Nebosh Exam Question and Answer

 

 

1. a. Outline how the BLEVE will develop? b. Excluding its explosive flammable nature identify two (2) hazardous properties of LPG. c. Outline the risks when draining water from an LPG Sphere. d. Outline the control measures that minimizes the risk when draining water from LPG Sphere:

a. BLEVE will develop with the following:

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The vessel is partially filled with pressurized pressuri zed hydrocarbon liquid. (i.e LPG) A certain amount of the space above it filled with with vapour. If the vessel is subjected to fire, the pressure in the tank will increase due to the liquid inside the vessel will reach its boiling point and turning it to vapour. The pressure relief valve will allow the overpressure to be vented into the atmosphere for first instance, but this will reduce the amount of the liquid inside the tank, and the potential for the flame to engage with a section of the tank containing vapour and not liquid will increase. If this happens, the tank wall will weaken at this point as the heat transfer to vapour is much less efficient than it is to a liquid. The result is likely to be a sudden and catastrophic failure of of the vessel, with a discharge of vapour followed by an explosion when the vapour reaches the flames.

b. b. –  – Asphyxiant  Asphyxiant - brittle fracture when contact to carbon steel - oxidize metal (rusting) (r usting) - Cold burn when contact on skin.

c. - High pressure ejection from the piping line / - Safety relief valve inoperable / defective - Poor illumination in the area - Slippery floor - Hydrate formation can occur when draining water from pressurized LPG spheres. This can lead to valve freezing, and if they are in open position. LPG will be allowed to escape which may lead to explosion.

 

 

1. Identify factors that influence the generation of the electrostatic charge? (4)

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The The The The The The

conductivity of the liquid amount of turbulence in the liquid velocity of the liquid presence of impurities in the liquid amount of surface area area contact between the liquid and other surfaces atmospheric condition, static build up is enhance enhance when the air is dry

2. Give three stages of static charges?

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Charge separation Charge accumulation Charge dissipation

2. Outline practical ways of minimizing the formation of an electrostatic charge? (4)

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of minimising the formation of an electrostatic charge: Humidific Humidification ation of the atmosphere Antistatic additives Reduce flow velocity Intrinsical Intrinsically ly safe equipment Bonding & Grounding of equipment & containers Avoid splash filling by submerging the fill pipe bellow the liquid level in the container -  Increasing the conductance of floors, footwear

- Design of the Equipment – Equipment – manufacturers  manufacturers design’s design’s the equipment specialize to overcome the issue of having spark which are expose to local atmosphere.(intrinsically safe) - Products Identification Label – Label – Each  Each piece of the equipment is signified by code which is marked on the equipment’s product identification label.  label.   - Bonding system - is where all the various pieces of equipment within a process system are connected together. This ensures that they all have the same electrical potential, which means there is no possibility of a discharge of electricity, by way of a spark, from one piece of equipment to another.

 

-Grounding - is where pieces pieces of equipment (which may be bonded together together or not) are connected to an earthing point. This ensures any electrical charge in the equipment is given the means to constantly flow to earth, thus ensuring there is no potentially dangerous build- up of charge which could lead to a sudden discharge of electricity, by way of a spark 3. Identify hazards associated with the sludge? (2)

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Skin irritant (possibly causing dermatitis) Inhalation (fumes or dust from dried sludges) Ingestion (poor hygiene, i.e. not not washing, not cleaning up, up, eating at work site) Radiation Carcinogenic Environmental (pollutant) Absorption through the skin (dermatitis) (dermatitis ) The main hazard of exposure to ionizing radiation  

4. Identify four control measures to reduce the workers exposed to the sludge. (4) Workers reduce exposure to the sludge by applying control measure such as:

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The provision of ventilation equipment to contain dusts and fumes The use of wet methods of working and good housekeeping to reduce the amount of of dust in the atmosphere Having equipment in place to collect sludge instead of using manual means Diluting sludge with water The use of permit-t o-work systems – systems – especially  especially if the concentrations of dust or fumes reach a level where only designated or classified persons are allowed to work under the restriction of a written safe system of work.

