarm if pressurebuildsup in the vessel. Thealarm system needs to be capableofbeing tested regularly to ensure that it is operable(see paragraph 133). 130

131 Arrange the compressed air or nitrogenconnection to the expansion vessel to avoid the possibility ofinadvertently pressurising the vessel. This may be achieved by physical disconnection, isolating blanking plates. or by double block valves supported by a safesystemofwork. Ifan expansion vessel serves more than one storage vessel, makearrangements for prompt response to a pressure alarm signal from it.

132 While the risk ofthe expansion vessel itselfbeing over-pressurised with chlorine is minimal because ofthe precautions described in paragraphs 128-131, you shouldestablish procedural or mechanical meansto ensure thatthis cannot occur.

Pressurealarms 133 There should be a high-pressure alarm on every storage vessel, and an additional pressure indicator/alarm at each important safetylocation on the relief arrangement. Thismeansthat one additional pressure alarm may suffice on each storage vesselthat has its ownexpansion vessel, and that alarmmay be eitherin the reliefline (ifthere is a single bursting disc) or on the expansion vessel. When one expansion vessel serves several storage vessels, thereshouldbean additional pressure alarm withineach reliefassemblyand also one on the expansion vessel. Test alarms regularly (at least monthly) by gas injection or moving contacts.

Safety advice forbulk chlorine installations

37

ARRANGEMENTSFOR UNLOADINGOFLIQUID CHLORINEFROM ROAD TANKERSTO STORAGE UnloadingUsingDry Compressed Airor DryNitrogen 134 The recommended system for transferring liquid chlorine from chlorine tankers to storage vessels, by 'padding' with dry air or dry nitrogen, is outlined in Figure 2 and in Appendix 6 which providesa soundbasisfor developing local procedures. Detailed requirements, whichsupplement information given in previous sections, are reviewed in paragraphs 135-147. You needto agreeyour arrangements with yoursupplierand design them to minimise the risk ofoverpressure. 1 35 A separate and independent dry compressed air or nitrogen system shouldbe used for chlorine duty, to minimise the possibility of'backdiffusion of chlorine which could lead to dangerous conditions in other air—consuming units, particularly instrumentation. Compressed nitrogen may be produced in a liquid nitrogen evaporation unit. 1 36 Ifyou use compressed air, your supply needs tobe oil-free and havea dew point below -40°C. Normally, air should be compressed to around 10 bar gaugeusinga truly oilfree compressor(1.5 m3/min free air capacity); ifan oil-lubricated compressor is Lised it must be fitted with an oil filter which must be regularly maintained.

137 The compressed air is cooledto remove part ofthe moisture content and finally dried, usinga regenerative-type drying system, to a dew point below 40°C. Thedew point shouldpreferably be monitored continuously using a monitorprovided with an alarmthat giveswarning ifthe dew point exceeds a pre—set figure. It is important to recharge or regenerate drying agents according to the equipment and chlorine suppliers'advice.

Hvgronwteralarm. At thisinstallationthc' compressed airdewpointisless (ha,, - 6(1k

38

Safety advice for bulk chlorineinstallations

138 A guardtower, filled with anhydrous calcium chloride or other suitable material. may be installed after the regenerative system as a further For small installations a

drieralone using anhydrous calcium chloride or other drying agent maybe adequate, provided that proper cheeks on the condition ofthe drying agentare made,

Supplyofdrypaddinggas to the system 139 The compressed dry air or dry nitrogen shouldbe stored in a pressure receiver. This shouldhe fitted with a relief valve set to operateat the chlorine storage plant's safeworkingpressure or 10 bar gauge,whichever is lower. From the receiverthe gas should passthrough a non-retuni valve, or a pressure-actuated shut-offvalve, followed by a reducing valve to give a supply at the pressure required for unloading thetankers. This supplywillalso be suitable for other purposes on the chlorine plant,such as drying out or purging ofpipelines and vessels providedprecautions aretakento prevent baekflow ofchlorine into theair system. Pressure gauges shouldbe installed upstream and downstream ofthe pressure reducingvalveso that cheekscan be made that the padding gas pressure is greaterthan the chlorine pressure. It is important to providesafeguards 23-25 to ensure that excessive gas pressures cannotbe applied to the chlorine system. This may be particularly important ifthe padding gas is supplied from high pressure cylinders. 140 The liquid chlorine discharge line on the chlorine tankershouldbe connected to thepermanent pipework at the unloading point (seeparagraphs 43-55). The pipework connecting the unloading point to the liquid chlorine storage vessels shouldbe reasonably short(see alsoparagraphs (53-60). Ifit is necessary to usea long liquid chlorine line to storage, you must consider the needto protectthis line

against overpressure (see paragraphs 61-67).

141 A pressure gauge, a vent line to the absorber and a connection for dry compressed gas shouldbe installed close to theend ofthe permanent pipework at the unloading point, with the necessary isolation valves, as detailed in Figure 2.

Unloadingusingchlorine gas pressure 142 Liquid chlorine may be transferred from the chlorine tankersto the storage vessels by padding with dry chlorine gas. The gas is normally taken from one ofthe stock tanksbut this should preferably not be the one into which the tankeris being unloaded. The supply of dry chlorine gas at the required pressure niaybe obtained by re-compressing chlorine vapourfrom a storage tank or by vaporisation ofliquid chlorine. A source ofdry, compressed, oil-freeair or nitrogen is still required. for drying out and purging the system.

Use ofre-compressedchlorine vapour 143 Selection ofthe appropriate compressorfor re-compression ofchlorine vapour requires careful consideration to ensure that the equipment can operate satisfactorily on an interniittent basis. Diaphragm compressorsor dry carbon ringreciprocating compressors are suitable for this duty provided that maintenance is carriedout on a regular basis.

Safety advice forbulkchlorineinstallations 39

144 Diaphragm compressors shoulduse stainless steel double diaphragms withinert fluid between them.Dry carbonring compressors shouldpreferablybe purged with dry air after use, to avoid problems resulting from residualchlorine in the compressorleakingfrom shaft glands. During operation ofthe compressor, the shaft glands should be pressurised with dry, compressed, inert gas. 145 Ifcooling ofthe compressor body is required, this shouldpreferably be accomplished by air cooling.Ifjacketcooling is necessary, this shouldbe achievedby circulation through an external heat exchangerwith provision to detectleakage ofchlorine into the heat exchange fluid. Direct water coolingshould be avoided. 146 The compressor needstobe fittedwith a bypassso that the chlorine can be recycled until its temperature is raised sufficiently to prevent liquefaction in the delivery lines. The temperature ofthe chlorine shouldbe monitored using an indicatorwhich is fitted with an alarm, set to soundifit exceeds90°C. 147 A pressure reliefsystemon the compressordelivery line should also be providedto prevent the delivery pressure exceeding a pre-setfigure (see paragraph 139).

CHLORiNE VAPORISERS 148 Vaporisers (also known as evaporators) convert liquid chlorine into gas. A major use ofchlorine vaporisersisin water treatment, to control weed and algae in coolingwater and to sterilise drinking water. Theseunitsare frequently supplied as part ofa package with

other dosing or analytical equipment. Vaporisers are always required with a fixed or demountable bulk tank, to obtain a regular. steadysupplyofgas to process. The drawing of gas from the vapourspace ofa bulk tank is unsatisfactory and unsafe.There is the risk of process liquids passing back into the tank, irregularity ofsupplyand the possible accumulation ofless volatile,dangerous impurities, such as explosive nitrogen trichloride in the tank.51 The safe handling ofchlorine containing nitrogen trichloride is discussed elsewhere.52 Types 149 There are fourmain typesofvaporiser(see also Appendix 7):

(a)

Vertical tube bundle. Theseresembleordinary heat exchangers, usuallywith the chlorine in the tubes. Alternative formats includethe common vaporiserused in water treatment (a cylinder with a dip-pipeliquid chlorine inlet immersed in the heating bath) or a shell and tubeheat exchangerwith the chlorine on the shell side. A bayonetvaporiser is very similar.

(b)

Coil. The chlorine is evaporated in a coil ofsteel tubingrunning insidea wet steam bath or a waterbath heated by steam or electricity.

(c)

Concentric tube. The heat exchange surface is a tube, typicallyfourinchesin diameter, surrounded by a heating jacket.

40

Safetyadvice forbulkchlorineinstallations

j

(d)

Kettle. Kettleevaporators are used on large capacity systems. They containa heatersystem (usually a tube bundleofhot wateror heated fluid- not steam)passing through a vessel containing liquid chlorine. Kettle evaporators do not superheat the chlorine vapour, other systemsdo.

Regulation ofthroughput Coilinbath vaponerheated bylowpressuresteam

Selfregulatingvaporisers

150 In sonictypes ofvaporiserthe liquid chlorine is fed in at the bottomand gas is drawn offvia a control valveat the top. Whendemandis high, the liquidchlorine level rises in the container, and a greaterheat exchange surface areais presented to the liquid. When demandis low, the greatervapourpressure at the temperature ofthe heating medium drives the liquid chlorine out ofthe vaporiserback into the storage vessel and the evaporation rate falls. This system is usually applicable to vaporisers witha relatively small chlorine capacity. ie vertical tubebundles,coil typesand concentric tubetypes. Bayonet vaporisers can be used for high vaporisation rates. On water treatment plantsa self-regulating vaporiser, with an electrically heated water bath is usually used.

Constantlevel vaporisers 151 Othertypes ofvaporisers, usually found only in large-capacity plants, sacrifice certain advantages ofthe self-regulating types to achievemuch larger vaporisation rates. These vaporisers requireseparate instrumentation and control arrangements to provide a constant level ofliquid chlorine in the kettle or shell with high and low level alarms. In such types(wherethere can be parts ofthe liquid chlorine pool which arenot well-mixed), there is a greatertendency to concentrate the less volatile impurities than in a self-regulating vaporiser. A separate purge and vaporisercircuitmay be required to deal periodically with the residues. The design and operation ofthese larger-capacity vaporisers is a specialised topic, and requires consultation between the user, the designer,and the chlorine supplieras the risk of 52 You nitrogentrichloride enrichmentand subsequent explosion is increased. should involve your supplier when assessing this risk.

5l

Methods ofheating 152 The methods ofheatingthe vaporiser shouldminimiseboth the risk of corrosion and vaporiserfailure. These include: heatingwithhot water; heating with low pressure steam and usingclosedcircuitheatingwith heattransfer fluids other than water. Directelectrical heating should not be used because ofthe risk oflocal overheating and chlorine/iron fires (see paragraph 158 and Appendix 2).

Safety advice for bulk chlorine installations 41

(a)

Heatingwith hot water. This isthe most frequently used method; the normal working temperature (60-70°C)is well belowthat at which any significant reaction ofcarbon steel occurs with dry chlorine.

(b)

I leating withsteam. The steam should be saturated and its pressure shouldbe limited to lessthan I bar gaugeto avoid overheating, particularly ifthe vaporiseris madeofmild steel.Any small leaks ofchlorine tothe watersideofhot water or steam types lead to veryrapid corrosion ofthe steel by moist chlorine (see pararaph 169). Steam systems must meet the requirements ofthe PSTGC Regulations.232 The greaterflexibility of steam heating is useful on plants using chlorine gas at high or at very variable rates.

(c)

I leat transferfluids (otherthan water). Electrical or steam heat can be applied to a heat

transferfluidwhich is relatively unreaetive towards chlorine. The available fluids (eg hexachlorobutadiene) are themselves hazardous, so that the hazardsofusingwater as heattransfermedium are in practiceaccepted,with suitable safeguards.

General installation 153 The vaporiser should be installed in the storage area orin an adjacentspace

as close as

possible tothe chlorine storage tanks in orderto keeppipelines carrying liquid chlorine short. Long pipe runswill require pressure relief(see paragraphs 61-67). Changeover of liquid chlorine supplyfromone storage tankto another canaffect operating conditions in the vaporisersystem and any such difficulties will be reduced ifthe spacing is not too great. eg lessthan 5 metres. Nevertheless, the space between the vaporiser and thestorage system should be such as to allow adequate access for emergency action in the eventofan incident at

the vaporiser. Hazards

154 The quantity of chlorine in a chlorine vaporisersystem is relatively small compared with that normally contained in the main chlorine storage tanks. Nevertheless, the systeni design should be such that failure ofequipmentcan bedetectedand rectified quickly and that any consequent releaseofchlorine to the environment is niinimised. 155 Potential hazards associated with chlorine vaporisers include:

(a)

Pinhole leaks leading to rapid corrosion and increased loss ofchlorine.

(b)

Rapid corrosion, ifany moisture is allowed into the chlorine system.

(e)

Possible concentration of inipurities in the chlorine as it is evaporated, such as explosive nitrogen triehloride. Thisneedsto be discussedwith your chlorine supplier.

(dl

Reverse flow of reaction fluids, caused by a fall in pressure in the vaporiser, or by excess pressure in the process,or by solution ofchlorine gas in the fluid. The presence ofthe fluid (water, solvent or reagent) in the vaporiser can cause corrosion or local violentreaction leadingto rapid overpressure and possible rupture ofthe vaporiser.

42

Safety advice forbulkchlorineinstallations

(e)

Carry-over ofliquid chlorine as bulkfluidor droplets into the gas line or into the process itself. Thiscan (depending on the materials ofconstruction and on the process) cause daniage or hazard.

(f)

Excessive gas pressure to the systemdue to overheating a vaporiser. since the vapourpressure of chlorine rises very steeply with temperature (see Appendix 2. Figure A2. I).

(g)

Excessive hydraulic forces, ifthe system is closed up and full of liquid due to the expansion of liquid chlorine when heated.

Thesebasichazardsare considered in more detail in paragraphs 156-161, but grouped according tothe type ofhazard. Floodingand liquidcarrv—o'er 156 Flooding (filling) ofthe chlorine vaporiser with liquid chlorine mayresult from operation ofthe equipment above its capacity, inadequate heating, or fouling ofthe heal transfersurfaces. The temperature oftheheatingmedium is usually controlled thermostatically. Ifthe temperature ofthe heatingmedium falls too low in a self-regulating evaporator, it is possible for the outgoinggas tobe inadequately superheated, or for flooding to occur. Flooding results in carry-over ofliquid chlorine into the vapour lines, and a potential hazard (depending on the process and plant materials). The same mayhappen ifthe level ofwater in a water bath falls. In theextreme, if chlorine is drawn offbut no heat is supplied tothevaporiser, itis possible thr ice to form on the heat exchangersurfaces and damage theni severely. You should consider installing a gas flow rate indicator. This may be ofvalueto the operator routine purposes. and will also indicate excessive withdrawal rates.

br

157 You should consider fitting a knockout pot (or spray catcher) to prevent chlorine droplets and sprayfrom passing into gas pipework when liquid chlorine might damage the material ofthe pipes, or cause the process to become unstable. In all caseswherethe possibility ofliquid passing to process is unacceptable, itis strongly recommended thata low temperature alarm be fittednear the knockout pot and arranged to cut off the liquid chlorine supplyto the vaporiseror (in selfregulating typesonly)the gaseouschlorine outlet maybe closed, driving the liquid chlorine back into the storage vessel(s). Adequate instrumentation and alarms shouldalwaysbe provided to give immediate warning ofthis condition. Highand low bathtemperature and level alarnis with shut-down facilities are recommended.

Acceleratedcorrosionand reaction (high temperature) 158 To avoid rapid corrosion of thewaterside ofheat exchange surfaces made from galvanised steel, operating temperatures shouldnot exceed 70°C. Ifoperation at highertemperatures is required. vaporisers madeofnickel or nickel alloys (such as Monel 400 or Inconel) should be used. In such cases, the downstream chlorine

Safety advice forbulkchlorineinstallations 43

gas pipework may alsoneed upgrading to ensure adequate resistance to corrosion at elevated temperatures. 159 lfthe heating medium is steam, the temperature can bemonitoredby low pressure and highpressurealarmson the steam inlet. The pressure of steam should normally be limitedto I bar gauge (120°C equivalent) and the steam has tobe saturated, not superheated.

Highpressure 160 Precautions must 23 be in place to protectthe systemagainstover-pressurisation,

eg a

pressure reliefdevice. Pressure reliefdevices and high pressure alarms, wherefitted, should be properly designedand installed, maintained in an effective workingorder,and tested regularly. They mustbe periodically examined by a competent person.53 A typical working temperature for a vaporiseris 70°C. The vapourpressure ofchlorine at 70°C exceeds 21 bar, (see Figure A2.1, Appendix 2). It follows that you need to take the following steps to: (a)

Ensure thatthe vaporiser is not isolated when full ofliquid chlorine. Strict observance of written procedures for shut-down is vital.

(b)

Avoid accidentally isolating the vaporiseron both sides. Care needsto betakento ensure that the closing arrangements for the emergency valves take this into account (see paragraphs 162-165).

(c)

Design the vaporiser shell and pipesto withstand the workingpressureand duty.

(d)

Implement operational controlswhich minimise the risk ofthe workingpressure being exceeded.

