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R 'W'- I Acetylene 11 Cylinder

Incidents

HM Fire Service Inspectorate


Fire Service Manual

Volume 2



HM Fire Service Inspectorate Publications Section

London: TSO

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Contents

Preface

Chapter 1 Acetylene - general properties 1.0 Introduction 1.1 Acetylene - general properties 1.2 Cylinder storage 1.3 Acetylene decomposition 1.4 Cylinder use 1.5 Incidents

1.6 The effects of catastrophic failure 1.7 The nature of the incident in which it is involved 1.8 Actions of the emergency services

Chapter 2 Pre-planning and Operations 2.1 Liaison 2.2 Site specific risk assessment 2.3 Information, instruction and training 2.4 Incident command 2.5 Safe systems of work 2.6 Closing the incident 2.7 Post incident considerations

Technical References

Appendices 1 Cylinder details

2 Case studies I Health & Safety Laboratory tests (1995/96) II Commercial garage fire (2001) III Remote quarry workshop (1989) IV Acetylene cylinder in domestic garage (1997) V Acetylene cylinder in engineering workshop (2002)

3 Example handout 4 Example handing over form

5 Considerations for Incident Commander (Acetylene cylinders heated or involved in fire)

6 Basic Risk Assessment

7 Glossary of Terms

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Acetylene Cylinder Incidents 111


Preface

This guidance will be of particular interest to officers in brigades responsible for operational policies and procedures, Hazardous Materials (Hazmats) and training. It will also be of interest to those who are part of local emergency planning arrangements.

Further research is being carried out to develop alternative methods of dealing with acetylene cylinders that have been exposed to heat.

This guidance replaces Technical Bulletin 2/1992, Generic Risk Assessment (GRA) 5.2 and the inter- im guidance issued in September 2001. The advice it contains will be reflected in the revision of the GRA's currently being carried out.

Appendix 5 is a revised "Considerations" aide memoir to replace that in section 5.2 of the GRA.

The guidance provided in this Manual represents a knowledge resource intended to support the development of people in accordance with the Emergency Fire Service role maps and the ODPM development modules. This will support and inform the Fire Service in:

1 Applying practices to maximise the health, safety and welfare of personnel and others in the built or natural environment.

2 Making and applying decisions based on the assessment of risk.

3 Making best use of sources and availability of information during acetylene cylinder incidents.

4 Applying Fire Service or other legislation.

This document is knowledge based and offers guidance on methods employed to deal with

incidents involving dissolved acetylene cylinders while reflecting issues concerning the selection, use, capabilities and limitations of personal and operational equipment.

The relevant units of the role maps are:

FF 3: SAVE AND PRESERVE ENDANGERED LIFE

FF 4: RESOLVE OPERATIONAL INCIDENTS

FF5: PROTECT THE ENVIRONMENT FROM THE EFFECTS OF HAZARDOUS MATERIALS

CM 2: Lead and support people to resolve operational incidents

SM 5: Provide information to support decision making

SM 8: Determine solutions to minimise hazards and risks identified by inspections and investigations to inform future practice

SM13: Lead, monitor and support people to resolve operational incidents

The relevant development modules drawn from the ODPM database are:

006 HEALTH, SAFETY AND RISK MANAGEMENT

008 INCIDENT COMMAND I- INITIAL RESPONSE AND MANAGEMENT

027 INCIDENT COMMAND 2

048 ENVIRONMENTAL RISKS AND CONTROL

057 DEALING WITH TRANSPORT INCIDENTS

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058 DEALING WITH FIRE INCIDENTS 059 DEALING WITH HAZMAT

INCIDENTS 076 ANALYSE TRAINING NEEDS 077 DESIGN CONTENT AND

DELIVERY OF TRAINING AND DELIVERY PROGRAMMES

079 DESIGN AND DEVELOP MATERIALS AND LEARNING AIDS

080 PRODUCE MATERIALS AND LEARNING AIDS FOR TRAINING AND DEVELOPMENT

086 INVESTIGATE THE SCENE OF FIRE OR EXPLOSION

Further reading

1 Fire Service Manual - Volume 1 - Fire Service Technology, Equipment and Media - Physics and Chemistry for Firefighters.

2 Fire Service Manual - Volume 2 - Fire Service Operations - Incident Command.

3 Dynamic management of risk at operational incidents. A Fire Service guide ISBN 0-11-341221-5.

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Acetylene Cylinder Incidents Chapter

1 Chapter 1 - Acetylene general properties 1.0 Introduction

All pressurised cylinders present significant hazards when involved in a fire. Acetylene along with other fuel gases such as butane, propane, propylene and hydrogen present particular risks because they are highly flammable materials stored in pressurised containers with the obvious risk of explosive detonation if involved in fires. Butane, propane and propylene, as liquefied petroleum gases, store a large amount of energy in the cylinder. There are detailed differences between the fuel gases such as energy stored, the cylinder's construction and ignition energy, but a similar approach is required if any are involved in fire.

Uniquely, however, unlike the other fuel gases, acetylene continues to represent a hazard after the fire has been extinguished and as such requires different treatment.

1.1 Acetylene - general properties

Industrial grade acetylene is a colourless, highly flammable gas with a garlic-like odour. It is an unstable gas at ambient temperature and pressure and is significantly more so at elevated temperatures and pressures. It is soluble in many organic liquids, especially acetone, which is the most common solvent used in acetylene storage.

Acetylene however is different in one respect, it can decompose to constituent elements if exposed to extreme heat and/or massive shock. This could result in a catastrophic failure similar to the combustion energy released from other fuel gas cylinders if they burst in a fire.

Acetylene is therefore unique amongst the industrial gases in general use. It is a stable gas at ambient temperature and pressure but can become unstable at elevated temperatures and pressures. To

make the gas suitable for use it is dissolved in a solvent (typically acetone) and then stored in cylinders that are filled with a porous mass (details below). The purpose is simply to ensure that acetylene is uniformly dispersed within the cylinder, and in this condition it is stable.

If gas cylinders are involved in fires then caution is

required, particularly if they are fuel gases. Whether there is combustion due to a leak/cylinder rupture, or acetylene decomposition, the hazards are substantial and the initial approach will not dif- fer between cylinder types.

Acetylene is distinguished from other flammable gases by its ability to decompose in the absence of air or oxygen into its constituent elements, carbon and hydrogen, with the evolution of large amounts of energy in the form of heat and light, which can lead to percussive explosions. Extreme heat and/or massive mechanical shock can initiate this decomposition (see Section 1.3).

Acetylene is slightly lighter than air, however for practical purposes, if it has leaked, it will mix with air and should be presumed to be present in an explosive mixture.

Acetylene is a highly flammable compound. The flammability limits when mixed in air are particularly wide, ranging from 2.5% (Lower Explosive Limit - LEL) to 80% (Upper Explosive Limit - UEL). When mixed with oxygen the upper limit

Whilst acetone presents certain hazards in its own right, such as mild toxicity, narcotic effects and skin irritation, for the purposes of this assessment the risks from acetylene are considered far greater.

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rises to 93%.1 This range is wider than any other commonly found flammable gas.'i

The ignition energy for acetylene is very low and the burning velocity and flame temperatures are exceedingly high. The minimum ignition energy for acetylene (and hydrogen) in air are amongst the lowest measured for flammable gases.

Acetylene can be ignited by a wide range of sources including:

Direct flame. A static discharge from a human finger or clothing. Sparks from aluminium rubbing on rusty steel. Friction. Shock.

An acetylene/air mixture, in common with other fuel gases, will explode violently in the open and with even more intensity when confined.

Pure acetylene is not toxic but in high concentrations may cause asphyxiation. In low concentrations it may cause narcotic effects, symptoms may include dizziness, nausea and loss of co-ordina- tion. It is anaesthetic in high concentrations. Loss of consciousness may result, leading to convul- sions, coma and death3. The main hazard however is from combustion and decomposition.

1.2 Cylinder Storage

1.2.1 Design

Acetylene is only slightly soluble in water but is much more soluble in many organic liquids especially acetone, which is the main solvent commonly used by the acetylene industry. Due to the instability of acetylene under pressure, it is stored

ii Free acetylene gas, when subject to pressures exceeding 620 mbar (9 psig), is deemed to be an explosive under the Explosives Act 1875 and is prohibited unless it is manufactured or kept under conditions approved by HSE. Acetylene is NOT deemed to be an explosive when it is kept in cylinders containing a porous mass approved by the HSE. Acetylene is usually used in industry at pressures that are less than 620 mbar (9 psig).

in cylinders containing a porous mass (see Appendix 1). This mass is an inert filler and absorbs the acetone. This prevents the formation of pockets of acetylene inside the main body of the cylinder. It also acts as a stabiliser. The combination of solution in the acetone is uniformly dispersed throughout the cylinder and is thus stable (see Section 1.3).

Withdrawal of acetylene results in gas being released from the solvent as the cylinder pressure falls. For each bar of pressure the acetone solvent absorbs 25 times its own volume of acetylene. Larger acetylene cylinders contain approximately 20 ltrs. of acetone and therefore contain approximately 7,500 litres of dissolved acetylene in solution when nominally charged to 15 Bars.

20 litres (acetone) x 25 (volume acetylene/bar) x 15 bars (gauge pressure) = 7,500 litres dissolved acetylene.

From this calculation it can be seen that for each bar of pressure reduction 500 litres of acetylene will be given off.

It should be noted that due to atmospheric pressure the acetone will still contain 500 litres of dissolved acetylene even though the gauge reads zero and the cylinder is considered to be empty.

Accordingly, an "empty" cylinder still represents a hazard in a fire.

The porous mass or filler used for new cylinders today is a monolithic mass poured in as slurry and baked in an oven to form a porous solid. Older Cylinders may be filled with a granular filler. The materials used for the mass or filler include:

Lime/silica /asbestos. Fibreglass/ lime/silica. Charcoal/kieselghur.

Cylinders containing granular type fillers are still in general use but can suffer from settlement problems. The significance of this is that it can allow free acetylene gas to collect at the head of the cylinder with consequential implications should a

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decomposition reaction occur (see Section 1.3).

Although monolithic type fillers are not prone to settlement problems they can suffer degradation through rough handling of the cylinder, leading to cracks and voids allowing pockets of free acetylene gas to collect. Gas companies are aware of both risks and routinely check by examining the external surface for signs of damage and internal investigation for signs of settlement or cracks in the monolithic mass.

In the UK cylinders are designed and manufactured to a number of British Standards4. These provide information on aspects of construction and colour coding of the cylinders. The standards provide for two types of mild steel shell, these being the welded type or drawn from a solid steel ingot (See Appendix 1).

Cylinders may be grouped together and joined by

common pipework. This arrangement is termed a "bundle" or MCP (Manifolded cylinder pallet or pack, see Appendix 1, Figure A.1.3). These bun- dles, which are normally found in open air, will present an increased risk.

1.2.2 Pressure relief devices

Many acetylene cylinders (the useable life of acetylene cylinders can be more than 50 years) are fitted with pressure relief devices such as fusible plugs or bursting discs. These are designed to release the gas if the temperature or pressure rises excessively (see Appendix 1). In general, steel welded type cylinders are fitted with two fusible plugs in the shoulder of the cylinder, whilst those drawn from solid ingots are fitted with bursting discs, usually in the valve group. Some older cylinders may still be in circulation with fusible plugs in the base.

Regardless of the type and location of the pressure relief device, its operation must NOT be taken as a signal that the cylinder is in a safe condition.

The gas companies approached the HSE request- ing permission to remove the relief devices because of incidents where these actually led to the development of the fire.

The functionality of these devices has been tested by HSE and found to offer no significant contribution to safety. The operation of the pressure relief device allows gas (ignited or unignited) to leak from the heated cylinder increasing the risk of an explosion of a cylinder or further feeding the fire (See Section 1.3).

The main reason for the ineffectiveness of the pressure relief devices is that they cannot vent gas generated by decomposition fast enough. They can also cause fresh acetylene to be drawn into a hot spot and feed the reaction, and any leaking gas can form a cloud around the cylinder.

