AS NZS 2381.1-1999 Electrical Equipment for Explosive Atmospheres (unlocked)...
AS/NZS 2381.1:1999 (Incorporating Amendment No. 1)
AS/NZS 2381.1
Australian/New Zealand Standard™ Electrical equipment for explosive atmospheres—Selection, installation and maintenance Part 1: General requirements
AS/NZS 2381.1:1999 This Joint Australian/New Zealand Standard was prepared by Joint Technical Committee EL-014, Electrical Equipment in Hazardous Areas. It was approved on behalf of the Council of Standards Australia on 18 November 1999 and on behalf of the Council of Standards New Zealand on 22 November 1999. It was published on 5 December 1999.
The following are represented on Committee EL-014: Association of Consulting Engineers Australia Auckland Regional Chamber of Commerce Australian Association of Certification Bodies Australian Chamber of Commerce and Industry Australian Coal Association Australian Electrical and Electronic Manufacturers Association Australian Gas Association Australian Industry Group Australian Institute of Petroleum Australian Institute of Refrigeration Air Conditioning and Heating Department of Mineral Resources, N.S.W. Department of Mines and Energy, Qld Electricity Supply Association of Australia Institute of Electrical Inspectors Institute of Instrumentation and Control Australia Institution of Engineers Australia Ministry of Commerce (New Zealand) National Electrical and Communications Association New Zealand Association of Marine, Aviation and Power Engineers New Zealand Employers and Manufacturers Association New Zealand Hazardous Areas Electrical Coordinating Committee Regulatory authorities (electrical) WorkCover New South Wales
Keeping Standards up-to-date Standards are living documents which reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments which may have been published since the Standard was purchased. Detailed information about joint Australian/New Zealand Standards can be found by visiting the Standards Australia web site at www.standards.com.au or Standards New Zealand web site at www.standards.co.nz and looking up the relevant Standard in the on-line catalogue. Alternatively, both organizations publish an annual printed Catalogue with full details of all current Standards. For more frequent listings or notification of revisions, amendments and withdrawals, Standards Australia and Standards New Zealand offer a number of update options. For information about these services, users should contact their respective national Standards organization. We also welcome suggestions for improvement in our Standards, and especially encourage readers to notify us immediately of any apparent inaccuracies or ambiguities. Please address your comments to the Chief Executive of either Standards Australia International or Standards New Zealand at the address shown on the back cover.
This Standard was issued in draft form for comment as DR 98297.
AS/NZS 2381.1:1999 (Incorporating Amendment No. 1)
Australian/New Zealand Standard™ Electrical equipment for explosive atmospheres—Selection, installation and maintenance Part 1: General requirements
Originated as AS 1076.1—1977. Revised and redesignated AS 2381.1—1991. Jointly revised and designated AS/NZS 2381.1:1999. Reissued incorporating Amendment No. 1 (March 2003).
COPYRIGHT © Standards Australia/Standards New Zealand All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher. Jointly published by Standards Australia International Ltd, GPO Box 5420, Sydney, NSW 2001 and Standards New Zealand, Private Bag 2439, Wellington 6020 ISBN 0 7337 3081 7
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PREFACE This Standard was prepared by the Joint Standards Australia/Standards New Zealand Committee EL/14, Electrical Equipment in Hazardous Areas, to supersede, AS 2381.1— 1991. It forms the first part of a series of Standards for the selection, installation and maintenance of electrical equipment for use in areas where flammable materials are generated, processed, handled or stored, and which therefore are potentially hazardous. This Standard incorporates Amendment No. 1 (March 2003). The changes required by the Amendment are indicated in the text by a marginal bar and amendment number against the clause, note, table, figure or part thereof affected. The Joint Committee EL/14 has endorsed the adoption of the IEC 60079 Gases and vapours and IEC 61241 Dusts series of Standards as Joint Australian/New Zealand Standards. In these series of Standards there is no reference to Class I and Class II areas. The different Zones are identified as Zone 0, 1, 2 for explosive gases atmospheres and Zone 20, 21, 22 for explosive dust atmospheres. Considering that the process of adoption of IEC Standards has started, references to Class I and Class II areas have been removed from this Standard to initiate the alignment with the upcoming adopted Standards. The presentation of this edition is more relevant to the electrical regulatory structures in Australia and New Zealand. Significant changes in this edition are as follows:
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(a)
Inclusion of the New Zealand requirements and references to allow the application of this Standard in New Zealand.
(b)
Deletion of all references to Class I (gases) and Class II (dusts) areas.
(c)
Inclusion of Zones 20, 21 and 22 to address the zoning of hazardous areas in explosive dust atmospheres.
(d)
Revision and expansion of definitions.
(e)
Addition to Section 1 of a specific clause covering documentation.
(f)
Addition to Section 2 of clauses clarifying the verification of acceptance of electrical equipment and the selection of repaired or existing equipment.
(g)
Revision and expansion of requirements regarding installation of equipment and wiring; addition of a clause addressing specific occupancies.
(h)
Restructure and expansion of Section 5 covering maintenance.
(i)
Addition of appendices showing the Standards and overseas certifications bodies recognized by regulatory authorities in New Zealand.
(j)
Addition of an appendix containing a report on the dangers from high-intensity light sources in hazardous areas.
(k)
Deletion of the appendix covering marking of explosion-protected equipment (see AS/NZS 60079.0 and AS 2380.1).
This Standard necessarily deals with existing conditions, but it is not intended to discourage invention or to exclude materials, equipment and methods which may be developed in the future. Revisions will be made from time to time in view of such developments and amendments to this edition will be made only where absolutely necessary. It is expected that the next edition will be issued approximately 5 years from the publication date of this edition.
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The terms ‘normative’ and ‘informative’ have been used in this Standard to define the application of the appendix to which they apply. A ‘normative’ appendix is an integral part of a Standard, whereas an ‘informative’ appendix is only for information and guidance. Statements expressed in mandatory terms in notes to tables and figures are deemed to be requirements of this Standard.
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CONTENTS Page FOREWORD ..............................................................................................................................6 SECTION 1 SCOPE AND GENERAL 1.1 SCOPE .........................................................................................................................7 1.2 APPLICATION............................................................................................................7 1.3 REFERENCED DOCUMENTS ...................................................................................7 1.4 DEFINITIONS .............................................................................................................8 1.5 STATUTORY REGULATIONS ................................................................................12 1.6 DOCUMENTATION .................................................................................................12 1.7 QUALIFICATIONS OF PERSONNEL .....................................................................13 1.8 CLASSIFICATION OF HAZARDOUS AREAS .......................................................14 1.9 OTHER CONSIDERATIONS....................................................................................14 1.10 PREVENTION OF EXPLOSION ..............................................................................16 1.11 PRECAUTIONS ........................................................................................................17 SECTION 2 SELECTION OF ELECTRICAL EQUIPMENT 2.1 SCOPE OF SECTION................................................................................................18 2.2 SPECIFIC EQUIPMENT NOT PERMITTED IN HAZARDOUS AREAS................18 2.3 PERMITTED EQUIPMENT......................................................................................18 2.4 ZONE 0, 1 AND 2 HAZARDOUS AREAS ...............................................................18 2.5 ZONE 20, 21 AND 22 HAZARDOUS AREAS .........................................................22 2.6 VERIFICATION OF ACCEPTANCE OF ELECTRICAL EQUIPMENT..................25 2.7 SELECTION OF REPAIRED OR EXISTING EQUIPMENT ...................................25 SECTION 3 INSTALLATION 3.1 SCOPE OF SECTION................................................................................................27 3.2 GENERAL INSTALLATION REQUIREMENTS.....................................................27 3.3 EARTHING ...............................................................................................................27 3.4 EQUIPOTENTIAL BONDING..................................................................................28 3.5 ELECTRICAL PROTECTION ..................................................................................29 3.6 ELECTRICAL ISOLATION......................................................................................29 3.7 EMERGENCY SWITCH-OFF...................................................................................30 3.8 WIRING SYSTEMS—GENERAL REQUIREMENTS .............................................30 3.9 EQUIPMENT — GENERAL REQUIREMENTS.......................................................36 3.10 ADDITIONAL REQUIREMENTS FOR INSTALLATIONS IN ZONE 0 AREAS ...38 3.11 ADDITIONAL REQUIREMENTS FOR INSTALLATIONS IN ZONE 1 AREAS ...38 3.12 ADDITIONAL REQUIREMENTS FOR INSTALLATIONS IN ZONE 2 AREAS ...40 3.13 ADDITIONAL REQUIREMENTS FOR INSTALLATIONS IN ZONE 20, 21 AND 22 AREAS .................................................................................................................41 3.14 SPECIFIC OCCUPANCIES .....................................................................................42 3.15 TRACE HEATING ....................................................................................................45 SECTION 4 INSPECTION AND TESTING INCLUDING COMMISSIONING 4.1 GENERAL .................................................................................................................46 4.2 DOCUMENTATION .................................................................................................46 4.3 INSPECTION ............................................................................................................46 4.4 ITEMS REQUIRING INSPECTION .........................................................................50 4.5 TESTING ...................................................................................................................50
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Page SECTION 5 MAINTENANCE 5.1 SCOPE OF SECTION................................................................................................51 5.2 REMEDIAL MEASURES AND MODIFICATIONS TO EQUIPMENT...................51 5.3 MAINTENANCE OF FLEXIBLE CABLES..............................................................51 5.4 WITHDRAWAL FROM SERVICE...........................................................................51 5.5 FASTENINGS AND TOOLS ....................................................................................51 5.6 ENVIRONMENTAL CONDITIONS.........................................................................51 5.7 EARTHING AND EQUIPOTENTIAL BONDING ...................................................52 5.8 CONDITIONS OF USE .............................................................................................52 5.9 MOVABLE EQUIPMENT AND ITS CONNECTIONS ............................................52 5.10 OVERHAUL AND REPAIR......................................................................................52
APPENDICES A LIST OF ADDITIONAL STANDARDS RECOGNIZED BY REGULATORY AUTHORITIES IN NEW ZEALAND .......................................................................53 B EUROPEAN CERTIFICATION BODIES WHO CAN ISSUE ELECTRICAL SAFETY CERTIFICATION ON ELECTRICAL EQUIPMENT FOR USE IN POTENTIALLY EXPLOSIVE ATMOSPHERES, UNDER EUROPEAN DIRECTIVE 94/9/CE.................................................................................................54 C FRICTIONAL SPARKING RISKS WITH LIGHT METALS AND THEIR ALLOYS ..............................................................................................57 D LIST OF REFERENCED DOCUMENTS..................................................................59 E ENCLOSURES WITH INTERNAL SOURCES OF RELEASE ................................63 F RELATIONSHIP BETWEEN EQUIPMENT GROUPS AND FORMER GAS GROUPS OR CLASSES ...................................................................................69 G REPORT ON THE DANGER FROM HIGH-INTENSITY LIGHT SOURCES IN HAZARDOUS ATMOSPHERES ..............................................................................70 H THE NATIONAL CERTIFICATION SCHEMES FOR EXPLOSION-PROTECTED ELECTRICAL EQUIPMENT (TERMED Ex EQUIPMENT)....................................................................................78 I PROPERTIES OF FLAMMABLE LIQUIDS, VAPOURS AND GASES..................82 J CALCULATION OF THE EXPLOSIVE LIMITS FOR A MIXTURE OF GASES...88
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FOREWORD Many gases, vapours and dusts which are generated, processed, handled and stored, are combustible. When ignited they can burn rapidly and with considerable explosive force if mixed with air in the appropriate proportions. It is often necessary to use electrical equipment in locations where such combustible materials are present, and suitable precautions must therefore be taken to ensure that all such equipment is adequately protected so as to reduce the likelihood of ignition of the external explosive atmosphere. In electrical equipment, potential ignition sources include electrical arcs and sparks, hot surfaces, and frictional sparks. Areas where gases and vapours, dusts, flyings and fibres occur in dangerous quantities are classified as hazardous. Generally, electrical safety is ensured by the implementation of one of two considerations, i.e. that electrical equipment be located where reasonably practicable outside hazardous areas and that electrical equipment be designed, installed and maintained in accordance with measures recommended for the area in which the equipment is located. Several techniques are available for the explosion-protection of electrical equipment in hazardous areas. This Standard describes the safety features of these types of explosionprotection techniques and specifies the installation and maintenance procedures to be adopted. It is most important that the correct selection, installation and maintenance procedures be followed to ensure the safe use of electrical equipment in hazardous areas.
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STANDARDS AUSTRALIA/STANDARDS NEW ZEALAND Australian/New Zealand Standard Electrical equipment for explosive atmospheres—Selection, installation and maintenance Part 1: General requirements
SECT I O N
1
SCOPE
AND
GENERA L
1.1 SCOPE This Standard specifies general requirements, additional to those required for basic electrical safety, for the selection of electrical equipment and instruments, and associated equipment, and for the electrical equipment’s installation and maintenance to ensure safe use in hazardous areas where flammable materials are generated, prepared, processed, handled, stored or otherwise used. This Standard does not apply to those materials which are specifically manufactured as explosives, or to materials which are inherently explosive or pyrophoric. Explosive materials may require special considerations which are beyond the scope of this Standard. The requirements of this Standard apply only to the use of electrical equipment under normal or near normal atmospheric conditions. For other conditions, additional precautions may be necessary. For example, most flammable materials and many materials which are normally regarded as non-flammable might burn vigorously under conditions of oxygen enrichment. Other precautions might also be necessary in the use of electrical equipment under conditions of extreme temperature and pressure. Such precautions are beyond the scope of this Standard. Precautions which may be necessary against the effects of static electricity and against lightning are also outside the scope of this Standard, except for the general recommendations indicated in Clause 1.9. 1.2 APPLICATION A1
The requirements specified in this Standard are supplementary to and not alternative to any requirements given in AS/NZS 3000. Any alterations or modifications to AS/NZS 3000 in this document are specifically stated. Installation of electrical equipment for explosive atmospheres shall comply with the requirements of this Standard and any additional requirements contained in other relevant parts of the AS 2381 series and AS/NZS 61241 series. However, the requirements of this Standard may be varied by other relevant parts of the AS 2381 series and AS/NZS 61241 series for the types of protection concerned, in which case the requirements of other parts shall take precedence over this Standard.
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Notwithstanding application of the installation requirements of this Standard to new installations, the requirements for inspection shall be applied to all electrical equipment and installations irrespective of age and date of installation. 1.3 REFERENCED DOCUMENTS A list of documents referred to in this Standard is given in Appendix D. COPYRIGHT
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1.4 DEFINITIONS For the purpose of this Standard, the definitions below apply. 1.4.1 Approved, approval With the approval of, acceptable to, the authority having jurisdiction. 1.4.2 Area A three-dimensional region or space. 1.4.3 Area, hazardous Area in which an explosive atmosphere is present or may be expected to be present, in quantities such as to require special precautions for the construction, installation and use of electrical equipment. 1.4.4 Area, non-hazardous Area in which an explosive atmosphere is not expected to be present in quantities such as to require special precautions for the construction, installation and use of electrical equipment. 1.4.5 Authority, authority having jurisdiction The regulatory authority, having statutory (legal) control over the installation. 1.4.6 Cable trunking system A system of trunking lengths and components, used for the accommodation and protection of cables. 1.4.7 Canned pump A motor pump unit in which the integral pump chamber opens to the rotor of an induction motor, no shaft seals being provided. 1.4.8 Chemical compatibility Suitability of materials used for the construction of the equipment and its installation, having regard to the solvent and corrosive agencies which may be present. 1.4.9 Cloud ignition temperature (of dusts) Lowest temperature at which a dust cloud ignites. 1.4.10 Combustible dust Dust that is combustible or ignitable in mixtures with air. 1.4.11 Competent person A person who can demonstrate a combination of knowledge and skills to effectively, efficiently and safely carry out activities in hazardous areas, covered by this Standard. Competency in some cases may be limited to one or more specific types of protection technique, e.g. Ex’d’, Ex’i’, etc and/or activity (e.g. design, selection, installation, maintenance, testing and inspection). 1.4.12 Degree of protection of enclosures Measure applied to the enclosures of electrical equipment as defined in AS 1939 to provide for— (a)
the protection of persons against contact with or approach to live parts and against contact with moving parts (other than smooth rotating shafts and the like) inside the enclosure and protection of the equipment against ingress of solid foreign bodies; and
(b)
the protection of the equipment inside the enclosure against harmful ingress of water.
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1.4.13 Earth sheath return (ESR) system A wiring system using the outer sheath of the cable as a combined neutral and earth return conductor. 1.4.14 Electrical apparatus Items applied as a whole or in part for the utilization of electrical energy. These include, among others, items for the generation, transmission, distribution, storage, measurement, regulation, conversion and consumption of electrical energy and items for telecommunications. NOTE: This definition is for alignment with the terminology contained in the IEC Standards being adopted by Australia/New Zealand.
1.4.15 Equipotential bonding The electrical connection of exposed metal parts so that they are at substantially the same voltage under normal and fault conditions. 1.4.16 Ex component A part of electrical apparatus for potentially explosive atmospheres, which is not intended to be used alone in such atmospheres and requires additional certification when incorporated into electrical apparatus or systems for use in potentially explosive atmospheres. 1.4.17 Explosive atmosphere Mixture with air under atmospheric conditions, of flammable materials in the form of gas, vapour, mist, dust or fibres in which, after ignition, combustion spreads throughout the unconsumed mixture. 1.4.18 Explosion-protection Technique of protection which is applied to equipment or part of equipment to prevent the ignition of flammable vapours and gases or combustible dusts in hazardous areas. NOTE: Whereas formerly it was common for an individual item of equipment to be protected by one type of protection only, increasingly equipment may be protected by two or more types of protection. Thus, a rotating machine may incorporate a motor carcass in type of protection Ex d: Flameproof enclosure, and a terminal box in type of protection Ex e: Increased safety. Strictly it is now more satisfactory to refer to ‘explosion-protected’ equipment rather than to any one type.
1.4.19 Flammable gas or vapour Gas or vapour which, when mixed with air in certain proportions, will form an explosive gas atmosphere. NOTE: This definition applies to all vapours of flammable liquids.
1.4.20 Flammable liquid Any Class 3.1 or Class 3.2 liquid having a flashpoint of not more than 61°C. 1.4.21 Flammable material Gas, vapour, liquid, dust or solid which can react continuously under appropriate concentration conditions with atmospheric oxygen and which may therefore sustain fire or explosion when such reaction is initiated by a suitable spark, flame or hot surface. NOTE: Many liquids and solids, though regarded as flammable, nevertheless do not normally burn. The application of heat to such materials serves to release vapour which may burn with atmospheric oxygen. The heat of the subsequent reaction serves to release further vapour for combustion. Flame may propagate throughout suspensions of dusts by this mechanism.
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1.4.22 Flashpoint Lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in sufficient quantity such as to be capable of forming an ignitable vapour/air mixture. NOTES: A1
1
Flashpoint data are normally associated with liquids, though they are also relevant to solids which sublime (refer to AS/NZS 60079.12 and AS/NZS 60079.20). Care must be taken in the use of flashpoint data in applications where the ignition source may itself raise the temperature of the combustible material.
2
The value for the flashpoint depends to some extent on the method of test. For the purposes of this Standard, flashpoint data are determined in accordance with AS 2106.
1.4.23 Hazard Presence, or the risk of the presence, of an explosive mixture of a flammable material with air. 1.4.24 Heavy maintenance (‘base maintenance’) Maintenance which generally consists of close and detailed checks to Standard JAR-145. NOTE: JAR-145 is used internationally by the aircraft industry for the maintenance of aircraft.
1.4.25 Ignition source Source of energy, which may comprise of naked flames, hot surfaces, exposed incandescent material, incendive sparks or hot particles, sufficient to ignite an explosive atmosphere. 1.4.26 Ignition temperature (of an explosive gas atmosphere) A1
Lowest temperature of a heated surface at which, under specified conditions in accordance with AS/NZS 60079.4, the ignition of a flammable material in the form of a gas or vapour in mixture with air, will occur. 1.4.27 Inherently explosive Denotes explosives which require only a specific level of energy for ignition. NOTE: An example of these materials is nitroglycerine.
1.4.28 Inspection An action comprising careful scrutiny of an item carried out either without dismantling or with partial dismantling as required, supplemented by means such as measurement, in order to arrive at a reliable conclusion as to the condition of an item. The different grades of inspection are as follows: (a)
Visual inspection—an inspection which identifies, without the use of access equipment or tools, those defects, such as missing bolts, which will be apparent to the eye.
(b)
Close inspection—an inspection which encompasses those aspects covered by a visual inspection and, in addition, identifies those defects, such as loose bolts, which will be apparent only by the use of access equipment, such as steps (where necessary) and tools. Close inspections do not normally require the enclosure to be opened or the equipment to be de-energized.
(c)
Detailed inspection—an inspection which encompasses those aspects covered by a close inspection and, in addition, identifies those defects, such as loose terminations, which will only be apparent by opening the enclosure, and using (where necessary) tools and test equipment.
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The different types of inspection are as follows: (i)
Initial inspection—an inspection of all electrical equipment, systems and installations before they are brought into service.
(ii)
Periodic inspection—an inspection of all electrical equipment, systems and installations carried out on routine basis.
(iii) Sample inspection—an inspection of a proportion of the electrical equipment, systems and installations. 1.4.29 Instrument Electrical or light-emitting equipment for the measurement, control or computation of physical or chemical quantities. 1.4.30 Layer ignition temperature (of dusts) Lowest temperature of a heated exposed surface at which a dust layer 5 mm thick ignites. 1.4.31 Lower explosive limit (LEL) Concentration of flammable gas, vapour or mist in air, below which an explosive gas atmosphere will not be formed. 1.4.32 Maintenance A combination of any actions carried out to retain an item in, or restore it to, conditions in which it is able to meet the requirements of the relevant specification and perform its required functions. 1.4.33 Maximum surface temperature Highest temperature attained in service under the most adverse conditions (but within the tolerances) by any part of the surface of electrical equipment which, if exceeded, would be able to produce an ignition of the surrounding atmosphere. NOTES: 1
The most adverse conditions include recognized overloads and any fault conditions recognized in the specific Standard for the type of protection concerned.
2
For equipment with type of protection ‘Ex d’, the surface to be considered is the external surface. For equipment with other types of explosion-protection, internal surfaces are equally important if the explosive atmosphere has access thereto.