If your chlorine vaporiser is not supplied with a pressure relief device you will needto adopt procedures. or fit suitable pressure relief, to ensure that the conditions in (a) to (d) are met. Reverse flow 161 You should eliminate the possibility ofsuck-back intothe vaporisers by suitable design. For example, water chlorinating package systenisusually incorporate a set ofvalvesin the control systemto prevent suck-back or push-back. The arrangements vary, and careneedsto be taken to ensure that the system provided does give protection intheeventof, eg, a leak at theejectornon-return valve. You should alsoconsiderfitting a low pressure gas alarm to the outletgas line. This gives warning ofloss ofsupplyto the process. and may indicate a needto start purging the systcm, usingdry air or other suitable dry gas (dewpoint lessthan -40°C)to prevent suck-back. Whatever method is used,the systemneedsto be regularly inspected and maintained, and adequate records kept.

44

Safety advice for bulkchlorineinstallations

Routine and emergency isolation _____

*

ii

77

162 The vaporiserhas to be capable ofbeing isolated for maintenance, orin an emergency, such as a failure ofthe vaporiseritselfthrough leakage or a failure ofthegas line downstream. In addition to a manual valve on the liquidinletand on the gas outlet. reniotelyor automatically operable valves are strongly recommended on both inlet and outlet. A pressure-reducing or flow control valve will almostalwaysbe fittedon the outlet and it is sometimes possible for this valve to be the remotely operable shut-offvalve.

163 Yourrisk assessment shouldconsiderthe need for additional protection in theeventthat automatic valves fail to operate (or remotelyoperable valves are ________________________ not activated)inan emergency. For example a flow restrictionin the liquid inlet (typically on the exit from Emergency shutdown push buttonat the vaporiser.Also the storage tank(s)), will limitthe releasewhichcould shown in oneofsix chlorine occur in theevent ofa majorplant failure. detectors atthisinstallation which canalso automatically 164 The hazards oftotally isolating the vaporiserare shutdown thechlorine considerable and will be most severe when the installation (seeparagraphs evaporator is full (eg ifthe valvesclose together in a _____________________ condition ofmajor gas line failure). Ifthere is a gas space abovethe liquid chlorine when the vaporiseris isolated and heated, the internal pressure will reachthat ofchlorine at the heating medium temperature. The vaporiser, linesand valvesneed to be designed to withstand such pressure or incorporate arrangements to relieve to a safe place. The control ofautomatic valvesneedsto be arranged so thatthe valves do not close together whenan alarm is raised(see alsoparagraph 160). One approach is to arrange for the gas control valve to closeon alarms related to improper working of the system (eg low gas pressure, downstream process alarms, low temperature) and the liquid control valveat the storage tank to closeon chlorine release(eg detectors local to the vaporiser and storage,or manual alarms). Ifthe plantis continually staffed, manual intervention maybe a suitable alternative to providingwholly automatic operation ofshut-down. However, procedures needtobe established to ensure that this does not introduce significant delays into the responsetoan alarm. An alternative approach isto use a pressure control globe valve for remoteisolation oftheoutlet line so that excessive pressures will lift it slightly off its seat, preventing excessive overpressures. Reliefpressuresand valvedirectionneed careful consideration and shouldbe discussed with the valvesupplier. 165 Isolation ofthe vaporiscris still possible, but interlocks betweenthe inlet and outletvalvesto prevent total isolation are rarely fitted. This is becauseit is occasionally necessary to close both valvesduring cleaning and overhaul. A safe system ofwork for maintenance and operation is thus a vital part ofthe safety 23 arrangements, and is a requirement underthe PSTGC Regulations.

Safety advice forbulkchlorineinstallations 45

Pressure control valve All vaporiserdesigns incorporate an elementofsuperheating ofthe vapour, either in the vaporiser itselfor as a separate unit. This is necessary to prevent chlorine reliquefying in the control valves, where it could cause problemsofirregularpressure in operation. These problems are avoided by reducing the gaspressureat the exit from the vaporiscr. A suitable pressurc-reducing control system is recommended. 166

Corrosion 167 CoiTosion of the vaporisertubesorcoils could lead to a loss-of-containment accident. The consequence ofa minorchlorine leak from the chlorine sideofa vaporiserheating bath could be very serious since the mixture ofchlorine and moisturewill lead to rapid corrosion of the evaporator surfaces and a substantial releaseofchlorine. 168 You must arrange for a competent person to periodically examine your vaporiser and other pressure systems in accordance with your written scheme ofexamination.4 A must certify thatthe written scheme for examination is sUitable for the competent person of purpose preventing reasonably foreseeable danger to people from the unintentional release of stored energyfrom the system. The written scheme ofexamination should describe the natureand frequency ofthe examination. This should bebased on risk assessment and give due consideration to the duty and the condition of the vaporiserwhen it was last inspected. The competent person will advise on suitable examination and test regimes, and when the vaporiser shouldhe replaced. Examination intervals betweenone and five years are typical. Coil-in-bath evaporators are commonly given a rigorous inspection every two years, and the coils are discarded ifseriously pitted. Some manufacturers advisethat the coils should be renewed every two years. Following examination the equipmentshouldbe thoroughly dried to a dew point lessthan —40°C before recommissioning. Moisture left in the system can lead to very rapid corrosion. The procedure shouldbe coveredby a writtenoperating procedure. 169 Corrosion of the heat exchanger surfaces is not directly monitored. Instead the evaporator vessel or tubes are frequently protected against water corrosion by cathodic protection. Typically the anodes should be checked visually every threeto six months. The frequency should be established by experience ofthe rate at which theanodesare consumed and replaced. Ifthe anodesare found whollyconsumed at inspection, a thorough examination ofthe vaporiser should be undertaken. The waterbathor condensate outlet should be monitored for chlorine leaks by redox or conductivity measurements. This earlywarning of minorleaks is helpful in all cases,and is very strongly recommended ifcathodic protection is not provided or not maintained. 170 Accumulation ofsolid deposits reducesthe effectiveness ofa vaporiserand can also enhance corrosion. The vaporiserneedstobe cleanedand dried to a dew point lessthan -40°C regularly. Closeattention tothe cleaning procedure will minimise corrosion but typically, the chlorine evaporator cylinder in a hot water bath (see Appendix 7, type Ic system) should be renewed after five years. The old one maybe submitted to a competent inspection body for certification for furtheruse if required.

46 Safety advice forbulk chlorine installations

CHLORINEABSORPTIONSYSTEM 171 You should give detailed consideration to ensure that in all chlorine—using operations chlorinecan. in an emergency, be ventcd to an absorber without emission to the environment. 172 Control ofchlorine emissions from prescribed processes(see paragraph 10) must be the subject of consultations with the Environment Agency in England and Wales and SEPA in Scotland. 1 73 In some installations, the nature of the eonsunimg process is such that absorption ofthe chlorineis possible without a special absorption unit. I lowever, in such circumstances operators need to ensure that duringillaintenance periods adequateabsorption capacity is alwayskept available to accommodate any chlorine emissions. A separate absorption plant may not he essential in, tor example cooling— watertreatment plants and bleach liquor productionplants.

174 For most bulk storage installations. however, a separatechlorineabsorptionplant is required and it should always he maintained in a state of readiness. The quantityofreagents available in the absorption system needs to he adequate to deal with any foreseeable emergency. The inlet to the scrubbing system should include a lute pipe (barometric leg) to prevent liquid fl'om the scrubbingsystem

-IJ

I toenpt'(buronuu'ou l(t!) (ltU/ In! mt ubsnrptioii\t'S!tJII

enteringthe chlorine system.

175 The responsibilityfor the installationof an adequate chlorineabsorption system rests with the consumer, but von should obtainthe cliIon ne supplicr's advice on the proposed installation.

176 Considercarefully the provisionofadequate instrumentation with alarms and the disposal of effluent from the chlorineabsorption plant. 177 Adequate standby equipment shouldbe providedto cover breakdowns and routineoverhauls. Essential circulatingpuml1, fans and instrumentation should be among those items which are connected both to the mains and to the factory emergency powersLipply there is one. When the absorption fiteility is required to be continuouslyavailable (eg vents from reactors) it is essential to provide emergency powerand stand-by circulatingpimpsor an emergency gravity—fed

if

supply ofabsorbing solution.

Vent collection system 178 The pipelines for the collection ofthe ventgasescontainingdry chlorinemay he made ofmild steel but back—diffusionof moistLire from the absorption system. which may occurif' ventings are intermittent,has to he prevented. Safety advice forbulk chlorine installations

47

179 Vent systemsfromrelief systems, whichare likelyto operateonly infrequently, maybe protectedfrom back-diffusion ofmoisture by theuse ofprotective membranes. In somecases it mayhelp to providea controlled dry gas purgethrough the vent lines. 180 lfthere is any risk ofmoisture contamination, the pipework has to be made of rubber-lined or plastic-lined carbon steel,or plastic resistantto wet chlorine (eg PVC, Hetron orAtlac 382), orglass. 181 lfthere is any possibility ofliquid chlorine carry-over, liquidgas separators shouldbe installed on the linesto avoid excesspressure or overloadingofthe absorption system; these separators arefittedwith a temperature alarmto indicate the presenceofliquid chlorine in the separator. Furthenirnre, ifit is possible for liquid chlorine carry-over to take place, plastic pipework shouldnot be used. Pipework shouldbe sized to take account ofthe maximum possible flows under themost unfavourable conditions.

Absorptionequipment 1 82 Varioustypes of absorbers are usedfor the treatment ofventgases; suitable absorbers may be basedon the useofpackedtowers, vent injectorsor sparge absorbers. It can be an advantage ifthe system selected givesa suction on the plant.

183 Caustic soda liquor is the most convenient reagent for absorption ofchlorine in waste

gases. The concentration ofcausticsoda should not exceed21% NaOH becauseofthe risk of salt deposit causingblockages in the absorption plant. It is recommended that theflow of chlorine is controlled or restricted by an orifice plate toan acceptable maximum, so that the temperature risc in theabsorberdoesnot reduceits effectiveness. 184 Alternatively, for installations where there is no bulk storage for caustic soda liquorand wherelime orsodaash is available on the site, a lime slurry or a soda ash solution may be

used.

Instrumentation 1 85 It is essential that faults aredetectedquickly. Adequateinstrumentation with alarms shouldbe providedon the ventabsorption plantto ensurethere is a warning if equipment fails.

Significant faults are:

(a)

Lossofcirculation.

(b)

Chemical depletionofthe absorbing solution. Depletion of the solution canbe monitored by theuse ofredox or conductivity measurement.

186 Consider providing a pressure indicator fittedwithan alarmto showifthere is excessive venting or a blockage in the absorption system.

48 Safety advice for bulk chlorine installations

187 A monitorto detectchlorine shouldbe installed on the outletfromthe absorber. On detecting chlorine the following actions are needed: (a)

raisethe alarm.

(b) isolate the flow ofchlorine and

to process;

(c) increase the flow of liquor to thevent scrubber.

Theflow from the ventline to the scrubber should be maintained. Isolating the flow to the scrubber may put peopleat risk. Disposalofeffluentfrom the chlorineabsorption plant 188 The disposal of the liquorfrom the chlorine absorption plant requires careful consideration, as the presence ofhypochlorite maycreateproblems. Ifthe waste liquoris discharged withouttreatment, the possibility of interaction with other effluents should be investigated (eg a mixturewithacideffluentcanlead to evolution ofchlorine inthe effluent mains, and with ammoniacal effluentcan lead to formation ofnitrogen trichloride).

Undersome circumstances it maybe necessary to treat the effluent to reduce hypochlorite contentto an acceptable level before discharging to a sewer.Your chlorine supplier and your local Environmental Health Officer should be consulted on an environmentally acceptable meansofdisposal. For highlycontaminated effluent you shouldconsult the Environment Agency or in Scotland, the Scottish 1 89

Environmental Protection Agency.

Safety advice forbulkchlorineinstallations 49

— OPERATING INSTRUCTIONS One ofthe main risksofchlorine escapetothecnironmentis from incorrect operation ofthe plant.Operating procedures and the selection and training of process operators are therefore extremely important considerations for the efficient and safeoperation ofchlorine installations. Your operating procedures needto coer each process operation and meet legal requirements eg see references 18. 23, and 55-60 and the standards recommended in industry guides (seeAppendix 4 and reference 22). 190

191

Written instructions are required for:

plantmaintenance (see paragraphs 193-198); plantcommissioning inspection and testing (seeparagraphs 199-209); (c) plant modification and shut-down (see paragraphs 210-213); (d) all process work and procedures ino1ved in the unloading ofliquid chlorine tankers (seeparagraphs 214,215); (e) operation ofthe storage installation and utilisation ofthe chlorine (see paragraphs 214-229); and (f) emergency action to deal with chlorine spillages and gas escapes (seeparagraphs 247-263).

(a) (h)

Thesemay take differentforms depending uponthe complexity ofthe installation, eg from simple guide cardsfor straightforward operations to complete manuals for complex operations and installations. You should make the site manageror other designated person responsible for authorising any amendments to the procedures or schedules. Youneedto ensure that copies of the instructions include a flowsheet and indicate the valvesto be closed in an emergency. Instructions needto be available inthe workingarea for operators, and in the control roomor control centre for operators and supervisors. Supervisors shouldcheck regularly that operations are carriedout precisely according to the written instructions. 192

Safety advice for bulkchlorineinstallations 51

MAINTENANCE,INSPECTIONANDINSTALLATION General maintenance requirements 193 Satisfactory maintenance ofplant, equipment and instrumentation is essential to minimise risks. Themain Regulations that you needto comply withare: COSHH Regulations20, MHSW Regulations 18, and PSTGC Regulations (regulation 12). 23-25 The CIMAH Regulations (to be replaced in February 1999 by the COMAH Regulations - see Appendix 3), will also apply, depending on the size ofthe installation and the operating conditions. 194 Youwill needto preparemaintenance schedules definingthe required frequency for servicing, testingand inspection. These schedules shouldbe strictlyadheredto. Appropriate recordsofthe results must be kept as required by the PSTGC Regulations 1989 and COSHFI Regulations. The needfora writtenscheme of examination (WSE) is a separate requirement (ie regulations 8 and 9) ofthe PSTGC Regulations. Other aspects of maintenance are indicated in paragraphs 19, 44, 51, 56-58, 71, 81, 86-89,98, 127, 136, 143, 160-162, 165, 169, 173, 174, 225, 232, 233, 237, and 255. 195 You needto ensure thatdetailedwritteninstructions covering all routinemaintenance operations are available. These should be formally approvedand issued by the responsible maintenance engineer. Supervisors should check regularly that work is carried out according to these procedures. Pay particular attention to corrosion (see alsoparagraphs 167-170 ), especially where lagging is used; and to chlorine detectorsystems to keep such monitoring equipment in effective operation.

196 Close liaison is necessary betweenthe maintenance engineerand the process manager, to ensure that maintenance work is started only afterthe equipment concerned has beenadequately prepared by processpersonnel and is free from chlorine. 197 Adequate training is required for all maintenance personnel. This should include basic information on the propertiesofchlorine, safetyprecautions and emergency procedures (see alsoparagraphs 231-234).

Maintenanceofconnections 198 The inspection and replacement procedures for hosesand connections mustbe documented in accordance with thewrittenscheme ofexamination. Records ofthe inspections and replacements shouldbe kept. You needto:

52

(a)

Carryout engineering inspections operations.

(b)

Renewconnections at regularintervals, or as required as a consequence ofthe engineering inspection. Flexible hoses shouldbe renewed on eithera fixed time schedule or numberoftransfers as advisedby the hose supplier.

(c)

Hydraulically pressure test replacement flexible connections and dry them with dry air to a dew point lessthan -40°C beforeuse.

ofhosesat least once a year, or per every 1000

Safety advice for bulkchlorineinstallations

Inspectionandcommissioningofchlorine tank installations 199 It is your responsibility to organise and control inspections, testing and the commissioning ofyour storage tank. Your chlorine supplier, as a matterofpolicy, will give advice ifrequestedto do so and visit the plant before it is commissioned. They deliverchlorine only ifthey consider your installation to be satisfactory. Your equipmentinstaller also has responsibilities underSection 6 ofthe Health and Safety at Worketc Act. Youand your installerhaveresponsibilities underthe PSTGC Regulations; in particularthewrittenscheme ofexamination (WSE)must be in placebefore the pressure system goes into service.