These pressure relief devices are, therefore, no longer fitted to new cylinders, and are being removed from older cylinders.

1.2.3 Type testing

All newly manufactured acetylene cylinders are type tested, to ensure they can withstand mistreat- ment and internal decomposition, to the require- ments of BS EN 1800, or equivalent standards. This internationally accepted standard requires a number of tests to be carried out on cylinders.

All cylinders have passed the following tests:

Drop test: to simulate heavy use, cylinders are overfilled and dropped from a height of 0.7 metres ten times. This simulates heavy abuse. The cylinder has to survive this without damage to the porous mass. Elevated temperature test: to simulate cylinders being kept in hot conditions, a cylinder is placed in a water bath and heated to 65°C, checking the cylinder does not burst. Backfire test: to simulate a flashback, cylinders are subject to an internal detonation to ignite a fire. To pass this test, the fire must extinguish itself, and the cylinder must not leak, explode or show any signs of distress. No cooling water is applied.

The cylinder has to withstand all of the above. These tests are then submitted to the HSE to obtain legal approval for the operation of the cylinders.


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Also, all acetylene cylinder shells are designed to withstand a minimum test pressure of 60 bar.

1.3 Acetylene decomposition

As stated in Section 1.1, acetylene gas differs from other gases in that within its chemical structure it has a triple bond. This means that the gas can undergo an internal decomposition reaction. The heat released through decomposition can lead to a rapid build up of pressure inside the cylinder, which can lead ultimately to the cylinder's catastrophic failure.

Cylinder design using acetone and porous mass is such that acetylene is uniformly dispersed. If acetylene is heated or some event causes a cavity to be created within the cylinder and filled with acetylene, then decomposition could occur.

The cylinder is designed to suppress decomposition and to self extinguish if it does occur. The porous mass contains thousands of small pores, which act as a stabiliser by dividing acetylene into small units. If decomposition were to occur, the acetylene would absorb heat to the stage where decomposition can no longer continue. This enables the cylinders to withstand most flashbacks and non severe heating.

Acetylene has to reach a temperature of approximately 400°C to decompose. Decomposition can be initiated by a flashback from welding or cutting equipment, or by exposure to intense heat. The lat- ter is normally only achieved by direct impingement of flames on a cylinder.

There is also a possibility of decomposition being initiated from a severe shock to an unheated cylinder, such as dropping from a height of several storeys off a building. If this damaged the cylinder sufficiently to collapse the porous mass and thus create a cavity, it would then leave the cylinder prone to decomposition from any subsequent shocks.

A cylinder that has been heated will be very sensitive to shock.

Prototype tests of acetylene cylinders have shown that should decomposition occur and the cylinder be left to cool down naturally, then the porous mass does extinguish the flame and the cylinder no longer represents a hazard. It is only if a sudden movement or impact is applied to the cylinder, at this point, that catastrophic failure becomes a possibility.

Heat is therefore a good indicator of the decomposition reaction occurring and this is why it is recommended that the wetting test be used to determine if the reaction is continuing to take place or has been extinguished.

1.4 Cylinder use

Oxygen and acetylene together produce a flame temperature of 3,150°C. They are the only combination of gases which can generate the temperature to weld steel. This ability to weld, cut, braze and solder means that acetylene cylinders can be found in many different types of premises. These can include:

Garages. Engineering workshops. Laboratories. Construction and demolition sites. Scrapyards. Factories. Steelworks. Domestic property.

Access to the use of acetylene equipment, including the gas, is not currently controlled by specific legislation. Users therefore rely on information available from their gas supplier and from the British Compressed Gases Association. Gas suppliers provide safety and technical data sheets. Despite the industry efforts some users have little or no appreciation of the hazards and risks associated with the use and storage of acetylene.

Acetylene cylinders are normally used in conjunction with oxygen cylinders. The presence of oxygen cylinders increases the hazard presented by the catastrophic failure of acetylene cylinder(s), as the explosion may propel them or involve them.


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1.5 Incidents

1.5.1 Introduction

For as long as any cylinder is exposed to direct heat in a fire there is a risk of catastrophic failure.

If acetylene cylinders are involved, then the risk of explosive detonation remains if the cylinders have been heat affected.

The unique feature of acetylene is its ability to decompose with massive energy release after any fire has been extinguished but whilst the cylinder is still hot.

It is important to assess whether the cylinder has been sufficiently heat damaged for decomposition to be initiated by exposure to intense heat. It requires heat in excess of 400°C to initiate decomposition. This is normally only achieved by direct impingement of flames on a cylinder.

There are signs, which can be used to detect possible heating:

Do any of the cylinder labels appear burnt? Are any of the plastic rings around the cylinder valve melted in any way? Is the cylinder paintwork burnt or blistered?

Lower heat levels can leave the cylinder at risk if shocked.

1.5.2 Wetting test

It is important to try to identify if an acetylene cylinder has undergone internal decomposition due to flashback or excessive heating. The wetting test will give evidence of whether the outer shell is hot and should be used together with other indicators and information when conducting a risk assessment.

The wetting test involves:

Getting a clear view of the cylinders from a safe location, protected from any possible blast

Spraying sufficient water on to the cylinder to wet the entire surface of it, Stopping the spray and looking for signs of steam rising from the surface of the cylinder If steam is not seen rising, does the wetted cylinder surface dry out quickly?

The test is also a useful indicator to show the progress of the cooling down operation.

Any leaking gas may accelerate the decomposition and cause the cylinder to rapidly re-heat.

1.5.3 Circumstances that Initiate Decomposition

Incidents involving cylinders can arise in any one or a combination of the following circumstances:

Flashback from a cutting/welding torch into the cylinder (not to be confused with a backfire) iii.

Hot work residue which can burn into the supply tubes and burn back to the cylinder.

Cylinders in the vicinity of a fire.

A backfire (a single cracking or `popping' sound) is when the flame has ignited the gases inside the nozzle and extinguished itself. This may happen when the torch is held too near the work piece.

A flashback (a shrill hissing sound) when the flame is burning inside the torch, is more severe. The flame may pass back through the torch mixing chamber to the hose. The most likely cause is incorrect gas pressures resulting in the gas velocity being too low. Alternatively, a situation may be created by a high pressure gas (acetylene) feeding up a lower pressure gas (oxygen) stream. This could occur if the oxygen cylinder is almost empty but other potential causes would be hose leaks, loose connections, or failure to adequately purge the hoses.

Non-return valves fitted to the hoses will detect and stop reverse gas flow preventing a flammable oxygen and acetylene mixture from forming in the hose. The flashback arrestor is an automatic flame trap device designed not only to quench the flame but also to prevent the flame from reaching the regulator. Flash backs into acetylene cylinders which may initiate decomposition are generally due to the failure to fit a flame arrestor.


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Cylinders that have otherwise been subjected to direct or indirect heat.

A hot cylinder that is dropped or otherwise suffers severe mechanical shock may potentially fail catastrophically.

In addition if decomposition has started it can be aggravated by:

Leaks from the heated cylinder's safety device (where fitted) or valve or associated equipment, whether the gas has been ignited or not.

An acetylene cylinder that has been subjected to heating (over 400°C) as a result of being involved in a flashback, or adjacent fire, is potentially dangerous. Decomposition of the acetylene contained within the cylinder takes place and will continue until all of the acetylene is consumed or until the cylinder is effectively cooled. Acetylene cylinders are designed and tested to withstand such decom- positions and will normally cool naturally without any problem; the porous mass is designed to assist in this. Cooling will slow the reaction and allow it to self extinguish. In the worst case, inadequate cooling (perhaps caused by shielding) can lead to potential catastrophic failure due to the weakening of some part of the steel wall of the cylinder.

Even when a hot acetylene cylinder appears to have been cooled externally, a residual internal hotspot could be present. If there is also a large internal cavity due to damage of the porous mass, movement of a cylinder may accelerate decomposition and result in catastrophic failure without warning.

In 1995 the Health & Safety Laboratory in Buxton5 undertook a number of live destructive tests on Acetylene cylinders. The Buxton tests involved subjecting cylinders to all round heating (designed to simulate fire situations) and localised heating (to simulate local flame impingement from an acetylene torch). These tests proved the pressure relief devices (bursting discs and fusible plugs) were not effective in preventing explosion of cylinders under such conditions. Further research was conducted with a joint study between London Fire Brigade and the Fire Research Division of DTLR

during 20006 which resulted in existing fire service procedures being questioned.

During the Buxton tests, it was identified that even when the cylinders were fully instrumented to continuously measure the internal pressure and wall temperature, it was not always possible to detect acetylene decomposition inside the cylinder. This was because the water was applied continuously keeping the external temperature monitors cool. The shell was externally cool because of this but the inner part of the cylinder mass was still hot.

If under test conditions decomposition inside a cylinder could not always be detected, it follows that equipment such as thermal imaging cameras or infrared thermometers may only provide an initial indicator that the surface of the cylinder is hot. They cannot and must not be relied upon as indicators of safety.

Heat through decomposition will be localised and the porous mass has low thermal conductivity. Decomposition can therefore be present within the core of the cylinder whilst the walls are cool. However there will usually be evidence of heating on the cylinder, valve assembly or associated equipment if it has been involved in fire or been subjected to a flashback.

An acetylene cylinder that has been heated and is leaking gas presents the greatest danger of catastrophic failure. This is due to the fact that fresh acetylene will be constantly released by the acetone. This fresh acetylene will travel through the internal mass of the cylinder and if a reaction is taking place may provide additional fuel for decomposition, ultimately increasing the rate of reaction and potential for catastrophic failure.

There is at present no practical reliable means of detecting decomposition deep within an acetylene cylinder.


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1.6 The effects of Catastrophic Failure

Post incident investigations into events that have resulted in the catastrophic failure of acetylene cylinders have provided evidence of the nature of the hazards that are presented (See Appendix 2 - Case Studies).

These hazards include:

A blast pressure wave. Fireball of up to 25 metres. Cylinder may be thrown up to 150 metres. Large fragments which have high looping trajectories. Flying shrapnel, valve assembly, carrying trolley and other ancillary equipment, which may be thrown up to 200 metres. Flying glass and other structural material. Structural damage to buildings in the vicinity. The spread of asbestos particulates either from the filler mass or building materials.

The severity of any or each of the above hazards is dependent upon the exact circumstances of each case. It is clear that the hazards caused by a catastrophic failure of an acetylene cylinder will put both members of the public and operational personnel in the vicinity of the incident at risk. Experience has shown that the outcomes of each of the above effects can lead to a range of injuries including:

Death. Blast injuries. Flash burns. Permanent hearing damage. Concussion. Bruising. Post-incident trauma.

The dangers and unpredictable nature of heated acetylene cylinders should not be underestimated.

1.7 The nature of the incident in which it is involved

The types of incidents that may involve acetylene cylinders vary widely. It is possible for the cylinder itself to be in the open, in a vehicle, building or partially/ completely buried in debris.

It may be that the incident itself will require the fire service to take some action to save life or prevent the spread of fire.

In some cases it may not always be evident that there are acetylene cylinders involved. Even if it is known or suspected that they are, it is not always possible to ascertain the exact number and location of the cylinders, for example a workshop where the cylinders are moved around on a trolley.

The immediate hazards of a fire involving acetylene cylinders are the same as for any gas cylinder. The difference is in the cooling off period required subsequent to extinguishing the fire.

1.8 Actions of the Emergency Services

Section 2 and Appendices 5 and 6 of this guidance outlines the control measures that are available to deal with acetylene incidents. It is very likely that any action taken by the emergency services at an incident of this kind will involve the establishment of a cordon and application of water.

The problems associated with the establishment of a cordon include:

If necessary, evacuating large numbers of the public from places of entertainment, homes and places of work. Stopping traffic on railways or road networks, leading to congestion and frustration/anger. Attracting a crowd of onlookers. Dealing with aggrieved business people.