1.4.34 Minimum dust cloud ignition energy Minimum energy at which a dust cloud ignites. 1.4.35 Non-incendive equipment Equipment, other than an enclosed-break device, with contacts for making and breaking a potentially incendive circuit where either the contacts, the contacting mechanism, or the enclosure in which the contacts are housed are so constructed that the equipment prevents ignition of the prescribed flammable gas or vapour under specified operating conditions. 1.4.36 Pyrophoric A substance that takes fire spontaneously on exposure to air (e.g. phosphorus) or water (e.g. potassium or sodium). 1.4.37 Overhaul Action to restore to a fully serviceable condition equipment which has been in use or in storage for a period of time but is not faulty.
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1.4.38 Repair Action to restore faulty equipment to its fully serviceable condition, in compliance with the relevant Standard. 1.4.39 Source of release Point or location from which a flammable material may be released into the atmosphere, so that an explosive atmosphere could be formed. 1.4.40 Temperature classification System of classification by which electrical equipment is allocated one of six temperature classes according to its maximum surface temperature. 1.4.41 Unprotected surface Surface to which an explosive atmosphere has access, and which is not explosion-protected other than by its own temperature limitation. 1.4.42 Upper explosive limit (UEL) Concentration of flammable gas, vapour or mist in air, above which an explosive gas atmosphere will not be formed. 1.4.43 Verification dossier A set of documents showing the compliance of electrical equipment and installations. 1.4.44 Wiring, open System of wiring in which unsheathed cables are installed without further protection. 1.4.45 Zones, hazardous The zones into which hazardous areas are classified based upon the frequency of the appearance and duration of an explosive atmosphere. 1.4.46 Zones in explosive gas atmospheres See AS 2430.1—1987 and NZ 6101.1—1988 for the definitions of Zones 0, 1 and 2. 1.4.47 Zones in explosive dust atmospheres See AS/NZS 61241.3 for the definitions of Zones 20, 21 and 22. 1.5 STATUTORY REGULATIONS Equipment and installations where hazardous areas exist are required to comply with the applicable regulations of New Zealand or the applicable Australian State or Territory. It should be borne in mind that an installation can come under the jurisdiction of several authorities with different areas of responsibility, e.g. mining, electrical safety, handling and transport of flammable materials and occupational health and safety. The installation and maintenance requirements contained in this Standard are supplementary and not alternative to any regulations which apply to installations in hazardous areas. 1.6 DOCUMENTATION It is necessary to ensure that any installation complies with the appropriate certification documents as well as with this Standard and any other requirements specific to the plant on which the installation takes place.
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To achieve this result, a verification dossier shall be prepared for every plant and shall be either kept on the premises or stored in another location in which case a document shall be left on the premises indicating who the owner or owners are and where that information is kept, so that when required, copies may be obtained. This dossier should contain the information detailed in the appropriate Parts of this series of Standards for the types of protection concerned. Up-to-date information typically required is as follows: (a)
Where applicable a statement of the identity of the person(s) having legal ownership of the installation or parts thereof and where the verification dossier is located.
(b)
The classification of hazardous areas and the Standards used for the classification.
(c)
Equipment group and temperature class.
(d)
Installation instructions.
(e)
Documentation/certification for electrical equipment, including those items with special conditions, for example, equipment with certificate numbers that have the suffix ‘X’.
(f)
Descriptive system document for the intrinsically safe system.
(g)
Documentation relating to the suitability of the equipment for the area and environment to which it will be exposed, e.g. T rating, Ex rating, IP rating, corrosion resistance.
(h)
Documentation certifying that the equipment is rated for the voltages and frequency applied during normal operation.
(i)
Manufacturer’s/qualified person’s declaration, e.g. tradesperson’s documentation and inspector’s inspection reports.
(j)
Records sufficient to enable the explosion-protected equipment to be maintained in accordance with its type of protection (for example, list and location of equipment, spares, technical information).
(k)
Records covering any maintenance, overhaul and repair of the equipment.
(l)
Records of selection criteria for cable entry systems for compliance with the requirements for the particular explosion technique.
(m)
Drawings and schedules relating to circuit identification (see Clause 3.8.16).
It shall be the responsibility of the person(s) having legal ownership of the installation or parts thereof to ensure that the relevant information is produced but the preparation of the document may be delegated to expert bodies/organizations. The dossier may be kept as hard copy or in electronic form. 1.7 QUALIFICATIONS OF PERSONNEL The design, construction, maintenance, testing and inspection of installations covered by this Standard shall be carried out only by competent persons whose training has included instruction on the various types of protection and installation practices, relevant rules and regulations and on the general principles of area classification. The competency of the person shall be relevant to the type of work to be undertaken. Appropriate continuing education or training should be undertaken by personnel on a regular basis. A1
Competency may be demonstrated in accordance with AS/NZS 4761, Competencies for working with electrical equipment for hazardous areas (EEHA), or equivalent training and assessment framework. COPYRIGHT
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1.8 CLASSIFICATION OF HAZARDOUS AREAS This Standard is based on the concept, which is accepted internationally, of dealing with the risk of fire and explosion by area classification. The classification of hazardous areas is dealt with within— (a)
(b)
Zone 0, 1 and 2 areas by— (i)
AS 2430.1 and the AS/NZS 2430.3 series in Australia; and
(ii)
NZS 6101.1 and the AS/NZS 2430.3 series in New Zealand.
Zone 20, 21 and 22 areas by AS/NZS 61241.3.
It shall be the responsibility of the person(s) having legal ownership of the electrical installation, or parts thereof, to provide the information to the electrical tradespersons as to what is the zoning of the hazardous area. 1.9 OTHER CONSIDERATIONS 1.9.1 Protection from mechanical damage and environmental injury influences All electrical equipment shall be designed, selected, installed and maintained to withstand damage which might reasonably be expected to result from mechanical damage and environmental influences likely to be encountered. Both the effect of the material causing the area to be classified as a hazardous area and the effect of the environment shall be taken into account. 1.9.2 Ambient temperature Particular attention should be paid to the ambient temperature in which the equipment is designed to operate as most equipment is designed for an ambient temperature of −20°C to +40°C. However, in some parts of Australia and New Zealand the ambient temperatures are outside this range. Therefore equipment may need to be selected, installed and maintained to take into account these higher or lower ambient temperatures. 1.9.3 Use of aluminium or light alloys Particular consideration shall be given to the location of equipment which incorporates aluminium or light alloys in the construction of its enclosure. The propensity for such materials to give rise to sparking which is incendive under conditions of frictional contact has been well established. Suitable precautions shall therefore be taken to ensure that such frictional contact is avoided (see Appendix C). 1.9.4 Toxic risks No account is taken in this Standard of the toxic risks which are associated with most flammable materials in concentrations which are usually very much less than the lower explosive limit. In locations where personnel may be exposed to potentially toxic concentrations of flammable material, appropriate precautions, which are outside the scope of this Standard, should be taken. NOTE: For further information, refer to the relevant departments/authorities in New Zealand or in each Australian State.
1.9.5 Non-electrical ignition sources In any installation, irrespective of size, there may be numerous sources of ignition apart from those associated with electrical equipment. Adequate precautions should be taken in these circumstances to ensure safety. Such precautions are beyond the scope of this Standard.
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1.9.6 Static electricity Static electrical charges may accumulate to levels which could be incendive. Static charges may be caused by such mechanisms as friction, or movement of non-conducting materials (such as plastics or paper) or gases or liquids flowing through pipelines. Measures shall be taken to control static electricity and various approaches may be adopted according to the particular conditions under consideration. Detailed recommendations for the control of risks due to static electricity are given in AS/NZS 1020. 1.9.7 Lightning In the design of electrical installations, steps shall be taken to reduce to a safe level the effects of lightning. Precautions to take against lightning are described in AS/NZS 1768. 1.9.8 Electromagnetic radiation It may be necessary to take special precautions for installations in the vicinity of sources of electromagnetic radiation, such as high-frequency radio and radar transmitters in which case reference should be made to BS 6656 and BS 6657. 1.9.9 Radiation from optical equipment It may be necessary to take special precautions for optical equipment in the form of lamps, lasers, LEDs, optical fibres, etc. which is used for lighting, surveying, communications, sensing and measurement. This optical equipment may be used in or near to explosive gas atmospheres, and in this case radiation from this equipment can pass through these atmospheres. The radiation can be absorbed by surfaces or particles, causing them to heat up, and in certain circumstances this allows them to attain a temperature that will ignite a surrounding gas atmosphere. NOTE: Appendix G contains a report on a research project into the safe operation of optical instruments using intense light sources. The conclusions give recommendations for certain limiting values of power and flux.
1.9.10 Cathodic protection Cathodically protected metallic parts located in hazardous areas are live extraneous conductive parts which shall be considered potentially dangerous (especially if equipped with an impressed current system) despite their low negative potential. No cathodic protection shall be provided for metallic parts in Zone 0 and Zone 20 unless it is specially designed for this application. NOTE: Detailed guidelines for the cathodic protection of metals are described in the various parts of AS 2832 and in BS 7361. BS 7361 should be used when reinspecting cathodic protection systems.
1.9.11 Personal equipment Items of personal equipment which are battery-operated (e.g. hearing aids, miniature transistor radios, key-ring torches, calculators, watches, pagers, cellular phones, and remote control car keys) are sometimes carried by personnel and might be taken, inadvertently, into a hazardous area. These items can constitute a potential source of ignition and should not be taken into a hazardous area unless—
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(a)
they have been approved for this purpose; or
(b)
they are verified as complying with the appropriate explosion-protection techniques; or
(c)
a permit guaranteeing the absence of an explosive atmosphere has been issued.
(d)
they can be considered as simple apparatus as defined in AS 2380.1 or AS/NZS 60079.11; AS/NZS 60079.11 defines simple apparatus as devices not generating more than 1.5 V or 100 mA or 25 mW. COPYRIGHT
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1.10 PREVENTION OF EXPLOSION 1.10.1 General Preventive measures aimed at the elimination of the risk of a simultaneous occurrence of a source of ignition and an explosive atmosphere in the area under consideration may be used. The problem may be approached in any one of the following ways, each of which has its own appropriate field of application: (a)
Suppression or avoidance of the hazardous condition.
(b)
The use of explosion-protected electrical equipment.
(c)
Conditions of control applied to procedural, automatic or manual means by which the simultaneous occurrence of an explosive atmosphere together with a source of ignition is prevented.
Although each method of prevention can be a complete solution to a particular problem in itself, it is permissible and sometimes advantageous to use a combination of techniques to obtain the required degree of safety. 1.10.2 Suppression or avoidance 1.10.2.1 Segregation The ultimate level of complete safety can only be assured when the hazardous materials are segregated. Where practicable, electrical equipment generally, switchgear and controlgear particularly, should be installed in a non-hazardous area. The equipment may be installed in a non-hazardous area in the open air, segregated in a room or compartment which is non-hazardous or, in some instances, behind an impervious barrier which separates the equipment from the hazardous area. 1.10.2.2 Total enclosure of flammable material It is sometimes possible to reduce the hazard by containing the flammable material in totally enclosed vessels and piping systems. 1.10.3 Explosion-protected electrical equipment Various techniques of explosion-protection may be applied to equipment or parts of equipment to provide an assurance of safety. The types of protection considered in this Standard are detailed in Clauses 2.4 and 2.5. Where more than one explosion-protection technique is used, each relevant part of the equipment or system shall maintain the properties of that particular technique. 1.10.4 Conditions of control In certain cases it is only by the addition of methods or conditions of control that the required degree of safety can be obtained. Such methods may include the use of procedures and/or the use of monitoring devices, such as gas detectors, or pressure, temperature or flow devices. Depending on the degree and type of hazard involved, the associated conditions of control initiated by the monitoring device may include one of the following: (a)
Automatic disconnection of the power supply.
(b)
Automatic initiation of an alarm followed by an associated manual procedure to restore the integrity of the system.
(c)
A manual procedure, whereby one or other of the parameters necessary for an explosive condition is retained under continuous control.
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1.11 PRECAUTIONS 1.11.1 General For equipment protected by other than intrinsic safety protection (see AS 2381.7), the precautions set out in Clauses 1.11.2 or 1.11.3, as applicable, shall be taken when carrying out installation, maintenance and inspection work in a hazardous area. 1.11.2 Equipment rendered ‘not alive’ Equipment rendered ‘not alive’ may be opened in hazardous areas. For equipment to be rendered ‘not alive’ the following conditions shall be met: (a)
(i)
the equipment has been disconnected from its source of supply; and
(ii)
effective measures, such as the locking of the isolating switch in the open position, have been taken to prevent equipment being enlivened before reassembly.
NOTES: Particular attention should be paid to equipment that may be live even after it has been disconnected from a source of supply. For heavy rotating machinery, the back e.m.f. of such plant should be considered and precautions will usually need to be taken to ensure that the equipment, or any associated equipment, is not opened until the rotating plant is stationary. Most power capacitors are fitted with discharge resistors and these take a finite time to bring the terminal voltage to a harmless value. Emergency lighting fittings, or other equipment using batteries, can be rendered ‘not alive’ providing the battery is fitted with a means of isolation and has no live exposed parts, or can be fully discharged before opening. Additional action may be also required to ensure that all sources of mains supply are isolated, as many emergency lighting fittings are wired with active, neutral, unswitched active, and possibly unswitched neutral.
1.11.3 Equipment not rendered ‘not alive’ In circumstances where work on live conductors is unavoidable, it shall be ensured that adequate precautions are taken both initially and periodically to verify that the presence of flammable gas, vapour or combustible dust, if any, does not constitute an explosive atmosphere. Such precautions may include the use of a suitable monitoring device. An audit trail shall be kept to verify that adequate precautions have been taken. NOTE: It is typical practice to have safe working limits for flammable gas or vapour concentration of 0% LEL for HOT WORK. The place of measurement should be judiciously chosen to determine the highest concentration of gas in the area. WARNING: MOST FLAMMABLE MATERIALS ARE TOXIC IN CONCENTRATIONS WHICH ARE USUALLY VERY MUCH LESS THAN THE LOWER EXPLOSIVE LIMIT (LEL).
1.11.4 Igniting agencies No operation involving the use of an open flame or other source of ignition shall be attempted in a hazardous area until the conditions have been made safe by the control of the flammable material which may give rise to the risk. Such operations shall only be undertaken on written authority confirming that adequate control measures have been taken and that tests have been made and are repeated at sufficiently frequent intervals to ensure that safe conditions are maintained. NOTE: See Note to Clause 1.11.3.
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SECT I O N
2
SE LECT I O N OF EQU IPME NT
E L ECT R ICA L
2.1 SCOPE OF SECTION This Section details the general factors to be considered in the selection of electrical equipment for hazardous areas. The selection procedures which apply to particular types of protection are described in the appropriate Parts of this series of Standards and AS/NZS 61241.1.2. 2.2 SPECIFIC EQUIPMENT NOT PERMITTED IN HAZARDOUS AREAS The following electrical equipment shall not be installed in hazardous areas: (a)
Battery chargers with their control equipment and batteries being charged, unless such equipment is suitable for the hazardous area.
(b)
Low pressure sodium vapour discharge lamps.
Transformers containing a liquid dielectric having a flashpoint less than 250°C, and similar equipment, shall not be installed in Zone 20, 21 and 22 areas. Such equipment may be segregated from the hazardous area by an enclosure, provided that any door or other opening between the enclosure and the hazardous area is arranged so that hazardous dust, fibres or flyings cannot enter the chamber in quantities sufficient to produce an explosive concentration or constitute a hazard. 2.3 PERMITTED EQUIPMENT Except where otherwise specified, electrical equipment selected for use in a hazardous area shall be protected by one or a combination of the explosion-protection techniques set out in Clause 2.4 for equipment in Zones 0, 1 and 2, and in Clause 2.5 for equipment in Zones 20, 21 and 22. 2.4 ZONE 0, 1 AND 2 HAZARDOUS AREAS 2.4.1 Required information Generally in order to select appropriate electrical equipment for use in a Zone 0, 1 and 2 area, the following required information shall be considered: (a)
The classification of the area, i.e. the zone.
(b)
The temperature class or ignition temperature of the gas or vapour involved, or the lowest value of ignition temperature if more than one flammable material could be present. This will permit determination of the temperature classification required for the equipment, or the upper limiting temperature for any unprotected surface.
(c)
Where applicable, the group or the characteristics of the gas or vapour involved in relation to—
(d)
(i)
igniting current or minimum ignition energy for installations of intrinsically safe equipment; or
(ii)
safe gap data in the case of installations for flameproof enclosures.
Other considerations in accordance with Clause 1.9.
NOTES: 1
Generally for equipment with types of protection ‘p’, ‘e’, ‘n’ and, where applicable, ‘s’, only the area classification and ignition temperature are required. However, where equipment is protected by Ex i (intrinsic safety) or Ex d (flameproof enclosure) in addition to one of these types of protection, it is necessary to determine the appropriate equipment grouping (see Clause 2.4.4). COPYRIGHT
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Where there is a combination of combustible dust and flammable gas or vapour, explosionprotection alone may not be sufficient. Until specific guidance is available, expert advice should be sought.
2.4.2 Selection with respect to area classification The type of explosion-protection technique for electrical equipment shall be selected according to the area classification. Electrical equipment in Zone 0, 1 and 2 areas shall be protected by one or a combination of explosion-protection techniques specified in Table 2.1 for the appropriate zonal area. In addition to the Standards listed in Table 2.1, Appendix A lists Standards that are recognized by regulatory authorities in New Zealand. Appendix B lists the overseas certification bodies from which certification to the Standards listed in this Standard is acceptable to regulatory authorities in New Zealand. 2.4.3 Selection with respect to temperature classification 2.4.3.1 Reference ambient temperature Electrical equipment for hazardous areas is normally designed for use in an ambient temperature range between −20°C and +40°C, unless otherwise marked. 2.4.3.2 Maximum surface temperature (temperature class) A hot surface can cause an ignition, therefore it is necessary to ensure that the surface temperature of equipment introduced into a hazardous area does not exceed the ignition temperature of the gas or vapour. The permitted maximum surface temperatures are classified as follows: (a)
(b)
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For Group I electrical equipment: (i)
Where coal dust can form a layer . . . . 150°C.
(ii)
For internal surfaces, where the above risk is avoided, e.g. by sealing against the ingress of dust . . . 450°C.
For Group II electrical equipment . . . . those values in Table 2.2 which correspond to the temperature class of equipment, having regard to the maximum ambient temperature for which the equipment is designed.
In decisions concerning the maximum surface temperature for equipment or the suitability of available equipment which is to operate in an area endangered by a particular material, the maximum surface temperature of the equipment should not exceed the ignition temperature of the gas or vapour. For example, naphtha has an ignition temperature of 290°C and the appropriate temperature classification for equipment would therefore be T3, implying a maximum surface temperature of 200°C. Equipment in the T2 category would not be suitable as this would imply surface temperatures of up to 300°C. However, special equipment limited specifically to a temperature below 290°C (e.g. 280°C) would be acceptable, and should be marked accordingly (see AS 2380.1 and AS/NZS 60079.0 for marking details). For components having a total surface area of not more than 10 cm 2 , e.g. integrated circuits, transistors or resistors used in intrinsically safe electrical circuits, their surface temperature may exceed that for the temperature class marked on the electrical equipment if it can be demonstrated that there is no risk of ignition from these components (see AS 2380.1 and AS/NZS 60079.0). Equipment designed for use in a maximum ambient temperature of 40°C may be used in higher temperatures provided that— (a)
the equipment is assigned a higher temperature classification;
(b)
the temperature rise of the equipment (related to 40°C) plus the higher ambient temperature is less than the ignition temperature of the flammable material; or COPYRIGHT
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the maximum temperature of the particular temperature class plus the higher ambient temperature is less than the ignition temperature of the flammable material.
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TABLE 2.1 EXPLOSION-PROTECTION TECHNIQUES FOR ELECTRICAL EQUIPMENT IN ZONE 0, 1 AND 2 HAZARDOUS AREAS Description of explosion protection technique
Applicable Standards and designated symbol
Remarks
ZONE 0 Intrinsically safe
AS 2380.7 AS/NZS 60079.11 Ex ia
Special protection
AS 1826 Ex s
In accordance with the requirements for Zone 0
ZONE 1* Intrinsically safe
AS 2380.7 AS/NZS 60079.11 Ex ib
Special protection
AS 1826 Ex s
Flameproof enclosure
Encapsulated
AS 2380.2 AS/NZS 60079.1 Ex d AS 2431 IEC 60079-18 Ex m
Pressurized rooms or pressurized enclosures
AS 2380.4 AS/NZS 60079.2 Ex p
Increased safety
AS 2380.6 AS/NZS 60079.7 Ex e
Ventilation
In accordance with the requirements for Zone 1
AS 1482 Ex v
Powder filling
AS/NZS 60079.5 Ex q
Oil immersion
AS/NZS 60079.6 Ex o
In accordance with the requirements for Zone 1
In accordance with the requirements for Zone 1
ZONE 2† Special protection Non-sparking
Ventilation Pressurized rooms or pressurized enclosures
AS 1826 Ex s AS 2380.9 IEC 60079-15 Ex n
In accordance with the requirements for Zone 2 2nd Edition (2001) of IEC 60079-15 is not acceptable
AS 1482 Ex v
In accordance with the requirements for Zone 2
AS 2380.4 AS/NZS 60079.2 Ex p
In accordance with the requirements for Zone 2
* Equipment suitable for use in Zone 0 can also be used in Zone 1 and Zone 2. † Equipment suitable for use in Zone 0 or Zone 1 can be also used in Zone 2. NOTE: All the Joint Standards (AS/NZS) shown in this Table are identical to the respective adopted IEC Standards. COPYRIGHT
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TABLE 2.2 CLASSIFICATION OF MAXIMUM SURFACE TEMPERATURES FOR GROUP II ELECTRICAL EQUIPMENT Temperature class
Maximum surface temperature °C
A1
T1
450
T2
300
T3
200
T4
135
T5
100
T6
85
NOTES: 1 A reference ambient temperature of 40°C is normally assumed when equipment is designed to operate within one of the temperature classes indicated in the Table. Where the reference temperature is outside the range of−20° to +40°C, the value is required to be marked on the equipment (see AS 2380.1 and AS/NZS 60079.0). 2 Ignition temperatures of flammable liquids, gases and volatile solids are given in AS/NZS 60079.20.