200 You should determine the scopeofthe scheme for the examination ofthe pressure system, with expertadvice being obtainedifrequired. The WSE must specify all inspection and testingtechniques employed as requiredby Regulation 8 of PSTGC Regulations. The WSE reportmust contain specific details ofany deterioration found in the vessel or vessel ancillaries (seeRegulations 9 of PSTGC Regulations). It shouldstate which parts ofthe systemhave been examined, the condition ofthose parts and the results of the examination. Initial inspection and testing should be carried out in accordance with the design code(seeparagraph88). Thefirst thorough in-service examination ofa vessel specified for liquid chlorine duty shouldbe madeby a conipetent inspecting authority 24 within five yearsofcommissioning and preferably within two or three years. Thereafter the frequency offurtherthorough examinations shouldbe determined by the inspecting authority and noted in the examination reportas required by Regulation 9 ofthe PSTGC Regulations. The WSEcan only be modified after an examination is complete. The examination interval should not normally exceed five years. 201

202 A competent person to carry out such examination shouldhave the knowledge, experience and resources to search for, detect and assess particular defects associated with systems containing chlorine. Resources should include accessto appropriate non-destructive testing and laboratory facilities, togetherwith professional technical ability to relate inspection findings to appraisal ofvessel integrity, safe working parameters and future use. The competent personmust assessthe vessel for continued use with chlorine with respect to: (a)

maximum and minimum safeworkingpressures:

(b)

maxinium and minimum safeworkingtemperatures; and

(c)

safeworking loadsat supports and foundations.

Suchinformation shouldbe noted on the examination report, together withthe latestdate forthe next examination. 203

For laggedtanks,you need to remove sufficient lagging to enable the ofthe tankto be assessed.

condition ofthe external surface

Safety advice forbulk chlorine installations 53

204 Routine hydrostatic testing is not normally recommended, It is, however, recommended ifany modifications aremade to the storage vessels. Such modifications require a further examination by the competent person.

Inspectionprocedure Preparationthr internal inspection Before opening the storage vessel for inspection (see also paragraph 168), the vessel needstobe emptied ofliquid chlorine and purged to remove all traces ofchlorine. Procedures for this should be covered by preciseoperating instructions 46 and normally 205

include:

of all pipework connections to the vessel by removal ofspoolsor by off

(a)

breaking blanking

(b)

removingthe manlid and filling the vessel with water to which soda ashhas been addedto neutralise acidicmaterial which forms whenwater is addedto ferric chloride - the contentsofthe vessel shouldbe stirred thoroughly throughout the process;

(c)

siphoning offthe water and checking the atmosphere inthe vessel for chlorine and oxygencontent;

(d) controlling internal inspection ofthe vessel in accordance with the conditions set out in the Confined Spaces Regulations 1997 and the Code ofPractice 60 (see Appendix 3). Re-assembly a/terinspection

206 Procedures for this include: (a) drainingoffall water; (b)

thoroughly drying the vessel by dry air or nitrogen and removing and replacing joints on all connections tothe vessel;

(c)

re-fittingthe manlid;

(d)

pressurisation ofthe vesselwith dry air and measurement ofthe dew point of theair released;

(e)

successive pressurisation with dry air and release until the dew point ofthe air leaving the vessel is less than -40°C.

207 It is goodpracticeto overhaul all valveson the vessel at the time ofinspection. Following overhaul they needtobe driedout and stored in individual plastic bags pending reinstallation. Ancillary equipmentshouldalso be overhauled at each inspection. Bursting discs should always be renewed.

54

Safety advice forbulk chlorine installations

Testing (See currentversionofHSE GuidanceNote GS4 Safety in Pressure Testing,)61

208 Following completion requiredlevel, you needto:

ofre-assembly oftheequipmentand drying out to the

(a)

leaktestwith dry compressed air or nitrogen at around 8 bar gauge for several

(b)

introduce a small quantity ofchlorine to the storage vessel and pressurise with compressed air or nitrogen to around 8 bar gauge;

(c)

test all joints for leakage by releasing ammonia vapourfrom an ammonia bottleand observing the absenceofthe formation ofwhite fumes of ammonium chloride (this is a very sensitive and well-established method).

hours; then

If thereis flO sign ofleakage, you should leavethetank underpressure for about a further 12 hours and then repeat the leakage test.

209 All associated pipelines, which needto have beendriedout to a dew point less than -40°C, are thengas-testedfor leakage. Anyleakingjoints needto bemade gastight before introducing liquid chlorine into the system.

MODIFICATIONOF THE CHLORINE SYSTEM AND CLEARANCEPROCEDURES 210 You shouldonly modify the chlorine system after conducting a risk assessment (and possibly HAZOP).50 This ensures that approval is given by responsible staff covering the operating and engineering sections involved, and that appropriate procedures are put in place to deal with any required alterations. Proposed major modifications should preferably be discussed with your chlorine supplier. The Pressure Systems and Transportable Gas Containers Regulations 1989 23 require (Regulation 4) you to make arrangements for propercontrol ofrepairs and modifications to pressure systems. Anymodifications orrepairswhich could affect the integrity ofthe systemhave tobe defined and overseenby a competent person. 211

Formal clearance procedures needto be established as part ofa permit-towork system 46 for: 212

(a)

ensuringthat the plant is in a satisfactory condition for maintenance and internal examination, appropriately isolated and free from chlorine;

(b)

covering all work inthe chlorine areawhichrequiresthe use of cranes, mobile equipment, welding sets or other plantwhich could lead to accidental damage tothechlorine system. This safeguard is necessary even ifthe work does not directly involve the chlorine-containing linesor equipment;

Safety advice forbulkchlorineinstallations

55

(c)

formally accepting thatthe plant issafeforoperation after theworkhas been completed.

213 The storage installation must be emptiedofliquid chlorine during inspection and maintenance ofthe expansion vessel unless provision has been made for alternative means ofreleaseofpressure.

UNLOADiNGOFLIQUID CHLORINEFROMROAD TANKERSTO STORAGE 214 Transfer ofliquidchlorine from tankers to liquid chlorine storage may be achieved either by use ofdry compressed air or dry nitrogen or by use ofchlorine gas pressure. The methods employing dry compressed air or nitrogenare simpler and theuse ofchlorine gas pressureis normally encountered only in special circumstances. The gas supplypressure needs to be about 1 .7bar above the pressure in the storage vessel (ie the saturated vapour pressureofchlorine at ambient temperature) to effectthe transferofliquidchlorine from thetransportvehicle to storage. 215 You should base your operating procedures for unloading on the outlinegiven in Appendix 6. The procedures should specify requirements for inspection and testingof couplings beforeuse (see paragraph 198). Some operational details are summarised in points(a)-ffl: (a)

Visual inspection, beforeuse, with particularattention to threads. (NB hydrocarbon oils or greasesmustnot be usedon threaded or other connections - see Appendix 2, and paragraph561j).)

(b)

Use ofnew gaskets(see paragraph 56(h)) each time connections are made to the tanker.Compressed asbestosfibre(CAF) gaskets are not recommended for environmental reasons.If CAF is used the discardedgaskets shouldbe collected and disposed ofsafely, bearingin mindthat they contain asbestos.

(c) Provingofthe tightness ofall connections before introducingliquid chlorine. A gaseouschlorine test is recommended (seeparagraph 208c)aftera dry air/nitrogen test. (d) Capping pipes afteruse and protecting pipes to reducethe possibility ofaccidental damage to threads or ingressofmoisture, and provide an additional safeguard againstan accidental releaseofchlorine due toan error in valve operation.

Testingfor leakswithammonia bottle (seealsopam208c). Thedriver tests thejointsnearthetanker dome

56

(e) Consider continuous purging with dry air or nitrogen (dewpoint less than-40°C).

Safety advice for bulkchlorineinstallations

(f)

It is important to vent padding gas' totheabsorption system (see paragraphs 171-184) afterthetransfer operation is complete, to restore tile pressurein the tankto about the vapourpressureofchlorine at tile temperature ofthe tank contents. Ifthis is not done, the tank mayover-pressurise as it warms up. and cause the relief system to operate.

USE OFISO(DEMOUNTABLE)TANK CONTAINERS

(h/urineISOfunk containeron route

ISOtankcontainer:derail 0/tile conhiectionpoint

216 An ISOtank container is a pressurevessel mounted in a substantial steel frame. They are used predominantly for rail and sea transport and where containers needtobe stacked. They vary in capacity. and in thecase of chlorine the largest vessels can holdabout 14 tonnes. ISO containers are usually sized to meet customer requirements and invariably eachtank is designated to a specific customer. Ifyour planned consumption ofchlorine is not enough to justify investment in a bulktank and too greatfortransportable containers I to be used,an ISO container may be appropriate. Ifthe containerchangeover periodexceedsfourweeks you should discuss the use ofone tonne drums with your proposed supplier. 217 Thedriveris responsible for ensuring that the ISO container traileris correctly berthed, the motiveunit is uncoupled, and that the landing legson thecornersofthe trailerare in place.

218 The design ofthe ISO berth should be similarto the requirements for an offloading bay for road tankers (see paragraphs 31-41) eg the ground must be level and the area well-lit, awayfromtrafficetc. The ground surface needstobe resilient enough to preventthe local loads from the landing legs damaging the surface or allowing sinking. Considerspill containment (eg use kerbing, serni-bunding or collection sumps) inthe eventofany incident. Although the frame provides substantial impactresistance, to prevent damage to thetank and its fittings you should providecrashprotection similarto that required for fixed tanks. Similarly, you should providecrash protection for yourplant against inadvertent movement during the berthing operation.

Safety advice forbulk chlorine installations

57

219 Youwill needto provide suitable flexible hose connections to connect the tank to your process. Theseshouldbe ofsufficient length and unobstructed routing so that a leg collapse would not stress the hose or connecting joint. 220 Youwill also needto drawup procedures for connecting and disconnecting the tank to your process. Theseprocedures and the associated interlocks are effectively thesame as for roadtanker unloading operations (see paragraphs 35, 39-41, 214, 215 and Appendix 6). They needto be carried out with the motive unit uncoupled and always with the driver present as it is thedriverwho is responsible for making/breaking and testing the integrity ofthejoint. Barriers should be lowered whentheISO is berthed and thebarrier linked mechanically or by softwaresequence tothe flexiblehose connection as drive away protection. Asthe ISO tankeris not fittedwith a reliefvalve(a regulatory requirement 14) measures must betaken to prevent overpressure from radiantheat sources such as stored flammables, or from inert gas supplied to raisethe pressure in thetanker transferring chlorine to the process.

You will need to agree precautions with yoursupplier to ensure there is no potential forreverse flow from your plant into the ISOtank (seeparagraphs 224-229) and

221

implement them.

TRANSFEROF CHLORiNE TO THE CONSUMINGUNITS 222 Transfer achieved by:

of liquid chlorine fromthe storage tanksto the consuming units maybe

(a)

using the vapourpressureofthe liquid chlorine alone;

(b)

padding the chlorine storage tank with dry compressed gas;

(c)

transfering the liquid chlorine to a separate tank from which it is pumped using a pump specially designedfor use with liquid chlorine.

Methods (a) and (b) are normally themost satisfactory for customer installations.

Underexceptional circumstances and by agreement with your chlorine supplier, liquid chlorine from the tankers maybe transferred directlyto your process or to a chlorine vaporiser. This is a specialand unusual arrangement; the adequacy ofthe control systems and procedures shouldbe verified by a risk assessment. Ifyou see a regular need for this arrangement you should consider the use of ISO tank containers (see paragraphs 216-221 ). 223

Transfer ofgaseous chlorine 224 With the exception ofventing, you shouldavoidthe discharge ofgaseouschlorine from tankers or storage vesselsdirectlyto a process. Such a procedurecancause a potential hazard51 by concentrating thetrace amounts ofthe unstable substance, nitrogen trichloride, normally present in the chlorine - see alsoAppendix 2, paragraphs 15, 20. In addition, a risk ofsuck-back ofmoisture or other materials into the vessel ortanker exists (seealso paragraphs 100,161).

58

Safety advice forbulk chlorine installations

Transfer ofliquidchlorine using vapourpressure 225 For many applications, the vapourpressureofthe liquid chlorine in the storage tank is adequate to transferthe liquid chlorine to the consuming unit, although theremay be problems in cold weatherwith outdoor installations, as the vapour pressure will fall as the liquid chlorine cools. Ifthe demandrate is likely to cause problems in cold weatherone ofthe methods below (paragraphs 226, 227) should be used. Whenthe liquid hasbeen removed fromthe tank, it may alsobe acceptablefor part ofthe remaining gas to be used on process. However, a minimum positive pressure should alwaysbe maintained in the storage vessels; this should be definedfor each system. You should be aware thatthis method increases therisk of nitrogen trichloride accumulation in the tankand you should implement additional monitoring. 52

Transfer ofliquidchlorine bypadding with dry compressed gas 226 Transfer by padding the storage tankswith dry compressed gas is straightforward; the action and precautions whichwill be requiredarc similarto thosedetailedin paragraphs 134-141. Transfer ofliquidchlorine usinga separate pumpingtank 227 Completely enclosed 'canned' pumpshavebeen developed fortransferof liquid chlorine: these are used when the chlorine is requiredat higher pressure, typicallyabove 7 bar gauge, or when the use ofdry inert compressed gas is not acceptable. The liquid chlorine is first transferred from storage to a separate pumpingtankwhichusually consistsofa pressurevessel with a bottom connection. The liquid chlorine is withdrawn from thebottomofthe pumpingtank to the suction ofthe pump. A remotelyoperated valve is preferably installed insidethe tank or between the pumping tank and the pump for isolationin emergency. The design ofthis system shouldensure thatthe nett-positive-suction head(NPSH) is adequate to meet the minimum requirements for the pump used. Ifyou see a need for this arrangement you should seek advice from your chlorine supplierat an early stage.

Precautions 228 You shouldmakearrangements to rapidly stop theflow ofliquid chlorine from the storage vessel in theeventoffailure at the chlorine consumingplant(see paragraphs 35, 79, 95-97). Longliquid chlorine pipelines to consuming units may need tobe protected against overpressure (see paragraphs 61-67).

229 You needto design the installation to prevent, or minimise the risk of suckback of aqueous solutions or process liquids from an absorption system. This requiresdetailedconsideration at the design stage and might involve the installation ofa non-siphoning barometric leg or a reverse flow/pressure-measuring device.

Safety advice for bulk chlorineinstallations 59

Generalguidelinesfortraining People have legal duties to comply with the safetyprocedures associatedwith theirwork. However, it is never sufficient simply topresume that staffwill know andunderstandwhat to do. Positiveinstruction and training is needed. Health andsafetytraining shouldtakeplace during working hours andshould bepart of thejob. Trainingis vital in helpingto preventincidentsandto minimise the consequences iftheydo happen. Thinkabout who should be trained, in what, andto what level

ofcompetence. Trainingwill helpemployees understandthe healthandsafetyaspects oftheir work. Initial trainingfor new staffshouldbefollowedup with newor refreshertraining as required. Training must includeanyone whoworks on the site. Operators, managers, staff

andoccasionalvisitors, such as maintenance contractors,may allneed some training.

Trainingcan take manyforms,rangingfrom on-the-job training linked to information notices, written instructions etc, toformaltraining courses. The type oftrainingshould be appropriatetotheactivities and dutiesofthose to be trained and thehazards at the site. Involve andconsultstaff Where there is a recognisedtrade unionsafety representative, theywillneed tobe consulted. They will know many ofthe hazards occurringin everyday situations. Caterfor unusualoccurrences. Information, instruction and training must be understoodby those to whom theyare given. Ifpoorperformanceshows that training is not working, the training will needto be reviewed andimproved. Do not assumethat previousexperience or formal qualcations will mean that new employees do notneed training. (You are advisedto keepa training recordfor each staffmember, so that it is clear what training they havereceivedand, therefore, which duties theycan be expected to perform.)

60 Safety advice for bulk chlorine installations

230 It is essential that the personnel selected are ofadequatephysical fitness and they shouldpass a medical examination beforeengagement. Operators needto be capable ofeffective communication and be reliable understress conditions. Previousexperience in the chemical or similarindustry is very desirable. TRAINING 23 I

Youneedto ensure that site personnel are properly trained and practised in each procedure. You should developand implement a training programmewhich includesboth 'off-the-job' and 'on-the-job'aspects. You shouldregularly assess the programme fir its effectiveness. 232 Off-the-job training needs to include basic information on the following: (a)

statutory requirements, ACOPsand guidance;

(b)

Physical, chemical, and toxic properties

(c)

safetyprecautions;

(d)

personal protective equipment;

(e)

processoperations and systemconfigurations;

(f)

safesystemsofwork including 'permits-to-work';

(g)

containertypes, methods ofhandling and security;

(h)

operational procedures;

(i)

maintenance procedures;

(j)

defectrectification;

(k)

automatic control systems;

(1)

leakage detection systems;

ofchlorine;

(m) emergency procedures, including leakagecontainment; and (n)

chlorine suppliers'support facilities.

Maintenance engineers needtobe providedwith more detailed training on these topics, together with training on system integrity testing, pressurereduction,and safetydevices. On-the-job training needsto be carriedout underthe guidance ofan experienced operator/maintenance engineer who is familiarwith the process,with 233

Safety advice forbulk chlorine installations 61

an emphasis on safety precautionsand methods ofdealingwith emergencies. Give particular attention to the following aspects: (a)

the hazards and characteristics ofchlorine;

(b)

safe methods ofplantoperation, including connection to and disconnection from supply systems, and regular monitoring and verification ofthe adequacy ofthe systems adopted;

(c)

niethods of maintenance and inspection, in particular the application ofrelevant standards and codes (seealso paragraphs 193-198).