The hazards/problems associated with the application of water include:


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Increased environmental damage from fire water run off. Overrunning of drains and interceptors, spreading hazardous substances into the area of operations. Concerns from the community regarding excess waste of water supplies. Run off into local water courses. Flooding of low-lying areas in the vicinity. The creation of concealed fall/trip hazards.


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Acetylene Cylinder Incidents Chapter

2 Chapter 2 - Pre-planning and Operations

2.1 Liaison

Brigades will need to liaise with local police, HSE, Environment Agency, Acetylene Cylinder Suppliers, Users and other Local Authority Agencies that will be affected by this type of incident. Liaison will ensure:

A possible reduction in the number of acetylene cylinder incidents. All parties involved understand the implications of such an incident. The safe and effective management of the incident. The safe and effective handover of affected cylinders.

2.2 Site specific risk assessment

Premises likely to contain acetylene cylinders should be identified as part of the brigades ongoing risk management system.

Brigades will need to consider the appropriate level of command and resources required due to the nature of the hazard and that the incident will be protracted.

2.3 Supporting and Developing people to deal with acetylene cylinder incidents

The service will need to have in place systems that support operational personnel in dealing with incidents involving acetylene cylinders and that will enable them to:

Apply practices to maximise the health, safety and welfare of themselves and others in the built or natural environment.

Make and apply decisions based on the assessment of risk. Make best use of sources and availability of information before, during and after the incident. Apply legislation to the situation.

The development of crews and individuals who are likely to be required to deal with acetylene cylinder incidents should be planned in a way that mitigates the risks accruing to such events. It is vital that crews should rehearse the safe systems of work described below in order to develop relevant task, task management, contingency and environmental skills in conjunction with the knowledge and understanding provided by this guidance document. Further amplification will be found in the list of relevant role map units and development modules to be found in the preface to this document.

Operational personnel must be made aware of the dangers posed by acetylene cylinders involved in fire and the unpredictable nature of this substance.

Personnel must be able to implement the key operational procedures for dealing with this type of incident at all role levels.

2.3.1 Learning and Development outcomes

People will be able to demonstrate that they have relevant knowledge, skills and understanding that will enable them to deal with acetylene cylinder incidents as safely as possible. This will include knowledge and understanding of the hazards posed by acetylene cylinders involved/not involved in fire and the skills to implement operational procedures for dealing with them, such as safe handling techniques.


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2.4 Incident Command

Acetylene cylinders that are suspected of having have been affected by heat should not be approached or moved under any circumstances.

2.4.1 Identifying the Hazard Zone

Firefighter and public safety are of paramount importance. Incidents involving acetylene cylinders will be protracted. When considering safety and resource implications it may be necessary to consider these as being major incidents. The immediate dynamic risk assessment will determine the tactical mode of operations (See Appendix 5 - Considerations for Incident Commander).

Extreme caution should be exercised at any incident where it is considered likely that acetylene is used or in use within the property, but where no information is available.

When it is suspected that acetylene cylinder(s) are or have been involved in fire, an initial "Hazard Zone" extending to a maximum of 2.00 metres from the cylinder(s) should be considered in liaison with the police. The assessment of the hazard zone has been based on the possible travel distance of fragments from an exploding acetylene cylinder in open air (see Section 1.3). The actual area of the hazard zone required will be determined by a number of factors including the type and extent of adjacent structures and the local topography (See Appendix 2 - Case Study V).

It is important that immediate steps are taken to:

Establish if the cylinders have been exposed to heating Establish the identity of the cylinder(s) concerned

This will require observation from a safe location for signs of blistered paint, melted plastic components or rings, burnt labels or obvious involvement in a fire.

Following an assessment of the hazard zone and using any available shielding in order to minimise risks to emergency personnel, the Incident

Commander should establish an inner cordon to control access to the vicinity of the cylinder.

The size of the hazard zone may be reduced following consideration of the protection provided by the surrounding environment and topography and/or the effect of the cooling process referred to in Section 2.5.2. Consideration should also be given to the use of any substantial, portable materials that might offer shielding between the hazard and a public highway, railway or other thorough- fare. This might be particularly possible where such materials are paletted and can easily be moved into place without subjecting the operative to any undue risk.

If it is established that the cylinders have not been exposed to heating then the hazard zone should be reduced or removed.

As with all cylinder incidents, consideration must be given to evacuation of the public and non-essential personnel. Liaison with the police will be necessary if evacuation is required. Where evacuation is not possible, or is considered inappropriate, all those remaining in the hazard zone should be warned of the risks and should be advised to stay away from doors and windows and make use of all available shielding. Appendix 4 gives an example of a handout for members of the public. (See also Appendix 2 - Case Study II.)

Personnel required to carry out tasks within the inner cordon should make use of all available shielding. Personal protective equipment appropriate to the immediate hazard should be worn, such as gloves, flashoods and eye protection in addition to full fire kit.

Consideration should be given to the attendance of Gas Cylinder suppliers for specialist advice at the time of the incident and for subsequent cylinder recovery.

2.4.2 Maintaining the cordon

Once the specific hazard zone has been established a cordon should be set up to ensure the incident ground is controlled and firefighter/public safety is maintained. Close liaison with the Police should


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be established to ensure that the cordon is maintained throughout the duration of the incident (see Appendix 2 - Case Study IV). The size of the cordon may be re-assessed if circumstances change during the incident, for example, the provision of suitable shielding or evidence that the cylinder walls are cool, i.e. they remain wet.

2.5 Safe Systems Of Work

2.5.1 Cylinders not affected by heat

Where cylinders are in the proximity of a fire but show no signs of direct heating such as paint damage or melting plastic guards or neck rings, they are likely to be safe to move. However, before doing so the coolness of the cylinder walls should be checked by spraying with water and seeing whether they remain wet.

Personnel must be made aware of the manual handling problems associated with moving an unheated cylinder to a safe location. Acetylene cylinders are comparatively heavy in relation to other cylinders and are awkward to carry, especially when wet.

Cylinders that have been subjected to severe shock (for example falling from an upper storey to the ground) should be treated in the same way as those affected by heat, as there is the potential to initiate decomposition.

Where it has been decided not to remove unaffect- ed cylinders they may be protected from radiated or direct heat by the use of cooling sprays.

2.5.2 Cylinders affected by heat

Where a cylinder is found involved in fire or suspected of having been subjected to heat, the Incident Commander should balance the dangers posed by the heated cylinder(s) against the need to deal with the incident.

The operation of a pressure relief disc or fusible plug with gas burning off or leaking, indicates an increased likelihood of catastrophic failure and should not be regarded as a sign of safety (see Section 1.2).

Water cooling is currently the most effective method of preventing catastrophic failure of an acetylene cylinder and should be used whenever it can be implemented without compromising the safety of firefighters, i.e. where protection is offered by suitable shielding.

If a decomposing cylinder is leaking or is moved, the rate of decomposition and heat generated may be increased to such an extent that the cylinder walls are weakened abnormally and rupture. Greater safety can be achieved if the decomposition process is slowed or arrested by cooling.

The period of greatest risk is when the cylinder shell is hot, so every effort should be made to cool it comprehensively taking full advantage of the use of monitors and/or lashed jets.

There may be circumstances where attempts to apply cooling water would expose firefighters to unacceptable levels of risk that outweigh the benefit likely to be gained. In such circumstances the alternative would be to leave the cylinder in situ without applying water. An example of this situation is:

Where no shielding is available; and There is no immediate risk to life.

Heated acetylene cylinders cannot be considered safe until at least 24 hours after initial cooling has commenced (whether this is via cooling water or allowing the cylinder(s) to cool naturally). The European Industrial Gases Association (EIGA) recommends a cooling period of 24 hours. British Compressed Gases Association (BCGA) also cor- roborate that cylinders can be regarded as safe after a cooling period of 24 hours.

Whilst the application of water is considered to be the most suitable method of cooling a cylinder, it is appreciated that the application of this medium might have to be interrupted or ceased dependent upon the Incident Commander's dynamic risk assessment. This assessment should consider factors such as:

The nature of the incident. The nature of surrounding/adjacent risks.

Acetylene Cylinder Incidents I I

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The risk to firefighters providing cooling water sprays. The adequacy of any shielding. The nature and effects of any cooling water run off.

' The environmental impact. Whether the cylinder walls are cool.

Acetylene cylinders should therefore be left in situ for a minimum period of 24 hours following removal of any heat source, with cooling water being applied for this duration where the situation permits.

If it is not possible to continually apply cooling water, cylinders should be left alone in situ to cool naturally for at least 24 hours.

The application of water will result in the cylinder shell cooling quicker and ultimately slow down any internal decomposition process occurring inside the cylinder. As a consequence of this, cordon size could be reduced as determined appropriate by the Incident Commander after undertaking a risk assessment and account of the points mentioned above.

Prior to reducing cordon size, the Incident Commander should consider the use of a "wetting test", the purpose of this being to determine whether the cylinder shell remains wet after the interruption of cooling water. This test is not to be interpreted as an indicator of total safety. It is simply an additional tactic that the Incident Commander can use when carrying out a risk assessment in order to test the feasibility of reducing cordon size.

Once the walls of the cylinder remain wetted for some time after the application of water has ceased, it can be assumed that they have regained their tensile strength in which case catastrophic failure is extremely unlikely. The hazard zone can then be reduced appropriately and cooling spray(s) or jet(s) reintroduced for the remainder of the 24- hour cooling period.

The appropriate reduction in the hazard zone area/inner cordon should be such that personnel or passers-by cannot gain access to or interfere with the affected cylinder(s). If available transportable

shielding such as that referred to in Section 2.4.1 should be used between the cylinder(s) and any nearby public footpath(s). Where roads, motor- ways and/or railway lines pass through the initial 200-metre hazard zone area but are outside the newly defined restricted area, these can in most cases be re-opened. Again, the use of portable materials to provide shielding should be resorted to where this is available. Consideration can also be given to allowing adjacent buildings to be re- occupied provided a safe route of ingress and egress can be obtained and occupants are advised to keep away from windows and other openings on the affected side.

2.5.3 Leaking Cylinders (Pre & Post Fire Situation)

Where leakage of acetylene gas is suspected, the possibility of an explosive atmosphere could exist and therefore the following should be considered:

Evacuation of immediate area. Elimination/separation of ignition sources. Water sprays to assist the dispersal of gas.

Leakage of acetylene from a cylinder may intensi- fy any decomposition in the cylinder resulting in it becoming hot. Always check to ensure that heating is not occurring by using the wetting test.

2.6 Closing the incident

Acetylene cylinder(s) cannot be considered safe until at least 24 hours after the removal of any external heat source and commencement of water or natural cooling.

Brigades need therefore, to either maintain a presence at the incident throughout the 24 hours or make arrangements to hand the incident over (including the management of the hazard zone) to a competent agency or organisation.

After the initial 24-hour period, the responsibility for the acetylene cylinder can be transferred to the owner of the cylinder.

Brigades must ensure that when handing over the cylinder(s) that the owner/occupier or competent person/agency/organisation is fully aware of the


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hazards, risks and control measures associated with the care of acetylene cylinders after they have been involved in fire. See Appendix 4 for an example of a handover form.

2.7 Post incident considerations

If an acetylene cylinder has failed catastrophically for no apparent reason, the Health & Safety Executive must be notified.

In addition, the HSE should also be notified where no catastrophic failure occurs but where the cylinder is the suspected cause of an incident. There is no reporting requirement where an acetylene cylinder does not fail after being subjected to some form of heating.

Brigades should monitor all acetylene cylinder incidents, lessons learned should be considered as part of the review process.


Technical References

1 Technical Data Summary - Acetylene. United Nations Substance Identification Number - SIN 1001.

2 Dangerous Properties of Industrial Materials, N Irving Sax & Richard Lewis Snr 7th Ed Vol II, pp48-49.

3 British Oxygen Company, Material safety data sheet, 6/l/99.

4 British Standard 5045 part 1 192 Transportable Gas Containers (Seamless steel construction). BSI.

British Standard 5045 part 1 1989 Transportable Gas Containers (Welded seam construction). BSI.