2.4.4 Selection with respect to equipment grouping 2.4.4.1 Group designation Electrical equipment for hazardous gas areas is grouped as follows:
A1 A1
(a)
Group I—electrical equipment for mines susceptible to methane.
(b)
Group II—electrical equipment for all places with an explosive gas atmosphere, other than mines susceptible to methane.
2.4.4.2 Group II subdivisions For certain types of protection, such as flameproof (Ex d) and intrinsic safety (Ex i), Group II is further subdivided into subgroups IIA, IIB or IIC and shall be selected in accordance with Table 2.3. (See Appendix I and AS/NZS 60079.20.) Where equipment is marked indicating it has been tested with a single gas or vapour, it shall only be permitted where other gases or vapours are present, when the equipment is verified as suitable. 2.4.5 Enclosures with internal sources of release When an enclosure contains an internal source of release of potentially explosive gas, vapour or mist, the type of explosion-protection required is dependent upon the area classification surrounding the enclosure and the type and extent of release of flammable substance within the enclosure. NOTE: For further information refer to Appendix E.
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2.4.6 Motors supplied at varying frequency and voltages Ex d motors supplied at varying frequency and voltages are required to meet the requirements of either Item (a) or Item (b), Ex e motors are required to comply with Item (b), and Ex n motors are required to comply with Item (b) or (c), as follows: (a)
There shall be means (or equipment) for direct temperature control by embedded temperature sensors specified in the motor manufacturer’s documentation or other effective measures for limiting the surface temperature of the motor housing. The action of the protective device shall be to cause the motor to be disconnected. The motor and convertor combined need not be tested together.
(b)
The motor shall be type-tested for this duty as a unit in association with the convertor specified in the descriptive documents and with the protective device provided.
(c)
The motor temperature rise shall be assessed by calculation in accordance with the requirements of AS 2380.9, for the duty required/specified.
NOTES:
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1
In some cases, the highest surface temperature occurs on the motor shaft.
2
For motors with protection type ‘e’ terminal boxes, and when using convertors with highfrequency pulses in the output, care should be taken to ensure that any overvoltage spikes and higher temperatures that may be produced in the terminal box are taken into consideration.
2.4.7 Trace heating Electrical resistance trace heating equipment should comply with AS/NZS 62086.1.
TABLE 2.3 RELATIONSHIP BETWEEN GAS/VAPOUR SUBDIVISIONS AND SUITABLE EQUIPMENT SUBGROUPS Gas/vapour subdivision
Suitable equipment subgroups
IIA
IIA, IIB, or IIC
IIB
IIB or IIC
IIC
IIC
2.5 ZONE 20, 21 AND 22 HAZARDOUS AREAS 2.5.1 Information required In order to select appropriate electrical equipment for use in a Zone 20, 21 and 22 hazardous area, the following information is required: (a)
The classification of the area, i.e. the zone.
(b)
The layer ignition temperature of the combustible dust, fibre or flying involved or the lowest layer ignition temperature if more than one combustible material might be present.
(c)
The cloud ignition temperature of the combustible dust, fibre or flying involved or the lowest value of cloud ignition temperature if more than one combustible material might be present.
(d)
Where applicable, the minimum cloud ignition energy of the dust, fibre or flying involved or the lowest minimum ignition energy if more than one combustible material might be present (see Clause 2.5.4).
(e)
Other considerations in accordance with Clause 1.9, as applicable. COPYRIGHT
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2.5.2 Selection with respect to area classification The type of explosion-protection shall be selected according to the area classification (see AS/NZS 61241.1.2). Electrical equipment in Zone 20, 21 and 22 areas shall be protected by one or a combination of the explosion-protection techniques specified in Clause 2.5.4, as appropriate. A1
2.5.3 Selection with respect to temperature classification 2.5.3.1 General The type of explosion-protection shall be selected according to the temperature classification (see AS/NZS 61241.1.2). Electrical equipment in Zone 20, 21 and 22 areas shall be protected by one or a combination of explosion-protection techniques specified in Clause 2.5.4, as appropriate. 2.5.3.2 Ambient temperature limitation Electrical equipment for Zone 20, 21 and 22 areas is normally intended for use at ambient temperatures not exceeding 40°C unless marked accordingly (see AS/NZS 61241.1.1). 2.5.3.3 Maximum surface temperature The temperature classification for electrical equipment in Zone 20, 21 and 22 areas shall be determined by the deduction of a safety margin of 50 K (except for enclosures as given in AS/NZS 61241.1.2), from either the cloud ignition temperature or the layer ignition temperature of the dust concerned, whichever is the lesser. 2.5.3.4 Ambient temperature consideration The temperature classification system assumes an ambient temperature of 40°C, unless the equipment is otherwise marked. Where equipment is installed in an area where the ambient temperature is likely to exceed 40°C, or where the equipment is subjected to heating from external sources (e.g. solar, electric heater, boiler), appropriate safeguards shall be taken to ensure that the equipment is suitable for safe operation at the higher temperature and that the higher temperature is taken into account when applying Clause 2.5.3.2. NOTES: 1
2
A higher ambient may be covered by assigning maximum temperature as follows: (a)
Actual ambient temperature = 50°C (i.e. 10°C above 40°C).
(b)
Temperature class of equipment = T4 (i.e. 135°C at 40°C ambient).
(c)
Assumed maximum external temperature at ambient of 50°C = 135°C + 10°C = 145°C.
The properties of the enclosure should be taken into account when considering higher ambient temperatures.
2.5.4 Types of explosion-protection One or a combination of the following types of explosion-protection shall be used to ensure the safety of electrical equipment in Zones 20, 21 and 22 (see AS/NZS 61241.1.2), within the limitations stipulated below: (a)
Dust ignition protection (DIP) DIP equipment complying with AS/NZS 61241.1.1. DIP equipment previously certified to AS 2236 under the ‘AUS Ex Scheme’ is considered equivalent to category A21 of AS/NZS 61241.1.1.
(b)
Encapsulated equipment (Ex m) Encapsulated equipment complying with AS 2431 or IEC 60079-18 provided that the equipment is installed in accordance with this Standard.
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Intrinsically safe apparatus (Ex i) Intrinsically safe apparatus complying with AS 2380.7 or AS/NZS 60079.11, provided that the following conditions are satisfied: (i)
(ii)
The apparatus complies with— (A)
Ex ia for Zone 20; or
(B)
Ex ib for Zones 21 or 22.
The apparatus is— (A)
Group IIA, IIB or IIC and the minimum dust cloud ignition energy to which the equipment will be exposed is higher than 15 mJ; or
(B)
Group IIB or IIC, and the minimum dust cloud ignition energy to which the equipment will be exposed is higher than 1 mJ; or
(C)
Group I, and coal dust is the only hazard present.
(iii) Associated safe area equipment is not installed in a Zone 20, 21 and 22 area unless protected by an appropriate protection technique. NOTE: Associated safe area equipment is identified by the inclusion of brackets in the marking, e.g. Ex (ia), Ex (ib), (Exia), (Exib).
(d)
(iv)
The apparatus is either encapsulated or protected by an enclosure complying with at least the degree of protection IP5X given in AS 1939.
(v)
The equipment is installed in accordance with the requirements of AS 2381.7.
Pressurized rooms or enclosures (Ex p) Pressurized rooms or pressurized enclosures complying with the requirements for dust hazardous areas, specified in AS 2380.4 or AS/NZS 61241.4, are acceptable in Zones 21 and 22.
Equipment intended for use in Zone 20 shall comply with the requirements of Zone 21 apparatus and be verified (in writing) by a Testing Station or the manufacturer, as suitable for use in Zone 20, with particular reference to the layer depth and all the characteristics of the material(s) being used. 2.5.5 Motors supplied at varying frequency and voltages DIP motors supplied at varying frequency and voltages shall meet the requirements of either Item (a) or Item (b), as follows: (a)
There shall be means (or equipment) for direct temperature control by embedded temperature sensors specified in the motor manufacturer’s documentation or other effective measures for limiting the surface temperature of the motor housing. The action of the protective device shall be to cause the motor to be disconnected. The motor and convertor combined need not be tested together.
(b)
The motor shall be type-tested for this duty as a unit in association with the convertor specified in the descriptive documents and with the protective device provided.
2.5.6 Heating equipment Heating equipment installed in Zones in explosive dust atmospheres shall comply with the following requirements: (a)
All heating appliances are permanently installed and connected to the electrical supply by means of fixed wiring. Portable heating equipment is not permitted in Zones in explosive dust atmospheres.
(b)
The maximum surface temperature of heating appliances complies with the requirements of Clause 2.5.3 under worst conditions, e.g. when any thermostatic control device or any forced air circulation has been rendered inoperative.
(c)
Notwithstanding the requirements specified in Clause 2.5.4, the heating element may be a mineral-insulated metal-sheathed type.
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2.6 VERIFICATION OF ACCEPTANCE OF ELECTRICAL EQUIPMENT A1
2.6.1 General requirements for both Australia and New Zealand Except where otherwise specified, electrical equipment selected for use in hazardous areas shall be protected by one or a combination of the explosion-protection techniques specified in Clauses 2.4 and 2.5, and shall comply with the requirements of Clauses 2.4 and 2.5 as appropriate. Proof of compliance with the applicable explosion-protection technique Standards detailed in Clauses 2.4 and 2.5 shall be provided by means of a certificate of conformity issued in accordance with either the National Certification Schemes—‘AUS Ex’ or ‘ANZEx’. Electrical equipment carrying IEC Ex certification in accordance with the IECEx Scheme Rules (Publication IEC Ex 02) and certified to the IEC Standards recognized by such scheme (or identical Standards), is deemed to comply with the requirements of Clauses 2.4 or 2.5, as appropriate, and therefore this is considered an acceptable alternative to the Certificate of Conformity issued in accordance with the National Certification Schemes— ‘AUS Ex’ or ‘ANZEx’. AS/NZS 61241.1.1 permits the manufacturer to assess DIP A22 and DIP B22 apparatus for compliance with the Standard rather than requiring third party certification; however DIP A22 and DIP B22 apparatus shall comply with Clause 2.6 of this Standard. NOTES: 1
Appendix H provides information and contact details regarding the National Certification Schemes—‘AUS Ex’ and ‘ANZEx’.
2
Further details regarding the IECEx Scheme can be obtained from the website ‘www.iecex.com.’.
2.6.2 Other acceptable certification 2.6.2.1 For Australia In Australia, electrical equipment certified to an alternative Standard to those referenced in Clauses 2.4 and 2.5, but shown to provide an equivalent level of safety, may be accepted by the relevant regulatory authority. 2.6.2.2 For New Zealand Proof of compliance with the relevant protection technique Standards detailed in Clauses 2.4 and 2.5 issued by the certification bodies listed below, is accepted by the electrical safety regulatory authority in New Zealand:
A1
•
Factory Mutual (FM) of the United States of America;
•
Canadian Standards Association (CSA) of Canada;
•
The certification bodies listed under the European Directive 94/9/EC who can issue electrical safety certification on electrical equipment for use in potentially explosive atmospheres. These certification bodies, known at the time of publication of this document, are listed in Appendix B.
2.7 SELECTION OF REPAIRED OR EXISTING EQUIPMENT When it is intended that existing equipment, or repaired equipment, is to be installed in a hazardous area that is deemed to be a new installation, the requirements of Clauses 2.2 to 2.6 apply, as appropriate. In addition, the procedure set out in Figure 2.1 shall be followed. NOTE: The act of introducing other than like for like apparatus in an existing installation may cause that installation to be deemed ‘new’.
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FIGURE 2.1 FLOW CHART PROCEDURE FOR SELECTION OF REPAIRED OR EXISTING EQUIPMENT
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SECT ION
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AS/NZS 2381.1:1999
I NSTA L L A T I ON
3.1 SCOPE OF SECTION This Section sets out general requirements for installations in hazardous areas. The installation procedures which apply to particular types of explosion-protection are described in the appropriate Parts of this series of Standards. 3.2 GENERAL INSTALLATION REQUIREMENTS 3.2.1 General The installation of equipment shall be carried out in a manner that does not reduce the type of explosion-protection afforded by the equipment design. 3.2.2 Access Installations generally shall be designed and the equipment and materials installed with a view to ensuring ease of access for inspection and maintenance. 3.2.3 Electrical rating Electrical equipment and materials shall be installed, used and maintained for use only within their electrical ratings. These ratings include power, voltage, current, frequency, duty and temperature. 3.2.4 Associated equipment located in non-hazardous areas Consideration shall be given to equipment associated with hazardous area equipment but which is located in non-hazardous area e.g. protection devices, variable speed controllers and the like. A1
3.2.5 Intrinsically safe installations Intrinsically safe installations shall comply with the requirements of Section 3 where applicable, except for Clauses 3.5, 3.6, 3.7, 3.8.8, 3.8.15.1, 3.8.15.2, 3.8.15.3, 3.10, 3.11 and 3.12. 3.3 EARTHING 3.3.1 General The metal parts of electrical equipment including ELV equipment, installed in hazardous areas, shall be earthed in accordance with AS/NZS 3000, plus any additional requirements specified in this Standard.
A1
In New Zealand, care should be taken to ensure that the safety hazardous area is not compromised by an earth potential rise created by a neutral current flowing in an earth conductor, as a result of links in switchboards between neutral and earth conductors in installations constructed prior to 1993. 3.3.2 Enclosure and termination of earthing conductors Any earthing conductor shall be enclosed with its associated live conductors within a conduit, cable sheath or cable armouring and shall be terminated in an enclosure, which maintains the appropriate type of explosion-protection, except that the following may apply, as appropriate:
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MIMS cable The sheathing of MIMS cable may be used as an earthing conductor provided that earthing connections to the sheathing are made within appropriate fittings and enclosures (e.g. a cable gland with a metal olive).
(b) A1
High voltage circuits Earthing conductors associated with high voltage circuits may be run externally provided that their insulation is not inferior to that specified for single-core unsheathed cable complying with AS/NZS 5000.1. Where such earth conductors are not tied to the associated live conductors at regular intervals, the earth conductors shall be marked at intervals not exceeding 30 m with the words ‘HV earthing conductor’.
(c)
Low voltage and extra low voltage circuits Where an earth core is included within the cable sheath it shall be connected to an earthing terminal within the enclosure(s). Cable armouring (if any) shall be earthed via appropriate metal glands and connections to the earthing facilities in the enclosure(s). Cable screens (if any) shall be earthed.
A1
(d)
Cable installations in Zone 2 areas In Zone 2 areas earthing conductors may be run externally to the associated live conductors provided that the earthing conductors insulation is not less than that specified for a single core unsheathed cable complying with AS/NZS 5000.1. Such earth conductors shall be strapped securely to the associated live conductors at intervals not exceeding 10 m.
3.3.3 Earthing of spare conductors In any equipment, except that meeting the requirements of the Standards relating to Ex i, all spare conductors shall be earthed at least at one end of the circuit. The earthing of spare cores of Ex i installations shall be in accordance with AS 2381.7. 3.3.4 Earthing of aircraft Under heavy maintenance conditions aircraft shall be earthed effectively to a point close to where the aircraft is located. 3.4 EQUIPOTENTIAL BONDING 3.4.1 General To avoid sparking between metallic parts of structures, potential equalization is always required for Zones 0, 1, 20 and 21 installations and may be necessary for installations in Zones 2 and 22. Where necessary, exposed and extraneous conductive parts shall be connected to the main or supplementary equipotential bonding system. The equipotential bonding system may include protective conductors, wiring enclosures, metal cable sheaths, steel wire armouring and metallic parts of structures but shall not include neutral conductors. The resistance between metallic parts of structures shall be less than or equal to a cross-sectional area of at least 10 mm2 of copper or 0.002 Ω per metre. Enclosures need not be separately connected to the equipotential bonding system if the enclosure is firmly secured to, and is in metallic contact with, structural parts or piping which are connected to the equipotential bonding system.
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NOTES: 1
Potential equalization between vehicles and fixed installations may require special means, e.g. between ships and shore when insulated flanges in connecting pipelines are used.
2
Adequate precautions should be taken to minimize the risk of corrosion at the points of connection of equipotential bonding conductors.
3.4.2 Temporary bonding It is recommended that the final connection of a temporary bonding connection should be made either—
A1
(a)
in a non-hazardous area;
(b)
using a connection suitable for the hazardous area; or
(c)
using a documented procedure which minimizes the risk of sparking.
For temporary bonding the resistance between metallic parts can be greater than that specified in Clause 3.4.1. NOTE: Examples of temporary bonding include that made to a portable drum or a vehicle.
3.4.3 Bonding of metallic enclosures, conduits, sheaths and armour Electrical continuity between metallic enclosures and conduit, or armour, or cable sheaths and armour, or across any joints in the conduit or armour, or cable sheaths and armour, shall be ensured by the integrity of the joint itself. If external bonding is necessary, it shall be connected directly across the joint to avoid risk of introducing a path of high surge impedance. 3.5 ELECTRICAL PROTECTION 3.5.1 General Any circuits and equipment in hazardous areas shall be provided with means to ensure disconnection quickly in the event of overcurrent, internal short-circuit or earth-fault conditions. All switchgear shall be capable of performing these functions without risk to the operator and without damage which renders the equipment unsuitable for further use. In circumstances where automatic disconnection of electrical equipment may introduce a safety risk which is more dangerous than that arising from the risk of ignition alone, a warning device (or devices) may be used as an alternative to automatic disconnection provided that operation of warning device (or devices) is immediately apparent so that prompt remedial action will be taken. 3.5.2 Location of protection and control equipment Protection and control equipment shall be located in a non-hazardous area unless otherwise protected with an appropriate type of explosion-protection. 3.5.3 Resetting of short-circuit and earth-fault protection devices Short-circuit and earth-fault protective devices shall be such that auto-reclosing under fault conditions is prevented. 3.5.4 Phase failure protection Precautions shall be taken to prevent the operation of a three-phase motor on the loss of a phase. 3.6 ELECTRICAL ISOLATION To allow work to be carried out safely, suitable means of isolation (e.g. isolators, fuses and links) shall be provided for each circuit or group of circuits, including all live conductors.
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Labelling shall be provided immediately adjacent to each means of isolation to permit rapid identification of the circuit or group of circuits thereby controlled. There shall be effective measures (e.g. means of isolation capable of being locked in the OFF position) or procedures to prevent the restoration of supply to equipment whilst the risk of exposing unprotected live conductors to an explosive atmosphere continues. 3.7 EMERGENCY SWITCH-OFF For emergency purposes, at a suitable point or points outside the hazardous area there shall be single or multiple means of switching off electrical supplies to the hazardous area. Electrical equipment that must continue to operate to prevent additional danger shall be on a separate circuit and shall not be included in the emergency switch-off circuit. 3.8 WIRING SYSTEMS—GENERAL REQUIREMENTS 3.8.1 Specific methods not permitted 3.8.1.1 In hazardous areas The following wiring systems shall not be installed in hazardous areas: (a)
Bare conductors.
(b)
Open wiring.
(c)
Earth sheath return (ESR) wiring systems not insulated to the equivalent of double insulation.
(d)
Busway systems.
(e)
Aerial wiring systems.
(f)
Single wire earth return systems.
(g)
Low and extra-low voltage track systems.
(h)
Cables with sheaths of a tensile strength lower than— (i)
(ii)
thermoplastic •
polyvinyl chloride (PVC)
...12.5 N/mm2
•
polyethylene
...10.0 N/mm2
elastomeric •
polychloroprene, chlorosulfonated polyethyle or similar polymers
...10.0 N/mm2
except when installed in conduit according to Table 3.1. NOTE: These cables are commonly known as ‘easy tear’ cables.
3.8.1.2 Above hazardous areas The following wiring systems shall not be installed above hazardous areas: (a)
Bare conductors.
(b)
Open wiring.
(c)
Aerial wiring systems.
(d)
Low and extra-low voltage track systems.
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3.8.2 Permitted types The wiring system shall— (a)
be one or a combination of the systems specified in Table 3.1 as appropriate; and
(b)
maintain the type of protection afforded by the equipment design.
3.8.3 Telecommunications circuits Telecommunication circuits shall comply with the requirements of this Standard in addition to any requirements of the relevant telecommunications Standards. 3.8.4 Avoidance of damage Cable systems and accessories should be installed, so far as practicable, in positions that will prevent them from being exposed to mechanical damage and to corrosion or chemical influences (e.g. solvents), and to the effects of heat or UV radiation. Where exposure of this nature is unavoidable, protective measures appropriate to the problem shall be taken or appropriate cables selected. Examples of protective measures to minimize risk of mechanical damage include the use of armoured, screened, seamless aluminium sheathed, mineral insulated metal sheathed or semi-rigid sheathed cables, or installation of cables in conduits. Examples of protective measures to minimize risk of UV radiation damage include installation of cables in conduits or the use of fitting covers to protect from sunlight. Where cable or conduit systems will be subject to vibration, they shall be designed to withstand the vibration or damage.
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TABLE 3.1
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WIRING SYSTEMS IN HAZARDOUS AREAS (Not applicable to coal mining areas) Type of wiring system
Zone 0
Zone 1
Zone 2
Zones 20, 21 and 22
Intrinsically safe systems in accordance with AS 2381.7.
X
X
X
X
Cables in metallic conduit and fittings complying with AS/NZS 2053.1 and AS/NZS 2053.7 and the appropriate protection technique for the area in which they are to be installed.
X
X
X
X
Served MIMS.
*
X
X
X
X
X
X
X
X
X
Thermoplastic, thermosetting or elastomeric sheathed unarmoured. Thermoplastic, thermosetting or elastomeric sheathed with armouring or braiding designed for mechanical protection.
*
X
Cables in rigid and corrugated, non-metallic conduit, minimum light duty, complying with AS/NZS 2053.1, AS/NZS 2053.2 and AS/NZS 2053.5. Metal sheathed, served and armoured.
*
X
X
X
Flexible cords and cables in accordance with Clause 3.11.1.
*
X
X
X
Metal sheathed, served and unarmoured.
X
Flexible steel conduit with non-metallic serving to AS/NZS 2053.1 and AS/NZS 2053.8.
X
Flexible steel conduit with non-metallic serving to AS/NZS 2053.1 and AS/NZS 2053.8 and fittings complying with AS/NZS 61241.1.1.
X
Trunking, ducts, pipes or trenches installed to meet the requirements of Clause 3.8.5.