5. Outline the following failure modes that may lead to loss of hydro carbon containment from the storage tank / vessel or pipelines (8) a. creep

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Solid material which is subjected to long term ex exposure posure to high level of stress and gradually deforms in shape or dimension. It is exacerbated when the subject is also exposed to high heat for a long period of time.

b. stress corrosion cracking -

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The materials is subjected to both stress and corrosion. Corrosion reduces the threshold of the material at some point causing it to weaken resulting in the stress causing crack at that point. Crack will only occur when both corrosion and stress are present.

 

- Occurs in pressure vessel, pipeworks, highly stressed component and in system when a deviation from the normal operating condition or environment occurs. -

c. thermal shock

- Thermal shock is the stress introduced into a material as a result of sudden and dramatic change in temperature. Temperature change caused the molecular structure of the material to expand, but this exposure is not uniform. Example (Boiling water poured to glass jar resulted to the broken jar) expansion only happened to the inner surface not the outside surface. - Superheated steam introduced into cold pipework would cause thermal shock on the pipework by expanding the inner surface of the pipes rapidly, whilst the outer surface would expand more slowly.

d. brittle fracture - Brittle material will is exposed to adverse condition such as high wind, sea state, lightning, - Brittle material snap when force is applied such as Tension or stress.

6. Describe the vapour cloud explosion? (3)

Vapour cloud explosion is described as any release of flammable liquids or gases that can result in the formation of a cloud of flammable vapour which, as it is likely to be more dense than the surrounding atmosphere, will stay at a low altitude as opposed to rising and dispersing in the upper atmosphere. If the cloud then meets a source of ignition, and it is within its flammability limits, it will result in a fire or explosion.

7. Describe the Three Types of Failure Mode? (3) Three types of failure mode can be describe as when a solid material which is subjected to long term exposure to high level of stress gradually deforms in shape or dimension which is called creep. When the materials is corrode it reduces the threshold of the material at some point causing it to weaken resulting in the stress causing crack at that point is called stress corrosion cracking. subjected to a dramatic change in temperature, a stress is introducedWhen calledthe thematerials thermal is shock.

 

  8. Describe a floating roof tank ? (3)

Floating roof tank is made up of cylindrical shell with fixed base. The shell then has a roof within which floats up and down on top of any liquid stored within the tank. This means that there is no vapour. It can be external floating roof tank or internal roof tank in which there is a fixed roof covering the tank

9. Describe the Hot Work Permit? (3)

- This is issued for work which involves the application of heat or sources of ignition to vessels or equipment which may contain or have contained flammable vapour. Also for areas in which there may be a flammable atmosphere. Hotwork permits are typically colored red or are red edged. 10. Describe an automatic fire detection system (3) Can be describe as detectors capable of automatically detecting and pinpointing a fire from long distance as soon as the fire start, It can give control room operators real time information about the state of the fire. These detector can make a recording of event prior to the incident.

11. Outline the reasons for preventing corrosion (4)?

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To prevent deterioration of the materials that may result to blockage to the pipes that will render them ineffective. To prevent direct exposure of of the pipe or vessel to saltwater which can accelerate corrosion of the materials.(offshore) To maintain the integrity of the material and prevent deterioration.

12. Identify who could be consulted on emergency planning? (6)

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Fire Brigade (ERT) Medical Response Team External Agencies / Local Authorities

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Process Engineers

 

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Maintenance Representative Representati ve Operation Manager / Plan Manager Safety Representative

13. Outline the reason why the accident should be investigated by employers (4) The following are the reason for the investigation of accident by the employers. -  To determine the root cause of the accident / incident -  To use the forthcoming information information from the investigation to take corrective correcti ve action in order to prevent recurrence. -  To meet the legal requirement that the employer must conduct investigation to determine the rootcause and take corrective action. . creep

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Solid material which is subjected to long term ex exposure posure to high level of stress and gradually deforms in shape or dimension. It is exacerbated when the subject is also exposed to high heat for a long period of

time. b. stress corrosion cracking -

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The materials is subjected to both stress and corrosion. Corrosion reduces the threshold of the material at some point causing it to weaken resulting in the stress causing crack at that point. Crack will only occur when both corrosion and stress are present.