British Standard 6061 1981 Transportable Acetylene Cylinders. BSI.

British Standard EN 1089 - 3:1997 Transportable Gas Cylinders - Cylinder Identification Part 3, Colour Coding. BSI.

5 Fire tests on Acetylene cylinders fitted with fusible plugs, Health and Safety Laboratory, 1995.

6 Improving Fire Service Management of Acetylene Cylinder Incidents, Sue Coles, DTLR 2001.



Appendices

1 Cylinder details

2 Case studies I Health & Safety Laboratory Tests (1995/96)

II Commercial garage fire (2001)

III Remote quarry workshop (1989)

IV Acetylene cylinder in domestic garage (1997)

V Acetylene cylinder in engineering workshop (2002)

3 Example handout

4 Example handing over form

5 Considerations for Incident Commander (Acetylene cylinders heated or involved in fire)


7 Glossary of Terms

Appendices


APPENDIX 1

Cylinder details

Figure A 1/ 1

Cross-section of welded type acetylene cylinder showing filler mass.


Figure A 1 /2 Range of dissolved acetylene cylinders.

Figure A 1/3 Typical

manifold pack.

APPENDIX 1

The Range of Dissolved Acetylene Cylinders (Maroon)

Solid Solid Solid tinder C t Welded Drawn Welded Welded Drawn Drawn Welded ruction ons Steel Steel Steel

Length 340 650 570 705 1050 1200 1120 mm Outside 172 159 172 204 213 264 286 diameter mm


APPENDIX 1

Cylinder details

Figure A 114

Fusible plug locations in shoulder of cylinder.

Figure A 1 /5 Cross-sectional view

of valve assembly showing location of bursting disc.


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APPENDIX 1

Figure A 1 /6 The unpredictability of acetylene cylinders. Not all fail catastrophically.


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APPENDIX 2 Case studies

Case Study I

Health & Safety Laboratory Tests (1995/96)

Identification of decomposition within cylinder

Unpredictable nature of acetylene cylinders involved in fire.

Difficulty in identifying whether decomposition has commenced even with sensitive temperature/pressure monitoring devices.

In 1995/96 the Health and Safety Laboratory in Buxton undertook a number of extensive live destructive tests on acetylene cylinders involved in fire. The primary purpose of the tests was to determine the value of safety devices (fusible plugs or bursting discs) fitted to acetylene cylinders, as in other European countries there is no requirement for these.

Two types of tests were conducted

the five cylinders tested only one failed catastrophically. However, one interesting observation was noted.

During one test, the cylinder shell reached a maximum temperature of 328°C (15 minutes into the test) with an internal pressure of 16 bars. After approximately one hour, the cylinder showed no additional increase in temperature; therefore, the torch was turned off and the test aborted. The dump valve attached to the cylinder was opened allowing the free acetylene within the cylinder to disperse to atmosphere. The cylinder was then cooled via a fixed water drencher system for 30 minutes. After this period, the thermocouples (spot-welded in various positions on the cylinder shell) recorded an increase in temperature. The deluge system was therefore reinstated to re-cool the cylinder for a further 30 minutes. This process was repeated a number of times before the cylinder remained cool enough to be approached and subsequently moved.

Pool fire test to simulate all round heating as in normal fire situation Torch fire test to simulate localised heating.

During the tests the cylinder shells were fitted with a number of thermocouples to measure localised temperature and pressure transducers fitted in the valve assembly to measure any increase in internal pressure.

Pool Fire Test

All five acetylene cylinders tested failed, two due to pressure temperature effects and three catastrophically.

Torch Fire Test

This test was designed to simulate an acetylene hose fire with flames directed upon the cylinder shell causing an area of localised heating. Out of

When the cylinder was finally approached, large amounts of carbon deposits were found on the ground at the base of the cylinder. It is assumed that these deposits formed as a result of incomplete combustion of the acetylene torch flame. As the temperature increase was small during the test, it is assumed that the carbon deposits formed an insu- lating blanket between the cylinder wall and flame. It would seem that operation of the deluge system washed off these deposits.

Before moving the cylinder the valve was closed and disconnected from the dump line. The cylinder was then carefully moved to a water dam that was lined with plastic sheets and submerged with the valve re-opened. Prior to leaving the site no bulging of the cylinder wall was observed. Some fourteen hours later when the Health and Safety personnel returned, they found the plastic salvage sheets underneath the submerged cylinder to have melted. The cylinder itself had a large bulge where localised heating had taken place. This illustrates


APPENDIX 2

the unpredictable nature of acetylene cylinders even when considered empty and fully immersed in a dam full of water.

If active temperature/pressure monitoring devices attached to cylinders are incapable of identifying whether a decomposition reaction is ongoing inside a cylinder, infra red cameras/thermometers or a hand contact must be regarded as totally inadequate. Therefore, as there is no accurate means of determining the presence of a decomposition reaction within a cylinder, the safest option must be to leave the cylinder in situ for a specified period of time.


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Case Study II

Commercial garage fire (2001)

Dangers posed by acetylene cylinders involved in fire

Projectile hazards

Structural Damage and Firefighter Injuries

Recognition of possible presence of acetylene cylinders due to premise type and appreciation of potential hazard

Fire crews were called to a fire in a commercial garage sometime around 0217hours. The first pump arrived at approximately 0227hours, with a further pump and an all terrain vehicle arriving shortly afterwards.

The building in question was of traditional construction (single storey double leaf cavity wall)

M Fn I

COMPRESSOR ROOM

DOUBLE

SKIN CAVITY / WALL

3 FIREFIGHTERS WITH JET FLASH BURNS -

A

WORKSHOP

V ORIGINAL

LOCATION OF

CYLINDERS

15m

°-- TOP OF CYLINDER

I

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ARGON CYLINDER

ACETYLENE CYLINDER

OXYGEN CYLINDER

ROOF CORRUGATED

I

Figure A 2/1 Diagram showing the layout of the incident site.

with corrugated asbestos sheet forming the roof. The fire was observed to be in the workshop area and well established. A forced entry was made via door `A' (see diagram below) with three firefighters getting a jet to work from this location. Whilst these firefighters were playing the jet on the fire from the door opening, an acetylene cylinder failed catastrophically.

The force of the explosion ejected the acetylene cylinder shell through the corrugated asbestos roof landing some 36 metres away from the workshop. The cylinder was split longitudinally with the filler mass and valve missing. (See Figure A 2/2.)

The oxygen cylinder that was next to the acetylene cylinder prior to the explosion was blown through one of the windows with such a force that it took out the double skin blockwork at the top and bottom of the window opening. The oxygen cylinder

ROADWAY

TOOK OUT TOP OF

WINDOW. BASE OF

CYLINDER TOOK OUT

WINDOWSILL AND - - - BRICK WALL

GARAGE YARD


APPENDIX 2

had not failed itself, but simply been ejected by the All the windows within the workshop failed due to energy released upon the catastrophic failure of the the pressure wave produced during the explosion. acetylene cylinder. The oxygen cylinder was found The filler mass within the acetylene cylinder had approximately 6m from the workshop wall, landing been ejected. This itself constituted a possible very close to two firefighters. (See Figure A 2/3.) asbestos hazard. (See Figure A 2/4.)

Figure A 2/2 Remains of acetylene cylinder, note distance from workshop in

background. (Photograph: North Wales

Fire Service)



In total nine firefighters were injured at this incident, three with flash burns (the three directing the jet into the building) and six others with cuts and bruises due to secondary projectiles striking them, i.e., flying glass and masonry. It should be noted that the four-wheel drive all terrain vehicle was also damaged by fragments.

The valve from the acetylene cylinder was never found. It can only be assumed that it was ejected

Figure A 2/3 The oxygen cylinder was blown through block cavity wall and landed close to two firefighters. (Photograph: North Wales

Fire Service)

Figure A 2/4 Rear view of the work-

shop. The cylinders were behind the central column prior to the catastrophic failure. Note no support to the lintel and a large crack running down the central pillar leaving the building in an unsafe condition. (Photograph: North Wales

Fire Service)

with such force that it travelled way beyond the immediate incident. The cylinder trolley was also thrown some distance.

This incident highlights the dangers posed by acetylene cylinders in fire. Even whilst undertaking firefighting operations from outside the building crews are still in danger, as standard construction is unable to significantly reduce the impact of flying projectiles.


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Case Study III

Remote Quarry Workshop (1989)

Firefighter fatalities and other injuries

Risks of handling heated acetylene cylinders

Exposure of firefighters to unacceptable risks where no real benefit can be achieved)

A fire crew was called to a cylinder on fire in an asbestos/steel framed workshop located within a quarry. On arrival it was found that both acetylene and oxygen cylinders had been involved in fire and were located in a small storeroom constructed from an old wood lined steel plate explosives mag- azine at the rear of the workshop. The likely cause of this fire was attributed to hot weld particles falling on the acetylene and oxygen supply hoses and other small amounts of combustible material. Using a jet, the fire in the workshop was quickly extinguished, but difficult access to the storeroom necessitated a hose reel being taken into the workshop under cover provided by a large earth moving machine.

It proved impossible to extinguish the fire in the storeroom as one of the acetylene cylinders was alight at the regulator (the supply hoses having burned back to the cylinders in the store room). It was successfully extinguished by shutting the regulator valve. Whilst cooling of this cylinder continued, its neighbouring cylinder (another full acetylene cylinder) was picked up by two firefighters, carried out of the storeroom and laid down on the ground nearby. Here it was cooled by a firefighter using a hosereel whilst others started to move the cylinder that had been on fire. (It was later cooled and transferred to a water dam without incident).

The cylinder that had been carried outside sudden- ly exploded into four pieces. One of the firefighters engaged in moving the other cylinder who was standing in close proximity to it was struck by at

APPENDIX 2

least one of these fragments, sustaining fatal injuries. Six of the other firefighters at the scene sustained flash burn injuries.

The cylinder that exploded had been heated by flames from either the burning hoses of the neighbouring cylinder, or the burning wooden lining of the storeroom itself. A decomposition reaction is

believed to have taken place within the cylinder causing it to fail catastrophically. A metallurgical study of the fragments of the cylinder did not show any evidence of corrosion or substandard material.

At the inquest, an expert witness from the supply industry stated that the decomposition process within an acetylene cylinder could be initiated from a hot area as small as 2.5mm2 leading to an extremely dangerous decomposition inside the cylinder. He also stated that the bursting discs provided on such cylinders might not protect against such an occurrence.


APPENDIX 2

Case studies

Case Study IV

Acetylene cylinder in domestic garage (1997)

Establishment and maintenance of effective cordon

Legal support for maintenance of public safety where Fire Service and Police consider it necessary

The Fire Service was called to a fire in a private dwelling garage. Upon arrival it was established that an acetylene cylinder was involved therefore a hazard zone of 100m was immediately established and all residents within this area evacuated.

Upon the arrival of the Brigade Hazmats Officer control measures were reassessed. Due to difficul- ties in applying cooling water to the acetylene cylinder (buried under fire debris) and the nature of the immediate area (residential type property) the hazard zone was increased. All evacuated residents were accommodated in the local school/ Community Centre.

Both Fire Service personnel and the Police effectively maintained the cordon and the admittance of non-essential personnel was restricted. During the time that the cordon was in operation a member of the public insisted upon entering. After being ver- bally warned of the dangers by both Fire Service personnel and the Police, the individual ignored this advice and physically breached the cordon.

This person was immediately arrested by the Police and charged under Section 30(2) Fire Services Act 1947, `obstructing a Fire Officer'. Upon conviction the individual concerned was fined £200 plus costs.


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APPENDIX 2

Case Study V

Acetylene cylinder in engineering workshop (2002)

Implementation of new procedures

Lack of information on original call

Establishment of cordon

Evidence of decomposition

Occupiers views of new procedure suggesting need for industry advice

Appliances were mobilised to a fire at an engineering workshop approximately 100 metres from a busy crossroads on the edge of a small town centre. Given the nature of the building, responding crews could have predicted the possible presence of acetylene cylinders. Unaware of the presence of cylinders the appliances were parked in the yard of the premises.