X
X
Trunking, ducts, pipes or trenches installed to meet the requirements of Clause 3.13.1 Flexible conduit assemblies complying with the relevant requirements of AS 2380.2 or AS/NZS 60079.1
X
X X
X
X denotes acceptable use. *
This wiring system may be installed in a Zone 0 area, if provided with additional protection to counter the harmful environmental effects detailed in Clause 3.8.4.
3.8.5 Passage and collection of flammables 3.8.5.1 General Where trunking, ducts, pipes or trenches are used to accommodate cables, precautions shall be taken to prevent the passage of flammable gases, vapours, liquids or dust from one area to another and to prevent the passage of flammable gases, vapours, liquids and dust in trenches. Such precautions may involve the sealing of trunking, ducts or pipes. For trenches, adequate venting or sand-filling may be used. Conduits and, in special cases, cables (e.g. where there is a pressure differential) shall be sealed, if necessary, so as to prevent the passage of liquids and gases. COPYRIGHT
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3.8.5.2 Openings in walls Openings in walls for cables and conduits between hazardous and non-hazardous areas shall be adequately sealed, for example by means of sand seals or mortar seals. 3.8.5.3 Canned pumps and process connections Where canned pumps, process connections for flow, pressure or analysis measurements or the like depend upon a single seal diaphragm or tube to prevent process fluids from entering the wiring system, an additional seal or barrier shall be provided in the wiring system with an adequate drain between the seals or barriers so that the occurrence of any leaks will become apparent. 3.8.6 Circuits traversing a hazardous area Where a circuit traverses a hazardous area, the wiring shall comply with the requirements of this Standard, for the particular hazardous area traversed by the circuit. 3.8.7 Fortuitous contact Except for trace-heating, fortuitous contact between the metallic armouring/sheathing of cables and pipework or equipment containing flammable gases, vapours or liquids shall be avoided. The insulation provided by non-metallic outer sheath on a cable will usually be sufficient to achieve this. 3.8.8 Flexible connections to fixed equipment Connections to fixed equipment may be required from time to time to be moved through a small distance (e.g. motors on slide rails). Examples of suitable connection include— (a)
armoured cables arranged to permit the necessary movement without detriment to the cable;
(b)
one of the types of cable suitable for portable equipment; and
(c)
flexible conduit.
Flexible metallic conduit and fittings shall maintain the type of Ex and ingress protection afforded by the equipment design. 3.8.9 Surge protection of circuits supplied from overhead lines Where overhead line is used for either power supply or telecommunications circuits, it shall be terminated outside the hazardous area and be fitted at or near the terminal pole with an effective surge protective device. 3.8.10 Wiring entry The wiring entry to the equipment, direct or indirect, shall maintain the type of explosionprotection used. 3.8.11 Unused entries Unused entries for cables or conduit entries in electrical equipment shall be closed with blanking elements suitable for the relevant type of protection. The means provided for this shall be such that the blanking element can be removed only with the aid of tools. 3.8.12 Jointing Cables run in hazardous areas should, where practicable, be uninterrupted. Where discontinuities cannot be avoided, the joint, shall be mechanically, electrically and environmentally suitable for the situation, and shall— (a)
be made in an enclosure with a type of explosion-protection appropriate to the zone; or
(b)
providing the joint is not subject to mechanical stress, be epoxy filled, compoundfilled or sleeved with heat-shrunk tubing, in accordance with the manufacturer=s instructions. COPYRIGHT
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The earth continuity of any armouring shall be maintained regardless of which method of jointing is used. Conductor connections, with the exception of those in conduits connected to flameproof equipment or intrinsically safe circuits, shall be made only by means of compression connectors, secured screw connectors, welding or brazing. Soldering is permissible if the conductors being connected are held together by suitable mechanical means and then soldered. 3.8.13 Protection of stranded ends If multi-stranded and, in particular, fine-stranded conductors are employed, the ends shall be protected against separation of the strands, e.g. by means of cable lugs or core end sleeves, or by the type of terminal, but not by soldering alone. Creepage distances and clearances in accordance with the type of explosion-protection of the equipment shall not be reduced by the method by which the conductors are connected to the terminals. 3.8.14 Glands and seals 3.8.14.1 General Close attention shall be paid to the cable glanding and sealing arrangements for all types of equipment, and to the need for maintaining the IP rating, the integrity of the type of Ex protection of the enclosure and protection against corrosion. No cable gland or seal should be reused where the seals or cones have been damaged, unless the certification documentation for the gland or seal allows for the replacement of the seals and cones. 3.8.14.2 Compound filled glands When selecting compound filled cable glands it should be verified that the compound is not susceptible to damage from the materials to which it is likely to be exposed. 3.8.15 Conduit systems 3.8.15.1 Conduit and fittings 3.8.15.1.1 General Conduit and fittings shall be manufactured in accordance with the appropriate Parts of AS/NZS 2053. A1
3.8.15.1.2 Compliance Conduit fittings shall comply with the appropriate Standard where fittings are required to maintain the integrity of the type of Ex protection, e.g. Ex d conduit fittings shall comply with AS 2380.2 or AS/NZS 60079.1, to be compatible with the equipment, and DIP conduit fittings shall comply with AS/NZS 61241.1.1. NOTE: Conduit fittings may be component certified or certified with the equipment.
3.8.15.2 Thread engagement Where the type of Ex protection technique is required to be maintained screwed metallic conduit and metallic fittings shall have the minimum lengths of thread engagement as per the requirements of the appropriate protection technique. A1
For Ex d a minimum of five threads, tolerance class 6g, engagement shall be provided between the conduit or fittings and the flameproof enclosure, or as accepted by the certification.
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3.8.15.3 Condensation drains Long runs of conduit shall be provided with suitable devices to ensure satisfactory draining of all condensate. All drains shall be to the bottom of equipment, as indicated in Figure 3.1. A1
FIGURE 3.1 LOCATION OF CONDUIT SEALS AND CONDENSATION DRAINS
3.8.15.4 Sealing Sealing of conduit systems shall comply with the following: A1
(a)
General To prevent the passage of gases, vapours or flames from one portion of the electrical installation to another, sealing fittings shall be installed as follows: (i)
In each conduit entering or leaving a flameproof enclosure, as indicated in Figure 3.1, sealing fittings shall be located at the enclosure. NOTE: This should not preclude the use of minor fittings such as nipples, thread adaptors, reducers, elbows and the like, for the purpose of making the required connections.
(ii)
In each conduit entering or leaving a hazardous area, the sealing fitting may be located on either side of the boundary of such a hazardous area but shall be designed and installed so that any gases or vapours that may enter the conduit system, within the Zone 0, Zone 1 or Zone 2 area, will not enter or be communicated to the conduit beyond the seal.
There shall be no union, coupling box, or fitting in the conduit between the sealing fitting and the point at which the conduit leaves the hazardous area. Where two or more flameproof enclosures are connected by nipples, a single seal in each nipple connection shall be sufficient. NOTE: Flameproof conduit fittings of the ‘L’, ‘T’ or ‘cross’ type are not usually classed as separate enclosures, if not larger than the nominal size of the conduit.
(b)
Type of seal The minimum depth of sealing material shall be not less than the nominal diameter of the conduit but in no case less than 16 mm. Any sealing material used shall comply with the following requirements: (i)
The seal shall be unaffected by the surrounding atmosphere or liquids.
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36
Poured seals and encapsulating material shall have a softening or melting point at least 20°C higher than the maximum expected operating temperature of the device or component and the sealing compound shall effectively wet all surfaces to be sealed.
(iii) The seals and encapsulating material shall retain their sealing properties over the expected life of the device or component. (iv) (c)
The seal shall be installed in accordance with the manufacturer’s instructions.
Cable joints No cable joint shall be made in any fitting which is designed solely for the purpose of sealing.
3.8.16 Equipment circuit identification The purpose of this requirement is to ensure that equipment is correctly isolated whenever work is to be done. This can be achieved as follows: (a)
Equipment is fitted with a permanent label which specifies the source of supply; or
(b)
Equipment is fitted with a tag number, or cable is fitted with a cable number adjacent to the equipment, in such a way that the source of supply can be determined from a drawing or schedule by reference to the tag number or cable number; or
(c)
Item is clearly and unambiguously shown on a drawing on which the source of supply is identified either directly or indirectly via a schedule.
NOTE: See Clause 1.6 for documentation/verification dossier.
3.9 EQUIPMENT — GENERAL REQUIREMENTS 3.9.1 Installation of equipment Equipment selected in accordance with Clauses 2.4 and 2.5 shall be installed in accordance with Table 3.2. 3.9.2 Lighting Illumination of hazardous areas through panels of glass or other transparent or translucent material shall be permissible only if the following conditions apply: (a)
Fixed luminaires are used as the sources of illumination.
(b)
The panel effectively segregates the hazardous area from the area in which the luminaire is located.
(c)
The panel is of a material or is protected (such as wired glass or armour plate glass) so that breakage will be unlikely. The panel material shall meet the thermal shock test and impact tests specified for glass in hazardous area enclosures specified in AS 2380.1.
(d)
The arrangement is such that normal accumulations of hazardous residue on the surface of the panel will not be raised to a dangerous temperature by radiation or conduction from the lighting.
3.9.3 Fastenings and tools Where the equipment requires special bolts or fastenings or tools, these items shall be available and shall be used.
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TABLE 3.2 EXPLOSION-PROTECTION TECHNIQUES AND THEIR ASSOCIATED INSTALLATION STANDARDS Description of the technique
Relevant Australian/New Zealand installation Standards
General criteria
AS/NZS 2381.1 (this Standard)
Flameproof equipment, Ex d
AS 2381.2
Pressurized rooms or enclosures, Ex p
AS 2380.4
Increased safety, Ex e
AS 2381.6
Intrinsically safe, Ex i
AS 2381.7
Special protection, Ex s
AS 1076.8
Non-sparking, Ex n
AS 1076.7
Equipment in combustible dust areas
AS/NZS 61241.1.2
Ventilation, Ex v
AS 1482
Encapsulation, Ex m
As per manufacturer’s instructions
Powder filling, Ex q
As per manufacturer’s instructions
Oil immersion, Ex o
As per manufacturer’s instructions
3.9.4 Equipment above hazardous areas 3.9.4.1 Above Zone 0 or Zone 20 areas Electrical equipment installed above a Zone 0 or Zone 20 area shall be— (a)
suitable for use in a Zone 0 or Zone 20 area respectively; or
(b)
suitably segregated from the hazard to prevent any ignition sources falling into the hazardous area.
3.9.4.2 Above Zone 1, 2, 21 and 22 areas Where the following equipment is located less than 3.5 m above a Zone 1, 2, 21 or 22 area it shall be either totally enclosed or provided with suitable guards or screens, to prevent any ignition sources falling into the hazardous area: (a)
Fuses that may produce arcs, sparks or hot particles.
(b)
Switches that may produce arcs, sparks or hot particles.
(c)
Motors or generators that have sliding contacts or brushes.
(d)
Heaters, heating elements or other equipment that may produce arcs, sparks or hot particles.
(e)
Auxiliary equipment such as ballasts, capacitors and starting switches for all types of discharge luminaires.
(f)
All lamps, including fluorescent lamps.
3.9.4.3 Low pressure sodium vapour discharge lamps Low pressure sodium vapour discharge lamps shall not be used above a hazardous area.
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3.9.4.4 High intensity discharge lamps High intensity discharge lamps may be installed above a hazardous area provided that either— (a)
the lamp is installed in a totally enclosed fitting; or
(b)
suitable guards or screens are provided in accordance with Clauses 3.9.4.1 and 3.9.4.2.
3.9.5 Non-electric entries For any non-electrical entry (e.g. air lines or fibre optical cable) the integrity of the enclosures shall be maintained. For Ex d enclosures, certified compound filled glands will be deemed to be acceptable. A1
3.9.6 Plugs Plugs shall not have parts which remain energized when not engaged in a socket-outlet. 3.9.7 Motors Motors subject to prolonged humidity and wide temperature variations shall be provided with suitable devices to ensure satisfactory prevention or draining of all condensate. 3.10 ADDITIONAL REQUIREMENTS FOR INSTALLATIONS IN ZONE 0 AREAS 3.10.1 Flexible cable systems Unprotected flexible cables shall not be used in Zone 0 areas except for unprotected flexible cables which are an integral part of electrical equipment where the equipment, including the cable, complies with the appropriate Standard for the type of explosion-protection concerned. 3.10.2 Conduit systems Metallic conduit and non-inspection type metallic conduit fittings may be used in Zone 0 areas provided that they comply with the appropriate Part(s) of AS/NZS 2053 and are installed in accordance with this Standard. 3.11 ADDITIONAL REQUIREMENTS FOR INSTALLATIONS IN ZONE 1 AREAS 3.11.1 Flexible connections 3.11.1.1 General Flexible connections shall be made by one of the types specified in Table 3.3, as appropriate, except for flexible cords or cables which are an integral part of electrical equipment where the equipment, including the cable, complies with the appropriate Standard for the type of explosion-protection concerned.
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TABLE 3.3 FLEXIBLE CONNECTIONS IN HAZARDOUS AREAS Type Ordinary dutysheathed
Application
Heavy-duty sheathed
Sheathed, metallic and screened overall
P
P3
Handheld or portable appliances and luminaires 1, 4
P
P3
Fixed equipment2
P
P
Other equipment1, 5
P
P denotes permitted use. 1 Restricted to flexible cables having a conductor cross-sectional area of not less than 1.5 mm 2 . 2 Subject to the restrictions of Clause 3.11.1.2. 3 Where a screened flexible cable is subject to continuous flexing, a composite type screen should be used. 4 Where the flexible cable is subjected to mechanical injury, further protection shall be provided. 5 Additional cable protection is required. Refer to Clause 3.8.4.
3.11.1.2 Fixed equipment Where a flexible connection is provided for fixed equipment such as control and monitoring devices, the following conditions shall be met:
A1
(a)
The flexible connection shall be made by way of a sheathed flexible cable or cord with functional and protective insulation not inferior to ordinary duty sheathed flexible cord complying with AS/NZS 3191.
(b)
The current-carrying capacity of the flexible cable or cord shall be not less than the rating of the circuit protective device at the origin of the final subcircuit and in any case the nominal cross-sectional area shall be not less than 1 mm2 .
(c)
The length of the flexible cable or cord, installed without further mechanical protection, shall be not greater than 600 mm, unless the flexible cable has been designed and certified as an integral part of a piece of equipment.
(d)
The flexible cable or cord shall not be installed in a position where it is subject to mechanical damage.
(e)
Terminations of the flexible cable or cord shall be appropriate to the hazardous area in which the equipment is located.
3.11.2 Cable glands Cable glands used in a cable system shall comply with— (a)
the requirements for Group II glands set out in AS 1828; or
(b)
for increased safety protected equipment, ‘Ex e’, the requirements of AS 1828 or AS 2380.6; or
(c)
the requirements of the AS/NZS 60079 series, as applicable to the type of explosionprotection,
except for glands which are an integral part of electrical equipment where the equipment, including the gland, complies with the appropriate Standard for the type of explosionprotection used.
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3.11.3 Plugs and socket-outlets 3.11.3.1 General Plugs and socket-outlets shall be used in combination with a suitable form of flexible connection as set out in Clause 3.11.1. 3.11.3.2 Interlocking Plugs and socket-outlets shall be interlocked mechanically or electrically so that they cannot be separated while the contacts are energized and so that the contacts cannot be energized while the plug and socket-outlet are separated. A1
3.11.4 Pendant luminaires A1
3.11.4.1 General Pendant luminaires shall be connected by either— (a)
cables in screwed steel conduit; or
(b)
suitable flexible cords fitted with glands at each end of the cord that shall comply with Clause 3.11.2.
When using ‘Ex e’ glands, the cord shall be supported adjacent to the gland entry. 3.11.4.2 Use of conduit Conduits longer than 0.3 m shall be provided with either— (a)
permanent and effective bracing against lateral displacement at a level not more than 0.3 m above the lower end of the conduit; or
(b)
flexibility (in the form of a fitting or flexible connectors approved for the purpose and the location) at not more than 0.3 m from the point of attachment to the supporting box or fitting.
3.11.5 Heating cables Heating cables shall be provided with appropriate mechanical protection. A1
3.12 ADDITIONAL REQUIREMENTS FOR INSTALLATIONS IN ZONE 2 AREAS 3.12.1 Wiring systems 3.12.1.1 General A1
Where it is necessary for a wiring system in a Zone 2 area to maintain the properties of a particular type of explosion-protection system used in another area, the appropriate wiring system shall be used in accordance with Table 3.1. Otherwise, any wiring system other than those precluded in Clause 3.8.1 may be used in a Zone 2 area. 3.12.1.2 Flexible connections Flexible connections shall comply with the requirements of Clause 3.11.1.
A1
3.12.1.3 Cable glands Cable glands complying with AS 1828 or AS/NZS 60079.0 and AS/NZS 60079.1 shall be provided where cables enter a flameproof enclosure.
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3.12.2 Pendant luminaires Pendant luminaires shall be connected either by means of cables in screwed steel conduit or by means of a suitable flexible cord. Conduits longer than 0.3 m shall be provided with either— (a)
permanent and effective bracing against lateral displacement at a level not more than 0.3 m above the lower end of the conduit; or
(b)
flexibility (in the form of a fitting or flexible connector appropriate for the purpose and the location) at not more than 0.3 m from the point of attachment to the supporting box or fitting.
3.13 ADDITIONAL REQUIREMENTS FOR INSTALLATIONS IN ZONE 20, 21 AND 22 AREAS 3.13.1 Wiring systems Installations in Zone 20, 21 and 22 areas shall comply with AS/NZS 61241.1.2 or Table 3.1. Cable trunking, ducts, pipes or trenches used to accommodate cables in Zone 20, 21 and 22 areas shall prevent the entry of dust, being either— (a)
manufactured to meet the requirements of AS/NZS 61241.1.1; or
(b)
sand filled.
3.13.2 Flexible connections Flexible connections shall comply with the requirements of Clause 3.11.1. 3.13.3 Cable glands/entries Cable glands/entries shall be used as required by this Standard for the types of explosion protected equipment permitted in Zones 20, 21 and 22 (see Clauses 2.5.4 (a), (b), (c) and (d)). 3.13.4 Dielectrics having a flashpoint exceeding 250°C Equipment containing a liquid dielectric having a flashpoint greater than 250°C shall be either— (a)
of DIP construction in accordance with AS/NZS 61241.1.1; or
(b)
segregated as specified in Clause 2.2.
3.13.5 Luminaires Luminaires shall— (a)
comply with AS/NZS 61241.1.1; and
(b)
be protected from mechanical damage by means of guards or by virtue of their location.
3.13.6 Pendant luminaires Where pendant luminaires are suspended on conduit drops longer than 0.3 m, they shall be provided with either— (a)
permanent and effective bracing against lateral displacement at a level not more than 0.3 m above the lower end of the conduit; or
(b)
flexibility (in the form of a fitting or flexible connector appropriate for the purpose and the location) at not more than 0.3 m from the point of attachment to the supporting box or fitting.
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3.13.7 Plugs and socket-outlets In Zone 20 plugs and socket-outlets are not permitted. For their use in Zones 21 and 22 the following requirements apply: (a)
General Plugs and socket-outlets shall be used in combination with a suitable form of flexible connection as set out in Clause 3.11.1.
(b)
Interlocking Plugs and socket-outlets shall be interlocked mechanically or electrically so that they cannot be separated while the contacts are energized and so that the contacts cannot be energized while the plug and socket-outlet are separated.
(c)
Plugs Plugs shall not have parts which remain energized when not engaged with a socketoutlet.
(d)
Mounting Socket-outlets shall be installed so that dust will not enter the socket-outlet with or without a plug in place. To minimize the ingress of dust in the event of a dust cap being accidentally left off, socket-outlets shall be positioned at an angle which is not more than 60 degrees to the vertical, and the opening facing downwards.
(e)
Location Socket-outlets shall be installed in locations so that the flexible cord required shall be as short as possible.
3.14 SPECIFIC OCCUPANCIES 3.14.1 General Guidance on the classification of areas relating to several specific occupancies is given in AS/NZS 2430.3 (all Parts). For the specific occupancies mentioned in Clauses 3.14.2 to 3.14.7, the requirements of this Clause (3.14) shall apply as appropriate. 3.14.2 Ovens Electrically heated Type 1 ovens in which flammable volatiles occur shall be verified as complying with and installed in accordance with AS 1681. The ovens shall be certified as set out in Clause 2.6. 3.14.3 Fuel dispensing Fuel dispensers shall be manufactured and verified as complying with the appropriate Part(s) of AS 2229 and NZS 6109. 3.14.4 Finishing processes 3.14.4.1 Spray and spray/bake booths 3.14.4.1.1 General Spray painting booths shall comply with the design, construction and testing requirements of AS/NZS 4114.1 and the installation requirements of AS/NZS 4114.2. 3.14.4.1.2 Compliance Proof of compliance shall be demonstrated by a certificate of conformity issued by a national certification body accredited by JAS-ANZ for product certification in accordance with AS/NZS 4114.1, or by other means acceptable to the Authority.
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3.14.4.1.3 Installation and maintenance Spray painting booths shall be installed and maintained in accordance with AS/NZS 4114.2. The manner in which this work is undertaken shall not reduce the electrical safety or explosion protection afforded by the equipment design or associated equipment such as motors, light fittings, control boxes and sensing devices. NOTE: The method of installation should pay particular attention to the explosion protection properties of explosion-protected electrical equipment (termed Ex equipment) including certification conditions that may be included on the Ex certification.
3.14.4.1.4 Associated rooms Associated rooms such as paint mixing and paint preparation rooms shall be correctly installed and maintained in accordance with this Standard. 3.14.4.2 Fixed electrostatic equipment Where fixed electrostatic spraying and deterring equipment is installed, such equipment shall comply with the following requirements: (a)
High voltage grids or electrodes shall be— (i)
located in suitable non-combustible booths or enclosures provided with adequate interlocked mechanical ventilation;
(ii)
rigidly supported and of substantial construction; and
(iii) effectively insulated from earth by means of suitable insulators. (b)
High voltage leads shall be— (i)
effectively and permanently supported on suitable insulators;
(ii)
effectively guarded against accidental contact or earthing; and
(iii) provided with automatic means for discharging any residual charge to earth when the supply voltage is interrupted. (c)
Goods being processed shall be supported on conveyors so that the minimum clearance between goods and high voltage grids or conductors cannot be less than twice the sparking distance. A visible and legible sign indicating the sparking distance shall be permanently located near the equipment.