14. Give the meaning of the Safe Operating Envelope.

Safe Operating Envelope is the parameter and conditions a plant must operate within to ensure it is not subjected to excessive stress which might introduce or encourage failure modes. ------ex. Safe working load, maximum flowrate, maximum pressure, maximum and / or minimum temperature.

15. Identify the hazards associated with the loading and unloading railway tanker operation? (6)

 

1. Outline the content of a typical permit to work (8) Title and Permit Number   – it  – it differs on the kind of activity such as hot work, cold work, and or equipment disjoining permit. Reference to other Permit / Isolation certificates in place Job Location – Location – Specific  Specific location of the activity Plant Identification – Identification –   Specific identification of the plant Description of Work – Work – the  the description of the activity to be undertaken Hazard Identification – Identification – Hazard  Hazard associate with the activity including the residual hazards. Precautionary Measure – Measure – precaution  precaution to undertake to avoid exposure to identified hazard Protective Equipment Required – Required – Protective  Protective equipment including PPE Permit Issue – Issue – Signature  Signature (of issuing authority) confirming that isolation and precautions are taken. Date and time duration of the permit is indicated here. Permit acceptance – acceptance – Signature  Signature confirming understanding of the work to be done, hazard involves and precautions required. Also confirming that permit information has been explained to all workers involved. Extension / shift handover procedures – procedures – Signature  Signature confirming that checks have been made and the plant remains safe to be worked on, and new performing authorities and permit users have been made fully aware of the hazards and precaution. New expiry date given. Hand Back – Back – Signed  Signed by performing authority certifying that work is complete. Signed by issuing authority certifying work completed and plant ready for testing and recommissioning.

Permit Cancellation – Cancellation – Certifying  Certifying work tested and plant satisfactorily recommissioned.

2. Outline how the content of the hotwork permit differs from that of a typical permit to work (4) - Hot work permit include testing of the atmospheric gas level to identify if flammable gases exist or if gasses is below the LFL to prevent fire and explosion. - Hot work permit indicates time name of the competent person designate to monitor the hotwork activity (Fire Watcher). 3. Other than smoke, identify products of combustion that may activate fire detection system? (4) - Heat - Flame -

 

4. Outline reasons for installing a heat detector instead of smoke detector in a kitchen (2)

Heat Detector is installed in the kitchen instead of smoke detector to prevent triggering the alarm when:

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the smoke (part of the process of cooking) comes out during cooking.

5. Identify documents that could be used to decide whether the contractor is competent to carry out the task safely? (8)

- Certificate Certificat e of experience in the type of oil or gas processed work to be carried out. - Records of Competency Training in Offshore / Onshore - Health and Safety Policy and Safe System of Work - Copy of previous Risk Assessment - Copy of their Safety Performance ( to identify number of accidents) - Copy of the enforcement action record if there is. - Copy of the previous accomplished proactive safety monitoring such as safety inspection, audit. -Up to date method statement - Certicate of qualification / competency - Referal document from previous contractor - Evidence of membership of a professional body or trade association - Copy of the availability of the employes liability and public liability insurance. - Copy of arrangement in how they select and appraise subcontractors.

1. Explain the key principles of the safe shift handover ? (10 points)

 A safe shift shift hand turnover turnover is a critical time for for passing information information about the the status of operations. It is measure to prevent miscommunication within the operation personnel especially during shifting schedule. For example: where one group has just completed a 12 hours shift and handover the operation to a new group just beginning their shift. This process can be critical if the information is properly the new group. must be a two way communication onnot both group communicated (on-coming andwithin off-going group) takeItjoint responsibility for

 

making all information accurate, using verbal and written communication. Base all information communicated at handover on a pre-determined analysis of what detail the incoming shift need to have. Ensure good operator support by use of shift log, maintenance record, information display based on operator’s need. Allow as much time as is necessary to ensure that communication is accurate and understood to prevent arising of critical safety issues from miscommunication.