Prior to commitment of any firefighters in to the building, the Incident Commander was informed that the fire involved an acetylene cylinder, which had suffered a flashback. The fire had been extinguished (four foot long flame) by the operator closing the cylinder valve.

Crews immediately ensured evacuation of the premises and withdrew appliances to a position adjacent to the crossroads where buildings provided reasonable cover. As some shielding existed a decision was made to apply cooling sprays from within the yard.

The Incident Commander, assisted by a Hazmat Officer, assessed the hazard zone and set up a cordon reflecting the cover and shielding afforded by the immediate topography. Pedestrians and road traffic were prevented from passing the area and the Police and Local Authority established

Figure A 2/5 Ordnance Survey map showing the location of the incident and arrangement of cordons.


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APPENDIX 2

Case studies

diversions (setting up temporary traffic lights where necessary). Occupiers of buildings immediately adjacent to the cordon boundaries were warned of the hazards and advised to stay away from doors and windows.

In order to improve safety and ease relief duties it was decided to feed the cooling spray directly from a fire hydrant and reposition the released appliance behind more substantial cover. Whilst undertaking this action the flow of cooling water was tem- porarily interrupted. During this time it was observed (from a safe distance using binoculars) that the affected cylinder was steaming consider- ably. It was clear to the Incident Commander that the original flashback had initiated a decomposition reaction in the cylinder, which was still in progress some two hours into the incident. Cooling water was re-applied for the remainder of the twenty-four hours.

During the course of this incident, the premises owner expressed concern in regard to the new procedure adopted by the Brigade and its impact on his business. He stated that on the last occasion the Fire Brigade had been called to his business to deal with an acetylene cylinder involved in fire, they had simply put it in a bath of water, therefore allowing work to carry on unhindered. He implied that in the future he would not call the fire service to this type of incident. His attitude serves to demonstrate the fact that many users have little appreciation of the dangers associated with acetylene cylinders.


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APPENDIX 3 Acetylene cylinders affected by heat-flow chart

Acetylene Cylinder Incident

DANGEROUS INCIDENT

The .......................................... Fire Brigade is dealing with an incident that involves an acetylene cylinder.

Your business or home may be affected for at least 24 hours while the incident is made safe.

A hazard zone has been set up around the cylinder.

Members of the public will not be allowed to enter this zone.

(Front)

What is acetylene?

Acetylene is a compressed gas, which can be used for a number of purposes. It is stored under pressure and is highly flammable. If

stored and treated correctly Acetylene cylinders pose little threat.

Why is it dangerous?

When an acetylene cylinder is heated excessively it can become unstable and may explode. Fragments from the cylinder, or the cylinder itself can be thrown long distances by the blast.

The cylinder can only be considered safe after it has been cooled for 24 hours.

(Back)

What we are doing to ensure your safety

For your safety the ......................... Fire Brigade has set up a hazard zone around the cylinder. This will be in force for at least 24 hours.

Only firefighters involved in fire-fighting operations will be allowed in the zone until the cylinder is made safe.

If your home is within the zone but you are unwilling or unable to leave for this period, may we offer the following safety advice.

Do not leave your home for the 24 hour period. If you do leave your home, you may not be allowed back in for safety reasons. Close your curtains and stay away from any windows. Position yourself in a room as far away from the incident as possible.


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APPENDIX 4 Example Handing over form

.......................................... Fire Brigade Acetylene Cylinder Form

Form number Number of copies

Date of incident: Time cooling period commenced:

Incident number: Time of hand over:

Time incident reported:

Site address:

Earliest recommended time of movement:

Person to whom site handed over:

Name of Fire Incident Commander:

Important Note

There has been a fire on the above mentioned site Name of Person Signing This Form: involving acetylene cylinders. Once acetylene has been (i.e. Person to Whom Site Handed Over) heated, it becomes extremely unpredictable and may explode. Manufacturers' guidance states that although an acetylene cylinder may appear to be cool after 24 hours Name of Organisation Represented (if applicable): of it being heated, this does not mean that the cylinder is safe.

Position in Organisation Represented (if applicable): You are advised, therefore, that any cylinder that has been exposed to heat should not be touched, used or moved for a minimum of 24 hours from Relationship to Site:

commencement of the cooling period stated above. e.g. Owner, Occupier, Managing Agent etc

It is your responsibility to ensure that the above guidance is complied with. I have read the above and I understand that I am

responsible for safety at the site. I will deal with any If you have any doubts or concerns, please contact the acetylene cylinder(s) in accordance with the guidance Fire Brigade immediately on above.

[enter contact number] Signed:

or 999, so that they can advise and, if necessary, return to the site to assist further.

Dated and Time:


APPENDIX 5 Considerations for Incident Commander (Acetylene cylinders heated or involved in fire)

Considerations for Incident Commander

Actions on arrival Siting of appliances

Gather information to determine likelihood of acetylene cylinders being involved and heated

Assess potential risk in order to determine operational actions

Operation of pressure release devices

Determine 200m hazard zone

Consider shielding

Establish Inner Cordons

Consider evacuation

As the incident develops Appoint safety officers

If possible apply cooling water

Determine tactical mode, any firefighting should be undertaken from behind shielding

Use of ground monitors and/or lashed branches

Wetting test

If cylinder remains cool consider reducing hazard zone

Key Actions

ACTION

Identify initial 200m hazard zone

y Carry out Dynamic Risk Assessment within hazard zone

+ Establish Cordons

4 Apply Water?

40

40

Re-assess risk and consider reducing hazard zone/cordons

After 24 Hours hand over to occupier/cylinder owner or other agency

CONSIDER

Type of structure Topography

Public safety Firefighter safety Liaise with Police

Accessibility of cylinder Public safety Firefighter safety. Environmental impact Operational restraints

Cylinder remains wetted and is not leaking Shielding

Earlier handover if suitable, safe and secure arrangements can be maintained

Fire Brigade incident closed

Gas supplier to recover


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APPENDIX 6 Basic Risk Assessment

Operational Activity

Task Hazard/

Hazards dealing with incidents involving acetylene cylinder

Level Risk Control Measures Risk of Risk Groups

Firefighting Death from catastrophic High All failure of cylinder.

Projectile Hazards.

Secondary Projectiles. Thermal Radiation.

Asbestos. (Long term)

Structural damage. High All

Establishing Death from catastrophic High All

hazard zone. failure of cylinder. Projectile Hazards.

Secondary Projectiles. Asbestos.

Maintaining Assault on personnel. Med A the cordon.

Public injury.

Pre-planning.

lid information.

Intelligence Gathering i.e. liaison with local authority planning depts etc.

Where information is not available assess premise likelihood of acetylene cylinders being present. Based on the nature of processes.

Development Programme to identify correct procedures to be followed during incidences of structural damage

Signs and Symptoms.

Safe Areas.

Vehicle Marshalling.

Maintain hazard Zone.

Evaluation of projectile travel distance

PPE.

Shielding.

BA.

Confrontation Management.

Police Attendance.

Public Campaigns led by local authority.

Med B, C Insufficient resources to undertake a

safe and expedient evacuation.

Provide information to public.

Use of premise owners building to act as shielding in instances of potential explosions e.g. Move occupiers to a safer part of building with sufficient distance between incident and them.


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Operational Activity Hazards dealing with incidents involving acetylene cylinder

Task Hazard/Risk

Applying Death from catastrophic cooling failure of cylinder. water.

Environmental damage.

Level Risk Control Measures of Risk Groups

High All Time.

Distance.

Shielding.

Med None Prohibit water run off from entering watercourse.

Develop environmental impact assessment programme.

Closing the Breakdown In Med B, C Establish clear lines of communication incident. Communications. with all relevant agencies, within the

area of responsibility e.g. railway companies, local government etc.

Risk Groups

A Firefighters

B Non-Service

C Public


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APPENDIX 7 Glossary of Terms

Term

Catastrophic failure

Decompose

Hazard Zone

IC

Inner Cordon

Manifolded Cylinder Pallets or Packs (MCP)

Shielding

Wetting Test

Meaning

Where a cylinder explodes and either splits open or becomes a projectile.

Separate into its constituent elements, with the release of heat/energy.

An area that contains a hazard to which a risk assessment should be applied in order to determine a suitable inner cordon.

Fire Incident Commander.

Area surrounding the immediate scene (hazard zone) and providing security for it. This may reduce as safety factors increase viz. Passage of time, water cooling of cylinders, etc.

A group of cylinders joined by common pipework.

Shielding walls, vehicles, rolling stock or earthbanks will provide a level of shielding. Shielding may allow a reduction in the cordon taking account of the explosive potential of a cylinder. For example a single skin brick wall will allow a reduction of the cordon, but should not be used as close proximity shielding for firefighters.

1 Application and subsequent interruption of water to a cylinder that is not being actively cooled by spray jet/s,

or,

2 The interruption of cooling water being applied to a cylinder.

In either case, once cooling water has been interrupted, the cylinder should be observed. If the cylinder remains wetted over its entire surface, it can be concluded that any internal heating is not affecting the cylinder shell. Conversely, if cooling water immediately evaporates or steams on the cylinder shell, heating may still be evident and cooling should be recommenced with safety cordons being maintained.



Acknowledgements

HM Fire Service Inspectorate is indebted to all who helped with the provision of information and expertise to assist the production of this Manual, in particular:

Greater Manchester Fire Service

British Compressed Gases Association

Health and Safety Executive

Health and Safety Laboratories

Fire Research Division, ODPM

Association of Chief Police Officers

Chief and Assistant Chief Fire Officers Association

HM Fire Service Inspectorate (Scotland)

Fire Service College

European Industrial Gases Association

London Fire Brigade

Fire Brigades Union

Swedish Rescue Services Agency

BOC

Linde Gas UK Ltd


Fire Service Manual

Volume 2



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HM Fire Service Inspectorate


Fire Service Manual

Volume 2 Fire Service Operations


HM Fire Service Inspectorate Publications Section

London: TSO

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f Published byTSO (The Stationery Office) and available from:

Online www.tso.co.uk/bookshop

Mail,Telephone, Fax & E-mail TSO

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Published with the permission of the Office of the Deputy Prime Minister on behalf of the Controller of Her Majesty's Stationery Office

© Crown Copyright 2003

Copyright in the typographical arrangement and design rests with the Crown.

This publication, excluding the Royal Arms and any logos, may be reproduced free of charge in

any format or medium for research, private study or for internal circulation within an organisation. This is subject to it being reproduced accurately and not used in a misleading context.The material must be acknowledged as Crown copyright and the title of the publication specified.

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Applications for reproduction should be made in writing to HMSO,The Licensing Division, St Clements House, 2-16 Colegate, Norwich, NR3 1 BQ Fax: 01603 723000 or e-mail: [email protected]

ISBN 0 11 341226 6

Cover and part-title photographs: North Wales Fire Service (Acetylene Cylinder Incidents)

Transco (Natural Gas Incidents)

Printed in the United Kingdom for The Stationery Office ID147968 8/03 C40 5673

vii


Preface

This section replaces chapter 2 of the Manual of Firemanship part 6b. It contains new material written to reflect the enormous changes which have taken place in the gas industry since 1967 when the first natural gas was piped ashore from the North Sea to mainland Britain. In the inter- vening years the demand for gas has increased many times and many power stations now use it in huge quantities as the fuel for the generation of electricity.

The transmission of gas by the National Transmis- sion System and, at lower pressure, by the Local Transmission System is a largely unseen technical and engineering achievement.

One end of the gas distribution system (beach). (Photograph: Transco)

By definition, fuels are of particular interest to the firefighter and careful study of this Manual will provide a sound theoretical knowledge of the subject and a base from which safe and effective operational techniques can be developed.

For the purpose of this book Natural Gas is defined as:

"a flammable gas consisting mainly of methane found in the earth's crust"

It excludes liquefied petroleum gases which has been covered in Fire Service Manual Volume 2 Fire Service Operations - Petrochemical Incidents.