(d)
Suitable automatic controls shall operate without time delay to disconnect the power supply and to signal the operator in the event of any of the following occurrences: (i)
Stoppage of ventilating fans or failure of ventilating equipment from any cause.
(ii)
Stoppage of the conveyor carrying goods through the high voltage field.
(iii) Occurrence of an earth or of an imminent earth at any point on the high voltage system. (iv)
Reduction of clearance below that specified in Item (c).
(e)
Adequate fencing, railings or guards which are electrically conducting and earthed shall be provided for safe isolation of the process.
(f)
Signs shall be permanently mounted designating the process zone as dangerous because of high voltage.
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3.14.4.3 Electrostatic hand sprayguns Electrostatic hand sprayguns shall be used only within a spray booth or approved spray area. Electrostatic hand sprayguns and equipment, and devices used in connection with paint spraying operations shall be of a suitable type and shall comply with the following requirements: (a)
The equipment shall be designed so that the maximum surface temperature of the equipment in the spraying area cannot exceed 65°C under any condition.
(b)
The electrostatically charged exposed elements of the spraygun shall be capable of being energized only by a switch which also controls the paint supply.
(c)
Transformers, power packs, control equipment, and all other electrical portions of the equipment, with the exception of the spraygun itself and its connections to the power supply, shall be located outside the hazardous area.
(d)
The handle of the spraygun shall be electrically connected to earth by a metallic connection.
NOTE: This requirement is to prevent build-up of a static charge on the operator’s body.
(e)
All electrically conductive objects in the spraying area shall be effectively earthed, including paint containers, wash cans and any other objects or devices in the area. The equipment shall carry a prominent permanently installed warning explaining the necessity of such earthing.
(f)
Objects being painted shall be maintained in metallic contact with the conveyor or other earthed support. To ensure an effective and continuous contact— (i)
hooks shall be regularly cleaned;
(ii)
areas of contact shall be sharp points or knife edges where possible;
(iii) points of support of the object shall be concealed from random spray where feasible; and (iv)
(g)
where objects are being sprayed and supported from a conveyor the point of attachment to the conveyor shall be located so as not to collect spray material during normal operation.
The spraying operation shall take place within a spray area that is adequately ventilated to remove solvent vapours released from the operation. The electrical equipment shall be interlocked with the ventilation of spraying areas so that the equipment cannot be operated unless the ventilation fans are in operation.
3.14.4.4 Powder coatings 3.14.4.4.1 General The hazard rating associated with the application of finely ground particles of protective finishing material in dry powder form is dependent upon the chemical composition of the material, particle size, shape and distribution. Hazards associated with both combustible dusts and vapours are inherent in this process and electrical equipment shall— (a)
be of a type suitable for use in Zone 1 and Zone 21 areas; and
(b)
comply with Clause 3.14.4.3(e).
3.14.4.4.2 Application Coating powders shall be applied by means of— (a)
fluidized bed;
(b)
electrostatic fluidized bed;
(c)
powder spraygun; or
(d)
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3.14.4.4.3 Fixed and hand electrostatic spraying equipment Fixed and hand electrostatic spraying equipment for the application of powder coatings shall comply with Clauses 3.14.4.2 and 3.14.4.3. 3.14.4.4.4 Electrostatic fluidized beds Electrostatic fluidized beds shall satisfy the following requirements: (a)
Electrostatic fluidized beds and associated equipment shall be of an approved type.
(b)
The maximum surface temperature of such equipment in the coating area shall not exceed 65°C.
(c)
The high voltage circuits and exposed electrodes shall not produce a spark sufficient to ignite any powder mixture or create an appreciable shock hazard upon coming in contact with an earthed object under normal operating conditions. The following additional requirements shall be satisfied when powder coating is carried out with electrostatic fluidized beds: (i)
Transformers, power packs, control equipment and other electrical portions of the equipment, except for charging electrodes and their connections to the power supply, shall be located outside the powder coating area or shall otherwise conform to the requirements of Clause 3.14.4.4.1.
(ii)
All electrically conductive objects in the charging influence of the electrodes shall be adequately earthed. The powder coating equipment shall carry a prominent, permanently installed warning explaining the necessity for earthing these objects.
(iii) Objects being coated shall be maintained in contact with the conveyor or other support in order to ensure proper earthing. To ensure effective contact, hangers shall be regularly cleaned and areas of contact shall be sharp points or knife edges where possible. (iv)
The electrical equipment shall be interlocked with a ventilation system so that the equipment cannot be operated unless the ventilation fans are in operation.
3.14.4.4.5 Use of metal floor ducts to enclose wiring Metal floor ducts may be used only for supplying ceiling outlets for extensions to the area below the floor of the hazardous area, but such ducts shall have no connections leading into or through the hazardous area above the floor unless suitable seals are provided in accordance with Clause 3.8.14. 3.14.5 Flammable medical agents The criteria for the minimizing of combustion hazards arising from medical use of flammable anaesthetic agents shall be as set out in AS 1169. 3.14.6 Laboratory fume cupboards A1
The criteria for the installation of fume cupboards in laboratories shall be as set out in AS/NZS 2243.8. 3.14.7 Secondary batteries in buildings Secondary batteries in buildings shall be installed, tested, maintained and replaced in accordance with AS 2676.1, AS 2676.2, AS 3011.1 and AS 3011.2.
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SECT ION 4 I NSPECT I ON AND TES T I NG I NC L U D I N G COMM ISS I O N I NG 4.1 GENERAL The inspection and testing procedures set out in this Section are for the preservation of explosion-protection only and shall be considered as additional to any inspection and testing which might be required for other reasons. All appropriate testing and inspections specified in this Section shall be carried out by competent persons during installation, maintenance and any other preset inspection periods. Regular inspection procedures shall be established to minimize explosion-protected electrical equipment acting as a source of ignition.
the
risk
of
The person having legal ownership of the installation should nominate a competent person (see Clause 1.4.11) to carry out or supervise regular inspection and testing procedures. 4.2 DOCUMENTATION It is necessary to ensure that any installation complies with the appropriate certification documents, with this Standard and with any other requirements specific to the plant on which installation takes place. To achieve this result, a verification dossier shall be prepared and used to ensure that the equipment and installation techniques used are appropriate for the areas in which they are installed. All test results and inspection reports for any testing or inspection required by this Standard shall be added to the verification dossier (see Clause 1.6). 4.3 INSPECTION 4.3.1 General Inspection requirements for the particular types of explosion-protection are described in the appropriate Parts of this series of Standards. Before plant or equipment is brought into service, it shall be given an initial inspection. To ensure that the installations are maintained in a satisfactory condition for continued use within a hazardous area there shall be either—
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(a)
regular periodic inspections; or
(b)
continuous supervision by competent personnel and, where necessary, maintenance.
NOTE: Continuous supervision is intended to apply to plants where regular maintenance activities are undertaken by competent personnel (see IEC 60079-17).
The periodic inspection interval shall be based upon the expected rate of deterioration. NOTE: The major factors affecting the deterioration of equipment include susceptibility to corrosion, exposure to chemicals or solvents, likelihood of accumulation of dust or dirt, likelihood of water ingress, exposure to excessive ambient temperature, risk of mechanical damage, exposure to undue vibration, training and experience of personnel, likelihood of unauthorized modifications or adjustments, likelihood of inappropriate maintenance such as that not in accordance with manufacturer’s recommendations.
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Once an inspection interval has been fixed, the installation shall be subjected to interim sample inspections to support or modify the proposed interval. Similarly, the grade of inspection shall be determined, and sample inspections shall be carried out to support or modify the proposed inspection grade. A regular review of the results of inspections shall be conducted to justify the inspection intervals and grades. A typical procedure undertaken to establish periodic inspection intervals is shown diagrammatically in Figure 4.1.
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FIGURE 4.1 TYPICAL PROCEDURES UNDERTAKEN TO ESTABLISH PERIODIC INSPECTIONS INTERVALS
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Following any replacement, repair, modification or adjustment of plant or equipment, the items concerned shall be inspected in accordance with the inspection schedules included in the Parts of the AS 2381 series covering the protection techniques concerned. If at any time there is a change in the area classification or if any equipment is moved from one location to another, a check shall be made to ensure that the type of explosionprotection, equipment group and temperature class, where appropriate, are suitable for the revised conditions. When large numbers of similar items such as luminaires and junction boxes are installed in a similar environment, it might be possible to carry out periodic inspections on a sample basis provided that the number of samples, in addition to the inspection frequency, is subjected to review, but all items should be subjected at least to visual inspection. If plant or equipment is dismantled during the course of an inspection, precautions shall be taken during reassembly to ensure that the integrity of the type of protection is not impaired. 4.3.2 Types of inspection Types of inspection shall be as follows: (a)
Initial inspection
Initial inspections shall be used to check that the selected type of protection and its installation are appropriate. They shall be detailed (D) as shown in the inspection schedules included in the Parts of the AS 2381 series covering the protection techniques concerned. NOTE: A full initial inspection is not required if an equivalent inspection has been done by the manufacturer, except where equipment has been disturbed.
(b)
Periodic inspection Periodic inspections may be visual (V) or close (C) as shown in the inspection schedules included in the Parts of the AS 2381 series covering the protection techniques concerned. A visual or close periodic inspection might lead to the need for a further detailed inspection. The grade of inspection and the interval between periodic inspections shall be determined taking account of the type of equipment, manufacturer’s guidance, if any, the factors governing the equipment deterioration (see Note to Clause 4.3.1), the zone of use and the results of previous inspections. Where inspection grades and intervals have been established for similar equipment, plants and environments, this experience may be used in determining the inspection strategy. The interval between periodic inspections shall not exceed four years, without seeking expert advice. Movable electrical equipment (hand-held, portable, and transportable) is particularly prone to damage or misuse and therefore the interval between periodic inspections need to be reduced and the equipment submitted to a close inspection at least every 12 months. Enclosures which are frequently opened (such as battery housings) shall be given a detailed inspection. In addition, the equipment shall be visually checked by the user, before use, to ensure that the equipment is not obviously damaged.
(c)
Sample inspection Sample inspection may be visual, close or detailed. The size and composition of all samples shall be determined with regard to the purpose of the inspection.
NOTE: Sample inspection should not be expected to reveal faults of a random nature, such as loose connections, but should be used to monitor the effects of environmental conditions, vibration and inherent design weakness.
The results of all types of inspections shall be recorded. COPYRIGHT
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4.3.3 Grades of inspection The grades of inspection shall be visual (V), close (C) or detailed (D). The inspection schedules for the protection technique concerned shall detail the specific checks required for all grades of inspection. Visual and close inspections may be performed with the equipment energized. For detailed inspections the equipment shall be isolated. 4.4 ITEMS REQUIRING INSPECTION Relevant details regarding the items to be inspected are given in the appropriate Parts of this series of Standards. 4.5 TESTING 4.5.1 General Periodical tests on a sample basis in accordance with a definite testing routine shall be made, recorded and included in the verification dossier. Test requirements for the particular types of explosion-protection are set out in the appropriate Parts of this series of Standards. 4.5.2 Pre-commissioning tests Tests carried out as part of pre-commissioning work shall include— (a)
insulation resistance;
(b)
earth and earth-continuity resistance including any special earthing in accordance with Clause 3.3.2;
(c)
setting and operation of protective devices.
NOTES: 1
Insulation resistance tests should not be made in such a way that the safety of the devices and insulation used in low energy equipment and circuits are subject to damage by excess voltages.
2
In hazardous areas, use of the testing methods prescribed in AS/NZS 3000 for normal installations may be inadvisable in view of the risk introduced by the test equipment, unless the equipment can be made safe.
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SECT I O N
5
AS/NZS 2381.1:1999
MA I NTEN ANCE
5.1 SCOPE OF SECTION This Section sets out the general recommendations for maintenance which are applicable to all types of explosion-protection techniques. The recommendations which apply only to specific types of explosion-protection techniques are described in the appropriate Parts of this series of Standards. 5.2 REMEDIAL MEASURES AND MODIFICATIONS TO EQUIPMENT The general condition of all equipment shall be noted in accordance with the requirements of Section 4, and appropriate remedial measures shall be taken where necessary. Care shall be taken, however, to maintain the integrity of the type of explosion-protection provided for the equipment; this might necessitate consultation with the manufacturer. Replacement parts shall be in accordance with the certification documents. Modifications to equipment shall be carried out in accordance with AS/NZS 3800. 5.3 MAINTENANCE OF FLEXIBLE CABLES Flexible cables, flexible conduits and their terminations are particularly prone to damage. They shall be inspected at regular intervals and shall be replaced if found to be damaged or defective. 5.4 WITHDRAWAL FROM SERVICE If it is necessary for maintenance purposes to withdraw equipment from service, the exposed conductors shall be— (a)
correctly terminated in an appropriate enclosure; or
(b)
isolated from all sources of power supply and insulated; or
(c)
isolated from all sources of power supply and earthed.
If the equipment is to be permanently withdrawn from service, the associated wiring, which shall be isolated from all sources of power supply, shall be removed, or correctly terminated in an appropriate enclosure. 5.5 FASTENINGS AND TOOLS Where the equipment requires special bolts or fastenings or tools, these items shall be available and shall be used. 5.6 ENVIRONMENTAL CONDITIONS Electrical equipment in a hazardous area can be adversely affected by the environmental conditions in which it is used. Some of the key elements are corrosion, ambient temperature, ultraviolet radiation, ingress of water, accumulation of dust or sand, mechanical effects and chemical attack. The corrosion of metal, or the influences of chemicals (particularly solvents) on plastic or elastomeric components, can affect the type and degree of protection of the equipment. If the enclosure or component is severely corroded, the part shall be replaced. Plastic enclosures might exhibit surface cracking which can affect the integrity of the enclosure. Metallic enclosures of equipment shall be treated with an appropriate protective coating as a precaution against corrosion; the frequency and nature of such treatment shall be determined by the environmental conditions. COPYRIGHT
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All parts of installations shall be kept clean and free from accumulations of dust and deleterious substances that could cause excessive rise in temperature. Care shall be taken to ensure that the weather protection of the equipment is maintained. Damaged gaskets shall be replaced. Anti-condensation devices, such as breathing, draining or heating elements, shall be checked to ensure correct operation. If the equipment is subject to vibration, special care shall be taken to ensure that bolts and cable entries remain tight. Care shall be taken to avoid the generation of static electricity during the cleaning of nonconductive electrical equipment. 5.7 EARTHING AND EQUIPOTENTIAL BONDING Care shall be taken to ensure that the earthing and potential equalization bonding provisions in hazardous areas are maintained in good condition. 5.8 CONDITIONS OF USE Special conditions for safe use apply to any type of certified explosion-protected electrical equipment where the certificate number has a suffix marking of ‘X’. The certification documents shall be studied to ascertain the conditions of use. 5.9 MOVABLE EQUIPMENT AND ITS CONNECTIONS Precautions shall be taken to ensure that movable electrical equipment (portable, transportable and hand-held) is used only in areas appropriate to its type of protection, gas group and temperature class. NOTE: Ordinary industrial movable equipment, welding equipment, etc. should not be used in a hazardous area unless its use is undertaken under a controlled procedure and the specific location has been assessed to ensure that there is no hazardous atmosphere present.
5.10 OVERHAUL AND REPAIR All overhaul and repair of explosion-protected electrical equipment shall comply with the requirements of AS/NZS 3800.
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APPENDIX A
LIST OF ADDITIONAL STANDARDS RECOGNIZED BY REGULATORY AUTHORITIES IN NEW ZEALAND (Normative—New Zealand only) BS EN 50014:1998
Electrical apparatus for potentially explosive atmospheres—General requirements
50015:1998
Electrical apparatus for potentially explosive atmospheres—Oil immersion ‘o’
50016:1996
Electrical apparatus for Pressurized apparatus ‘p’
50017:1998
Electrical apparatus for potentially explosive atmospheres—Powder filling ‘q’
50018:2000
Electrical apparatus for Flameproof enclosure ‘d’
potentially
explosive
atmospheres—
50019:2000
Electrical apparatus Increased safety ‘e’
potentially
explosive
atmospheres—
50020:1995
Electrical apparatus for potentially explosive atmospheres—Intrinsic safety ‘i’
61779-1:2000
Electrical apparatus for the detection and measurement of flammable gases—General requirements and test methods
61779-2:2000
Electrical apparatus for the detection and measurement of flammable gases—Performance requirements for group 1 apparatus indicating a volume fraction up to 5% methane in the air
61779-3:2000
Electrical apparatus for the detection and measurement of flammable gases—Performance requirements for group 1 apparatus indicating a volume fraction up to 100% methane in the air
61779-4:2000
Electrical apparatus for the detection and measurement of flammable gases—Performance requirements for group 1 apparatus indicating a volume fraction up to 100% lower explosive limit
61779-5:2000
Electrical apparatus for the detection and measurement of flammable gases—Performance requirements for group 1 apparatus indicating a volume fraction up to 100% gas
for
potentially
explosive
atmospheres—
EN 50028:1987
Electrical apparatus Encapsulation ‘m’
for
potentially
50039:1980
Electrical apparatus for potentially explosive atmospheres— Specification for intrinsically safe electrical systems ‘i’
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APPENDIX B
EUROPEAN CERTIFICATION BODIES WHO CAN ISSUE ELECTRICAL SAFETY CERTIFICATION ON ELECTRICAL EQUIPMENT FOR USE IN POTENTIALLY EXPLOSIVE ATMOSPHERES, UNDER EUROPEAN DIRECTIVE 94/9/CE (Informative—New Zealand only) Austria TÜV Österreich e.v. Prufzentrum Wien DeutschstraBe 10 A-1230 Wien Austria Belgium Institut Scientifique de Service Public (ISSep) Division de Colfontaine Rue Grande 60 B-7340 Paturages Belgium Denmark DEMKO (Formerly Danmarks Electriske Materielkontrol) Lyskaer 8 DK-2730 Herlev Denmark Finland VTT P.O. Box 13051 FIN-02044 VTT Espoo Finland France Laboratoire Central des Industries Electriques (L.C.I.E.) 33 avenue du Général Leclerc BP 8 F - 92266 Fontenay-aux-Roses Cedex France Institut national de l’environnement industriel et des risques (INERIS) BP No. 2 F - 60550 Verneuil-en-Halatte France
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Germany Physilakish-Technische Bundesanstalt (PTB) Bundesallee 100 D - 33116 Braunschweig Germany Berggewerkschaftliche Versuchsstreke (BVS) Fatchstelle fur Sicherheit elektrischer Bertriebsmittel der DMT-Gesellscaft fur Forschung und Prufung mbH Beylingstrasse 65 D - 44329 Dortmund 14 (DERNE) Germany
Italy Centro Elettrotecnico Sperimentale Italiano (CESI) Via Rubattino 54 I - 20134 Milano Italy
Netherlands NV KEMA Utrechtseweg 310 PO Box 9035 NL-6800 ET Arnhem Netherlands Norway NEMKO A/S P.O. Box 73 N-0314 Oslo Norway Spain Laboratorio Oficial Jose Maria Madariaga (LOM) Calle Alenza, 1 y 2 E - 28003 Madrid Spain
Sweden SP Swedish National Testing and Research Institute Box 857 S-501 15 Borås Sweden
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United Kingdom of Great Britain and Northern Ireland Electrical Equipment Certification Services (EECS) (formerly BASEEFA) Health and Safety Executive Harpur Hill Buxton UK-Derbyshire SK 17 9JN
Industrial Science Centre Department of Economic Development 17 Antrim Road Lisburn Co. Antrim BT28 3AL Sira Certification Services South Hill SG-Chislehurst BR7 5EH
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APPENDIX C
FRICTIONAL SPARKING RISKS WITH LIGHT METALS* AND THEIR ALLOYS (Normative) C1 GENERAL Incendive frictional sparking can occur in circumstances where light metals or their alloys are brought into suitable contact with other materials, particularly when the other material is an oxygen carrier such as rust. Suitable safeguards shall therefore be taken to prevent the occurrence of such frictional contact in circumstances where an explosive atmosphere may be present, because the simultaneous occurrence of the two sets of circumstances could lead to ignition. Explosive atmospheres shall be avoided and the equipment, whenever practicable, shall be sited in locations where such atmospheres are not likely to occur. C2 RIGIDLY MOUNTED EQUIPMENT For rigidly mounted electrical equipment with light metal enclosures, and also for aluminium-armoured or sheathed cable sited in Zone 2 areas, the frictional sparking risk may be disregarded except in those particular circumstances where heavy impact might also initiate the release of flammable material. This also applies in Zone 1 areas, unless the impact risk is high in which case the use of light metal enclosures or aluminium-protected cables shall be avoided. Such equipment and cables shall not be used in Zone 0 areas. C3 PORTABLE AND TRANSPORTABLE EQUIPMENT Portable and transportable equipment with light metal or light alloy enclosures, which are otherwise unprotected against frictional contact, shall not be taken into hazardous areas unless special precautions are taken to ensure safety. Such precautions may include a special permit to work in the assured absence of an explosive atmosphere, though more satisfactory safeguards may be taken, e.g. coating the equipment with a suitable abrasionresistant material. Where coatings are used, they shall be subject to regular and careful inspection. Use of the equipment shall not be permitted if inspection reveals that the protective material has become damaged to the extent that the underlying protected metal is visible. Precautions shall be adopted even for equipment intended for use in Zone 2 areas only, since it might be difficult in practice to prevent the transfer of unprotected portable equipment to an area of greater risk. C4 FANS Provided that the protective cowls for light metal fans, e.g. on motors, are designed so that they are not readily deformed, such fans may be used in Zone 1 and Zone 2 areas since other modes of failure, e.g. bearing failure, are more likely to create a source of ignition. If plastic fans or cowls are used as alternatives, they shall be of anti-static material.
* The term ‘light metal’ refers to such materials as aluminium, magnesium and titanium, which are characterized by their ability when finely divided to react exothermically with atmospheric oxygen and, as a result, to ignite an explosive atmosphere. The term ‘light alloy’ refers to an alloy containing at least 50 percent of a light metal by atomic proportions. COPYRIGHT
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C5 ALUMINIUM CONDUCTORS The use of aluminium conductors in flameproof enclosures shall be avoided in those cases where a fault leading to potentially severe arcing involving the conductors might occur in the vicinity of a plain flanged joint. Adequate protection may be afforded by suitable conductor and terminal insulation to prevent the occurrence of faults or by the use of enclosures with spigot or threaded joints.