(d)

46 special operations; eg, plant shut-down and start-up, methods ofisolation and of for maintenance and preparation equipment periodic inspection;

(e)

the location and operation of emergency shut-offvalves, ventilation equipment, alarms,

(f)

the procedures to be followed ifa release occurs, these should include isolation and containment ofthe releaseand emergency plans; the procedures will needto be sitespecific and cover different scalesofrelease(see alsoparagraphs 247-263);

(g)

leak detectors dc:

training in the use ofall personal protectiveequipment (PPE)supplied (seeparagraph 237). Maintenance staff should also cover defect rectification.

Competency and audit 234 Competence in the abovetopicsneeds to be assessed through post-training assessments using documented procedures. Itis recommended that training and safety procedures are auditedannually by management or an auditteamwithrelevantexperience as part ofyour company's auditprogramme. Internal auditsniay be supplemented by external audits from chlorine suppliers underthe CIA's initiativefor responsible careand product stewardship. or by other competent peopleat intervals of approximately three years.

PERSONALPROTECTIVEEQUIPMENT(PPE) 235 Chlorine is a highly toxicsubstance: acute exposure can be fatal (see Appendix I). You thereforeneedto establish safe working practices and controlmeasures (including PPE) and ensure that theyare understood by operatives. Safe procedures are vital where it is necessary to enteran enclosed storage space or a room where a chlorine leak has occurred. Work in such Guidance on how to confined spaces is subject to The Confined Spaces Regulations 1997. 60 comply with the Regulations is given in an Approved CodeofPractice. The precautions identified must be implemented and suitable traininggiven to operators.

236 A common soLirce of exposure to chlorine is in operations involving the making and breaking ofchlorine pipework connections, particularly to containers. Stepsshouldbe takento

62 Safety advice for bulkchlorineinstallations

preventor, wherethat is not reasonably practicable, i-educe personal exposure to chlorine 20 by means otherthan personal protective equipment. When PPE, including respiratory protective equipment, needstobe worn, equipment manufactured after 30 June 1995 should carry the 'CE' mark, to indicatethatthe equipmenthas beendesignedand tested to meetthe basic requirements ofCouncil Directive 89/686/EEC.

237 Respiratory protective equipment (RPE) that has beenapprovedby the HSE or is claimed by the manufacturer to conform to a standard approved by HSE, and whichwas manufactured before 1 July 1995, can continue to be used at work, providedthat it is still suitable and maintained in good condition. All personnel who arerequired to use RPE (eg, respirators, breathingapparatus, or escape breathing apparatus) must receive adequate instruction and training in its safeand correctuse. The RPE mustbe thoroughly examined and tested in accordance with the manufacturer'srecommendations (typically at least onceevery month) and records kept.20

Selectingsuitable respiratoryprotectiveequipment(RPE) 238 Where PPE including respiratory protectiveequipment (RPE) needsto be worn, you must ensure that it is properly selected and that it provides adequate 64 66 protection. 63. When selectingRPE you shouldconsult relevantguidance 65, 20 and base your selection on the results of a risk assessment. The selected RPE must: (a)

provide adequate protection for yourparticularcircumstances (eg for specific tasksor for emergency escape); and

(b)

be compatible with other demands ofthejob and the working environment.

The selected RPE should make theoverall risk ofinjurywhile wearing RPE as low as reasonably practicable. 239 When selectingRPE for a particularapplication, a two-stage selection procedure is therefore recommended: (a)

Based on theresultsofyour exposure risk assessment: (i)

decide whethera respiratoror BA, or eithermay be used;then

(ii)

determine the minimum protection required from the RPE. This is done using the equationbelow. In deciding the maximum allowable concentration insidethe facepiece you will needto take account of recognised exposure limits (see Appendix 1) or takeaccountofyour inhouse limits.

Minimum ProtectionRequired

Workplace concentrationoutside thefacepiece ottheRPE Maximum allowableconcentration insidethe faccpiece ofthe RPE

Safety advice for bulkchlorineinstallations 63

For emergency escape purposes where the exposure will be lessthan 15 minutes, the maximum allowable concentration in the above expression is the Short-Term Exposure Lmit (STEL) (see Appendix 1). Now compare the Minimum Protection Required value with the Assigned ProtectionFactors (APF) indicated in HSG5366and identify a selection ofequpment. (APFs shown in HS(G)53 havebeenpublished by the British Standards institution ).6 These APF figures are a guide, not a hardand fast rule. Indeed, it should be recognised that protection levels belowthe APF are possible whenRPE is unsuitable for thetaskand is not suited to the wearer and the environment. Where advice given in HSG53 is properly takeninto account, it is possible to achieve protection at or above the published APF values. Youmay use higherAPFs ifyou have good quality information (eg satisfactory face-fit results forthosewearing RPE) to demonstrate that theyapply in your workplace conditions and to the selected RPE. Youcanuse the AFF for the equipment selected to estimate concentration insidethe facepiece. Concentration inside the facepiece

= Workplace concentration outsidethe facepiece APF

Note: NominalProtectionFactors (NPF)values have been used in thepast, for iclentij5'ing aselection ofequipment. This procedureis no longer validbecauseworkplace studies haveshown that mani' wearersmar notachievethelevel ofprotectionindicatedby NPFs. (b) The next stage isto take accountofthe factors detailedin paragraphs36-47 of HSGS3 to help narrow down the choice. Alwaysinvolve the wearers inthe selectionprocess, and wherepossible provide them with a choice ofsuitable RPE. This will helpto ensure that it is suited to them individually, and increase the chances that it will be acceptedand worn correctly. Where there is doubtaboutthe choice, you needto confirm with the manufacturer or supplier that thechosen equipment is suitable for the task and the conditions in which it istobe used. They have dutiesunderthe Healthand Safetyat WorkAct etc 1974 to provideinformation on thelimitations and capabilities oftheir RPE. 240 At somechlorine installations it is common practice for personnel to carry halfmask respirators fitted with suitable filters (eg: type and class: B 1; colour: grey) for protection againstchlorine. The

purposeofthis type ofrespiratoris to providean immediate protection inthe eventofan incident involving low concentrations ofchlorine gas so that the wearercan escape into freshair. This type ofhalfmask respiratorhas an APF = 10, ie the maximum allowable workplace concentration = 10 x STEL = 10 ppm.

241 A full facemaskwith cartridgeor canisterhas an APF of40. Theuse ofthis type ofrespiratorwould typically be inor very near the open air duringthe connecting up or disconnecting ofcontainers or breaking into previouslypurgedchlorine systems. The operating procedures specific tothe site should state whether the

64 Safety advice forbulk chlorine installations

respiratorhas tobe wornfor each operation, or be 'at the ready' to be put on in case ofneed. A respirator(eg a maskfittedwith a filter or canister) is not suitable for use in atmospheres which are immediately dangerous to life or health. In other words, respiratorsare not suitable for operations where there is a potential for a significant releaseofchlorine gas. In these circumstances a suitable breathing apparatus (BA) shouldbe worn. 242 Filters havea shelf-life specified by the manufacturers beyond which they shouldnot be used. Oncefilter-canister seals have beenbroken, filterlife will depend on usage, contaminent concentrations, breathing rateetc. Your risk assessment, combined with information from the filter manufacturer, will determine the useful life ofrespiratorfilters; yourdecisionsneedto be communicated to the wearers. Once unsealed, filters should not be stored for re-use, but they may be used over a numberofconsecutive days, providedthey havenot been exposed to concentrations of chlorine similartoor abovethose they are providedfor.

A negative pressuredemandBA withfull face maskhas an APF of40. For major leaks a positivepressure demand BA with full face mask(ie a self-contained BA)wouldbe appropriate, providedthe minimum protection requiredwas consistent with the APF (2000), see paragraph 253.A self-contained breathing apparatus (SCBA) shouldalwaysbe worn (possibly with a gas-tight chemical protective suit) when entering an enclosed space or chlorine roomwherea significant leak hasbeen detected or suspected. This isbecausethe chlorine detector maybe some distance away from the source of the leak or pocketsof 'trapped' gas which are not dispersed by the ventilation system. The concentration in such areas maybe much higherthanthosedetectedby the alarm system. 243

244

In certain circumstances, compressed airline breathing apparatus (CABA) may

be suitable. However, theserestrictthemovement ofthepersonnel and thetrailing hose canadd to therisk in areaswith obstructions. In such situations a selfcontained breathing apparatus maybe appropriate.

245 Forindoorinstallations with multi-stage alarms, the forced ventilation system willhavebeen switchedoffon activation ofthe higherlevel alarm. People entering the area to identify and eliminate the source ofthe leak should wear suitableBA, see paragraphs 252-255). No personshouldworkalonein these circumstances. Any back-up staff in attendance for emergency action should wear suitable BA 'at the ready'. 246 Emergency escape BA is not intended for use duringnormal work and therefore it is not recommended by HSE for anything other than emergency escape use.

Safety advice forbulkchlorineinstallations 65

,

Note: Further guidance will be available when the COMAII Regulations come into force in February 1999. 247 You needto inform the appropriate Fire Authority and Police Force of the presence ofchlorine at your site. You shouldalso involve them and your chlorine supplier at an early stage whendeveloping and updating your emergency plan and procedures. Your emergency arrangements shouldbe basedon a risk assessment and include procedures on how gas releases maybe dealtwith safelyby site 69, 70 Your personnel and on whetherto call for assistance from beyondthe risk assessment shoLild also address fire safety ofthe process or installation and possible impacts from neighbouring sites. General fire precautions should comply with the requirements of the FirePrecautions (Workplace) Regulations l997.

site.'

Your emergency planshouldcoverthe foreseeable range ofchlorine releases for your site: a summary of sonicofthe important elements ofa plan is given in Appendix 8. A copy ofthe plan should be made available to all personnel involved in its implementation. It is recommended that the plan includes thenamesor positions ofthe personswho will sound the off-site alarm. This may be someone on-site, or it may undersomecircumstances be the responsibility ofthe first Fire Officer on the site in the event of an emergency. The plan shouldalso include firstaid (see Appendix I ) and evacuation arrangements both oil-site and, ifappropriate, off-site (see Appendix 8). 248

249 Each installation needs to have means ofwarning all workers that a gas escape has occurred. A wind direction indicator, mounted in a highly visible location, needs to be provided to help personnel decide the bestdirection in whichto escape. The appropriate actionto hetaken following a gas escape warning shouldbe defined in written mstructions, and appropriate training given. 25() For a minorgas escape, you mayonly need to plan simple actions. In other circumstances however, a further system ofspecialwarnings maybe required, which initiatesthe emergency plan and, ifnecessary, the off-site emergency plan. The first call for assistance shouldbetothe eniergency servicesfor incident control and rescue, and then to Chlor-Aid, through your supplier who will offer advice on

Safety advice forbulkchlorineinstallations 67

how to deal withthe release. UnderChlorAid the chlorine producers and suppliers (see Appendix 4) collaborate in dealingwith chlorine emergencies at bulk installations 71 throughout the UK.The arrangements are outlined in a booklet publishedby the CIA underthe chemical industry'sResponsible Care initiative. Arrange regularpractices ofthe emergency plan. Someoftheseshouldinvolve the emergency services, whowill advise on a suitable frequency. 251

EMERGENCYEQUIPMENT 252 Yourrisk assessment should considerthe extent, type, and location ofthe emergency equipment, including theneed for chemical protection suits whichprovidetotal encapsulation. These can be compressed airline supplied full suits or full protective suits worn over self-contained breathing apparatus (SCBA). SCBA with fullfacemask confoniiingto BSEN 137 (SCBA) 72 or airline BA confonmng to BSEN 139 has an APF of2000 (butsee paragraphs238-246). Selfcontained equipment will supply air for up to about 40 minutess (seethe manufacturer's details). Thesesets are providedwith a warning systemto alert thewearerto leavethe contaminated areawhenthe air cylinders are becoming empty. Compressed airline breathing apparatus providesthe same protection withouta time limit, but doesrestrict freedom of movement in search and rescue operation. 253

254 As withother RPE,emergency escape breathing apparatusshouldbe CE-markedand incorporateface protection(eg in theform ofa hood orfull face mask). SuitableHSE-approved escapeequipmentmayalso be used ifit was manufacturedbefore 1 July 1995. Such equipment is for escapeonly and not for use during routine work. 255 Emergency and rescueequipmentshouldbe

available and readily accessible in all chlorine plant areas, and its location suitablymarked. Such equipment needs tobe regularly inspected and maintained. An inventory ofthe equipmentshould be kept and attached to the plantoperational and emergency procedures.

CONTROLOF LEAKAGES 256 Local alarmstationsto provide earlywarning of chlorine escapesare an essential link in the emergency procedure. The use ofchlorine detectors and alarms is coveredin paragraphs 113-118. Localalarm stations (push-button type preferred) should be located at strategic pointsnear chlorine storage installations; generally two alarm stations on convenient escape routesfrom the chlorine unloading terminal! storage tank areaare sufficient. The local alarm stationsmay actuate the worksemergency alarm directlyor indirectly by raising an alarmin theemergency control centre and the main control room. Preferably in largeworks the local

68

Safety advice forbulk chlorine installations

alarm station should actuate a distinct local chlorine alarm to warn people offfrom

theaffected area.

257 The alarmstationsmay also actuate the remotelyoperated shut-offvalveson thechlorine storage tankswherethis is consistent with thesafe operation oftheuser plant. 258 Materials and equipment including sand and plastic sheetsto contain spills of liquidchlorine shouldbe readilyavailable. Covering a stabilised spill with plastic sheetsis often the best action. Application of foam would cause renewed evolution ofvapourbecauseofthe heat supplied. The needfor foamand water spraysshould be discussed withthe chlorine supplierand local fire authority, sincethe useof foamand water may, in certaincircumstances, aggravate the problem. The fire authoritymaycarry stocks ofsuitable foam, but the decision to use it shouldbe takenin conjunction with the senior technical manageron site. 259 Watershouldneverbe added to a spillage of liquid chlorine or sprayed ontoa leakingtank. However, water hoses or fog sprays directed at a chlorine gas cloud can helpdilute it as a result ofthe air entrainment generated by the jets ofwater.

Releasesinside buildings

Ifthe spill is indoors and contained by the useofsand or a bund it will rapidly coveritself with a coatingofslushychlorine hydrate and a cold vapour layer. Such a stabilised spill shouldbe coveredwith a plastic sheet(seeparagraphs 258 and 259). Fora severe leak,possiblyarising from a failure ofpipework, the chlorine buildingwill providesome delay to the release of the gas to the open air, provided vents and apertures areclosedor sealed. Thiswill give moretime forthe technical staffand management to identify and deal withthe source ofthe release. In dispersing the contained release from a chlorine roomit is stillessentialto consider the off-site consequences and it maybe necessary to sound the off-site alarm(when fitted)to alert people to go indoors and remainthere. It is for the emergency services to consider clearingpeoplefrom the area immediately downwind of the installation after such a release.

260

A significantreduction inthe releaseofchlorine from a buildingis only obtainedifthe leak is quickly controlled and the rate ofair change in the chlorine roomis low. The ventilation systemshould, therefore, be switched off(unless a scrubbing systemis installed to remove chlorine from the exhaustgas) and all apertures needto be closed or sealed. 261

262 Consider usingan additional sensorcapable of measuring concentrations up to 500 ppm and giving a visual display outside the chlorine room and inthe works control room. Sucha display is useful for assessing the significance ofthe leak and whether it can be isolated safely. Once concentrations exceed 1000 ppm (this is

Safety advice for bulkchlorineinstallations 69

about the threshold concentration for thecloud tobe visible),personnel dealingwith the release should take additional precautions and shouldwithdraw to a safe area as soon as they are aware that they are breathing contaminated air.