The other end oJ'the gas distribution system (burner). (Photograph: G. Cooper)

Natural Gas Incidents 111

The guidance provided in this Manual represents a knowledge resource intended to support the development of people in accordance with the Emergency Fire Service role maps and the ODPM development modules. This will support and inform the Fire Service in:

1 Applying practices to maximise the health, safety and welfare of personnel and others in the built or natural environment.

2 Making and applying decisions based on the assessment of risk.

3 Making best use of sources and availability of information during natural gas incidents.

4 Applying Fire Service or other legislation.

This document is knowledge based and offers guidance on methods employed to deal with incidents involving natural gas while reflecting issues concerning the selection, use, capabilities and limitations of personal and operational equipment.

The relevant units of the role maps are:

027 INCIDENT COMMAND 2 048 ENVIRONMENTAL RISKS AND

CONTROL 057 DEALING WITH TRANSPORT

INCIDENTS 058 DEALING WITH FIRE INCIDENTS 059 DEALING WITH HAZMAT

INCIDENTS 076 ANALYSE TRAINING NEEDS 077 DESIGN CONTENT AND

DELIVERY OF TRAINING AND DELIVERY PROGRAMMES

079 DESIGN AND DEVELOP MATERIALS AND LEARNING AIDS

080 PRODUCE MATERIALS AND LEARNING AIDS FOR TRAINING AND DEVELOPMENT

086 INVESTIGATE THE SCENE OF FIRE OR EXPLOSION

Further reading

1 Fire Service Manual - Volume I - FF 3: SAVE AND PRESERVE

ENDANGERED LIFE Fire Service Technology, Equipment and Media - Physics and Chemistry for

FF 4: RESOLVE OPERATIONAL INCIDENTS

Firefighters.

FF5: PROTECT THE ENVIRONMENT FROM THE EFFECTS OF HAZARDOUS MATERIALS

2 Fire Service Manual - Volume 2 - Fire Service Operations - Incident Command.

CM 2:

SM 5:

Lead and support people to resolve operational incidents

Provide information to support decision

3 Fire Service Manual - Volume 2 - Fire Service Operations - Petrochemical Incidents.

making 4 Dynamic management of risk at

SM 8: Determine solutions to minimise hazards and risks identified by

operational incidents. A Fire Service guide

inspections and investigations to inform future practice

ISBN 0-11-341221-5.

SM 13: Lead, monitor and support people to resolve operational incidents

The relevant development modules drawn from the ODPM database are:

006 HEALTH, SAFETY AND RISK MANAGEMENT

008 INCIDENT COMMAND 1- INITIAL RESPONSE AND MANAGEMENT

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Contents

Page

Preface

Chapter 1 "From beach to burner" 1.1 Introduction 1.2 Gas Processing Facility 1.2.1 General 1.2.2 Firefighting on site 1.3 Reception Centres 1.3.1 General 1.3.2 Firefighting on site 1.4 Natural gas - its properties (and some comparisons) 1.4.1 Pseudonyms 1.4.2 Placarding for bulk transport

Chapter 2 The National Transmission System (NTS) 2.1 Transport and storage of gas 2.2 Transmisssion Network 2.3 Gas Compressor Stations 2.4 Distribution 2.5 Storage of Natural Gas 2.5.1 Demand for Natural Gas 2.5.2 Gas storage methods 2.6 Liquefied Natural Gas properties 2.6.1 Firefighting 2.7 High Pressure Storage Vessels (HPSVs) 2.8 Odorisation of Fuel Gases 2.8.1 General 2.8.2 Tertiary Butyl Mercaptan (TBM) 2.8.3 Operational Information

Chapter 3 Domestic Gas Supplies 3.1 General 3.1.1 Conection to the gas main 3.1.2 The Meter Box 3.2 Gas Escapes 3.2.1 General 3.2.2 Escapes of gas in buildings 3.3 Gas Detection Instruments (Explosimeters) 3.3.1 General

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3.4 Gas Escapes in open air 3.4.1 General 3.4.2

3.4.3

3.4.4

3.4.5

Action by the Fire Service Meteorological Forecasts Aides-Memoires Dealing with gas escapes which are burning

Chapter 4 Cylinders of compressed gas

18

18

19

19

19

20

3

4.1 General 23 4.1.1 Cylinders of Compressed Natura Gas (CNG) 23

4.1.2 Dealing with fire 24 4.2 Direct or indirect heating of cylinders of CNG 24 4.2.1 General 24 4.2.2 Failure of CNG cylinders (RIDDOR) 24

Chapter 5 Landfill sites and spoil tips 27

5.1 General 27 5.2 Fires in rubbish tips 29

Chapter 6 Natural gas and the generation of electricity 31

6.1 General 31

6.1.1 A typical CCGT station 31

6.1.2 Alternative fuel supplies 31

6.1.3 Firefighting on CCGT sites 32 6.1.4 Combined Heat and Power plants (CHP) 32 6.1.5 Small Scale CHP systems 33 6.1.6 Operational considerations 33

Chapter 7 Natural gas as a fuel for vehicles 35

7.1 Introduction 35 7.2 Fuel storage on Natural Gas Vehicles (NGVs) 35 7.2.1 Cylinders of CNG 35 7.2.2 Tanks of CNG 36 7.2.3 Refuelling CNG vehicles 37 7.2.4 Fire involving CNG refuelling facilities 37 7.3 Incidents involving Natural Gas Powered Vehicles (NGVs) 38 7.3.1 General information 38 7.3.2 Action at incidents 40

Appendices 43

1 Considerations for Incident Commander (Gas cylinders heated or involved in fire) 45

2 Basic Risk Assessment 46

3 Some significant dates in the development of gas as a fuel 48

4 Glossary of Terms 49

Acknowledgements 53

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Natural Gas Incidents Chapter

1 Chapter 1

1.1 Introduction

`From beach to burner'

Natural gas from the North Sea was first brought ashore in commercial quantities in 1967 and with it a revolution in the gas industry began. The chemical composition of the `new' gas which is predominantly methane (CH4) is totally different from the `old' town gas which was largely manufactured from coal and consisted mainly, of carbon monoxide (CO). The burning characteristics of the two gases are totally different and prior to the nationwide changeover to natural gas all premises using gas had to be visited so that burners suitable for the new gas could be fitted to each gas appliance. It was a mammoth operation.

Town gas is no longer manufactured. It has been replaced by Natural Gas, a fossil fuel harvested from huge reserves found principally beneath the North Sea from where it is collected and piped ashore. Constant exploration and improving rates of recovery from the reserves mean that the supply of gas from the North Sea will continue for the foreseeable future.

1.2 Gas Processing Facility

1.2.1 General

Gas from the many offshore gas fields and oil- fields is treated at one of seven gas processing facilities. On the east coast they are at St Fergus (N.E. Scotland), Teeside, Easington (E. Yorkshire), Theddlethorpe (Lincolnshire) and Bacton (Norfolk). On the west coast gas is processed at Barrow (Cumbria) and Burton Point (Cheshire). Each facility covers an area of hundreds of hectares and is often adjacent to similar sites operated by other gas producers.

The gas processing facility is the site which "blends or purifies gas, removes from gas any of its constituent gases or separates from gas any oil or water".

The product received from the gas production facilities (usually offshore platforms), vary widely in their chemical composition, even between sam- ples taken from adjacent fields, and the treatment it receives reflects this.

The following serves as an example of the product received at one gas processing facility and the treatment it receives. There will be variations between this and the other six sites.

1. NATURAL GAS AS RECEIVED %

METHANE 94.6 ETHANE 3.06 NITROGEN 1.14

PROPANE 0.49

HEXANE 0.26

others to 100%

Other components of the product as it is received are:

2. CONDENSATE consisting of %

OCTANES 12.45 BENZENE 10.66 HEPTANES 9.93 NONANES 9.50 HEXANES 7.59

DECANES 6.86

TOLUENE 6.62

METHYL CYCLOHEXANE 6.19 CYCLOHEXANE 3.73

n - BUTANE 3.10

n - PENTANE 3.04

(continued overleaf)

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PROPANE

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3. SEA WATER

4. MONO ETHYLENE GLYCOL

(added at the gas production facility as an anti freeze to prevent ice forming in the pipeline).

On arrival at the gas processing facility the product passes through an array of pipework known as the "slugcatcher" where most of the liquids are recovered. A refrigeration process, sometimes using liquid propane as the refrigerant, then cools the product to temperatures as low as -43° C in an "inlet separator" to remove the final traces of condensate, sea water and glycol.

The glycol is piped back to the offshore installation for re-use. The condensate is piped a few miles inland to a rail terminal, where it is taken to an oil refinery for conversion into substances used by the chemical and plastic industries.

Naturally occurring low level radioactive materials can be found in the untreated gas and condensate but it is considered that these do not present a significant hazard.

Gas processing facilities do not normally store the gas they process, and after a final filter to remove traces of sand the gas is passed by pipeline to a BG Transco reception terminal.

1.2.2 Firefighting on site

All of the sites are subject to the Control of Major Accident Hazard Regulations (COMAH) and the COMAH Safety Report will outline the processing undertaken on site and list the hazardous substances held on site. The greatest risk is generally considered to be an accidental release of flammable gas to atmosphere but it is for each brigade with a gas processing facility on their ground to make individual risk assessments and to establish

close links with the management. The value of l(l)(d) visits and exercises cannot be overempha- sised.

Emergency plans held at COMAH sites are com- prehensive and will of course vary between sites, but water/foam monitors, deluge systems and high flow hydrants will almost always be found as will a works fire brigade. Gas detection equipment, both portable and fixed will provide early warning of leaks and emergency shutdown (ESD) valves are provided to isolate plant. In extreme circumstances it will often be possible for the gas content of the plant to be vented to open air, but such dras- tic action cannot be undertaken lightly or rapidly.

Advice about the control of fire water run off from COMAH sites to prevent environmental damage is

contained in HSE guidance note EH 70 published in 1995. Many of the control methods suggested in the note will be found at these gas processing facilities and these include bunds, lagoons, catch-pits and drain covers.

1.3 Reception Centres

1.3.1 General

Seven Transco Reception Terminals take gas from their nearby gas processing facilities and prepare it for release into the National Transmission System (NTS) and its journey through the network of pipes to the end user. On arrival at the terminal the gas is

filtered, analysed and its volume measured. Particular attention is paid to its calorific value and should this be below 39 Mega Joules/metre3 (MJm3) the gas is blended with a richer supply until the required calorific value is obtained.

The plant, on sites which can cover 80 hectares, is controlled from a central control room and although gas is not stored on site, the quantity of gas within the pipework at any time is sufficient to require compliance with the COMAH regulations.

1.3.2 Firefighting on site

As with any complicated industrial or chemical plant, safe and successful firefighting can only be undertaken with the assistance and guidance of technical staff from the plant. Fire brigades with


Figure 1.1

Part of a typical gas processing facility. (Photograph: Transco)

Figure 1.2

A typical reception centre. (Photograph: Transco)

Reception Terminals on their ground will need to chemical compositions of natural gas can vary. establish sound relationships with management Despite these differences the physical performance and conduct regular 1(1)(d) visits and exercises. of natural gas supplied to the customer conforms

to a uniformly high standard. 1.4 Natural gas - its properties (and

some comparisons)

Because of the differences in product supplied for processing from the many gas and oil fields the


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Typically natural gas supplied to the consumer will consist of:

METHANE CH4 92.37

ETHANE C2 H6 3.25

NITROGEN N2 2.60

PROPANE C3H8 0.87

CARBON DIOXIDE CO2 0.40

BUTANES C4H10 0.24 PENTANE C5H12 0.22

VAPOUR DENSITY (air = 1.)