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APPENDIX D
LIST OF REFERENCED DOCUMENTS (Normative) The following documents are referred to in this Standard: AS 1076
1076.7 1076.8
Code of practice for the selection, installation and maintenance of electrical apparatus and associated equipment for use in explosive atmospheres (Other than mining applications) Part 7: Apparatus with type of protection ‘n’ — Non-sparking apparatus Part 8: Apparatus with type of protection ‘s’ — Special protection
1169
Minimizing of combustion hazards arising from the medical use of flammable anaesthetic agents
1482
Electrical equipment for explosive ventilation—Type of protection v
1681
Safety requirements for electrically heated Type 1 ovens in which flammable volatiles occur
1826
Electrical equipment for explosive atmospheres—Special protection— Type of protection s
1828
Electrical equipment for explosive atmospheres—Cable glands
1939
Degrees of protection provided by enclosures for electrical equipment (IP Code)
2106
Methods for the determination of the flashpoint of flammable liquids (closed cup)
2229
Electrical equipment for explosive atmosphere—Electrical systems of dispensing equipment Part 1: Flammable liquid dispensing equipment Part 2: Liquefied petroleum gas dispensing equipment
2229.1 2229.2
atmospheres—Protection
by
A1
2380 2380.1 2380.2 2380.4 2380.6 2380.7 2380.9 2381
Electrical equipment for explosive atmospheres—Explosion-protection techniques Part 1: General requirements Part 2: Flameproof enclosure d Part 4: Pressurized rooms or pressurized enclosures Part 6: Increased safety Part 7: Intrinsic safety i Part 9: Type of protection n—Non-sparking
2381.2 2381.6 2381.7
Electrical equipment for explosive installation and maintenance Part 2: Flameproof enclosure d Part 6: Increased safety e Part 7: Intrinsic safety ‘i’
2430 2430.1
Classification of hazardous areas Part 1: Explosive gas atmospheres COPYRIGHT
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Electrical equipment for explosive apparatus—Type of protection m
atmospheres—Encapsulated
2676.1 2676.2
Guide to the installation, maintenance, testing and replacement of secondary batteries in buildings Part 1: Vented cells Part 2: Sealed cells
2832
Guide to the cathodic protection of metals (all Parts)
3011 3011.1 3011.2
Electrical installations—Secondary batteries installed in buildings Part 1: Vented cells Part 2: Sealed cells
AS/NZS 1020
The control of undesirable static electricity
1768
Lightning protection
2053 2053.1 2053.2 2053.5 2053.7 2053.8
Conduits and fitting for electrical installations Part 1: General requirements Part 2: Rigid plain conduits and fittings of insulating material Part 5: Corrugated conduits and fittings of insulating material Part 7: Rigid metal conduits and fittings Part 8: Flexible conduits and fittings of metal or composite material
2243 2243.8
Safety in laboratories Part 8: Fume cupboards
2381 2381.7 2381.8 2381.9
Electrical equipment for explosive atmospheres—Selection installation and maintenance Part 7: Intrinsic safety i Part 8: Special protection ‘s’ Part 9: Type of protection ‘n’—Non-sparking
2430 2430.3
Classification of hazardous areas Part 3: Examples of area classification (all Parts)
3000
Electrical installations (known as the Australian/New Zealand Wiring Rules)
3191
Approval and test specification—Electric flexible cords
3800
Electrical equipment for explosive atmospheres—Overhaul and repair
4114 4114.1 4114.2
Spray painting booths Part 1: Design, construction and testing Part 2: Selection, installation and maintenance
4761 4761.1 4761.2
Competencies for working with electrical equipment for hazardous areas (EEHA) Part 1: Competency Standards Part 2: Guide for training and assessment
5000 5000.1
Electric cables—Polymeric insulated Part 1: For working voltages up to and including 0.6/1 kV
A1 A1
A1
A1
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AS/NZS 60079 60079.0 60079.1 60079.2 60079.4 60079.5 60079.6 60079.7 60079.11 60079.12
60079.20 61241 61241.1.1 61241.1.2 61241.3 A1
61241.4 62086 62086.1 62086.2 IEC 60079
AS/NZS 2381.1:1999
Electrical apparatus for explosive gas atmospheres Part 0: General requirements Part 1: Flameproof enclosures ‘d’ Part 2: Pressurized enclosures ‘p’ Part 4: Method of test for ignition temperature Part 5: Powder filling ‘q’ Part 6: Oil-immersion ‘o’ Part 7: Increased safety ‘e’ Part 11: Intrinsic safety ‘i’ Part 12: Classification of mixtures of gases or vapours with air according to their maximum experimental safe gaps and minimum igniting currents Part 20: Data for flammable gases and vapours, relating to the use of electrical apparatus Electrical apparatus for use in the presence of combustible dust Part 1.1: Electrical apparatus protected by enclosures and surface temperature limitation—Specification for apparatus Part 1.2: Electrical apparatus protected by enclosures and surface temperature limitation—Selection, installation and maintenance Part 3: Classification of areas where combustible dusts are or may be present Part 4: Type of protection ‘pD’ Electrical apparatus for explosive gas atmospheres—Electrical resistance trace heating Part 1: General and testing requirements Part 2: Application guide for design, installation and maintenance Electrical equipment for explosive gas atmospheres
A1
60079-1A
Part 1A: First supplement to Publication 60079-1 (1971), Electrical apparatus for explosive gas atmospheres Part 1: Construction and test of flameproof enclosures of electrical apparatus Appendix D: Method of test for ascertainment of maximum experimental safe gap
60079-18
Part 18: Encapsulation ‘m’
A1
A1
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BS 6656
Guide to prevention of inadvertent ignition of flammable atmospheres by radio-frequency radiation
6657
Guide to prevention of inadvertent initiation of electro-explosive devices by radio-frequency radiation
7361
Cathodic protection (all Parts)
NZS 6101 6101.1
Classification of hazardous areas Part 1.1: Flammable gas and vapour atmospheres
6109 6109.1 6109.2
Electrical systems of dispensing equipment for explosive atmospheres Part 1: Flammable liquids dispensing equipment Part 2: Liquefied petroleum gas dispensing equipment
JAA JAR-145
Joint Aviation Authority Joint Aviation Regulation
A1
NFPA 325
Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids
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APPENDIX E
ENCLOSURES WITH INTERNAL SOURCES OF RELEASE (Informative) E1 GENERAL When an enclosure contains an internal source of release, the type of explosion-protection required is dependent upon the area classification surrounding the enclosure and the type and extent of release of flammable substance within the enclosure. When one or more enclosures are placed one within another, it is necessary to assess the probability of a flammable substance or explosive mixture being present between each successive enclosure boundary before proceeding to determine the type of explosionprotection required inside each enclosure. In placing one or more enclosures within another, the atmosphere surrounding the inner enclosures may prove more significant in determining the types of explosion-protection for equipment inside than the area classification in the zone of application. The types of explosion-protection acceptable within successive enclosures can be determined by combining the area classification, the type of flammable substance or explosive mixture between outer and inner enclosures, and the possible type and extent of release of flammable substance inside each enclosure. E2 TYPE AND EXTENT OF INTERNAL RELEASE The possible types of release within an enclosure are as follows: (a)
Normal release—release of flammable substance occurring under normal conditions. Normal release is divided into the following three categories: (i)
None—no release of flammable substance.
(ii)
Limited—a predictable small release of flammable substance characterised by its limited influence on its surrounding atmosphere.
(iii) Unlimited—a free release of flammable substance. (b)
Abnormal release—release of a flammable substance occurring only under abnormal conditions. Abnormal release is divided into the following three categories: (i)
None—no release of flammable substance.
(ii)
Restricted—release in which the maximum rate of release is intentionally restricted to a known value. The restriction should ensure that the rate of release of a flammable substance into an enclosure will not impair a continuous dilution system (see AS 2380.4).
(iii) Unrestricted—release in which the rate of release of flammable substance is not intentionally restricted to a value that can be safely diluted and therefore is assumed to be large. NOTE: A normal release is equivalent to a continuous or a primary grade source of release and an abnormal release is equivalent to a secondary grade source of release (see AS 2430.1 for further details).
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E3 COMBINATION OF TYPES OF RELEASE E3.1 General Of the nine theoretical combinations of types of release, the following five combinations are relevant: Combination 1:
No normal release, restricted abnormal release (see Paragraph E3.2).
Combination 2:
No normal release, Paragraph E3.3).
Combination 3:
Limited normal Paragraph E3.4).
Combination 4:
Limited normal Paragraph E3.5).
Combination 5:
Unlimited release (see Paragraph E3.6).
unrestricted
release, release,
restricted unrestricted
abnormal abnormal abnormal
release
(see
release
(see
release
(see
E3.2 Combination 1: No normal release, restricted abnormal release Synopsis:
An enclosure containing an instrument or instrument system not releasing any flammable substance into the enclosure in normal operation, but where there is a low probability of an abnormal condition during which a restricted release is possible.
Typical example:
An enclosure containing a small number of fallible components (such as flexible members) where the probability of failure of such components is low and where the maximum supply of flammable substances is intentionally restricted externally to a known value.
Specific example:
A bellows-type pressure switch with an integral restriction at the inlet.
E3.3 Combination 2: No normal release, unrestricted abnormal release Synopsis:
An enclosure containing an instrument or instrument system not releasing any flammable substance into the enclosure in normal operation, but where there is a low probability of an abnormal condition during which an unrestricted release is possible.
Typical example:
An enclosure containing a small number of fallible components (such as flexible members) where the probability of failure of such components is low and where the supply of flammable substances is not intentionally restricted.
Specific example:
A bellows-type pressure switch with an unrestricted inlet.
E3.4 Combination 3: Limited normal release, restricted abnormal release Synopsis:
An enclosure containing an instrument or instrument system where there is a probability of the release of a limited quantity of flammable substance and where the maximum rate of abnormal release is intentionally restricted externally to a known value.
Typical example:
An enclosure containing a number of fallible components (such as flanges, tube fittings, seals and flexible members) where consequent on their number there is an increased probability of a normal release of flammable substances and where the maximum rate of abnormal release is intentionally restricted externally to a known value.
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Specific example:
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An analyser system where a flammable substance is contained by a closed system including a large number of tube fittings and where the maximum release from any combination of failures is externally restricted, such as an analyser house with an externally mounted flow restrictor in all the sample lines entering and leaving the house.
E3.5 Combination 4: Limited normal release, unrestricted abnormal release Synopsis:
An enclosure containing an instrument or instrument system where there is a probability of the release of a limited quantity of flammable substance into the enclosure in normal operation and where there is a low probability of an abnormal condition during which an unrestricted release is possible.
Typical example:
An enclosure containing a number of fallible components (such as flanges, tube fittings, seals and flexible members) where consequent on their number there is an increased probability of a normal release of flammable substances and where the maximum rate of abnormal release is not intentionally restricted.
Specific example:
An analyser system where a flammable substance is contained by a closed system including a large number of tube fittings and where the maximum release from any combination of failures is not restricted.
E3.6 Combination 5: Unlimited release Synopsis:
An enclosure containing an instrument or instrument system releasing an unlimited amount of flammable substance into the enclosure in normal operation. Under such conditions the abnormal release is not relevant.
Typical example:
An enclosure surrounding—
Specific example:
(a)
open containers, glands of small pumps or valves, etc., which because of their construction can produce an unlimited release of flammable substance; or
(b)
components containing a flammable substance and constructed of material liable to easy breakage.
An analyser where a flammable substance is contained in an open system.
E4 EFFECT OF THE COMBINATIONS OF TYPES OF RELEASE ON AREA CLASSIFICATION After the installation of an instrument containing a source of release, the area classification in the area of application might change depending on the type of extent of release inside the enclosure, as in the following examples: (a)
Combinations 1 and 3 could present a secondary grade source of release, but with continuous dilution as type of protection, the original area classification will not be affected. Continuous dilution will bring the concentration of the flammable substance below 20 percent of the lower explosive level (see AS 2380.4).
(b)
Combinations 2 and 4 could present a secondary grade source of release.
(c)
Combination 5 could present a primary grade source of release.
The effect on the surrounding area classification of intermittent or continuous venting of flammable substances from instrument systems, such as laboratory sampling, points, relief valves and vents, should also be considered. COPYRIGHT
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E5 PROTECTION FOR ENCLOSURES CONTAINING A SOURCE OF RELEASE E5.1 Types of enclosure The types of enclosure in which an electrical equipment is installed affects the type of explosion-protection that should be applied, as follows: (a)
If the enclosure is flameproof, it forms a complete type of explosion-protection (see Paragraph E5.2).
(b)
If the enclosure forms part of the type of explosion-protection, as with pressurization or continuous dilution, it should be able to withstand an over-pressure and fulfil requirements with respect to gas-tightness (see AS 2380.4).
(c)
If the enclosure serves only as a mechanical protection and does not form part of any explosion-protection, then the electrical equipment within the enclosure should be protected by an established type of protection suitable for the area classification (see Section 2).
E5.2 Flameproof enclosure A flameproof enclosure may be used for instruments containing a source of release. However, a release within the enclosure could cause the internal pressure to rise above atmospheric pressure before explosion occurs and the enclosure should be designed accordingly. This may be achieved by increased strength, and application of a flame arrester to release pressure should be considered. This is necessary only when the flammable substance is contained within fallible components. The possibility of the occurrence of repeated internal explosions should also be considered, since these may damage the internal equipment and the enclosure, or raise its temperature to a dangerous level. The flammable substance that could be released inside the enclosure may demand a type of protection suitable for a more severe temperature class and/or enclosure group than that required for the external atmosphere (see Section 2). This type of explosion-protection is permitted in all zones except Zone 0. E5.3 Pressurized and continuously diluted enclosures Where a source of release is present within an enclosure, pressurization with air does not provide adequate explosion-protection unless the air pressure applied is greater than the pressure of the potential source of release and air can be allowed to enter the process. Should the air pressure or construction of the enclosure be inadequate to meet these criteria or where the process does not allow intrusion of air, then pressurization with inert gas or continuous dilution is necessary. AS 2380.4 specifies selection and protection requirements for the various combinations of area classification and internal sources of release. E5.4 Other enclosures An enclosure that is not flameproof, pressurized or continuously diluted, cannot be used in a hazardous area unless the electrical equipment within the enclosure is explosion-protected by an established type of explosion-protection suitable for the area classification (see Section 2). E6 SELECTION OF A TYPE OF EXPLOSION-PROTECTION E6.1 For enclosures containing a source of release For enclosures containing a source of release, Table El sets out the types of explosionprotection against types and extent of internal release and external area classification.
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Entry to Table E1 is by type of release (see Paragraph E3), via the appropriate area classification, to give all permitted types of explosion-protection. A number in a space under the heading ‘Enclosure/Type of explosion-protection’ indicates the area classification to be used as entry to Table 2.1 (or for a second entry to Table El for nested enclosures— see Paragraph E1) in the determination of the additional type of explosion-protection to be applied to electrical equipment located within the enclosure. Table E1 may also be entered by type of explosion-protection to give all combinations of zones and types of internal release for which a given type of explosion-protection is permitted. E6.2 Using Table E1 The following example illustrates the use of Table El: Data:
A hydrocarbon analyser of the gas chromatographic type is to be installed in a Zone 2 area. The sample-handling system within the analyser contains a number of valves and fittings creating the possibility of limited normal release. Flow restrictors in the sample and carrier gas inlets limit the maximum rate of release under abnormal conditions.
Required:
The type of enclosure/explosion-protection permitted.
Method:
Since flammable gas is introduced into the instrument enclosure, reference is first made to Table E1. Combination 3 (see Paragraph E3.4) applies and is used as entry into the Table. Reading horizontally from Combination 3, four types of explosionprotection are permitted.
Solution:
1
The analyser components may have been housed inside a suitable flameproof enclosure.
2
Inert gas pressurization may be applied provided that—
3
4
(a)
all electrical components within the analyser are suitable for Zone 2 (additional explosion-protection from Table 2.1) and an alarm is initiated on pressurization failure; or
(b)
all electricity supplies to the analyser are automatically isolated on pressurization failure.
Continuous dilution with air may be applied provided that— (a)
all electrical components within the analyser are suitable for Zone 2 (additional explosion-protection from Table 2.1) and an alarm is initiated on dilution flow failure; or
(b
all electricity supplies to the analyser are automatically isolated on dilution flow failure.
All electrical components within the analyser enclosure have already been made suitable for Zone 1 (explosion-protection from Table 2.1).
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TABLE E1 ENCLOSURES CONTAINING A SOURCE OF RELEASE Classification of hazard Type and extent of internal release Combination
1
2
3
Normal
None
None
Limited
Abnormal
Restricted
Enclosure/Type of explosion-protection (Note 1)
Area classification external to enclosure (Note 3)
Flameproof (Note 4) Ex d
Continuously diluted with air (Note 2)
Alarm (Note 5)
Isolate (Note 6)
Alarm (Note 3)
Isolate (Note 8)
P
P
P
P
P
2
Zone 1
P
2
P
2
P
1
P
P
P
2
2
2
Zone 1
P
2
P
2
2
1
Non-haz/Zone 2
P
2
P
2 P
1
2
1
0
0
0
0
Zone 1 4
Limited
Unrestricted Non-haz/Zone 2
P
2
P
2
Zone 1 5
Unlimited
Non-haz/Zone 2
0
2
P
0
Zone 1 All combinations
Other enclosure
Non-haz/Zone 2
Unrestricted Non-haz/Zone 2
Restricted
Pressurized with inert gas (Note 2)
Zone 0
0
0
0
0
LEGEND: P = permitted 0 = permitted provided that the electrical equipment is separately protected for Zone 0. 1 = permitted provided that the electrical equipment is separately protected for Zone 1. 2 = permitted provided that the electrical equipment is separately protected for Zone 2. NOTES: 1 All types of explosion-protection should comply with requirements of relevant temperature class and, where applicable, with relevant enclosure group of gases and vapours (see Section 2). 2 Enclosed to be purged prior to energizing electrical circuits and to be cooled prior to opening (see AS 2380.4). 3 Area classification may change after installation of an instrument containing a source of release inside its enclosure (see Paragraph E4). 4 Release inside Ex d enclosure should not cause pressure to rise above atmospheric pressure or above the pressure for which the enclosure is designed (see Paragraph E5.2). 5 Alarm to be initiated on failure of protective gas pressure (see AS 2380.4). 6 Automatic isolation of electrical supplies on failure of protective gas pressure (see AS 2380.4). 7 Alarm to be initiated on failure of protective gas flow (see AS 2380.4). 8 Automatic isolation of electrical supplies on failure of protective gas flow (see AS 2380.4).
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APPENDIX F
RELATIONSHIP BETWEEN EQUIPMENT GROUPS AND FORMER GAS GROUPS OR CLASSES (Informative) In AS C98—1961* and AS C376—1968†, flammable gases and vapours were grouped or classified respectively according to the experimental data for limiting safe gaps or igniting currents measured under precisely specified conditions. In AS C376, many compounds were classified according to their chemical similarity with gases and vapours, which were already classified on the bases of experimental data. Neither method of grouping took into account the need for surface temperature classification, since ignition temperatures generally are not related to other explosion characteristics. It is therefore inaccurate to assume that any particular equipment complying with the design requirements for a group of gases could be used safely with all compounds allocated to that group. A1
For that reason, instead of grouping gases, equipment itself is now grouped according to design criteria (see Appendix I and AS/NZS 60079.20). The temperatures of unprotected surfaces are classified according to the system described in Clause 2.4.3. Equipment may then be used safely only with compounds allocated to the appropriate equipment group, as indicated in AS/NZS 60079.20, whose ignition temperatures are not less than the maximum temperature of the temperature classification of the equipment (see Section 2). The general relationship between the current equipment groupings and the former gas classifications are indicated in Table F1, and are illustrated with typical gases.
TABLE F1 RELATIONSHIP BETWEEN EQUIPMENT GROUPS AND FORMER GAS GROUPS OR CLASSES Equipment group
Representative gas
Former definitions AS C98—1961 Gas group
AS C376—1968 Gas class
I
Methane
Group I
Class 1
IIA
Propane
Group II
Class 2c
IIB
Ethylene
Group III
Class 2d
IIC
Hydrogen
Group IV
Class 2e
IIC
Acetylene
Group IV
Class 2f
* AS C98—1961, Flameproof enclosure of electrical equipment. † AS C376—1968, Intrinsically safe electrical equipment and circuits. COPYRIGHT
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APPENDIX G
REPORT ON THE DANGER FROM HIGH-INTENSITY LIGHT SOURCES IN HAZARDOUS ATMOSPHERES (Informative) G1 INTRODUCTION This appendix summarises the results of work undertaken in the period December 1990 to May 1994. The project was part funded by the Bureau of Reference of the European Commission, and the participants were INERIS (France), PTB (Germany), Sira Test and Certification Ltd (SIRA), Imperial College and Leeds University (UK). OSCA (Optical Sensor Collaborative Association) and HSE (Health and Safety Executive) provided balancing funds for the UK work, whilst in France and Germany the balancing funds were provided by the respective partners. The objective of the work was to investigate the conditions in which optical instruments using intense light sources (such as lasers) can operate safely in hazardous atmospheres (containing vapours of combustible products and/or combustible particles). The work comprised both experimental studies and mechanistic investigations leading to predictive methods. In the experimental work the parameters of importance were the nature of the light (in terms of coherence, intensity, wavelength, spectral width and modulation), the characteristics of the illuminated particles (such as size, chemical and physical nature, and means of presentation to the light beam), and the nature of the gaseous environment (with the aim of classifying the optical hazard in terms analogous to those for electrical equipment employed in hazardous atmospheres). It was anticipated that links might be made with parameters relevant to the electrical case, notably the minimum ignition energy, the auto ignition temperature and the burning velocity of the atmosphere. G2 BREADTH OF EXPERIMENTAL INVESTIGATIONS The number of individual experimental measurements made approaches one million. Of these, something less than 50% represented a significant event i.e. the observation of an ignition, whilst the major fraction of these experiments represented a nil result, in that no ignition event was observed. The range of variables which have been investigated during the work is as follows: (a)
Radiation sources and beam delivery Studies were carried out using infra-red radiation from a carbon dioxide laser, and from a Nd:YAG laser, using an Argon ion laser in the optical wavelength, arc lamps (in particular xenon lamps) and using an infra-red laser diode with an integral 100 µm core fibre pigtail and proprietary driver. Apart from the latter pigtail beam delivery, beams propagating through free space, emerging from the ends of optical fibres and re-focused beams emerging from optical fibres were employed. The bulk of the optical fibre experiments was carried out with multimode fibres.