Aftera leak or substantial releasehas beendealtwith it will be necessary to ventilate the chlorine rooni thoroughly. Operators should not remove any RPE until they haveremoved clothing (whichmay be contaminated with chlorine) and are in a safe environment. 263

70

Safety advice for bulkchlorineinstallations

—

D1

TOXICITY

Chlorinehas a perceptible odour that can he detected by most people at a concentrationof 0.3 ppm (v/v) and by some at concentrationsas low as 0.02 ppm. The Occupational Exposure Standard (OES)74 for exposureto chlorine is 0.5 ppm: this is a time-weighted average concentrationover a period of' 8 hours. The Short-Term Exposure Limit (STEL)74 is I ppm: a time-weighted average over 15 minutes. I

2

It producesclear sensory irritation at concentrations of 05-1 ppm and

aboe.7 Irritationof the mucousmembranesof the eye and nose, and especially of the throat and lungs, is caused by exposureto chlorine at levels ofaround 1-15

ppm. In general. irritation becomes intolerable at concentrations ofabout 4 ppm.76 Concentrationsof 50 ppm or more aredangerouseven for exposures of about 5-10 mins; they may cause inflammation of the lungs with accumulation of fluid. Occasionally the development of respiratory symptomsmay be delayed for up to two days after exposure. However, there is no convincing evidence of serious long-term sequelae following recovery from a single exposure to chlorine.75 Exposure to 1000 ppm may be fatal after a few breaths.77 Death results from lung damage. It can either occur rapidly (from within hours to a couple of days post-exposure). due to oedemaand congestion, or it can be somewhat more delayed (several days) due to secondary pneumonia. 3

4 The harm from exposure to chlorine is proportional to the 'toxic load' defined as the product of the square ofthe concentration and exposure time. For risk assessment work, HSE uses a 'dangerous toxic load' 78 (DTL) of: DTL 108 000 ppm2min hich is potentially fatal to the most vulnerable members of the population. Thus exposures to 104 ppm for 10 minutesor 73 ppm for 20 minutesetc are potentiall) fatal; the chance of fatality depends on many factors.78 Safety advice forbulkchlorineinstallations 71

FIRSTAID 5 When liquid chlorine comes into contact with the skin or mucousmembranesii can produce seriousburns which need to be treated by a medically competent person. People who have inhaled chlorine gas should be moved as quickly as possible into 'fresh air', laid in a resifLil position with thehead and chest raised, and kept warm. It is essential that qualified medical attention is obtained quickly, as serious symptoms may develop up to 48 hours later. Anyonewho has been affected by chlorine gas should be examined locally by a medically competent person or sent to hospitalby ambulance.

First-aidattendantsshould be aware ofthe dangers arising from gassing by chlorine. The following basic rules shouldbe observed: 6

(a) if chlorine has affected the eyes. they shouldbe irrigated with plenty of clean (preferably rap) water: (b) contaminated clothingshould be removed washed with plenty ofwater (c)

in a well-ventilated area and affected skin

mouth-to-mouthresuscitation should not be given ifthe patient is breathing, becausethere is a risk ofthe attendant being harmed. However, oxygen may be administered or resuscitation equipmentused by suitablyqualified personnel.

More comprehensive guidanceis given elsewhere.79

72 Safety advice for bulk chlorineinstallations

i Chlorine is a grecnish-yel1ogas at ambient temperatureand pressure. supplied commercial1 as a liquid under pressure.

I

It is

Commercial liquid chlorine conforms to BS 3947:l976. This Standard specifics a minimum limit for the chlorine contentand maximum levels for water content and residue on eaporation details ofthe methodsof analysis for gaseous impurities (carbon dioxide, oxygen and nitrogen), water content, nitrogen trichloride. and residue on evaporation are also given.

2

3 Traces of dissolved gaseous impurities in chlorine arenot normallysignificant for most applications moisture contenthoweveris extremely important because of the corrosive nature of wet chlorine.

Trace residues which are left on evaporation,usually chlorinated organic productsor ferric chloride, may lead to blockage of pipelines, valves or instruments. Nitrogen trichloride can be potentially dangerous5 L52 if the vaporisationprocess leads to its concentrationin residues, but this is generally not considered to be a problem in drum and cylinder installations. 4

5

Physicalproperties

Atomic weight

35.46

Molecular weight

70.91

Density liquid

1561 kg/m3 at -35°C

1468 kg/rn3 at 0°C 1410 kg/rn3 at 20°C

gas

3.173 kg/rn3 at 0°C and at 20°C relative to air)

I bar absolute(relative density 2.490

Safetyadvice for bulkchlorineinstallations 73

Boiling point at 1.0133 bar absolute Meltingpoint Critical temperature Critical pressure Vapour pressure at 20°C Viscosity: liquid at 20°C

-34.05°C -101.6°C 144°C 77.1 barsabsolute

6.7 bars absolute 0.35 cp

I volume of liquid chlorine = 463 volumes of chlorine gas at 0°C and I bar absolute 1

kg of liquid chlorine

0.3 19 m3 ofchlorinegas at 0°C and

I bar absolute

The variationof the vapour pressure of liquid chlorine with temperature is given in Figure A2.l.

Thermalproperties' Specific heat (liquid chlorine between 1°C and 27°C) 0.236 kcal/kg!°C Specific heat (gas at constant pressure at 6.9 bars absolute or less and between 1°C and 27°C) 0.11 3 kcal/kg/°C

Ratio of specific heat at constant pressure to specific heatat constant volume 1.355 Latentheat of fusion

21.6 kcal/kg

Latent heal of vaporisation at 0°C

63.2 kcal/kg

Coefficient of cubicexpansion (liquid chlorine

at 20°C)

0.002! per °C

This coefficient is sufficiently largeto result in excessive pressure should liquid chlorine be trapped in pipework between two closed valves with no gas space. Heat of reaction of chlorine gas with sodium hydroxide liquor 348 kcal/kgof chlorine. 6 While the above data give a general summaryof the physical and thermal propertiesof chlorine, more detailedinformation is needed fiir use in plant design calculations.

74 Safety advice forbulk chlorine installations

Figure1 Variation ofchlorine vapour pressure with temperature 20 .0

19 18

U) U)

17 16

K!)

15 14

13

12 11 10

9 8 7 6 5 4 3

(1

60

50

40

30

20

0

0

10

20

30

40

50

60

Temperature C

Solubilitp?t chlorine in waler 7 Chlorine dissolves slightly in water to give a solution which has oxidising, bleaching and germicidal properties. The solubility ofchlorinein water increases with the partial pressure ofthe chlorine. The table belowgives the solubility of chlorinein waler at differenttemperatures for a total pressure of I bar absolute: ° Temperalure C gramsofchlorineper litreoJwater

10

15

9.97

8.5

20 7.29

25 6.41

For a total pressureof I bar absolute, thepartial pressure ofchlorine reduces as the water temperature(and hence the partial pressure of waler vapour) increases.

Safety advice forbulk chlorine installations 75

8 On cooling below 9.6°C, crystals ofchlorinehydrate (C12.8H20)are deposited. For this reason, wet chlorine in process must always be kept above this temperatureto avoid the blockages which would otherwise occur as a result ofthe formation of solid chlorine hydrate. 9

A solution of chlorine in water forms hydrochloric acid and hypochlorousacid: Cl7 + H,0

HCI + HOCI

chemicalproperties Dry chlorine at ambient temperaturesreacts directly with many of the elements producing chlorides both of non-metals (eg sulphuror phosphorus)and of metals (eg iron in a finely divided form, aluminium or titanium).Dry chlorine at ambient temperaturedoes not attack steel, copper or nickel, but these metals are attacked at highertemperatures. Steel combineswith dry chlorine above 200°C and, since the reaction is exothermic, the rate ofreaction may increase rapidly. Reactionwith nickel does not take place until the temperatureexceeds 500°C. 10

II Traces of moisture in chlorine lead to rapid corrosion of steel, copper and nickel. 12 Titaniumis resistantto wet chlorine between 15°C and 100°C but reacts violently with dry chlorine and shouldnot be used: but see paragraph 18.

Chlorine dissolves in cool aqueous solutionsof alkalis to produce solutionsof hypochiorites; in hot or boiling aqueousalkalis,chloratescan be produced. 13

Chlorine reacts vigorously with many organiccompoundsincluding mineral oils and greases, producing chlorinated products. The mechanism is either directaddition to unsaturatedbonds or substitutionof hydrogen. In the latter case, hydrogen chloride is formed as a by-product. 14

Mixtures ofchlorine and hydrogen are explosive over a large range of concentrations; the explosion may be initiated by a spark, by photochemical action or by a catalyst. Undercertain conditions chlorine reacts withammonia to produce nitrogen trichloride, which is spontaneously explosive. This is not a risk when testing for leaks with a bottle ofammonia. 15

76 Safety advice for bulkchlorineinstallations

Selection ofmaterials oJ construction 16 The choice ofappropriate materials of construction for chlorine systems is considered in detail elsewhere.81Your options should be selected only after a detailed survey of all possible variations in operatingconditions,and your preferred option decided in consultationwith your chlorine supplier. 17 A system constructedofsteel, which is appropriate for dry chlorine, must itselfbe dried adequately beforecommissioning. This may be done by purging with dry air or inert gas until the exit purge has a dew point below -40°C. However, the upper operatingtemperaturemust be limited.

The useof titaniummetal for wet chlorine is satisfactory,81 providedthat the moisture level is always kept high and that controlis exercised over the upper and 18

loweroperatingtemperaturelimit. Maintenanceand inspection proceduresmust include awareness ofthe possibility of crevice corrosion.However, where titanium is used in plantscontainingwet chlorine (gas or liquid)consideration should be given to the possibility ofa fault condition giving rise to contact between titanium and dry chlorine gas or liquid. If such a fault could possibly arise it may be best to consider alternativeconstructionmaterials. 19 Materials which are resistant to attack by both wet or dry gaseouschlorine at ambient temperaturesinclude glass, stoneware, porcelain, tantalum, ebonite and certain plastics. The use ofplastic materials with liquidchlorine is unsatisfactory.

LEARNINGFROMINCiDENTS 20

An interesting selection of incidents, which illustrate some ofthe above

hazards (including a nitrogen trichloride explosion, a titaniumlchlorine fireand external corrosion)and the means for controlling them, is reviewed in GEST/API 82

Safety advice forbulk chlorine installations 77

__

_

Si

—4

'0

,

i

[I

L.J fl•fl I The basis of health and safety law in the UK is the Health and Safety at Work etc Act 1974. This sets oUt general duties which employers have towards employees and members of the public, and thosethat employees have to themselves and each other. These duties are qualified in the Act by the principle of so far as is reasonably practicable' ie the extent ofthemeasurestaken to avoid or reduce a particularrisk to health and safety needs to he balancedagainst the time, trouble, cost, and physical difficulty involved. This balancing process83 is often referred to as making risks as low as is reasonably practicable'(ALARP).

2 In essence, what health and safety legislation requires is what good management and common sense would lead employers to do anyway: that is to look at what the risks are and take sensible measuresto make them ALARP. This broad requirement is made explicit in the Management of Healthand Safety at Work Regulations l99219 (referred to asthe Management Regulations). Like the Act, these RegLilationsapply to every work activity. Other regulations are more specific, eg the Manual HandlingOperationsRegulations (MHO)57 or the Control of Substances Hazardous to Health Regulations (COSHH).2t 3 A full list3 of current legislation, ApprovedCodes of Practice and some guidanceis published annually. The list contains legislation, which, although in existence, is spent or has lapsed. A price list84 ofall available USE publications is published annually by HSE Books. Contact details areon the inside ofthe back

cover.

A number of regulations (eg COSI-IH, MHO, PPE,64 Management Regulations etc) specifically require you to undertake a risk assessment. A leaflet85 is available describing how these assessments are linked together and what the requirements at-c: however, it does not deal with highly specialised risks such as major hazards. 4

Safety advice for bulkchlorineinstallations 79

5

Under the basic legal requirements you must:

(a)

have a written, up-to-datehealth and safety policy if you employ five or more people;

(b) carry out a risk assessment (and if you employfive or more people, record the main findings and yourarrangementsfor health and safety); (C)

notifyoccupationof premises to yourlocal inspector if you are a commercial or industrial business;

a current certificate as requiredby the Employers' Liability (Compulsory Insurance)Act 1969 if you employ anyone;

(d) display

(e) display the Healthand Safety (f)

Law poster for employees or giveout the leaflet;86

notify certain types of injuries, occupationaldiseases and events (see paragraph 23); and

(g) consult employees and any appointed union safety representatives87 on certain issues, such as any changes which might affect health and safetyand any information,instruction and training which has to be provided. 6 The ALARP principle and the need for risk assessment enables the Health and Safety Commission, where appropriate,to make Regulations in a goal-setting form: ie setting out what must be achieved, but not how it must be done. Sometimes it is necessary to prescribe in detail what must be done and set absolute standards.

Some activities or substances are so inherently hazardous that they requireadditional arrangements. For example, chlorine installations which store 10 tonnes or moreneed to meet the general requirements ofthe CIMAH Regulations (see paragraph9). 7

THENOTIFICATIONOFINSTALLATIONS HANDLiNGHAZARDOUS SUBSTANCES (NIHHS)REGULATiONS 1982' These Regulations implement a notification scheme for installations with inventories greater or equal to specified quantities(10 tonnes for chlorine). Notification is to the Health and Safety Executive via your Local Area Office (see Appendix 4). Under NIHHS the 8

following requirements apply:

80

Safety advice forbulkchlorineinstallations

(a) beforechlorine is used or stored at a site, at least three months noticemust be given to HSE and certain details specified;

(b) the notificationmust be updatedwhenever there is a change in activity on site or there is an increase or reduction in the operationalquantity of chlorine on site; and (c) the amount of chlorine on site must not be increased to three or more times the quantity originally notified,unless a newnotificationis made. (Any increases in inventorylevels must ofcoursecomplywith other legislation, in particularsection 3 ofthe HSW Act, ie that the risks to people off-site are ALARP).

THE CONTROL OFINDUSTRIALMAJORACCiDENTHAZARDS (CIMAH,)REGULATIONS 1984 9 These Regulationsimplement the requirements of the European Directive (82/501/EEC) on the major hazards ofcertain industrial activities commonly referred to as the 'Seveso' Directive. They apply to the storage and processing of hazardous substances. The Regulations have been amendeda number of times.3 These include the 1988 amendment(revision of threshold quantities for certain substances) and the 1990 modification ofthe controls on storage following a serious warehouse fire. Two levels of activity arc defined. The lowerlevel requirements require companies to take the precautionsthat are necessary to prevent a major accidentand to limit the consequences, and generally to demonstratesafe operation (regulation 4), and to report any major accident (regulation 5). Installations in which chlorine is involved in a process under Schedule 4 are subject to these general requirements regardless ofthe quantity present, unless the operation is incapable of producing a major accident hazard. Larger(ie top-tier) installations which store 75 or more tonnes, or installations with 25 tonnes or more which carry out process activities under Schedule 4, additionally require the preparation of safety reports. emergency plans and the provision of informationto the public (regulations 7-13). Guidanceon the CIMAH Regulations is available.69'88These Regulationswill be withdrawnwhen the proposed Control of Major Accident Hazards (COMAH)Regulationsare implemented in February 1999.

Safety advice forbulkchlorineinstallations

81

THE COMAH REGULATIONS These Regulations will implement the requirements of The Control of Major Accident Hazards Involving Dangerous Substances Directive (96/82/EC) which was adopted by the EU on 9 December 1996. The Directive is referred to as the 'Seveso II' Directive. The Regulations follow the Directive closely and mirror the Seveso l/CIMAH regime, in having two levels of duties: 10

(a) general duties on all operators subject to the Regulations: to notify the competent authoritiesof their activities, to takeall measures necessary for the prevention and mitigationof major accidents, to prepare a major accident prcvention policy, and report major accidents (b) top-tier duties on operatorsof sites where the quantitiesofdangeroussubstances exceed the higher thresholds. These operatorsmust, in additionto the duties in the above paragraph,submit safety reports,prepare and test emergency plans and provide information to the public.

In thecase of chlorine the thresholdquantities are 10 tonnes for the generalduties and 25 tonnes forthe top-tier duties. Application depends solely on the presence or anticipated presence of the thresholdquantitiesof dangeroussubstances, including dangerous substances which might be generated in the course ofan accident due to loss of control of an industrial chemical process, with no differentiation between storage and processing. The general duty for operatorsto take 'all measures necessary for the prevention and mitigation of major accidents' is similar to theCIMAH Regulations which require manufacturersto

'take adequate steps to prevent ... major accidents... and limit their consequences ...'. In judging how this duty should be complied with in practice. the competentauthoritieswill base their view on whetherrisks have been reduced to ALARP. The main new requirements are:

•

All operators within the scope of the Directive must produce a major-accident prevention policy (MAPP) and ensure that it is properly implemented to guaranteea high level of protection for humansand the environmentby appropriate means, structures, and management systems.

• •

Land-useplanningis brought within the scopeof the Directive.

82

Safety reports (top-tier sites only) have to be made availableto the public, but companies can request that certain information,including commercial and personal confidential information,is withheld.

Safety advice for bulkchlorineinstallations

•

The competentauthorities, HSE and tile EnvironmentalAgency (EA) in England and Wales, and HSE and the Scottish Environmental Protection Agency (SEPA) in Scotland, must prohibit operations where the measures taken by operators to prevent and mitigate major accidents are seriously deficient.