2. Outline the main operational issues communicated at shift handover? (10)

- Operational status of the installation installati on process - Maintenance operations carried out and completed - Maintenance issues begun but not completed - Clearance of permit to work - Handover of permit to work still open - Situation where safety system is overridden (e.g. fire deluge system was switched to manual operation) - Deviation from normal working, such as breakdowns, lack of spare parts, replacement equipment. - Emergencies occurred during the shift. - Incident or injuries following accident during the shift. - Operational issues that will occur in the on-coming shift. - Maintenance operation plan during the on-coming shift. - Events (drill or exercise) planned during the on-coming shift. 3. Outline typical content of safety case and safety report documents? - Identification of of major accident hazards using risk assessment (Q, SQ,

QRA) bow tie

diagram, etc. and criteria from previous operation and incidents records, as well as design drawing and calculation. - Evaluation of major accident risk and measures taken (or to be taken) to control those risk, using details of existing “designed in” precautionary and safety measures. Risk control are required to demonstrate ALARP. - Arrangement for audit and audit reports with a plan showing the type of audit (internal / external), how often they will carried out, what areas they will be conducted, how recommendation will be dealt and who is the responsible for completion. - Having an adequate safety management system in place, including the management of contractors and sub-contractors. Selection criteria and approved list of contractors would be held, together with all returned data.

 

- Major accident prevention policies – policies – in  in the case of safety reports these would need supporting information from the safety management system - Identification of safety critical elements that are in place to manage major accident hazard. -Details of the emergency plan. This would include the layout drawing of the installation, showing locations of all safety and emergency equipment, control points, isolation and shut-off controls, safe access route and escape ladders.

4. Identify two (2) examples of passive fire protection to protect vessels? (2)

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Enclosure – Enclosure  – Fire  Fire Resisting Boxes placed around safety critical equipment Spray Coating – Coating  – Spraying  Spraying of of such epoxy resin based intumescent, cement – cement  –   based plaster and endothermic coating. Seals / Sealants – Sealants – example  example of provision of intumescent door seal placed around a fire door designed to arrest the passage of smoke and fire and activated by heat. Flexible Jacket – Jacket – These  These wrap arounds a structure often based on woven glass. Preformed – (boards, Preformed –  (boards, panels, cladding, wall lining, pipe shells) – shells)  – often  often inorganic fibres (e.g. glass, mineral or ceramic) mixed with organic polymer or cement binder. Can also be made of epoxy resin intumescent materials or Portland cement. Pre fabricated – fabricated  – this  this is a fire resisting structure pre- fabricated off site for on site erection.Fire door is an example.

5. Outline why the metal legs of the vessel should be protected (4)?

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To protect the integrity of the metal legs from corrosion. Metal leg is exposed to the saltwater which will cause corrosion if not protected. The legs must also be protected to avoid risk of personnel injury to personnel on deck caused by loosed objects and marine growth breaking loose and falling from the legs.

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6. Outline how a fixed water deluge system could provide fire protection. (4)

7. identify two additional examples of active fire protection (2) - Water / foam deluge system

 

- sprinklers - Monitors and extinguishers

1. Oil and gas production installations installati ons use flare system and blowdown to protect safety critical equipment. a flare System are use as part of the pressure relief system where steam is used at the flare stack. Outline the purpose of flare (2)

Systems (also known as gas flares) are an important piece of equipment for plants Flare Systems (also and refineries. Gas flares will burn up the flammable gases released by pressure relief valves when flammable gases are emitted by different types of plant equipment. This prevents these excess gases, which may be harmful, from leaking into the area immediately surrounding the equipment. Flaring most m ost often occurs during startup and shutdown, when large amounts of excess gas are built up. Flaring begins when excess gases are mixed with steam or air as they are pumped through large piping systems. These systems push the mixtures to flare stacks where they are then burnt, producing relatively safe water vapor and an d carbon dioxide. In this way, the process is very similar to the burning of liquid petroleum gases. Flares work on the basis of introducing air at the point where fuel gas is combusted so that efficient and complete combustion is achieved and smoke is kept to a minimum. Exactly how this is achieved will depend on the characteristics of the fuel gas, including its composition and velocity. Outline the purpose of using steam in flare system (1) These types of flares are the most prevalent in the oil and gas industry. They employ a system which injects steam into the flare at the flare tip. This introduces air into the flame, which makes the flame more efficient whilst at the same time reducing the tendency for the flame to emit smoke.