(b)
Absorbers Amongst the absorbers employed were white Kaowool (a proprietary ceramic fibre mat) and this material blackened with a range of particulate materials including iron oxide, silicon carbide, charcoal, coal, cork, dust, wood, and lycopodium. Commercially available thermistors, resistors, planar and spherical sensor substrates were also used, together with short rods made of magnesium oxide sometimes coated with, for example, grey silicon.
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(c)
Atmospheres Amongst the atmospheres employed were stoichiometric mixtures of methane, propane, diethyl ether, hydrogen and carbon disulphide. In addition various composition ratios of diethyl ether and air, carbon disulphide and air, n-pentane and air, acetylene and air and ethylene and air mixtures were employed.
(d)
Atmospheres seeded with particles Methane/air mixtures seeded with carborundum particles in different size ranges were investigated at a range of different particle densities. Combustible dust/air mixtures were investigated in the mass particle concentration range from zero up to more than 4,000 particles per cm3. Amongst the particles investigated in this group were coal, starch, sulphur, lycopodium and aluminium. Starch particles were coated on to Kaowool and combustible dusts layered on the target included starch, sulphur and lycopodium.
G3 REFERENCE EXPERIMENTS Reference experiments were devised so that any discrepancies arising from differences in the respective test rigs could be compared. This was considered to be an essential part of the work, as it was known that the geometry and size of the test chamber sometimes affected the power required to cause ignition. The reference experiments involved the ignition of known concentrations of diethyl ether or carbon disulphide in air. The source of ignition was a thermistor which could be heated both electrically and by incident radiation. The errors arising at the different laboratories, of the order of ±20 percent of the mean, could be accounted for by the different shapes and volumes of the equipment employed, combined with the observation that the flame when initiated sometimes appears well above the heated body giving rise to some experimental difficulties in correlating when ignition has actually occurred. The results of the reference experiments were therefore satisfactory. G4 CORRELATION WITH KNOWN IGNITION PARAMETERS Model atmospheres were employed, notably carbon disulphide/air mixtures, in order to obtain a phenomenological understanding of radiation ignition. The model absorber was chosen so as to be a practical ‘worst case’. This was a fine fibrous organic body which presented a large cross-sectional area to the incident radiation beam but had low thermal capacity. This combination of properties also ensures that the absorber achieves an equilibrium elevated temperature reasonably rapidly and thereby facilitates experimental productivity. The work involved lasers of varying wavelengths from the infra-red to the optical, but excluding the ultraviolet. The fundamental quantities of the beam are its energy, E, cross-sectional area, A, and the time, t, over which it is incident (normally the time to ignition). Additional parameters can be derived relative to particular conditions such as power, P, (energy ÷ time), power flux or irradiance, I, (energy ÷ the product of area and time), and energy flux, F, (energy ÷ area). The chosen model system involves argon ion laser radiation incident on a charcoal dusted absorbed in an atmosphere of 2.5 percent carbon disulphide in air. With this system it was found that ignition depended upon time and area of the beam: a power flux or 67 mW/mm 2 caused ignition at large area and long times, a power of 319 mW caused ignition at small areas fibre diameters below the quenching distance of the mixture) whilst 169 mJ was the minimum energy for a brief pulse of radiation (156 mJ/mm 2 ignited the mixture instantaneously over a large area). These values are derived from an experimentally determined equation linking the appropriate radiation parameter to the area of the beam and to time. The equation can be postulated to be universal in nature, the values of the individual coefficients being dependent upon the combination of absorber, radiation wavelength and atmosphere. It takes the following form: ...(1) E = E min. + P min. t + F min. A + I min. A t This equation can be recast in terms of power by dividing through by t: P = E min. . / t + P min. + F min. . A / t + I min. . A
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and in terms of power flux by further dividing through by A: I = E min. / A t + P min. / A + F min. . / t + I min.
...(3)
In combustion generally, basic theory tends to concentrate on two extreme situations, approximating either to instantaneous point ignition sources (where the ignition criterion is an absolute minimum ignition energy) or to extended large volumes (where the controlling factor is an ignition temperature). A laser beam expanding from the end of a small optical fibre of dimension below that of the quenching distance for the particular environment, interacting with a particle of variable size and position is almost unique in being able with very minor adjustments in geometry to give rise to conditions at either end of this scale as well as any duration of irradiated areas in between. The limiting coefficients identified above are in general any four combinations of any pair of area and time tending to zero or infinity (examples are small area and short time or long time and small area). Thus, when A and t tend to zero, Equation (1) shows that E min is the important quantity. This situation is found, for example, for typical optical fibres and pulsed radiation. When A and t both tend to infinity, Equation (3) shows that I min is the important quantity. A high intensity lamp would be a relevant practical example. When A is small and t is long (optical fibres radiating continuous wave light), P min is most important (Equation 2). Equations 1 to 3 allow the critical ignition parameters for any combination of area and time to be predicted for practical situations (of absorber, wavelength and atmosphere) for which the limiting coefficients have been determined. They are represented graphically in Figure D1 for the carbon disulphide/air mixtures referred to in this paragraph D4, together with the less relevant energy flux plot. The limiting parameters can be understood in terms of more fundamental physical quantities. In general, the gas temperature in the volume surrounding the target must be sufficient for ignition to occur and the energy contained within the volume must be sufficient for the flame to spread to the rest of the reactant mixture, i.e., the volume dimensions must exceed a critical minimum. As area and time tends to infinity the volume criterion is always satisfied so that attainment of the ignition temperature of the mixture by the different laser target combinations is the sole criterion. As area and time tend to zero the gas temperature criterion is exceeded by a generous margin so that the minimum ignition volume of minimum ignition energy becomes the critical criterion. These two cases, familiar to combustion theory and electrical ignition, are shown as a result of the present research to be special cases of the more general problem studied here. The hazard which arises when area tends to zero while the time tends to infinity relates directly to the case of the end of an optical fibre. Because of the infinite time the criterion must be an ignition temperature but to ensure continued propagation, the reaction volume must be at least of quenching distance dimensions. For the remaining case of area tending to infinity while time tends to zero there needs to be the equivalent of a self-sustaining flame front instantaneously. The required minimum energy flux (F min ) can be shown to be approximately independent of the composition of the atmosphere. In the discussion of the previous paragraph, correlating fundamental combustion parameters with the four limiting coefficients, heat losses have been neglected. In the case of laser irradiation measurements, only a tiny fraction of the instant energy finds its way into the gas—most of it is evidently either reflected, not absorbed or re-radiated. Much of the energy supplied by electrical heating in gas mixtures is lost to the gas by radiation, and the greatest hazard arises for a ‘white surface’ or, generally at typical ignition temperatures, radiation so greatly exceeds conduction and convection to the gas that calculating surface temperature from a Stefan’s Law approximation is often likely to be acceptable.
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From studies on gas mixtures seeded with inert particles and dust-air mixtures it was demonstrated that particles in suspension subjected to a laser beam are far less hazardous than when the laser beam is trapped by a layer of the same particles deposited on a target. Attempts to estimate the ratio between the required power for igniting a dust-air mixture by direct absorption of the light by particles deposited on a substrate surrounded by the flammable atmosphere and by absorption of the light by a layer of particles in suspension, showed that the first configuration might be an order of magnitude more hazardous than the second situation. Because ignitions of dust clouds occurred at significantly high beam intensities than for thin layers or isolated particles, the difficulty of relating these ignitions to standard ignition parameters assumed less importance during the work. Thus it is possible for the ‘worst case’ to demonstrate that the hazard associated with lasers may be related not only to fundamental combustion parameters in terms of the absorptivity/emissivity data for each particular laser wavelength/target combination but, more directly, to electrical safety standards which have been established for many years. Most of the situations considered have an electrical equivalent which becomes comparable by multiplying the limiting input power by the product of irradiated area and its surface absorptivity for the laser wavelength. G5 PREDICTIVE COMPUTATIONS Predictive computations were made in order to generalize the results obtained and to crosscorrelate them with calculations based upon detailed ignition reaction schemes for particular gases. Two models were employed, firstly a spherical model, and subsequently, to more accurately reflect the practical experimental set-ups, a model with cylindrical geometry. For reactive systems an ignition criterion was developed and applied to hydrogen/air mixtures. The times to ignition were also calculated together with critical powers. This work was undertaken at different hydrogen/air compositions and subsequently extended to the calculations of critical powers for carbon monoxide/air and diethyl ether/air mixtures. Where experimental results are available a reasonable correlation between calculated and experimentally determined minimum critical powers was obtained, downward curvature rather than the flattening off determined experimentally. There are questions as to whether the localized ignition in the trapped gas, which is what is modelled, would lead to a subsequent propagating combustion event, which is what is studied in the experiments. The computations carried out generally confirm the qualitative arguments with regard to the correlation between fundamental combustion parameters and the critical energy/time/area relationship discussed above. G6 LIMITING SAFETY CRITERIA AND COMPARISON WITH EXPERIMENTAL RESULTS It is possible using the general equation given in Paragraph D4 above to set the individual coefficients at levels determined from first principles to be conservative and therefore safe. These can be limiting levels rendered independent of the flammable mixture target composition and laser wavelength by taking the worst case of each. This worst case would, however, still strictly be confined only to targets which do not disperse, gasify or react on irradiation. Both theory and experiment suggest that E min in Equation (1) could fall as low as the minimum spark ignition energy for a black body, and 0.01 mJ is proposed on the grounds that 0.015 mJ—the minimum value for carbon disulphide—is the lowest value encountered during the work. The precise value of E min is important only at exceedingly short times and small areas. As regards F min it was proposed in Paragraph D4 that it is approximately independent of composition and calculation suggests that the value 2 mJ would be safe. I min and P min have been determined from experimental measurements made by the partners during the work. The values chosen are 35 mW and 5 mW/mm2 ,which have been adopted provisionally on the basis of being approximately half the experimental minima determined (for carbon disulphide) during the work. This gives the following equation: COPYRIGHT
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E = 0.01 + 35t + 2A + 5 A t
...(4)
and the corresponding equations for power and irradiance as the limiting equation for safe operating conditions, and largely independent of most practical circumstances likely to be encountered. The practical consequences of this equation are that provided the radiated power is less than 35 mW or the peak radiation flux is less than 5 mW/mm2 the radiation can be considered to be safe in an industrial environment. In Figure D2 the limiting criteria are plotted together with a representative population of ignition events, the vast bulk of which fall above or to the right of the limits. The asymptotic value of 5 mW/mm2 irradiance gives a comforting correlation with the Zone 0 permitted irradiance of the German Explosionschutz-Richtlinien (guidelines for explosion protection). The constant radiant power of 35 mW is a completely new result although care should be taken in extrapolating this value below an irradiated area of 0.001 mm5 as only a single point at sizes lower this has been obtained. The limiting values were compared with practical minimum igniting powers and minimum igniting power densities, in the former case for one very small area and in the latter case for one very large area, with the different target materials being in powdered form on the Kaowool absorber. There is no single ‘most hazardous’ target. While match head powder is the most hazardous for small areas, several other targets including the industrially important coal dust ignite at low power fluxes at larger areas, though not at fluxes below the 5 mW/mm 2 level. One of the most interesting findings is the large difference, more than an order of magnitude, between different target materials as regards ratio of minimum irradiance to minimum power. These two quantities are generally independent of one another and it is possible that ignition of a particular target material could occur when the beam emerging from the optical fibre has diverged to a larger area than the same power intercepted close to the fibre which may not lead to ignition. The only ignition criterion which falls below that predicted by the limiting equation is the minimum igniting power for ground match head compositions, a result which is hardly surprising in view of the formulation of this material for maximum incendivity. G7 CONCLUSIONS The safety of optical measurement techniques in hazardous industrial environment has been studied by investigating thermal ignition arising from radiation hearing an absorber. During the work, the number of individual measurements approached one million, and of that a significant fraction gave rise to ignition events. Five different light sources, including lasers and optical fibre delivery, ten different atmospheres both inert and chemically active in the form of both dust layers and clouds were investigated. Reference experiments were undertaken in four participating laboratories and showed satisfactory agreement. A phenomenological correlation of radiation ignition with known ignition parameters has been established and linked through physical theories to previous understanding of electrical and thermal ignition. Predicted computations have been undertaken which correlate broadly with the observed experimental results. A limiting safety criterion has been proposed which shows a satisfactory comparison with the body of experimental results generated both within this project and published elsewhere in the literature. It can be concluded that, for the type of material to which the study was limited, the basic theory proposed adequately links all the different criteria and the four numerical constants chosen for the limiting equation allow a margin of safety by comparison with any hazards observed during the work. To the extent that the project has concentrated upon the situations perceived to be ‘the most hazardous’ the arising recommendations can be considered to be satisfactorily conservative. It is concluded broadly, that continuous wave devices radiating in the visible and the near visible are not hazardous provided either— (a)
the radiated power is less than 35 mW; or
(b)
the peak radiation flux is less than 5 mW/mm2 .
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For pulsed or intermittent light sources, specific atmospheres, sources of area smaller than 0.00003 mm 2 and where sensitive materials are present, different values of power and flux may be appropriate.
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FIGURE G1 GRAPHIC REPRESENTATIONS OF ENERGY, ENERGY FLUX, POWER AND POWER FLUX
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FIGURE G2 GRAPHIC REPRESENTATION OF THE LIMITING CRITERIA AND SOME REPRESENTATIVE IGNITION EVENTS
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APPENDIX H
THE NATIONAL CERTIFICATION SCHEMES FOR EXPLOSION-PROTECTED ELECTRICAL EQUIPMENT (TERMED Ex EQUIPMENT) (Informative) H1 INTRODUCTION The safe use of electrical equipment in areas where flammable gases and vapours or combustible dusts are handled or stored (termed explosive atmospheres) relies on the following: (a)
Classifying the area Determine type and extent of the explosion hazard. Refer to AS 2430.1, NZ 6101.1, AS/NZS 2430.3.1 to AS/NZS 2430.3.9 and AS/NZS 61241.3 for guidance.
(b)
Selection of equipment Select equipment incorporating an explosion-protection technique suitable for the classified area and the environment. Refer to AS/NZS 3000 Section 7.9, this Standard and AS/NZS 61241.1.2 for guidance.
(c)
Installation of equipment Install equipment ensuring the explosion-protection properties of the equipment are maintained. Refer to AS/NZS 3000, AS 2381 series and AS/NZS 61241.1.2 and relevant certification documents for guidance.
(d)
Maintenance of equipment Repair and maintain equipment to ensure the explosionprotection properties are maintained. Refer to AS 2381 Series, AS/NZS 61241.1.2 and AS/NZS 3800 for guidance.
An Australian National Ex Certification Scheme has been in operation, in various forms, since the early 1960s and has been regarded as the nationally accepted means of providing proof of compliance with Standards specifying design, construction and testing requirements of Ex equipment. H2 AUS Ex SCHEME In its more recent form, the AUS Ex Scheme is operated by the Standards Australia Ex Mark Management Committee, P-008 and administered by SAI Global; contact details for SAI Global are as follows: SAI Global Limited GPO Box 5420 Sydney Sydney NSW 2001 Australia Phones: 02 8206 6060 1300 360 314 Facsimile: 02 8206 6061 Website: www.sai-global.com E-mail:
[email protected] The Scheme is accepted throughout Australia and New Zealand by Electrical and Mining Regulatory Bodies as well as the Insurance Council of Australia for demonstrating compliance with Standards.
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Under the ‘AUS Ex’ Scheme (Australian National Certification Scheme—‘AUS Ex’), Ex equipment can be tested by any of the three Australian laboratories, listed below: (a) TestSafe Australia (formerly LOSC) 919 Londonderry Road Londonderry NSW 2753 PO Box 592 Richmond NSW 2753 Phone: Facsimile: Website: E-mail:
02 4724 4900 02 4724 4999 www.workcover.nsw.gov.au
[email protected]
(b) The Safety In Mines Test And Research Station (Simtars) 2 Smith Street Redbank Qld 4301 PO Box 467 Goodna Qld 4300 Phone: Facsimile: Website: E-mail:
07 3810 6370 07 3810 6366 www.nrm.qld.gov.au/mines/
[email protected]
(c) International Testing and Certification Services (ITACS) 4-6 Second Street Bowden SA 5007 PO Box 300 Hindmarsh SA 5007 Phone: Facsimile: Website: E-mail:
08 8346 8680 08 8346 7072 www.ozemail.com.au/~itacs/
[email protected]
Currently both TESTSAFE Australia and Simtars operate under an agency arrangement with SAI Global to accept applications and issue certificates, thereby providing a ‘one stop shop’ approach to certification. Alternatively applications can be made directly to SAI Global or ITACS. Products certified under this Scheme are marked to indicate compliance. The following is an example of the information apart from manufacturer, model number and electrical ratings, that should be marked: Parameter Example Certificate number: Method of protection: Equipment Group: Temperature rating: IP rating:
AUS Ex 999 Ex d I, IIA, IIB or IIC T4 IP65
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In some instances the letter ‘X’ or ‘U’ is added to the certificate number; for example: AUS Ex 999X ‘X’
This is used to indicate that there are conditions that have been applied to the certificate to ensure safe use. While the installation of Ex equipment should not be attempted until the installer is in possession of copies of the area classification, installation standards, certification documents and other information relevant to the installation, it is certainly more critical to be in possession of certification documents for equipment bearing an ‘X’ after the certificate number. The presence of the ‘X’ may indicate a requirement that the Ex equipment be installed in a certain manner to ensure that the integrity of the explosion protection technique is maintained.
‘U’
This is used to identify that the product is a component of an assembly. As most Ex products are stand alone products this suffix is rarely used.
One important point to note is the validity date of new Ex certificates, as these Certificates used to have a 10 year life; currently and during the phasing out/in period of the Ex Schemes, applications under the AUSEx Scheme are required to comply with the following Transitory Rules, as determined by the Ex Mark Management Committee (P-008 Committee): (a)
The limit date for lodging new applications for Certification under the current AUSEx Scheme (MP 69:1993 and Q7134) is 31 December 2003.
(b)
The limit date for lodging applications for a Supplementary Certificate to cover only the revalidation of any existing Ex Certificate under the current AUSEx Scheme is 31 December 2003.
(c)
The expiry date for any new Ex Certificate issued under (a) and/or any revalidation (Supplementary Certificate) issued under (b), shall be 31 December 2006, irrespective of their issue date.
(d)
Although there is no limit date for lodging applications for Supplementary Certificates for other reasons than revalidation, the expiry date of the original Certificate shall not be extended (i.e. expiry date of the Supplementary Certificate shall coincide with the expiry date of the original Certificate).
(e)
These Transitory Rules take effect from 1 October 2002.
The validity date is displayed clearly on Page 1 of the certificate. The Scheme provides for a national database with internet access from the SAI Global home page www. sai-global.com and provides industry with a ready reference list of certificates issued. The information on the database is updated on a regular basis. H3 ANZEx SCHEME H3.1 Background The AUS Ex Scheme has served the Australian industry well over the past 30 years but Australia’s participation in the new international IECEx Scheme meant that a stocktake of the AUS Ex Scheme was necessary to ensure that the Australian National Scheme continued to cater to the needs of industry. Therefore, a review of the operational procedures was conducted by the P-008 Ex Mark Management Committee with the aim of accommodating both Australia and New Zealand’s participation in the IECEx Scheme, as well as aligning with international practice for Conformity Assessment. To date the AUS Ex Scheme has been operating as an ISO Type 1 (Type Tests) scheme.
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Changing commercial and industrial conditions due to takeovers and different distribution outlets, where more than one Certificate may be issued for the same product, highlight the limitations of Type Test Certification. Identification of the ‘manufacturer’ becomes important and this has led some overseas approval and certification agencies to include assessment of manufacturers’ Product Quality Planning as a mandatory requirement of Ex Certification. H3.2 Outline of ANZEx Scheme The ANZEx Scheme permits the use of the Certificate Number and Prefix on product listed in the respective Certificate of Conformity, and thus provides distinctive third party evidence to confirm a manufacturer’s claimed compliance to the relevant Standards and that it was manufactured under the ANZEx Quality Management System Requirements. All applications for certification under this ANZEx Scheme, will be subject to the requirements detailed throughout document MP 87. Applications for amendments to certificates for nonexpired AUS Ex Certificates are exempt, since such Certificates were issued under the previous phase of the Scheme (AUS Ex) and have a 10 year life from issue date. As with the AUS Ex Scheme, the ANZEx Scheme is overseen by the Joint Standards Australia/Standards New Zealand Policy Committee P-008; the Committee has delegated administration of the Scheme to SAI Global, a wholly owned subsidiary of Standards Australia International. A phasing in period until December 2003 is operating, during which time manufacturers have the option of applying for either an AUSEx Certificate or an ANZEx Certificate. During the phasing out/in period of the Ex Schemes, applications under the AUSEx Scheme are required to comply with the applicable transitory rules, as outlined in Paragraph H2. The ANZEx Scheme embodies all the independent product testing requirements of the AUS Ex Scheme, however it goes further by requiring independent assessment of the manufacturers’ quality system for compliance with the requirements laid down in MP 87, both at the application stage and on an ongoing basis. As the ANZEx Scheme incorporates ongoing surveillance of the manufacturer, ANZEx Certification does not have a set expiry date. The ANZEx Scheme has been designed to fully align with the new IECEx Scheme. Testing laboratories accepted under the AUS Ex Scheme are also accepted under the ANZEx Scheme. Further information or application details can be obtained by contacting any of the testing laboratories or by referring to document MP 87.