The Seveso II requirements place much more emphasison the management of safety and tile role ofthe safetyreport than in the original Seveso Directive (implemented by the CIMAH Regulations). Paragraphs 11-23summarise the main requirements of other legislation that is relevant to the control of risks posed by installations handling chlorine. THEPLANNING(HAZARDOUS SUBSTANCES) ACT1990AND PLANNING(HAZARDOUS SUBSTANCES) REGULATIONS 1992

'

II Tile Act and Regulations introduce planningcontrols which are designed to ensure that hazardous substances can be kept or used in significant amounts only after the responsible authoritieshave had the opportunityto assess the degreeof risk to peoplein tile surroundingarea and are satisfied that the risks are tolerable. In essence the Act and Regulationsrequire sites to apply for hazardous substances consent for inventory levels at or above specific amountsknown as the controlled quantity - 10 tonnes in the case of chlorine. Neighbouringsites within 500 m. and controlled by the same person. must be taken into account when deciding the maximum inventory. New sites must obtain hazardous substances consent at an early stage in tile life cycle. In England and Wales the controls are enforced by the Hazardous Substances Authority(HSA), usually the District or London Borough Council for the land in question, C tile Local PlanningAuthority(LPA). In Scotlandthe equivalent regulations are The Town and Country Planning(Hazardous Substances) (Scotland) Regulations 1993. They arc enforced by the Scottish Office. Environment Department(SOED). HSE is a statutory eonsultee under the Act and advises HSAsand SOED on the nature and severity of the residualrisk. The Act recognises that safety must be an overriding control. The controls apply. regardless of whetherplanning permission is required under other legislation. 12

13 Guidanceon applying for hazardous substances consent in England and Wales is given in Ha:ardousSubstances Consent: Guidance Industry (produced by the Department of the Environment and the Welsh Office. 92 PLAN000I). SOED has issued circular 16/1993 Hazardous Substances Consent: Guidancefor Industry.

Jr

Safety advice for bulkchlorineinstallations

83

THE DANGEROUS SUBSTANCES (NOTIFICATiON ANDMARKING OF SITES) REGULATIONS 199039,40 Wheremore than 25 tonnes ofdangeroussubstances are present on a site (including chlorine) notification must be made to the fire authority and appropriate signs placed at site access points. The enforcing authorityis the fire authority except in specified circumstances when it is HSE. The Regulations requireall signs to conform to BS537841 and to be kept cleanand free froni obstructions. 14

THEMANAGEMENT OFHEALTHAND SAFETYATWORK REGULATIONS 1992 18 15 These Regulations implement CouncilDirectives 89/391/EEC (OJ No L183. 29.6.89, p1) and 91/383/EEC (OJ No L206, 29.7.91, p19) on the introductionof measures to encourageimprovements in safety and health of workers at work. Under the Regulationsyou must:

(a) assess the risks to thehealth and safety ofyouremployees and non-employees arising in, or from, youractivities and review the assessment when there is significant change. Recordsof significant findings of the assessment must be kept where there are five or more employees; (b) plan, organise, control, monitor and review the preventative and protective measures taken as a result ofthe assessment: (c) appoint any competent person(s) needed to help you comply with legal obligations. for example, when havingpressure systems examined:

(d) set out what should be done in case of serious and imminentdanger at your premises, such asthe spillage ofan appreciableamount of chlorine: (e) tell employees about the risks and precautionsinvolved in their work; and (f)

provide health surveillance where necessary.

THE LIFTING PLANTANDEQUIPMENT(RECORDSOF TESTAND EXAMINATIONS ETC) REGULATIONS 199289, 16

You must:

(a) have certificates of test and examination (normally providedby manufacturersand suppliers) specifying safe working loadsbefore first using chains, ropes and lifting tackle;

84

Safety advice forbulk chlorine installations

(b) have chains, ropes. lifting tackle, hoists and lifts thoroughlyexamined every six months by a competent person (often employed by an insurance company)and obtain and keep the report; (c) ensure tests and thorough examinations ofcranes are carried out before they are first used and obtain a certificate of test and examinationspecifying safe working loads. Periodic thorough examinations at least every 12 months are also required, for which a report should be obtainedand kept. HSE guidanceis available.90 Vote: These Regulations 'ill he revokedand i'eplacedin December 1998hi' the Litiing Operations (01(1 lifting Equipment LOLER) Regulatiom (SI 1998/2307i. Guidance sill he publishedin an 4pprored (ode of Practiceon Safe Ue of Lifting Equipinesit. TheProvLdon and Ue of Work Lqu,pmentRegulations1098 (see paragraph19) also app/c to ff11 ng equipment.

THEMANUAL HANDLINGOPERATIONS REGULATIONS 1992 These Regulations implement the substantiveprovisions ofCouncil Directive 90/269/EEC (OJ No LI56. 21.6.90, p9) on the health and safety requirements for the manual handling of loadswhere there is a risk ofback injury to workers. Employers must: 17

(a) avoid the need for hazardous manual lifting and handling practicable;

if reasonably

(b) assess the risk of injury from any hazardous manual lifting and handling which cannot be avoided;and (c)

reducethe risk of injulyaccordingly.

Employees must: (a) follow safe systems of work laid down by their employers;

(b) use mechanical aids providedby their employers properly; and (c)

remember to use the trainingprovidedon lifting.

Safety advice forbulkchlorineinstallations

85

THE CONTROL OF SUBSTANCES HAZARDOUS TOHEALTH REGULATIONS 1994 20 18 These regulations re-enact, with minor modifications, the COSHH Regulations 1988 (SI 1988/1657). They impose requirements on employers using substances hazardousto health to protect employees and other peoplewho may be exposed to such substances. They also impose certain duties on employees concerning their own protection from

exposure. Employers must:

(a) assess risks to health; (b) preventexposure; (c)

where prevention is not reasonably practicable, control exposure by, for example, isolatingor enclosing the process or, if this is not reasonably practicable, local exhaust ventilation;

(d) maintaincontrolmeasuresin efficient working order and ensurethat a thorough test and examination ofengineering controls are carried out at suitable intervals. Records ofsuch maintenance must be kept for at least five years;

or controlis insufficient on its own, provide personal protective and maintain equipment it;

(e) where prevention

(1)

inform,instructand train employees; and

(g) carry outair monitoringand health surveillance where necessary. THEPROVISIONAND USE OF WORKEQUIPMENTREGULATIONS (PUWER) 1992 55,56 These Regulations impose health and safety requirements with respect to the provision and use of work equipment(machinery, appliances, tools etc). They impose requirements upon employers, including the need to: 19

(a) provide work equipmentthat is suitable for the purposefor which it is used or supplied;

86

Safety advice for bulkchlorineinstallations

(b) take steps to ensurethat the equipmentis not used under conditionsfor which it is not suitable; maintainwork (c) equipmentin an efficient workingorder and good repair and that any maintenance log is kept up to date: (d) provide peoplewho use work equipmentwith: (i) clear health and safety information and, where appropriate,written instructions; and

(ii) adequatetraining, including the risks involved and the precautionsto be taken. (This also applies to supervisors and managersof such people.) (e)

protect people from dangerousparts of machineryby suitable protection devices;

(f) providesuitable and sufficient lighting at any place wherea person uses work equipment; (g) ensure that work equipmentis marked in a clear and visible manner with appropriatehealth and safety information and warnings and

(hj ensure that any warning device is unambiguous and easily perceived and understood. \'ote: These Regulations icill he revokedand re—enactedin December 1998. The newPLIWER Regulations (SI 1998/2306) include neii provisionsbr mobilework equipment.

THECONFINEDSPACES REGULATIONS 199759,60 20 These Regulations apply when it is necessary for workersto carry out work in a confined space including a chamber, tank, flue or a similar space, which, by virtue of its enclosed nature, gives rise to a 'foreseeable specified risk'. In the case of chlorine installations the most likely foreseeable specified risk is 'the loss of consciousness or asphyxiation ofany person at work arisingfrom gas, fume vapour or the lack of oxygen'. The Regulationsprohibitthe entry into a confined space for the purposeof carryingout work where it is reasonably practicable to carry outthe work by other means. In other situations(for example, the isolation of a leak in a chlorine room) they impose requirements on employers including theneed to:

(a) establish safe systems of work for entry to, or carrying out work in, or leaving a confined space that rendersthe activities safe and withoutrisks to health:

Safety advice forbulk chlorine installations

87

(b) establish suitable and sufficient arrangements for the rescue of people in the confined space in the event of an emergency (c)

ensurecompliance, so far as is reasonably practicable. with the provisions of the Regulations in respect of any work carried out by employees, or other people - in which case the mattersneed to be within the employer's control.

THEPRESSURESYSTEMANDTRANSPORTABLE GASCONTAINERS REGULATIONS 198923,24,25 These Regulations impose requirements for pressure systems containinga gas or liquefied gas at a pressuregreater than 0.5 bar above atmosphericpressure. They impose requirements on designers. suppliers of pressure systems and on employers of people who modify or repair such systems. Tile intentionofthe Regulations is to prevent the risk of serious injury from stored energy as a result ofthe failure of a pressure system or part of it. A measure ofthe stored energy is given by multiplying the system pressure (bar gauge) and volume (litres). A pressure system is: 21

(a)

a system comprising one or more pressurevessels ofrigid construction, any associated pipework and protectivedevices (systems with a stored energyof 250 bar litre or less are exempt from some requirements, eg the written scheme of examination):

(b)

the pipework with its protective devices to which a transportablegas containeris. or is intendedto be, connected; or

(c)

a pipeline and its protectivedevices.

The transportablegas containeris not part ofthe system. Employers must ensure that: (a) all plant and systems are designed. constructedand installed to prevent danger;

(b) systems are properly maintained: (c) modifications

or repairs do not cause danger;

(d) there is a written scheme for examination54 ofcertain pressure vessels, such as chlonne vaporisers, fittings and pipework, drawn up by a competent person;

88

Safetyadvice for bulkchlorineinstallations

(e) examinations as set out in the writtenscheme are carried out by a competent person; and (f) records are kept. Note: The transportable go container ( TGC') part ofthese Regulations 'as i'c'rokedin /996 and inc'o;porated into The Carriage of Dangerous Goods (Classification, Packaging and L/'Iling) and Crc of Transportable Pressure Receptacles Regulations /996. These PSTGCRegulations i/I be replacedin jVorenilier199') hi ThePrescoreEquipmentRegulationsand The PressureSi'stems Sii/iii' Regulations.

THE PERSONAL PROTECTIVE EQUIPMENTATWORKREGULATIONS 1992 63,64

22 These Regulations impose health and safety requirements when providing PPE and using it to protectpeople in the workplace. Employers must:

(a) provide suitable PPE free ofcharge to protect employees against risks which have not been controlled by other means; (b) (c)

take all reasonablesteps to ensureit is properly used; before providing PPE, assess risks to health and safety which have not been avoidedby other meansand define the characteristics requiredby PPE to make the risks ALARP:then select suitable PPE by matchingthose characteristics with those ofPPE available:

(d) maintain the PPE provided in cleanand efficient working order and provide suitable storage for it when not in use; and (e) give information,instructionand training.

Employees must:

(a) use PPE provided; and (b) report any loss or obviousdefect to the employer.

Safety advice forbulkchlorineinstallations

89

THEREPORTINGOFINJURIES,DISEASESANDDANGEROUS OCCURRENCESREGULATIONS (RIDDOR)1995 91,92,93 23

These apply to all employers and self-employed people and cover everyone at work.

The main points are that you must:

(a) notifyyour inspector immediately, normally by telephone, if anybodydies, receives a major injury or is seriously affected by, for example. an electric shock or poisoning: (b) notify yourinspector immediately if there is a dangerousoccurrence, eg a fire or explosion, which stops work for more than 24 hours; (c)

confirmtelephone notifications in writing within ten days on F2508;

(d) report within seven days (on form F2508) injuries which keep an employee offwork or unable to do theirnormaljob for more than three days; (e) report certain diseases suffered by workers on form F2508A; and (f) keepdetails of reported incidents.

ENFORCINGTHE LAW 24 Health and safety laws relatingto your firm will usually be enforced by a health and safety inspector from USE. In somecases, eg a public swimming pool, health and safety law is enforced by the local authority. 25 Inspectors may visit workplaces without notice but you are entitled to see their identification before they come in. Theymay want to investigate an accident or complaint, or inspect safety, health and welfare at your premises. They have the right to talk to employees and safety representatives, take photographsand samples, and even in certain cases to impounddangerousequipment. They are entitled to co-operationand answers to questions. 26 Inspectorswill be aware of the main risksin handling chlorine and will giveyou help and advice on how to comply with the law. Ifthere is a problem, they may issue a formal notice requiring improvements or, where serious danger exists, one which prohibits the use of a process or equipment. Inspectors have powers to prosecutea firm (or an individual) for breaking health and safety law.

90

Safety advice forbulk chlorine installations

CHLORINEPRODUCERSAND SUPPLIERS Hays Process ChemicalsSandbach, Cheshire CWI I 3PZ ImperialChemicalIndustries plc, ChiorChemicalsP0 Box 13, The Heath, Runcorn, CheshireWA7 4QF RhodiaLtd Staveley, Chesterfield S43 2PB The Associated Octel Co Ltd P0 Box 17, Ellesmere Port, Wirral, CheshireL65 4HF BOC Ltd Special Gases 24 Deer Park Road, London SWI9 31JF (Note: BOC supplies only cylinders.)

Air Products(GB) Ltd Speciality Gases Department,Weston Road, Crewe CWI 1 DF (Note: Air Products supplies only drums and cylinders.) OTHER USEFUL CONTACTS

ChemicalIndustriesAssociation (CIA)Kings Buildings, Smith Square, London SWIP 3JJ Tel: 0171 834 3399 The CIA runs a chlorine committeedealing with technical and liaison issues. Water ServicesAssociation ofEnglandand Wales 1 Queen Anne's Gate. London SWIH 9BTTeI: 0171 957 4567: Fax: 0171 9574666

Safety advice forbulkchlorineinstallations 91

HSE You can find details of your local HSE office in your local telephone directory or the currentedition of HSE35 The Healthand Safbtv Executive. Working withemployers, available from HSE Books. You can find details of USE Booksand HSE's enquiry service on the inside back cover of this booklet. ChlorineInstituteInc. 2001 L Street,NW, WashingtonDC 20036 USA EuroChior Avenue E Van Nieuwenhuyse 4, Box 2. B-I 160 Brussels, Belgium Tel: +32267672 II; Fax: +322 676 7241 Euro Chior publishes a wide range of relevant reports.22 The new series (AP) of pamphletson learning fiwin accidents is essential reading(eg see reference 82). UK suppliers ofEuroChior approvedglobe valves Descote Ltd 19 Sandy Lane, Weston Point, Runcorn, Cheshire WA7 4EX Tel: 01928 565666; Fax: 01928 565646

Shaw,Son & Greenhalgh Ltd AlbertStreet, Lockwood, Huddersfield HDI 3QG Tel: 01484 532425; Fax: 01484 512426

BritishStandardsInstitute

BSI Salesand CustomerServices, 389 Chiswick High Road, London W4 4AL Tel: 0181 996 7000: Fax: 0181 996 7001

British Standardsare available from the above address. Standards relevantto chlorine Specification fbrpipe threads/brtubesandfittingswherepressure-tightjoints are nade on thethreads (metric dimensions) BS 21:1985

Specification/hrliquidchlorineBS 3947:1976 (1997) Specification forfillingratios and developedpressures/br liquefiable andpermanent gases BS 5355:1976

92 Safety advice forbulk chlorine installations

Specification/orunfiredfhsion welded pressure vessels BS 5500:1997 Specification/hrflatproducts madeofsteels forpressurepurposes BS EN 10028: Parts 1,2,3:1993and4:1995 Specficationfhr toleranceson dimensions, shape and mass/br hotrolled steel plates 3mm thickor above BS EN 10029:1991 Circularflangesfbrpipes, valves and fittings. Part 3: Section 3.1 Specification jbr steelflanges. Part3 Section 3.3 Specificationfhr copperalloyand composite flangesBS 1560: Part 3: 1989

fbr boltingforflanges andpressurecontaining purposesBS 4882: 1990 Specification Specification for compressed asbestosfibrejointing BS 1832:1991(1997) Specification for burstingdiscs and burstingdiscdevices BS 2915: 1990 Transportable gas containers. Part 1 Specificationforseamlesssteelgas containers above 0.5 litrewater capacityBS 5045: Part 11982; Part2 Specificationforsteel containersof0.5 L up to 450 L water capacitywith welded seams BS 5045: Part2 1989

Specficationfbrfillingratios anddevelopedpressuresfor liquefiable and permanentgasesBS 5355: 1976 Safe/v signs andcolours. Part1 Specificationfbr colourand design BS 5378: Part 1980 (1995); Part3 Specificationforadditionalsigns to thosegiven in BS 5378: Part] BS 5378: Part 3 1982 (1995)

1

Polytetrafluoroethylene (PFTE) materialsandproducts. Specificationfor fbbricated unfilledpolytetrafluoroethylene productsBS 6564: Part2 1991 (1996) Specificationfor identification ofpipelinesandservicesBS 1710: 1984 (1991) Schedule ofpaintcoloursfor buildingpurposesBS 4800: 1989 (1994) Guide to implementing an effective respiratoryprotectivedevice programme

BS4275: 1997

Safety advice forbulkchlorineinstallations 93

Specification/orrespiratoryprotectivedevices: selficontainedopen-circuit compressed air breathingapparatus BS EN 137: 1993 Respiratory protectivedevices: compressed airline breathingapparatusJbr use with afiill Jbce mask, hal/mask, or mouthpiece assembly. Requirements, testing, marking BS EN 139: 1995 Steels /brpressure purposes.Part3 Specification/brcorrosion andheat-resistingsteels: plates, sheet andstrip BS 1501: Part 3 1990 Specification/br steelsJbr firedand unfiredpressurevessels: sections BS 1502: 1982 (1990)

94

Safety advice forbulkchlorineinstallations

andbars

Ui3]c

—

I Bulk chlorine installations should preferably he located in the open air. Sometimes it may be appropriate to locate the installationin a building.