Identify additional types of flare system used in oil and gas production installation. (3)

2. Give the meaning of the term “Blowdown” in the context of the oil and gas industry.  industry. 

 

Blow down is a system that is used to relieve r elieve pressure within a process and deal with it in a safe and controlled manner. The pressure relief may involve liquid or gas, depending on the process and/or the situation.

1. Outline reason why accident should be investigated (4)

- To determine the root cause - Forthcoming information from the investigation can be use formulate control measure to prevent recurrence of the accident. 2. Other than the employer, identify organizations and person who may want to investigate incident (4)

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Insurance Representative Local Government Representative or Police, Fire Department,

3. Outline the control measures that could help reduce risk associated with a fixed (cone) roof storage tank (8)

4. Give the meaning of the term “Safe Operating Procedure” (3)  (3)   Is a sequence of written instruction and accessible to worker.

5. Identify possible causes of low hydrocarbon flow through the heater tube (2)

6. Outline controls that prevent heater tube failure (6)

7. Identify suitable controls for traffic management on a large refinery site? (8)

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Traffic routes should be wide enough for the safe movement of of the largest vehicle permitted to use them. Traffic routes should have enough height clearance for the tallest vehicle permitted to use them. A person should be appointed to be responsible and oversee traffic movements

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on routes site. should be well lit. All

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Any hazardous section of the route, such as sharp bends or or adverse camber should be clearly signed. Drivers should be trained and authorized to drive vehicle on site. Visiting driver should be briefed about the site traffic movement rules. Reversing vehicle should be avoided or controlled. A contingency plan, and he resource to implement must be in place in case of adverse weather condition such as snow and ice. Periodic surveys and safety tours should be conducted to ensure traffic rules are being complied.

8. Following an annual shutdown of a process plant, outline operational control measures that could reduce the risk of incident before filling equipment in preparation for startup? (8)

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All materials / equipment which have been used during the construct / modify / maintain the process system conform to the design criteria. All of the following have been inspected, tested and certified such as o  Process system and hardware (including computer control logic) o

   Alarm and safety instrument Relief and devices and signal system o  Fire protection and prevention system Safety, fire prevention and emergency response procedure have been formulated, reviewed and tested and are appropriate and adequate. Start-up procedure are in place and all appropriate actions have been taken. A process hazard analysis has been conducted and any resulting recommendations have been implemented or resolved and any action have been documented. All training (initial, induction and/or refresher) has been undertaken for all personnel and that it included training in. o  Emergency Response o  Process Hazard o

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  Health Hazard All procedures have been completed and are in place; including o  Operating procedure (both normal and upset) and operating manual o  Equipment procedure o  Maintenance procedures – procedures  – finalization  finalization of maintenance procedures will include ensuring all pipes and drains opened during maintenance activities are closed off as required, all instrumentation has been replaced, calibrated and in good working order, and that all spades, blinds or spectacle blinds have been removed o  Any management of of change requirement for new processes and modifications to existing process have been met. o

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9. Concept and commissioning are process plant project phases where risk management applies. Identify four (4) additional project phases where risk management applies (4)?

 

 

-  Design -  Construction -  Pre-Commissioning -  Commisioning -  Shutdown - 

Star-up 10. Outline the concept of ALARP” as long as reasonably practicable in risk management? (2)

 ALARP is the the weighing weighing down the risk versus versus the trouble, trouble, money, money, time needed needed to control the the risk. 11. Identify how quantitative risk assessment mainly differs from qualitative assessment ? (2)

Quantitative risk assessment approach is where after evaluation of the risk , it rank the risk into numeric value / estimate while qualitative risk assessment rank the risk into very high, high, medium low very low

QUANTITATIVE (Quantified) Risk Assessment (QRA) This method is mainly used for complex risk and are based on equations related to probabilities. In its simplest form for m it may be used to establish probability of failu failure re of a component that has safety critical implications, such as a pressure relief valve.