HYDROGEN 0.07 NATURAL GAS 0.55 CARBON MONOXIDE 0.97

PROPANE (LPG) 1.5

FLAMMABLE LIMITS %(by volume in air)

HYDROGEN 4.0 - 75

NATURAL GAS 3.8 - 15

CARBON MONOXIDE 12.5 - 75

PROPANE (LPG) 2.2 - 10

SPONTANEOUS IGNITION TEMPERATURE °C

HYDROGEN

NATURAL GAS

CARBON MONOXIDE PROPANE (LPG)

580 480 - 650

570 466

TOXICITY

HYDROGEN

NATURAL GAS CARBON MONOXIDE

PROPANE (LPG)

Non-toxic Asphyxiant Virtually non-toxic Toxic

Toxic

1.4.1 Pseudonyms

Methane, the principal constituent of natural gas, is also known as:

MARSH GAS

METHYL HYDRIDE

FIRE DAMP

European names for Natural Gas and Methane

Language NATURAL GAS METHANE

Dutch (NL) AARDGAS METHAAN French (F) Le GAZ NATUREL le METHANE

German (D) ERDGAS METHAN

Spanish (E) GAS NATURAL METANO

Italian (I) GAS NATURALE METANO

Danish (DK) YORD GAS METHAN

1.4.2 Placarding for bulk transport

Figure 1.3 Hazard Warning plate. UK Hazard Information System (UKHIS) for compressed Natural Gas or compressed Methane gas.

23 1971

Figure 1.4 ADR system for compressed Natural Gas or compressed Methane gas.


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2 Chapter 2 - The National Transmission System (NTS)

2.1 Transport and storage of gas

The Public Gas Transporter (PGT), Transco operates a nation-wide gas distribution network consisting of about 271,000kms of iron, steel and polyethylene pipes almost all of which are laid underground. Other companies are expected to build networks in the future to enable them to be licensed as a PGT.

The stations can be remotely or locally operated, and are often unattended. Sophisticated security systems, both passive and active, are installed to protect the sites which often cover an area of about one hundred hectare

Unless life is known to be at risk, operational crews are advised not to enter the site without the assistance of TRANSCO staff

2.2 Transmission Network

About 6,000km of the Transco network operates at pressures of up to 85 bar and it is this part which is known as the National Transmission System (NTS). Made from high quality steel, constructed and laid to very high standards the pipes can be up to 1.2m in diameter. Pressure changes within the system are closely monitored so that an accurate assessment of the pipe's fatigue life can be made. More than 120 offtake installations take the NTS supply directly to very large users of gas such as power stations and industrial consumers as well as to the Local Distribution Zones (LDZ) transmission systems, which continue the distribution network.

The entire NTS is monitored and controlled from a central operations room and in an emergency more than four hundred remotely operated valves can be actuated to isolate any section of the network.

2.3 Gas Compressor Stations

Gas within the NTS can travel at speeds of 40 kph and to maintain flow, particularly at times of high demand, pressure can be boosted by any of the twenty two compressor stations strategically sited on the system.

Outside normal working hours, Transco staff are on standby rota and can normally attend a site within thirty minutes

Each compressor is driven by an industrialised jet engine and together they are housed as an inde- pendent unit. When the engines are running they are, externally, deceptively quiet, but inside the building, despite the use of double skinned acoustic insulation, noise levels can exceed 120 decibels. In the unlikely event of firecrews being requested to enter the building when the turbine and compressor are running, ear protection must be used. Normally, in the event of an incident in the building and the operation of the automatic fire detection/suppression system, the engine will be stopped, gas supply isolated, and the plant ventilated. Fuel for the engines is taken from the NTS.

Although incidents requiring the attendance of the Fire Brigade are rare, the value of well conducted 1(1)(d) inspections will be obvious. Particular points of interest for the visit will include:

location and approach to site and PDA entry to site (Contact telephone numbers) rendezvous points control points and centres liaison with staff on-site response


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water supplies (Surrounding risks) venting stack fixed installations

The station's staff usually work weekday shifts and an appointment to visit the site should be made with the Transmission Operations Manager at the station.

Fire protection of the jet engine and its associated equipment is provided by a high pressure water fog/nitrogen cylinder system. Sensors which can detect a range of physical conditions within the engine house actuate the system.

Unlike many AFD systems which require two or more sensors to detect a fire situation before the extinguishing medium is released, this system will actuate on the operation of a single detector head.

2.4 Distribution

After re-pressurisation at the compressor station the gas re-enters the NTS and continues it journey. From the high pressures of the NTS, the gas passes via pressure reducers, (known in the industry as governors), to the Local Transmission System (LTS) of the Local Distribution Zones (LDZ).

The maximum gas pressure within the LTS is 42 bar and within the LDZs gas pressure is reduced to suit operational and consumer demands until it reaches domestic users at a pressure of 75 mbar (max).

NTS 85 bar

(max)

- -*-a- LTS 42 bar (max)

LTS HIGH PRESSURE

INTERMEDIATE

PRESSURE

MEDIUM

PRESSURE

LOW PRESSURE

42 bar - 7 bar

7 bar - 2 bar

2 - 75mbar

75mbar max

The LDZ must be regarded as the source of authoritative advice for action within their zone

Pipelines must not be shut down without the approval and/or assistance of LDZ personnel

Since about 1980 most gas pipelines in the low, medium and intermediate pressure stages have been laid using the familiar yellow polyethylene pipe but many kilometres of steel and ductile iron remains, some in service, some abandoned. A feature of the local distribution system are the numerous valves, which are fitted to isolate or divert gas supply. These are usually manually operated but it is sometimes possible for parts of the system to be remotely isolated at their offtake from the NTS. Such isolation is a lengthy process.

2.5 Storage of Natural Gas

2.5.1 Demand for Natural Gas

Demand for natural gas varies widely both season- ally and during a twenty four hour period. Figure 2.2 indicates the seasonal period.

2.5.2 Gas storage methods

Because it is not possible to rapidly increase the production of gas from offshore production facilities to cope with these wide variations, gas is stored at sites throughout the country ready to be injected into the supply network at times of high demand.

The methods of storage include:

(a) Line Pack (using the NTS as a storage resource) The capacity of the NTS and LTS varies in direct proportion to its pressure and high demand causes its pressure and hence its capacity to drop. Opportunity is taken at times of lower demand following a peak to "pack" gas into the network. As the pressure rises within the network so does the volume of gas stored within it.


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winter summer

iiiiI!1P1P!iiii Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Annual patterns of gas demand

Typical capacity 225,000m3 ft 75m bar

Figure 2.3 Waterless seal, used by non-telescopic gas holders.

(b) Low Pressure Gas Holders There are about five hundred of these large familiar structures throughout the country the vast majority being of the "water seal"

Figure 2.1 (left) Annual pattern of gas demand (Graph courtesy ofTransco)

Figure 2.2 (below) Daily pattern of gas demand (Graph courtesy ofTransco)

A

Telescopic section (Lift) Rises and falls with contents

Roller guide \ I I `* / The largest

freeze The smallest mixture. 1500 m3

anti-

gas holder contains (when full)

Water/ -. 15m bar. , 280,000 m3

Note different levels

Figure 2.4 Water seal, used by telescopic gas holders.

type. Together they hold about 27.5 million m3 of gas and, despite in some cases being about one hundred years old, they remain vital to the distribution network at times of


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a rigid, non-telescopic structure. A piston acting as a false roof and supported by gas pressure separates the gas from the air in the upper, empty, part of the gasholder. The piston rises and falls as the amount of gas being stored varies. A gas tight seal is

maintained between the circumference of the piston and the sides of the gasholder by a tar and rubbing plate. Figure 2.3 shows the most commonly used type of seal.

Figure 2.5 The less common, rigid, waterless seal type of gas holder. (Photograph: Transco)

high demand. The largest gasholder is in Glasgow and it holds enough gas to supply 40,000 houses for a day.

When the holder is empty its telescopic sections known as "lifts" sit inside each other and as gas is introduced at very low pressure (about 75 mbar) the lifts rise in sequence the inner-most first. When all the lifts are fully exposed the gasholder is full.

Gas is prevented from escaping from the overlap of the lift sections by use of a water cup seal at the circumference of the lift. See Figure 2.4.

The pressure inside the gasholder is in the region of 75 mbar and most gas-holders have been fitted with equipment to boost the pressure of the gas as it leaves the holder.

A less commonly found type of gasholder uses a waterless seal to contain gas within

(c) Salt caverns Two sites, Seal Sands, Teeside and Hornsea, East Yorkshire store gas about 1,800m below ground in caverns which were left following the extraction of salt.

Hornsea, with a huge capacity of over 322.4 million m3 of gas is by far the larger site and when full holds about 9% of the total stored gas capacity available to the NTS. (See Figure 2.7.)

Seal Sands, with a storage capacity of 1.83 million m3 is used only to supplement gas supplies to the Teeside area.

(d) Gas field storage A depleted gas field 29 km off the Humberside coast has been extensively developed to hold 82 per cent of the UK's stored gas. When full the Rough Field site holds 2.8 billion m3 of gas, which can be supplied to the NTS at up to 42 million m3

a day. This is the equivalent of 10% of the national demand on the coldest winter day. (See Figure 2.8.)

(e) Liquid Natural Gas (LNG) storage When liquefied, natural gas occupies only 1/630th of the volume it requires in the gaseous state at standard conditions of temperature and pressure (15° C/ 1013 mbar).

Liquefaction of the gas is therefore an extremely effective method of storing and transporting the maximum amount of the substance in the least possible volume.


Aberdeen

Kirriemuir

Glenmavis

Moffat

Transco LDZs

Scotland North and Yorkshire North West East of England

West Midlands

Wales and South West North London

fl South of England

Avonmouth

Hatton

Peterboro

Huntingdon

A Terminals

Compressor Stations

o Regulators

in LNG Storage sites

Aylesbury

kertey

Kings Lynn

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Figure 2.6 Map of 'TRANSCO Local Distribution Zones (LDZs) and network. (Map courtesy (?/fTRANSCO)

For ALL gas emergencies, call National Gas Emergency number 0800 111 999

Carnforth

Administrative matters are dealt with by regional networks. For more information, see Transco website: www.transco.uk.coin

Scunthorpe

Partington


Figure 2.7 Above ground, Hornsea. (Photograph: Transco)

Figure 2.8 Rough Field off the Humberside coast. (Photograph: Transco)


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Five storage sites (Glenmarvis, Portington, Avonmouth, Dynevar Arms and the Isle of Grain) take gas from the NTS, liquefy it and stored it at -162°C in huge tanks each with a capacity of 21,000 tonnes.

Despite a thermal insulation barrier 5m thick, external ambient temperature and pressure change cause "boil off" of the liquid and this is recycled back into the local transmission system.

One full tank of LNG contains the equivalent of 25 million m3 of gas and seven such tanks could supply enough gas to sustain the entire country for one day.

2.6 Liquefied Natural Gas properties

Liquefied Natural Gas

Uses

(i) Fuel

(ii) Feed-stock in the manufacture of METHANOL,

ACETYLENE, HYDROGEN

Hazards Vaporises rapidly to form a highly flammable gas. Initially whilst still cold will collect at ground level until

atmospheric warming allows it to rise.

Risk of frostbite Considered non toxic but asphyxient as it displaces air.

Physical Appearance Water white clear liquid

Odour None

Auto Ignition Temperature Between 482°C - 650°C

(Varies depending on exact composition)

Flammable Limits Lower 3.8 - 6. 5% in Air Upper 13 - 17% in Air (Varies depending on exact composition)

Volume Increase Liquid - Vapour 630 x volumes

(e.g. 1 litre of liquid natural gas released in air could produce approximately 16,500 litres flammable/ explosive mixture)

Figure 2.9 Isle of Grain (Photograph: Transco)

Specific Gravity of Liquid (Water = 1)

0.42

Vapour Density (Air = 1)

0.55 at 15°C

Chemical Reactions Will react explosively at room temperature with chlorine and bromine May explode on contact with chlorine trifluoride

2.6.1 Firefighting

Liquefied Natural Gas leaking from a container or pipe work presents a challenge to the firefighter. Its density will vary as it gains heat and vaporises, from a liquid a little less than half the weight of water to a gas much lighter than air.