The building may enclose the entire installation or part of it. eg the manlids, valves, associated pipework,gauges and other equipment, leavingthe tank itself 2

outside. 3 The advantages, disadvantages and consequent requirements for outside or inside installations are listed in paragraphs 4-8.

OUTSiDE INSTALL4TIONS 4

The advantages of outside installationsare that:

(a) leakagesare not confined, so the source of leakage is more safely accessible

from upwind: (b)

it is easier to identify the point of leakage and take immediate local corrective action:

(c) access

for installationand for major maintenance is simpler;and

(d) building costs are lower. 5

The disadvantages of outside installationsare that:

(a) leakages may be detected at an early stage only from downwind positions; (b) small leakages, particularly thosearising from corrosion,can develop unnoticed;

Safety advice for bulk chlorine installations

95

(c) maintenance and repair work may have to be carried out in adverseweather conditions;

(d) there is no containmentto reducethe rate of release to the atmosphere; (e) surface corrosionis more likely; any leak may rapidly escalate; and (f)

there is less security.

6

It follows that outdoor installations require:

(a) strict vigilance and protection against corrosion; (b) protectionagainstpossible mechanical damage and unauthorisedaccess; (c)

an appropriate emergency system, possibly including proceduresfor theuse of water sprays for gas clouds (see also main text paragraphs247-263);

(d) weatherprotection for maintenance in critical areas; this could be eithera permanentcanopyor temporary sheeting; and (e)

continuousstaffingon the site ifa chlorine release could presentserious consequences on or off site.

INSiDE INSTALLATIONS 7

Theadvantagesof inside installations are that:

(a) valves and other equipmentare protectedfrom rain and snow, and provided the buildingis kept dry, there will be less risk of corrosion;

(b) backgroundheatingis possible, to help providedry surroundings and increased chlorine vapourpressure for processes where inert gas/airpadding is not acceptable; (c) controlled ventilation is possible, limiting the external effects if the leak is fairly small;

(d) there is greater likelihood of a monitoringdevice detecting a leak; this is a particularadvantage on an unattended plant; and

96

Safety advice forbulk chlorine installations

(e)

theinstallation is protected from accidental mechanical damage,explosion or fire in adjacentplant or interference by unauthorisedpersons.

8

The disadvantages of inside installations are that:

(a) following a medium or major leak, emergency access may have to be made

to a closed room with a high chlorine concentration;

(b)

thepoint of leakagemay be difficult to identify, owing to lack of dispersion, and mist formation;

(c)

ifthe building is heated, there will be greatergroundevaporationand flash from a liquid leak; and

(d) access for maintenanceis likely to be more difficult. 9

It follows that indoor installations require:

(a)

adequate forced ventilation systems, including start-up from operating points outside as well as inside the building; and

(b) careful consideration of plant layout and provision and escape respiratory equipment.

ofadequate escape routes

Safety advice forbulk chlorine installations 97

JL iVote: This typicalprocedure assunies 1/ia! the storage tanks and avvociateditems of equipment hine sate Forking pressure of at least 12 bar gauge. If this is not the case,

i

then steps isilIneed to he taken (eg adjust theair sssteni pressure, and relief va/ic settings) to el/sure that the saf' working limitsfor the storage vessels and delivery vvvtein are not exceeded. It is important that more detailed andsite—spe(i/ic procedures are developed and agreed hj' the customer, Ijaulier and chlorinesupplier. Action by

Actionneeded

Joint

The procedures need to be designed to minimise potential leaks by ensuring that all newly made joints are tested by gas pressure with, at most, only a small amount of liquid. During these test operations a gas mask must be worn. Similarly, a suitable gas mask (see paragraphs 235-246) must be worn during the disconnecting operation when thereis a possibilityof the escape of a small quantity of residual vapour. During the rest of the operations it should be kept readily available.

Customer

Will operate all valves on the bulk storage installation, including the filling pipe.

Driver

3

Driver

4

1

2

On arrival at the works, will weigh off on the site weighbridgeand proceed to the discharge berth. Will position the tanker at the discharge berth

and employ the drive-away protection. A variety of techniques may be used, eg interlocks to the tanker brakes, wheel chocks, and the removal of the vehicle ignition key to a controlled location. These are in addition (see paragraph 7 below) to any drive-away protection barriers and any interlocks to shut down the discharge should movement of the vehicle or should chlorine be detected (see main text, paragraphs 39-41). Safety advice forbulkchlorineinstallations 99

Driver

5

Presents the delivery notes to a responsible official.

In signing these notes the customer accepts the responsibility that there is sufficient space available in the storage tank to receive the full load from the road tank and that the installation is fit and ready for the discharge

to proceed. Will tell the plant operator the weight of chlorine in the tanker so that the operatorcan determine where the final reading will be on the weighing machine dial or load cell indicator.

Driver

6

Customer

7

Will ensure that any warning notices are displayed and barriers are erected, and will operate any safety interlocks associated with the road

vehicle berth. Customer

Where there are two or more tanks the customer will determine which tank is to receive and check that the storage tank cannotbe overfilled. The pressure on the tank before starting the discharge should not normally be greater than 5.9 bar gauge but in very hot weather it may be 8

higher.

Customer

The customer will ensure he,ftredischarge that the vent valve on the stock tank filling pipe is closed. When fitted, the barrier mechanical interlock key is used to activate the control panel sequence for the discharging operation and release the off-loading arm.

Driver

10 Establish the vehicle movement detection interlock and activate

9

interlocks to the chlorine detection system before operating valves on the tanker and installation. Wearing a gas mask, remove both caps from the road tank valves and the customer's filling arms and test for leaks. Using new PTFE. aramid fibre or other suitable material for joint rings (preferably not CAF, see paragraph 56), connect both air supply and liquid discharge arms to the appropriate valves on the tanker. Joint

Wearing a gas mask, apply pressure to the discharge connection, preferably by brieflyopening the valve to the stock tank. An alternative but less desirable method is to open the tanker discharge valve monientarilv. The driver (wearing a gas mask) tests the joints on the discharge pipe using ammonia water. satisfactory, the driver can remove his gas mask and then request the plant operatorto open the valve on the stock filling line afterthe drop arm. The liquid valve on the 11

f

100 Safety advice for bulk chlorineinstallations

tanker can he s/ow/v openedto fill the delivery line: tile pi-essure observed will be the pressure on the road tanker. Alternatively. and oilly wllen the driver is satisfied with the integrity of the connections, the instrumeilt air connections are made which will allow tile discharge valves to be operated. This may also activate a brake interlock wilich is integral with the custonler's shutdown systenl. Joint

12 Start the air compressor and when tile line pressure is .3 bar gauge open it to the road tanker. When tile road tanker pressure (as indicated on tile filling pipe to the stock tank) is bar gauge above that of the stock tank request the plant operator to open tile valve to tile appropriate stock tank arid commence discharge of tile road tanker.

1.7

Joint

13 Observe tile discilarge of the road tanker is proceeding satisfactorilyby reference to the weighing machine dial or load cell indicator.

Joint

Observe the stock tank pressure as the discharge is proceeding. Should this rises to 6.2 bar gauge the driver requests the customer to crack open tile vent valve on the tank to reduce 14

tile pressure. joint

15 Indication that the road tanker has been completely discharged is:

(a) fluctuation of pressure gauge on the liquid chlorine delivery line;

(b) equalisation of tanker and line pressure readings. Joint

16

The plant operatorcloses the storage tank inlet valve and

the padding air supply valve. Vent excess pressure from the tanker via the vent valve to the scrubber. The driver then closes the padding air inlet to the tankerand tIle liquid chlorine outlet from the tailker, and disconnectstile operating air leads to them so the tanker valves cannot be reopened. The connecting pipe for padding air can now be vented and disconnected and the tanker padding air connection capped. The operatorcracks open the vent valve on tile liquid chlorine delivery line to the stock tank filling pipe. When the pressure gauge on the liquid Safetyadvice for bulkchlorineinstallations 101

chlorine delivery line shows zero (and any hoar froston the vent valve has begun to disappear) the operatorcloses the valve on the chlorine delivery line at the tanker dischargepoint. Close the delivery line vent valve.

Customer

17 Crack open the vent valve on the stock tank for about one minute in order to check that the level of liquid chlorine in the tank is below the bottom of the vent dip pipe (no frosting should appear). This operation also vents non-condensable gases. Check that the pressure in the tank is reasonable for the temperature of the chlorine. The storage is now isolated from the discharge line to the scrubber and the delivery line is purged by pressurising and depressurising(open vent valve and close it when pressure gauge shows zero) with dry air for a minimum of live cycles. The operatorcan now shut down the air compressor if it is not needed for other operations.

Driver

18 Wearing a gas mask, disconnect the liquid discharge pipe from the tanker, replace the sealingplug to prevent the entry of moist air, and swivel back to the staging. Tell the plant operator that the vent can be closed. The short connecting pipes from the liquid and air valves can be disconnected, both valves capped and the tanker dome securely fastened. The RPE can now be removed.

Customer

Underno circumstancesallow any section of the pipeline to be left u;ivented wit/i liquid chlorine trapped between closed valves.

Driver

19

20 Before leaving the storage plant ask the designated responsibleperson

to sign the advice note and consignment note after the words all operations connected with the discharge of the road tank have been completed satisfactorily'. Handone copy to the responsibleperson. On leaving the works weigh again on the site weighbridge.

102 Safety advice forbulkchlorineinstallations

Chlorine vaporisers may be divided into four basic types: (a) (b) (c) (d)

Vertical tube bundle. Coiled tube immersed in a heating bath. Concentric tube. Kettle-type evaporator.

VERTICAL TUBEBUNDLE(TYPE 1)

la Shell and tube

lb Steam bayonet

Chlorine qas

Chlorine gas

S!eam

Liquid

chlorine] Steam

----—

I iqidctoeire

Safety advice forbulkchlorineinstallations

103

Advantagesof this type of system are:

Ic Hot water bath

(a)

small overall size for relatively large heat transfer surfaces;

(h)

easy maintenance; and

(c)

for the mode of operation in which the chlorine is in tubes, the liquid chlorine is automatically displaced by overpressure when the vapour supply to theconsumingplant is shut off.

Chlorine gas

Liquid chlorine

Waterbath —

Disadvantages ofthis type of system are: (a)

Electric heater

for the mode of operation in which the chlorine is in the tubes, there is a risk of instability at high throughput owing to variation ofliquid levels and a possibility of corrosion in the region of

the liquid surface; and (b)

forthe mode of operation in which the chlorine is in the shell, it is difficult to dry out the shell.

COILED TUBEIMMERSEDIN A HEATING BATH (TYPE2) Advantages of this type of vaporiserare:

2 Coil in bath

(a) -

operate;

Hotwateroutlet

Hotwaterbath L>(J Chlorine gas

it is simpleto maintain and

(b)

the long coil generally ensures adequate superheating;

(c)

there are no problemswith differential thermal expansion;

(d)

plug flow operation avoids concentrationof high boiling

Coil

Liquid chlorine

Sted

- -

impurities; 104 Safety advice for bulkchlorineinstallations

(e) drying out of equipmentbefore use is relatively easy: and (f) liquid chlorine is automatically displaced when the vapour supply to the consuming plant is shut off. Disadvantagesof this type of vaporiserarc: (a) low throughput;

(b) external corrosion of the iLibe can easily occur, especially near the liquid surface; (c) irregular internal erosionof the coil may occur: and (d) internal inspection and cleaning of the coil is difficult.

CONCENTRICTUBEUNITS(TYPE3)

3 Concentric lube unit

Chlonne gas

Advantages of this type of system are:

(a)

simple construction with minimum weldingrequirements;

(h)

easy maintenance and operation;

(c)

easy provision of adequate

Steam

corrosion allowance;

Condensate

Liquid chlorine

(d)

automatic displacement ofliquid chlorine when the vapour supply to theconsumingplant is shut off; and

(e)

plug-flow operation abovea certain minimum flow avoids concentrationof high boiling impurities.

Safetyadvice forbulkchlorineinstallations 105

Disadvantages of this type of system are:

potential instability of operation at high and low throughput;

(a)

(b) limitation

of unit capacity owing to relatively small heattransfer surface area; and

greater difficulty in obtainingadequate superheating ofthe chlorine.

(c)

KETTLE-TYPE EVAPORATOR (TYPE 4)

4 Kettle-type evaporator Liquid chlorine

Chlorinegas

Control to inlet

Level measuring device

-T

Heating medium in

H

[J

//// LiquidCl2

medium out

Advantages of this type of system are:

(a) it can be designed for large throughput; (b) allowance for thermal expansion (c)

caneasily be made; and

operation is stable, providedthat either the level of chlorine in the kettle or the pressureof chlorine fed to the vaporiser. is controlled.

Disadvantages of this type of system are:

(a) since the vessel contains a relatively largeamount ofliquidchlorine,leakage or excess pressure in the vessel pose a greaterpotential hazard; (b)

a reliefsystemwith a large capacity is required, unless thevaporiseris designed for high pressure:

(c) operation can result in concentrationof nitrogen trichloride; the purging process required to i-educethis hazard may be difficult to carry out on consumerpremises:

(d) drying ofthe equipmenton the chlorine side is difficult; and (e) dismantling of the tubes is difficult and requiresa large space.

106

Safety advice forbulk chlorine installations

(Note: A tullerdivcussion at einergencr plansappears in HSEc 11SG2569 and re,ferences and 71. Additional guidance iii! be issued Iv support the COMA H Regulaiion,r.

/7, 70

I The works shouldhave an on-site emergency plan for dealing with a major chlorine release. The plan should include instructions for the emergency team and for non-essential personnel, and for liaison with the emergency services. The emergency plan should be based on paragraphs247-263. Your plan will depend on the results ofyourrisk assessment and the need to comply with health and safety legislation, eg section 3 of the HSWAct.2The following paragraphs contain some

elementsof a plan.

2

The plan may include detailedinstructions for:

(a) raising the alarm;

(h) investigating and assessing the source and extent of the chlorine release; (c) alerting all personnel on-site or in neighbouring premises and the emergency services;setting up emergency control centres, assessment by key personnel of the incident and consequentemergency measures on and off-site; (d) methodsfor controlling

thechlorine release;

(e)

search systems for casualties, and accountingfor personnel on-site;

(1)

methodsfor assessing the directional spread and concentration ofthe gas cloud;

(g) criteria for determining whether to evacuatenon-essential personnel or to advise them to stay inside buildings with doors, windows and ventilation shut;

Safety advice forbulk chlorine installations 107

(Ii) methods for assessing whether corresponding actionsare advisable for people off-site and, in particular,liaison with the managerat any adjacent underground workings where chlorine could enter the ventilation system: advice to emergency services on the direction,spread and concentration ofthe gas cloud; and (i)

first aid to on-site casualties, and arrangements for evacuation where advisable and practicable; advice to ambulance service on routes to use.

Since each installation will have its own special features, a detailed plan relating to the particLilarplant will be required. Local management should be responsible for preparation of the plan which shouldhe developed iii co-operation with the local authority, the police, fire, hospitaland ambulanceservices, andthe chlorine supplier. Specific duties are laid on some of these people by the Control of Industrial Major AccidentHazards Regulations 1984. These will he superseded by the requirements of the COMAH Regulationsin 1999. 3

EMERGENCYCONTROL CENTRES 4 Basic requirements for a satisfactory system to deal with serious escape ofchlorine are outlined as follows:

an emergency resulting from a

(a) two control centres should be providedso that, in the event of a gas escape, operationscan be controlled from the centre which is least affected under prevailing atmospheric conditions: (b) each centre should be providedwith a separate external telephoneline, as well as withconnectionsto the factory's external and internal telephone system; (c)

adequateemergency equipment(self-contained breathingapparatus, supplies of suitable foam as agreed with the emergency services, protective clothing, etc) should he available (see section on emergency equipment):

(d) emergency first-aid fitcilities, including equipmentfor administering oxygen, need to he provided; (e)

a large-scale map (1:25 000 or 1:10000) ofthe surroundingarea should be available to help determine which parts of the factory and the local neighbourhoodare likely to be affected;

(f)

wind directionindicators have to be visible from, or indicated in, eachcontrol centre; and

108 Safety advice for bulkchlorineinstallations

(g) equipmentand information are needed to assess the likely extent of the gas cloud for various sizes of release and variousweatherconditions.