The qualitative method of risk assessment can generally be considered to not involve equations based on numbers to evaluate risk. Using a qualitative approach, a cable trailing in a walkway used by infirm older patients may be evaluated as being a "high" risk, because it is felt that somebody is bound to trip over it and the consequences would be severe. This is a useful, straightforward approach; though it is a relatively subjective method that can easily lead management to take action to control the risk, which is the purpose of risk assessments.

12. Identify EIGHT marine hazards associated with all types of floating production, storage and offloading units (FPSOs).

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Extreme weather conditions, Long term exposure to environmental conditions, Additional motions/stresses motions/str esses from a ship-like ship-lik e structure, Wave loading against the ship,

 

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Operational hazards of unloading, Anchoring failures Collisions with passing supply vessels.

13. Petroleum storage tank fires have been substantially reduced by using floating roofs but a fire risk may still exist. a. Outline how a fire risk may still exist with floating roof tanks. (4)

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Sinking the roof due to insufficient water drainage, Failure of the annular annular seal between the floating roof tank and annular seal and ignition through static electricity.

b. Identify TWO examples of a fire protection system used on floating roof tanks. (2)

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Over the top systems, Foam based types and examples of chemical types such as Du Pont FE36.

14. Process modules in an oil and gas installation installati on often contain computer rooms that require fire protection. a.Identify TWO examples of fire extinguishing media that could be used in a computer room. (2)

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CO2, water mist and inert gas.

15. Outline the following failure modes that may lead to loss of hydrocarbon containment from storage tanks/vessels or pipelines: (a) creep; (2) Is slow movement under stress, made more severe with heat for long periods, especially with increases in temperature approaching melting points. (b) stress corrosion cracking; (2) Occurs under tensile stress and is worse in a corrosive environment at elevated temperatures. (c) thermal shock; (2) Cracking associated with rapid temperature change with different parts of an object expanding by different amounts where the stress overcomes the strength of the materials. (d) brittle fracture. (2) Rapid run of cracks through a stressed material with plastic deformation before failure caused by such things as repetition of inappropriate heating or pressurizing rates

17. Give the meaning of vapour pressure (2)?

 

Pressure exerted by vapour when liquid molecule at the surface escape escape into the gas phase. 18. Outline the purpose of HAZOP? (3) The purpose of hazop are: 

  To systemically systemicall examine part of the process or operation in order to find out how deviation from ythe normalevery operation can happen.   To identify if further control measure are required to prevent hazard, which have evolved from the study, from happening

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19. Identify the kind of persons you would expect to be part of a Hazop team (5)          

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Chairperson Design Engineer Electrical Engineer Process Engineer Operation Manager

20. An onshore safety report is made up of Five Main Sections. Describe what each of those sections is and what issues they cover.(10)

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Descriptive information – information – overview  overview of the facilities and its activities, information about dangerous substances being used at the facility, and information about the surrounding environment. Information on Management Measure to Prevent Major Incident: It sets out the company on the prevention of major incident / accident and must include all elements of the PSM standards. Information on Potential Major Incidents – Incidents  – Description  Description of the process and possible scenarios that could lead to major incident occurring. Information on Measures to prevent and mitigate the consequences of major incident – incident  – details  details of operating parameters and what measures are in place to ensure they are not exceeded, emergency shutdown elements, detection equipment, firefighting arrangements, and emergency evacuation procedure. Information on the emergency response measure of a major incident emergency plan – plan  – description  description of the protection and intervention measures for the facilities, and also the arrangements for involving external emergency services and agencies for offshore facilities.

Hierarchy of Control NEBOS

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Elimination Substitution Changing of Work method / pattern Reduced or eliminate exposure Engineering control (Isolation / barrier / ventilation) Good Housekeeping Safe System of Work (Permit / checklist)

 

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Training and Information PPE Welfare Monitoring and Supervision Review