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APPENDIX I
PROPERTIES OF FLAMMABLE LIQUIDS, VAPOURS AND GASES (Informative) I1 SCOPE In this Appendix, the physical properties of materials which must be considered when the degree of risk appropriate to a particular application or installation is being considered are defined and discussed (see also NFPA 325). I2 FLASHPOINT I2.1 General Flashpoint of the liquid is the minimum temperature at which it gives off sufficient vapour to form an ignitable mixture with the air near the surface of the liquid or within the vessel used. An ‘ignitable mixture’ is a mixture within the explosive range (between upper and lower limits) that is capable of the propagation of flame away from the source of ignition when ignited. Some evaporation takes place below the flashpoint but not in sufficient quantities to form an ignitable mixture. The term flashpoint applies mostly to flammable liquids, although there are certain solids, such as camphor and naphthalene, that slowly evaporate or volatilize at ordinary room temperature, or liquids such as benzene that freeze at relatively high temperatures and therefore have flashpoints while in the solid state. The test apparatus used for the measurement of flashpoint is normally one of two types, of which there are several variants. These are generally called ‘open-cup’ and ‘closed-cup’ flashpoint testers. For most liquids, the flashpoint as determined by the closed-cup method is slightly lower (in the region of 5 percent to 10 percent, in degrees Celsius) than that determined by the open-cup method. flashpoints measured by the more sensitive closed-cup method are therefore normally used. I2.2 Materials having high flashpoints Some compounds have such high flashpoints that they do not form flammable mixtures with air at normal ambient temperatures, even under tropical conditions. These should not be discounted as ignition hazards, however, since exposure to a suitably hot surface, or use of the material at a temperature above its flashpoint, may create an explosive mixture locally, which may be ignited by the same hot surface, or an alternative ignition source. It is therefore necessary to consider the limitation of surface temperatures, even when compounds of high flashpoint are being processed. It should be noted also that compounds having high flashpoints may be used in processes involving high temperatures and possibly high pressures. The normal or accidental release to the atmosphere of compounds under such conditions may present local explosion risks which would not normally be associated with high flashpoint materials. I2.3 Classification of flashpoints In some industries, it has been found convenient to group compounds into prescribed ranges of flammability according to their flashpoints to facilitate safe handling. In certain applications, legislation specifies the limits for these ranges.
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I3 IGNITION TEMPERATURE I3.1 General Ignition temperature of a substance, whether solid, liquid, or gaseous, is the minimum temperature required to initiate or cause self-sustained combustion independently of the heating or heated element. I3.2 Use of ignition temperature The direct result of established ignition temperatures is the limitation of the surface temperatures of electrical equipment in hazardous areas so that these do not present an ignition risk. Precautions must be taken where additional hazards are introduced by particular circumstances such as recognized overloads, and environmental conditions such as dust deposits, catalytic or pyrophoric effects, impurities in the gas or vapour, and large volumes of gas or vapour being contained therein. Where more than one flammable material may be present in a particular application, the surface temperature should be limited to the lowest value of the ignition temperatures of the material concerned. It should be noted that the value for ignition temperature is dependent on the method chosen for its measurement. In particular, factors such as the geometry, dimensions and materials of the test apparatus all influence the measured ignition temperature. NOTE: The ignition temperature of a compound increases as the pressure decreases below one atmosphere, i.e. 101.325 kPa, the rate of change depending on the compound concerned; e.g. it can be as much as 0.7°K/0.133 322 kPa for a linear rate of change. This rate of change may however, not necessarily be linear. For the above reasons, the acceptance of ignition temperatures determined by laboratories at elevated altitudes for installations at lower altitudes, e.g. at sea level, could lead to danger. The degree of danger can be quantified only for each individual case.
I4 EXPLOSIVE (FLAMMABLE) LIMITS Every flammable gas and vapour is characterized by explosive (flammable) limits, between which the gas or vapour mixed with air is capable of sustaining the propagation of flame, and therefore explosion. These limits are called the ‘lower explosive limit’ (LEL) and the ‘upper explosive limit’ (UEL), and are usually expressed as percentages of the material mixed with air by volume. They are sometimes expressed alternatively as grams of compound per cubic metre of air. NOTE: It should be noted that the majority of flammable materials will present toxic risks at concentrations which are, in most cases, very much less than the appropriate lower explosive limits. Further information in this respect may be obtained by consulting the relevant department in each State.
I5 EXPLOSIVE (FLAMMABILITY) RANGE The range of gas or vapour mixtures with air between the explosive (flammable) limits over which the gas mixtures are continuously explosive is called the ‘explosive (flammability) range’. Gas mixtures outside this range are, therefore, non-explosive (non-flammable) under normal atmospheric conditions. I6 VAPOUR DENSITY I6.1 General The vapour density of a compound is the mass of a given volume of the compound in its gaseous or vapour form compared with the mass of an equal volume of dry air, at the same temperature and pressure. It is often calculated as the ratio of the molecular mass of the compound to the average molecular mass of air. COPYRIGHT
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Where a substantial volume of gas or vapour is released into the atmosphere from a localized source, a vapour density less than one, i.e. lighter than air, for the material indicates that the gas or vapour will rise in a comparatively still atmosphere. A vapour density greater than one, i.e. heavier than air, indicates the gas or vapour will tend to sink, and may thereby spread some distance horizontally and at a low level. The latter effects will increase with compounds of greater vapour density. However, care should be taken in the application of the data. For example, where a compound is released into the atmosphere at a comparatively slow rate so that it is rapidly diluted to a low concentration, its subsequent movement cannot be considered separately from that of the air in which it is effectively suspended. The vapour density of a given volume of a mixture of a material and air will differ from that of air only according to the proportion of material which is present. With the majority of materials at normal temperature and pressure, this results in an overall vapour density for a given material mixed with air which is not sufficiently distinct from that of air itself to permit confident prediction of the movement of the mixture without a detailed knowledge of the prevailing environmental conditions. It may be assumed generally that, for low release rates, gravitational effects associated with vapour density will be small compared with the effects arising from normal and uncontrolled air movement. I6.2 Effects of temperature changes When the movement and spread of flammable gas or vapour is being assessed, due account should be taken of the effect of local temperatures on vapour density and of the increased rate of evaporation of liquids with increasing temperature. The possibility of temperature inversion should also be recognized. This is a phenomenon whereby rising gas or vapour is cooled rapidly with the result that its movement may be reversed on account of its increasing density. In some industries, the boundary between compounds which may be considered lighter than air and comparable with or heavier than air is drawn arbitrarily at a vapour density of 0.75. This limit is chosen so as to provide a factor of safety for those compounds whose densities are close to that of air, and whose movement cannot therefore be predicted without a detailed assessment of local conditions. I7 BOILING POINT Boiling point data should be regarded as approximate, since such characteristics are modified by the type and quantity of impurity which may be present. Particular consideration should be given also to the properties of mixtures of liquids. Generally it may be expected that each component of a multi-component mixture will continue to behave as an individual compound; however, this may not always be the case. There may be mixtures of compounds where, for example, catalytic or other chemical effects modify significantly the individual physical properties of the components present. Where such effects are suspected and are considered important, expert advice should be sought. The term ‘initial boiling point’ is used for multi-component mixtures to indicate the lowest value of boiling point for the range of liquids present. I8 TEMPERATURE CLASSIFICATION For a description of the concept of temperature classification, see Clause 2.5.3. I9 CLASSIFICATION OF GASES AND VAPOURS I9.1 General For the purposes of flameproof enclosures and intrinsic safety, gases and vapours can be classified according to the group or sub-group of equipment required for use in the particular gas or vapour atmosphere. NOTE: Appendix F details the general relationship between equipment groups (as described in this Paragraph) and former gas classifications as used in earlier Australian Standards. COPYRIGHT
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I9.2 Classification according to the Maximum Experimental Safe Gaps (MESG) For flameproof enclosures of electrical equipment, gases and vapours are subdivided according to their maximum experimental safe gaps (MESG) determined by means of an experimental vessel having a width of joint of 25 mm. The standard method of determining MESG is with the vessel described in IEC 60079-1A, but if the determinations have been made only with an 8-litre sphere with ignition close to the joint these can be accepted provisionally. The limits are as follows: (a)
Group IIA: MESG above 0.9 mm.
(b)
Group IIB: MESG between 0.5 mm and 0.9 mm.
(c)
Group IIC: MESG below 0.5 mm.
I9.3 Classification according to the Minimum Igniting Currents (MIC) For intrinsically safe electrical equipment, gases and vapours are subdivided according to the ratio of their minimum igniting currents (MIC) to that of laboratory methane. The standard method of determining this ratio is with the apparatus described in IEC 60079-11, but if these determinations have been made only with other apparatus these can be accepted provisionally. The limits are as follows: (a)
Group IIA: MIC ratio above 0.8.
(b)
Group IIB: MIC ratio between 0.45 and 0.8.
(c)
Group IIC: MIC ratio below 0.45.
I9.4 Classification according to MESG and MIC For most gases and vapours it is sufficient to make only one of these determinations (either MESG or MIC ratio) to place the gas or vapour in the appropriate subdivision. A single determination is sufficient in the following cases: (a)
Group IIA: When the MESG exceeds 0.9 mm or the MIC ratio exceeds 0.9.
(b)
Group IIB: When the MESG is between 0.55 mm and 0.9 mm or the MIC ratio is between 0.5 and 0.8.
(c)
Group IIC:
When the MESG is less than 0.5 mm or the MIC ratio is less than 0.45.
It is necessary to determine both the MESG and MIC ratio in the following cases: (i)
Only the MIC ratio has been determined and its value is between 0.8 and 0.9: the determination of the MESG is necessary to determine the subdivision.
(ii)
Only the MIC ratio has been determined and its value is between 0.45 and 0.5: the determination of the MESG is necessary to determine the subdivision.
(iii) Only the MESG has been determined and its value is between 0.5 mm and 0.55 mm: the determination of the MIC ratio is necessary to determine the subdivision. I9.5 Classification according to a similarity of chemical structure When a gas or vapour belongs to a homologous series of compounds, the appropriate subdivision of the gas or vapour can provisionally be inferred from the results of the determinations of other compounds of the series with lower molecular masses.
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I10 GENERAL CONSIDERATIONS I10.1 Relation between ignition temperature and maximum surface temperature The vapour given off from a flammable liquid will form an explosive mixture with air, provided that the temperature of the liquid is at or above its flashpoint. The spread of the explosive mixture from the vapour source will depend on its temperature. If the local ambient temperature is above the flashpoint, the spread of explosive vapour/air mixture will be maintained. The explosive mixture may then be ignited by one of several means: a flame, a suitable frictional spark, an electrical spark of sufficient energy or a hot surface. If, on the other hand, the local ambient temperature.. and that of electrical equipment, etc is below the flashpoint, the vapour will eventually condense to a mist of liquid droplets which will spread both through the atmosphere (see also Paragraph A10.3) and over the surfaces of equipment. It is in the latter respect that adequate resistance to chemical attack may be particularly important. For ignition by a hot surface, the surface temperature is generally greater than the ignition temperature of the flammable material. Therefore, to ensure that ignition by hot surfaces does not occur, it is necessary that the temperature of all unprotected surfaces exposed to the gas or the vapour/air mixture should not be greater than the ignition temperature. This has led to the concept of temperature classification described in Clause 2.5.3. I10.2 Mixtures of compounds Single component materials are not often encountered in practice. Most frequently mixtures of two or more compounds are present in ratios which may vary between prescribed limits. Consideration must then be given to the appropriate requirements for electrical equipment in the light of the characteristics of each individual material present. Often this will impose no difficulty since, by the nature of the process, the various constituents will possess similar chemical properties and, therefore, often similar ‘explosion’ properties. There are occasions, however, when this is not the case. The constituents may be of different gas classifications or have widely different ignition temperatures. For these cases, it is possible to give only the most general guidance. In general, it should be assumed that, at some time during the process or the life of the plant, the component in the mixture having the most severe of the characteristics being considered, e.g. the gas classification, the explosive limits, the Flashpoint or ignition temperature, will be present in preponderance and the electrical installation should be designed accordingly. However, this can impose limitations which may be severe, and further consideration of the relative rates and quantities of the components used in the process, and the degree of control thereof may be required. Some relaxation may then be possible, but expert advice should always be sought in these circumstances. Particular consideration should be given to those compounds whose behaviour may be anomalous. For example, it is known that carbon monoxide, with which Group IIA equipment may be safely used, may be added in considerable quantity to hydrogen without altering the group of equipment, viz Group IIC, which must be used with this latter compound. Carbon monoxide also exhibits unusual behaviour under other test conditions; e.g. it has been shown that the addition of moisture to mixtures of carbon monoxide with air to the point of saturation serves to change the gas classification for this material from Group IIA to Group IIB. This change in gas classification is also observed if methane is added to carbon monoxide in the proportion 15:85 methane to carbon monoxide. Where the individual components of mixtures and their proportions of the total moisture are precisely known or can be estimated, it is often possible to calculate the resultant explosive limits for the mixture with air. Examples of this are described in Appendix J.
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I10.3 Mists The characteristics described in this Standard appertain to mixtures of gases and vapours only with air. The distinction to be drawn between a gas and vapour in this context is simply that the vapour may be in contact with its liquid phase at normal temperature and pressure, whereas a gas cannot be liquefied under normal atmospheric conditions. However, it should also be remembered that mists consisting of clouds of condensed vapour can occur in practice. In general, the characteristics described herein should be considered applicable to mists since local ignition sources or hot surfaces generally may serve to restore the condensed material to its vapour phase. I10.4 Impurities A small amount of impurity may appreciably after the value of the ignition temperature. For example, at one laboratory it has been found that pure trichlorosilane gives an ignition temperature of 230°C when a newly prepared sample is used in the test. After ageing and possible contamination by moisture, the value of the ignition temperature was found to have fallen to 185°C. I10.5 Effect of environments having other than normal atmospheric conditions It should be noted that the data presented in NFPA 325 apply only to mixtures of gases and vapours with air under normal conditions of atmospheric temperature and pressure or at suitably elevated temperatures if the flashpoint of the vapour is above the normal ambient temperature. Caution should therefore be exercised in assessing the explosivity of gas or vapour with air under environmental conditions which are other than normal. It is only possible in this Standard to give general guidance on the influence of changes in temperature, pressure and oxygen content of the mixture. Generally, the effect of increased temperature or pressure is to lower the lower explosive limit and to raise the upper explosive limit. Reduction in temperature or pressure has the opposite effect. An increase in oxygen content of a gas mixture, as compared with a mixture of the gas or vapour with air only, has little or no effect on the lower explosive limit, but generally results in an increased upper explosive limit. The increase in the upper limit depends on the degree of oxygen enrichment, and may be substantial. Thus the effect generally of an increase in oxygen content is to broaden the explosive range.
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APPENDIX J
CALCULATION OF THE EXPLOSIVE LIMITS FOR A MIXTURE OF GASES (Informative) J1 LIMITS FOR SIMPLE MIXTURES Explosion risks frequently arise from mixtures of flammable material with air. Though only the most general of rules can be indicated for ensuring the safe use of electrical equipment with mixtures of gases, it is often desirable to be able to establish with some degree of confidence the explosive limits for such mixtures in order that local explosion risks might be avoided. A method which may be used to calculate the explosive limits for most mixtures of flammable gases is described below. Though this method achieves a satisfactory degree of accuracy for most applications, it is always advisable to apply caution where the expected total concentration of gas is near to the calculated value for the appropriate explosive limit. Particular care should also be taken in circumstances where catalytic effects between individual components of a mixture are suspected. General purpose calculations cannot take such effects into account. The relationship between the lower explosive limits for any two gases in air with the lower limit for any mixture of them is —
n1 n = 2 =1 N1 N 2 where N I and N2 are the lower explosive limits in air for each combustible gas separately, and n 1 and n 2 are the actual percentages of each gas present in any mixture of them which is itself a lower limit mixture. The equation indicates, for example, that a mixture of air, carbon monoxide and hydrogen which contains one-quarter of the amount of carbon monoxide and three-quarters of the amount of hydrogen necessary to form lower limit mixtures with air independently (i.e. one-quarter of 14 percent approximately and threequarters of 4 percent respectively) will itself be a lower limit mixture. The equation may be generalized to apply to any number of gases. Thus —
n3 n1 n + 2 + + ...... = 1 N1 N 2 N 3
J(1)
The equation may be applied also to upper limit mixtures with suitable re-definition of the terms n 1, etc, and N1 , etc. The equation may be rendered more useful as follows: It is assumed that the terms used are consistent, i.e. they are all lower limit mixtures or they are all upper limit mixtures. Let p 1, p 2, p3 , etc represent the proportions of each flammable gas present, ignoring air and inert gases, so that — p 1 + p 2 + p 3 + . . . . = 100 and let L represent the explosive limit so that — L = n1 + n2 + n3 + . . . . Since
n1 p = 1 L 100
then, substituting in Equation J(1) — p p L p1 + 2 + 3 ... . 100 N1 N 2 N 3
= 1 COPYRIGHT
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and therefore — L=
100
J(2)
p1 p p + 2 + 3 .... N1 N 2 N 3
Example: As an example of the use of this equation, consider the determination of the lower limit for a gas mixture representative of natural gas. The natural gas might comprise — Methane in the proportion of 80 percent (p 1)
(lower limit 5.3 percent)
Ethane in the proportion of 15 percent (p 2)
(lower limit 3.22 percent)
Propane in the proportion of 4 percent (p 3)
(lower limit 2.37 percent)
Butane in the proportion of 1 percent (p4)
(lower limit 1.86 percent)
Then the lower explosive limit of this mixture with air would be — L=
100 15 4 1 80 + + + 5.3 3.22 2.37 1.86
= 4.55 percent
J2 LIMITS FOR COMPLEX INDUSTRIAL GAS MIXTURES The main component gases encountered in many industrial processes are hydrogen, carbon monoxide, methane, nitrogen, carbon dioxide, and oxygen. The procedure to be used for calculating the explosive limits for mixtures of these gases is as follows: (d)
The composition of the mixture is first re-calculated on an air-free basis. The amount of each gas is expressed therefore as a percentage of the total air-free mixture.
(e)
A somewhat arbitrary dissection of the air-free mixture developed from Step (a) is made into simpler mixtures, each of which contains only one flammable gas and part or all of the nitrogen and carbon dioxide.
(f)
The appropriate limits for each of the mixtures obtained from Step (b) are obtained from available data (see Figures Jl and J2 which indicate available data for the explosive limits of hydrogen, carbon monoxide, methane, ethane, ethylene and benzene with various amounts of carbon dioxide and nitrogen as inert diluent components).
(g)
The limits of the air-free mixture are then calculated from the data for the dissected mixtures obtained in Step (c) by the equation — L=
100 p1 p p + 2 + 3 . . . . N1 N 2 N 3
where P I, P 2, P3 ,etc are the proportions of the dissected mixtures, in percentages, and N I , N 2, N 3, etc are their respective limits. (h)
From the limits of the air-free complex mixture thus obtained, the limits of the original complex mixture which included air can be deduced.
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Example: The following is an example of the step-by-step calculation outlined above: (i)
The constituent components of the gas mixture are indicated in Table Jl. The composition of the air-free mixture, as indicated in the table, may be calculated as follows: The amount of air in the mixture is 2.8 × 100/20.9 or 13.4 percent. The air-free mixture is therefore 86.6 percent of the whole. When the original proportions of carbon dioxide, carbon monoxide, methane, and hydrogen are divided by 86.6 and multiplied by 100, the air-free percentages are obtained. The nitrogen percentage is the difference between 100 and the sum of these percentages.
(ii)
The flammable gases are paired with the inert gases to form separate mixtures, as shown in Table J2.
(iii) The explosive limits for the separate or dissected mixtures, taken from Figure Jl are indicated in columns 6 and 7 of Table J2. TABLE J1 STEP (i) OF WORKED EXAMPLE OF PARAGRAPH J2 Constituent components of industrial gas mixture
Percentage
Carbon dioxide
Percentage calculated on air-free basis
13.8
15.9
Oxygen
2.8
0.0
Carbon monoxide
4.3
5.0
Methane
3.3
3.8
Hydrogen
4.9
5.7
Nitrogen
70.9
69.6
TABLE J2 STEP (ii) OF WORKED EXAMPLE OF PARAGRAPH J2 1
2
3
4
5
6
7
Flammable gas
Percentage
Carbon dioxide
Nitrogen
Total
Ratio of inert to flammable
Explosive limits from Figure J1
percent
percent
percent
LEL
UEL
Carbon monoxide
5.0
17.5
22.5
3.5
61
73.0
Methane
3.8
20.9
24.7
5.5
36
41.5
31.2
34.2
10.4
50
76.0
18.6
5.9
32
64.0
Hydrogen
5.7
(3.0 (2.7
Total
14.5
(iv)
15.9 15.9
69.6
100.0
The values for the explosive limits and for the total percentage of the overall air-free mixture indicated in column 5 of Table J2 taken together permit calculation of the explosive limits for the complex air-free mixture.
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Thus— Lower explosive limit
=
100 22.5 24.7 34.2 18.6 + + + 41.5 50 32 61
= 43 percent and Upper explosive limit
=
100 22.5 24.7 34.2 18.6 + + + 41.5 76 64 73
The explosive range of the air-free mixture is therefore 43 to 61 percent. (v)
As the air-free mixture is 86.6 percent of the complete sample mixture, the explosive limits in air for the sample mixture are 43 × 100/86.6 and 61 × 100/86.6 or 50 and 70 percent respectively. Thus the original sample will be explosive within the limits of 50 and 70 percent in air.
Further notes of the limitations of and the precautions that should be taken with calculations of this type are available (see Coward, H.F., and Jones, G.W., ‘Limits of Flammability of Gases and Vapours’, Bureau of Mines Bulletin, 503, 1952).
FIGURE J1 EXPLOSIVE LIMITS OF HYDROGEN, CARBON MONOXIDE, AND METHANE CONTAINING VARIOUS AMOUNTS OF CARBON DIOXIDE AND NITROGEN
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FIGURE J2 EXPLOSIVE LIMITS OF ETHANE, ETHYLENE AND BENZENE CONTAINING VARIOUS AMOUNTS OF CARBON DIOXIDE AND NITROGEN
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AMENDMENT CONTROL SHEET AS/NZS 2381.1:1999 Amendment No. 1 (2003)
REVISED TEXT SUMMARY: This Amendment applies to the PREFACE, Clauses 1.2, 1.4.22, 1.4.26, 1.7, 1.9.11, 2.4.3.2, 2.4.4.2, 2.5.3, 2.5.4, 2.6.1, 2.7, 3.2.5, 3.3.1, 3.3.2, 3.4.2, 3.8.15.1.2, 3.8.15.2, 3.8.15.4(a), 3.11.2, 3.11.3.3, 3.11.4.1, 3.11.6, 3.12.1.1, 3.12.1.3, 3.14.6 and 4.3.1(b) and TABLES 2.1, 2.2 & 3.1, and FIGURE 3.1 and APPENDICES A, D, F and H. Published on 3 March 2003.
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NOTES
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