The emergency plan should specify in advance the individuals and deputies responsible for the action necessary to deal with the emergency. 5

SITEEMERGENCYTEAM 6

There shouldhe a trained emergency team with the following key personnel:

(a) Site incidentcontrol/er- the senior person on-site responsible for the direction of on-site operations (b) Sitemain control/er- normally the works manager or deputy with overall responsibility for the operation ofthe emergency plan, maintaining close liaison with the police and lire services, and for advising them on the risk and (c)

Otherkeypersonnel - including: (i)

the team responsible for the control ofthe chlorine release

(ii)

the team responsible for the search for casualties, for first aid and for the control of evacuation.

7 The police will be responsible for dealing with members of the public who might be affected by the chlorine escape they will need to be advised ofthe size and expected duration of the release together with the areas which could be affected, to allow the police and the site main controller to agree whether the pLiblic should remain indoors or be evacuated.

EMERGENCYASSEMBLY AREAS 8

Emergency assembly areas should be designated for use in a chlorine emergency by personnel not involved in the emergency team.The assembly areas allow for counting of personnel and for controlled evacuation ifthe need should arise. Preferably, the assembly area should he at the periphery of the works site with good exit for evacuation. A building with upper storeys at a location upwind of the chlorine release may offer sufficient protectionwhile the release is brought under control. Evacuation of personnel to the assembly areas should be directed

Safety advice forbulk chlorine installations 109

by a seniormemberof the emergency team who will takewind directionintoaccount. There will be occasions when evacuating off-site is not the best action, for example, when the release is sudden and oflimited duration. CASUALTIES 9

First-aid treatment for casualties is discussed in Appendix

110 Safety advice for bulkchlorineinstallations

1.

I

Safe haiidlingof ciiloriiie f/on! (1/71/115(1/id ci'linders HSG4O I ISE Books 1999 ISBN 0 7176 16460

2

Health and Sak'tvat Worketc Act /974

3

List ofcurrenthealth and sa/tv legislation 1996 HSE Books 1997 1SBN07176 13119

4

The NotifIcatwn ofInstallationsHandlingHazardousSubstances Regulations 1982 SI 1982/1357 HMSO

5

The Controlof industrialMajorAccident HazardsRegulations1984 SI 1984/1902 HMSO

6

CouncilDirective96/82/ECControlofmajor-accidenthazards involving dangeroussubstancesOfficial Jofthe EC No LI0/40 CEC January 1997

7

The Planning(HazardousSubstances Regulations 1992 SI 1992/0656 HMSO

8

Risk criteria/orland-useplanning inthe vicinity ofmajor industrial hazards HSEBooks 1989 ISBN 0 II 885491 7

9

Environmental Protection (PrescribedProcessesand Substances) Regulations 199/ SI 1991/0472 HMSO

10

Environmental Protection Act 1990

11

Alkali and WorksRegulation Act 1906

12

Health andSafety (Emissions into the AtmosphereRegulations 1983 SI 1983/0943 HMSO

Safety advice forbulk chlorine installations 111

13

The Carriage ofDangerous Goods (Classification, Packagingand Labelling) and Use of Transportable Pressure Receptacles Regulations 1996 SI 1996/2092 HMSO

14

The Carriage ofDangerousGoods by Road Regulations 1996 SI 1996/2095 HMSO

15

Areyou involved in the carriage ofdangerousgoods by road or rail? 1NDG234 HSE free leaflet 1996

16

Success/uI health andsafi'tymanagement HSG65 1-ISE Books 1997 ISBNO7I76 12767

17

Formula fir healthand safety: guidance small to medium-sizedfirms in the chemical manu/iicturing industry HSGI66 HSE Books 1996 ISBN 0 717609960

18

The Management ofHealthand Saftv at WorkRegulations 1992 SI 1992 /2051 HMSO

19

Management ofhealth andsafetyat work. Approved Codeof Practice. Management of Healthand SatCtv at WorkRegulations 1992 L21 HSE BooksI992ISBN 071760412 8

20

The Control ofSubstances Hazardousto HealthRegulations 1994SI 1994 /3246 HMSO

21

The Fire Precautions(Workplace,)Regulations 1997 SI 1997 /1840 TSO

22

Publications: Literatureand technicaldocumentation Euro Chlor 1997*

23

br

/

ThePresscire Systems and Transportable GasContainersRegulations 989 SI 1989/

2169 HMSO 24

SatCiv ofpressure systems. Pressuresystems and Transportable Gas Container.s Regulations /989. Approved codeofpractice COP37 HSEBooks 1990 ISBN 0 11 885514 X

25

A guide to thePressure Systems and Transportable

Gas Containers Regulations 1989

HSR3OHSE Books 1990 ISBN 0717604896

112

26

The Carriage o/ DangerousGoods by road (Driver Training.)Regulations 1996 SI 1996/2094 HMSO

27

The Carriage ofDangerous Goods hi; Rail Regulations /996 SI 1996/2089 HMSO

28

SpecifIcation/erpipc'threads/or tubesand fittings where pressure—tightjoints are made on thethreads (nietric dimensions) BS 21: 1985

Safety advice forbulk chlorine installations

29

GEST 75/45 Flexible Monelhosesfor thetransfer ofgaseousor liquid chlorine 5th Ed May 1996 Euro Chlor*

30

GEST 75/43 Flexible steelcoils for the transferofgaseousor liquid chlorine 7th Ed May 1996 Euro Chlor.

31

GEST 75/44 Articulated armsfor the transferofgaseousor liquid chlorine 9th Ed May 1996 Euro Chlor*

32

Processpiping B31.3 American

33

Chemical plantandpetroleumrefinerypiping Supplement to B31 .3 American

Society ofMechanical Engineers 1996

Society ofMechanical Engineers 1995 34

for boltingfor flanges andpressure containingpurposes

Specification

BS4882: 1990

forpipes, valves andfittings. Part3 Steel, castironand copper alloy flanges BS 1560: Part 3 Sections 1-3: 1989

35

Circularflanges

36

Pipeflanges andflangedfittings B16-5 NPS 1-2 through NPS24 American Society ofMechanical Engineers 1988

37 38

for compressed asbestosfibrejointing BS 1832: 1991 (1997)

Specification

Polytetrafluoroethylene

(PFTE) materialsandproducts Part 2 SpecUlcation

forfabricated unfilled polytetrafluoroethylene productsBS6564: Part2 1991 (1996) 39

The DangerousSubstances (Notification and MarkingofSites) Regulations 1990 SI 1990/0304 HMSO

40 Notification and marking ofsites. The DangerousSubstances (Notification and MarkingofSites) Regulations 1990. Guidanceon RegulationsHSR29 HSEBooks 1990 ISBN 0 11 885435 6 41

I

Safety signs and colours. Part Specificationfor colour anddesign BS 5378: Part 1: 1980/(1995);Part3. SpecJicationfor additional signs to thosegiven in

BS5378 Part] BS 5378: Part3 1982 (1995)

for identification ofpipelinesand services BS 1710: 1984 (1991)

42

Specfication

43

Schedule ofpaintcoloursforbuildingpurposes BS4800: 1989 (1994)

Safety advice forbulk chlorine installations 113

44

The Healthand Sa/tv (Sq/en' Signs and Signals) Regulations 1996 SI

1996/0341

HMSO 45

Saf'tv signs and signals. The Healthand Sak'tv(Safe/v Signs and Signals) Regulations 1996. Guidanceon Regulations L64 HSE Books 1997 ISBN 0 717608700

46

HSC Oil Industry Advisory Committee HSEBooks 1997 ISBN 071760871 9

47

The

saf isolation ofplant and equipment

fr

SpecifIcation fillingratios anddeveloped pressuresfor liquefiable andpermanent gases BS 5355: 1976

48

Specification fi.r unfired fusion weldedpressure vessels BS 5500: 1997

49

Specification flr burstingdiscsand burstingdisc devices BS 2915: 1990

50

Kletz TA Hazop and Hazan: Identifying and assessingprocess industry hazards3rd ed IChemE 1992 ISBN 0 85295 285 6

51

GEST 76/55 Maximum levels ofnitrogen trichloride in liquid chlorine 1990 Euro Chlor*

52

Safe handling ofchlorine containingnitrogen trichiorideChlorine Institute Pamphlet I52**

53

introducingcompetent persons. Pressure Systems and TransportableGas Containers Regulations 1989 1ND529 HSEfree leaflet 1990

54

Writtenschemes of examination. Pressure Systems and Transportable Gas Containers Regulations 1989 INDGI78HSEfree leaflet 1994

55

Provision and Use of Work Equipment Regulations 1992 SI 1992/2932 HMSO

56

Work equipment. Provisionand Use of WorkEquipment Regulations

1992 Guidance on

Regulations L22 HSE Books 1992 ISBN 0 717604144 57

The Manual HandlingOperationsRegulations 1992 SI 1992/2793 HMSO

58

Manualhandling. ManualHandlingOperationsRegulations 1992. Guidance on Regulations L23 HSE Books 1992 ISBN 071760411 X

59

The Confined Spaces Regulations 1997 SI 1997/1713 TSO

114 Safety advice forbulkchlorineinstallations

60

SafL work in confined spaces. Confined SpacesRegulations 1997. Approved

CodeofPractice and GuidanceLI 01 HSE Books 1997 ISBN 0 7176 1405 0 USEBooks 1992 ISBN 071760811

61

SafL'ty in pressure testingGS4(rev)

62

Permit-to-work systems INDG98(rev3) HSEfreeleaflet 1998

63

The Personal Protective Equipment at WorkRegulations 1992 SI 1992/2966 HMSO

64

Personalprotectiveequipment at work: PersonalProtectiveEquipment at WorkRegulations 1992. Guidanceon regulations L25 HSE Books 1992

5

ISBN 0717604152 65

GEST 92/171 Personal protective equipment for use with chlorine 1995 Euro Chlor*

66

The selection, use and maintenance ofrespiratoryprotectiveequipment: practical guide I-15G53 1998 HSE Books ISBN0 7176 1537 5

67

A

Guide to implementing an effective respiratoryprotectivedevice programme

BS4275: 1997

jr emergency 1NDG246HSEfree leaflet 1997

68

Prepared

69

ControlofIndustrialMajorHazardsRegulations1984 (CJMAH): Further guidanceon emergency plans HSG25 1985 HSEBooksISBN0 11 883831 8

70

Robinson BWand UK Chlorine Producers Generalguidanceon emergency planning within the CJMAJ-1 Regulations fbr chlorine installations l986

71

Inter-company collaborationforchlorineemergencies CIA 1992 ISBN0 900 6231

72

Specification for respiratoryprotectivedevices: selficontained open-circuit compressed air breathingapparatus BS EN 137:1993

73

Respiratoryprotectivedevices. Compressed airline breathingapparatusfbr use with afidlflice mask, halfmaskor mouthpiece assembly. Requirements, testing, markingBS EN 139: 1995

Safetyadvice for bulkchlorineinstallations 115

74

Occupational exposurelimits EH4O/98 HSE Books (updated annually) ISBN 07176 14743

75

WHO International Programme on Chemical SafetyEnvironmental Health Criteria21 Chlorineandhydrogen chloride World Health Organisation, Geneva, 1982

76

Summary criteriafor occupational exposurelimits EH64 HSE Books (updated annually)

ISBN07176 15766 77

Lewis RJ Sax's dangerouspropertiesofindustrialmaterials(9th ed) Van Nostrand Rheinhold 1996 ISBN 0 4420 2025 2

78

TurnerRM and Fairhurst S Toxicologyofsubstancesin relation to major hazards: ChlorineHSEBooks 1990 ISBN 0 11 885528 X

79

GEST 89/145 Guidelines for medical management ofchlorine exposure (3rd ed) 1995 Euro Chlor*

80

Speci/ication for liquid chlorine BS 3947: 1976(1997)

81

GEST 79/82 Choice ofmaterials EuroChlor 1995*

82

GEST/AP1 Learning from accidents 1996. Euro Chlor*

83

The setting ofsafetystandards:A reportby the interdepartmental group and external advisors1996HM Treasurytt

84

Price listHSEBooks(publishedannually)

85

A guide to risk assessment requirements: Commonprovisionsin health andsafetylaw INDG218 HSEfree leaflet 1996

86

Health andSafety Law. Whatyou shouldknow (poster) HSE Books IBSN0 7176 1380

87

The Health and Safety (Consultation with Employees) Regulations 1996 SI 1996/1513

ofconstruction for use in contactwith chlorine (7th ed)

ISO 88

A guide to the ControlofIndustrialMajorAccident HazardsRegulations 1984 HSR21 (rev) HSE Books 1990 ISBN0 11 8855794

116 Safety advice for bulkchlorineinstallations

1

89

The Lifting Plant andEquipment (Records of Test and Examination etc) Regulations 1992 SI 1992 /0195 HMSO

90

A guide to the LiftingPlant andEquipment (Records ofTestand Exwninution etç) Regulations 1992 L20HSEBooks 1992 ISBN 071760488 8

91

The Reporting ofinjuries,DiseasesandDangerousOccurrencesRegulations 1995 SI 1995/3163 FIMSO

92 A guide to the ReportingofInjuries, DiseasesandDangerous Occurrences Regulations 1995 L73 HSEBooks 1996 ISBN 0 7176 1012 8 93

Everyone'sguide to RIDDOR HSE3 I HSEfree leaflet 1996

The futureavailability and accuracyofthe references listedin this publication cannotbe guaranteed. CurrentRegulations, guidanceand ACOPs, and current HSE publications are listed in the latestversionofreferences 3 and 84 respectively. *

Availablefrom Euro Chlor, see addressin Appendix 4. Available from CIA, see address in Appendix 4. Available from CIAor chlorine producers, see addresses in Appendix 4. Available from The Public Enquiry Unit, HM Treasury, Parliament Street, London SWIP3AG Tel: 0171 2704558

Fordetails on howto obtain HSE pricedand free publications, see insideback cover.

Safety advice forbulk chlorine installations 117

ACOP ALARP ANSI

APF ASME BA BS

CABA CAF CEC CIA CIMAH

COMAH COSHH DTL EA EEC EU HAZOP HMSO

HSA HSE I-ISR

HSW ISO

LOLER

ApprovedCode of Practice As Low As Reasonably Practicable American National Standards Institute Assigned ProtectionFactor American Society of Mechanical Engineering Breathing Apparatus British Standard Compressed Airline Breathing Apparatus Compressed Asbestos Fibre Commission of the EuropeanCommunities Chemical Industries Association

Control of IndustrialMajor Accident Hazards (Regulations) Control of Major Accident Hazards (Regulations) Control of Substances Hazardousto Health (Regulations) Dangerous Toxic Lnad EnvironmentAgency European Economic Community European Union Hazard and Operability Her Majestys StationeryOffice Hazardous Substances Authority Health and Safety Executive Healthand Safety Regulations(Booklet) Health and Safety at Work International StandardsOrganisation Lifting Operationsand Lifting EquipmentRegulations

Safety advice forbulkchlorineinstallations 119

LPA

MHO MHSW NIHHS OEL OES

OJ PPE ppm PSTGC PTFE PUWER RIDDOR RPE SCBA SEPA SI

Local PlanningAuthority Manual HandlingOperations(Regulations) Management of Health and Safety at Work (Regulations) Notificationof installationsHandlingHazardous Substances (Regulations) Occupational Exposure Limit Occupational Exposure Standard Official Journal (of the European Communities) PersonalProtective Equipment Parts per million (by volume) Pressure Systems and TransportableGas Containers (Regulations) Polytetrafluoroethylene

Provisionand Use of Work EquipmentRegulations Reporting of injuries,Diseases and Dangerous Occurrence (Regulations) RespiratoryProtective Equipment SelfContained Breathing Apparatus Scottish EnvironmentalProtectionAgency

UK

Statutory Instrument Scottish Office, EnvironmentDepartment Short-TermExposure Limit TransportableGas Container The StationeryOffice United Kingdom

UPYC WSE

Unplasticised Polyvinyl Chloride Written Scheme of Examination

SOED STEL

TGC TSO

Printed and published by the Health and Safety Executive

120 Safety advice forbulk chlorine installations

1/99

C40

HSE

BOOKS MAIL ORDER HSE priced and free publicationsare available from: HSE Books P0 Box 1999 Sudbury Suffolk C010 6FS Tel: 01787881165 Fax: 01787 313995

RETAIL HSE priced publications are availablefrom good booksellers HEALTH AND SAFETY ENQUIRIES HSEInfoLine Tel: 054! 545500

or write to: HSE Information Centre Broad Lane Sheffield S3 7H0 HSEhome page on the World Wide Web: http://www.open.gov.uk/hse/hsehome.htm

This booklet gives guidance on the safe handling of chlorine at sites which receive bulk deliveries of chlorine by road or rail tanker.

It is aimed at the managers of these installations, but it is also relevant for plant supervisors, design and maintenance engineers and safety professionals.

£14.00 ISBN 0—7176—1645—2

9 780717 616459 HSG28(rev)

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