This, together with its wide explosive range, will create a situation where contact with any source of ignition will result in the instant ignition of the entire gas cloud. As it burns it will release about twice as much heat as a similar amount of petrol.

Firefighting and control techniques employed must be compatible with the properties of liquefied natural gas and reflect the very high risks a leak or fire will present to firefighters attending the incident.

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Figure 2.10 High Pressure Storage vessels used to store gas ready for instant release into the distribution network at times of high demand. The frame of an empty low-pressure gas holder is in the background. (Photograph: G. Coope,)

Detailed guidance on dealing with LNG incidents can be found in Fire Service Manual, Volume 2, "Petro-Chemical Incidents" Chapter 7 - Liquefied Natural Gas.

2.8 Odorisation of Fuel Gases

2.8.1 General

2.7 High Pressure Storage Vessels (HPSVs)

Often known colloquially as "bullets", HPSVs take gas from the NTS or the LTS at times of low demand and store it ready for release into the LTS at time of high demand. Charging and discharging is remotely controlled from the Regional Control Centre.

Typically a storage site will consist of up to six HPSV(s) mounted horizontally on concrete piers. Each cylinder measures about 70m long and 3.7m in diameter and when fully charged to 42 bar the six will contain a total of 175,000 m3

of gas.

There are many such sites around the country and although all are securely fenced many will be unattended much of the time. Fixed firefighting equipment is not normally provided.

All commonly used fuel gases (natural gas, butane and propane) are flammable and in most cases explosive in air at concentrations below the normal combustion level at which they are used.

Additionally, as they displace the air in the space they are entering, they create an increasingly asphxiant atmosphere.

Because naturally they have little or no smell, these hazards can be insidious and to minimise the risk of gas escapes, remaining undetected fuel gases are given a distinctive smell.

The odorant used to impart a smell to natural gas is TERTIARY BUTYL MERCAPTAN (TBM) and this gives the distinctive sulphur smell, which has been associated with gas since the days it was produced from coal. This smell is used internationally to "mark" fuel gases although it may be derived outside the UK from substances other than TBM.


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TBM is added to the gas in sufficient amounts to ensure the gas is detectable by an "average nose" when it is at 20% of its lower explosive limit.

In its pure, undiluted form it is very smelly, sufficiently so to make most people vomit if it is inhaled!

2.8.2 Tertiary Butyl Mercaptan (TBM)

Fact File

Tertiary Butyl Mercaptan (TBM)

In Bulk Form A colourless to pale yellow liquid with a strong unpleasant odour.

Hazards Highly flammable liquid

Flash Pt -31°C Boiling Pt 55 °C

Auto ign temp 247 °C

Decomposes at 450 °C

Vapour density 2.0 Insoluble in water

UN No 1993 ADR/RID Class 3

Firefighting EAC 3WE

Hazard identification 33 Wear BA: use foam, dry powder or CO2 to extinguish fire

DO NOT USE WATER

Water spray can be used to cool containers

First Aid

Wash skin Remove contaminated clothing with soap and water In case of inhalation, remove from exposure; keep warm; rest Irrigate thoroughly if TBM enters eyes. If discomfort persists, seek medical advice If ingested, seek medical advice

Until recently all gas was odorised before it entered the NTS but the introduction of the Gas Safety Management Regulations (GS(M)R) has allowed it to be unodorised when in a pipeline

Figure 2.11 Hazard Warning plate. UK Hazard Information System (UKHIS) for Tertiary Butyl Mercaptan (TBM).

33 1993

Figure 2.12 ADR system. Tertiary Butyl Mercaptan (TBM).

operating at a pressure of 7 bar or more. This will significantly reduce sulphur emissions from gas- fired power stations and other large industrial users.

Additionally, at chemical works where the gas is used as a feedstock, it will no longer be necessary to remove the sulphur smell prior to its use.

2.8.3 Operational Information

GAS AT PRESSURES BELOW 7 BAR WILL HAVE A DISTINCTIVE AND CHARACTERISTIC ODOUR.

GAS IN PIPELINES ABOVE 7 BAR WILL NOT BE ODORISED.

TBM is stored in bunded tanks of up to 22,000 litres capacity and is injected into the gas network by pumps controlled by sophisticated telemetry. Standards of containment and engineering are high,


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but in the event of a spill, all sources of ignition should be removed and the area evacuated. If the spill is not contained within the bund, use sand or earth to contain it.

USE CHEMICAL PROTECTIVE CLOTHING AND BA.

If contained within the bund, the liquid should be pumped into a closed container if this is possible. If not, use an absorbent material to collect the spilt liquid and place into a sealable container.

Odorant smell can be destroyed by incineration or by diluting with a solution of hydrogen peroxide or sodium hypochlorite in water containing a detergent.

It is important to remember:

THE ABSENCE OF A `GASSY' SMELL DOES NOT NECESSARILY INDICATE THE ABSENCE OF GAS

The leak may be from the National Transmission System, (up to 85 bar) or the High Pressure System of the LTS which operates at pressures above 7 bar.

The odour given to gas is intended to be distinctive, but despite this, it can be confused with other smells amongst which may be smells from animal product works, landfill sites, rotting vegetables, farm slurry, newly creosoted wood, vapour from liquid fuels, vent pipes from sewers, hydrocarbon product pipelines etc.

The odour threshold for TBM is 1 part per billion.


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3 Chapter 3

3.1 General

Domestic Gas Supplies

3.1.1 Connection to the gas main

Domestic property is generally supplied with gas from a service main laid underground outside the property. It is preferred, where possible, to lay the service main beneath the footpath and a simple `T' junction takes the gas pipe underground to each individual property where it surfaces, usually to a meter box. Increasingly these are being fitted externally.

3.1.2 The Meter Box

Immediately inside the box, (which is provided with a door, lockable with a standard triangular key), is the emergency control valve together with its operating lever (see Figure 3.1(a)). The normal operating position of the lever (i.e. gas is being supplied to appliances within the building) is when it is in line with the supply pipe.

TO STOP THE FLOW OF GAS, MOVE THE LEVER SO THAT IT IS AT RIGHT ANGLES TO THE PIPE

If the lever is missing, hand tools (pliers, a spanner or a wrench) can be used to move the square head to the valve which the lever is normally fitted to. A line is cast or engraved across this valve and the valve is closed when the line is across the pipe. If it is in line with the pipe gas will flow.

When the emergency control valve is in its open position, gas flows through the valve via a flexible steel pipe to a filter/governor and into the meter where its volume is measured. The filter cleans the incoming gas and the governor maintains it at a constant pre-set pressure, matched to the require- ments of the appliances within the property. After

metering, the gas supply system becomes the responsibility of the owner/occupier of the property. (See Figure 3.1.)

In some older installations the inlet is connected to the meter by a lead pipe secured by wiped joints. In a fire situation the lead may melt and allow gas to escape.

3.2 Gas Escapes

3.2.1 General

Regulation 7(1) of the Gas Safety (Management) Regulations 1996 (GS(M)R) requires British Gas plc (BG) to provide a continuously manned telephone service (contactable within the UK by the use of one telephone number) to enable people to report an escape of gas from a network or from a gas fitting supplied with gas from the network. The regulation includes as an "escape of gas" the actual or suspected emission of carbon monoxide from gas appliances and a fire or explosion where gas is suspected to have been involved.

The GS(M)R also requires the gas transporter/ emergency service provider to attend the emergency. "with competent operatives with sufficient knowledge, appropriate for all foreseeable emergency situations".

TRANSCO RESPONDS TO ALL REPORTS OF A GAS ESCAPE. IT WILL REPAIR LEAKS IN THE SUPPLY PIPEWORK UP TO AND INCLUDING THE METER. IF THE LEAK IS BEYOND THE METER ON THE CUSTOMER'S SIDE IT WILL MAKE THE SITUATION SAFE.


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The standard advice given to the public about actions to take in the event of a gas leak is:

DON'T TURN ELECTRIC SWITCHES ON OR OFF

DON'T SMOKE

DO TURN OFF THE GAS SUPPLY AT THE METER

DO OPEN DOORS AND WINDOWS TO GET RID OF THE GAS

Gas flow into property

Start of customer's responsibility

End of public gas transporter's (PGT) responsibility

Handle in vertical (operating) position

Engraved or cast line in vertical (operating) position

Figure 3.1 Diagram of a typical gas meter and lockable cabinet.

Figure 3.1 (a) Gas meter and lockable cabinet in situ. (Photograph. Transco)

CALL NOW FOR AN EMERGENCY AT ANY TIME

CALL FREE 0800-111-999

MINICOM/TEXTPHONE PROVIDED FOR VERY DEAF AND HARD OF HEARING CUSTOMERS

0800-37-17-87


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Experience shows that the vast majority of calls reporting gas leaks are made to the BG telephone number. On the few occasions such calls are made to the fire service, it is usual for an attendance to be sent and for Brigade Control to pass the details of the call to the BG free phone number.

The priorities applied by the gas emergency service provider in all cases of dealing with a reported gas escape are:

(a) to safeguard life (b) to safeguard property

(c) to find and secure all gas escapes (d) to complete a final investigation before

leaving the site.

3.2.2 Escapes of gas in buildings

If the fire brigade is first to arrive on site, priority should be given to saving life and property. It is likely that actions to achieve this will fall into three categories (but not necessarily in this order).

(a) Evacuation if the occupier's safety is at risk if persons have been overcome by gas or products of combustion if gas concentration exceeds 20% LFL (assuming a gas detector is readily available).

Evacuation could involve more than one property and may extend to include a neighbourhood. Consideration will need to be given to the welfare of the evacuees, the involvement of the police and, possibly, the local authority.

(b) Isolation In most cases isolation of the gas supply to a domestic property will simply involve finding the meter and moving the emergency control valve lever to the closed (i.e. lever at right angles to the pipe) position. At other premises the means of isolation may not be so obvious and a `competent person'* may have to identify and isolate the source of supply.

*COMPETENT PERSON is defined as: "A person having sufficient knowledge, appropriate equipment, practical skills and experience to deal with all foreseeable emergency situations." Guide to GS(M)Regs 1996 para 44(b).

If it is remote from the gas-filled area, it may also be advisable to turn off the main electrical isolation switch of an evacuated or unoccupied building. This should not be done if it delays evacuation or if the concentration of gas above and below the switch exceeds 70% LFL.

Other potential ignition sources which need to be considered include:

electrical equipment (if the electricity has not been isolated) static electricity

sparks from tools, footwear torches etc. smoking materials battery operated equipment portable heating equipment (e.g. LPG powered) open fires/furnaces nearby vehicles

(c) Ventilation The object of ventilation is to reduce the percentage of gas within premises to an amount as far below the lower flammable limit (LFL) as possible. Obviously 0% is the aim. The lower flammable limit for commonly found fuel gases are:

Natural gas 3.8% butane gas 1.9% propane gas 2.2%

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Window and doors at all levels should be opened to encourage as much air movement as possible, and particular attention should be paid to the extremities of the building, the upper levels for natural gas (lighter than air), and the lower levels (including basements) for heavier than air gases such as butane and propane. Consideration should be given to the use of suitable air movement equipment (e.g. PPV fans) if this is available and can be safely positioned in clean air to achieve the desired effect.

3.3 Gas Detection Instruments (Explosimeters)

3.3.1 General

Most gas engineers will have immediate access to gas detection and monitoring equipment and, when


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correctly used, these will indicate the gas concentration as a percentage of gas in air or as a percentage of the LFL of the gas.

Many fire brigades have purchased such instruments and these are often held as "non mobile equipment" until specifically requested. Success- ful and safe use of the equipment requires skill and practice by the operator and the use of a detector suitable for the gas involved. Reference is sometimes made to "family" gases in connection with this equipment. The three families of gases are:

1st family 2nd family 3rd family

TOWN (coal) gas NATURAL gas LIQUEFIED PETROLEUM GAS (butane/propane)

The detection equipment must be either designated or specified, and if appropriate, calibrated for the type of gas, which is suspected to be involved. It is not safe to use an instrument intended to detect the gas of one "family" to measure a concentration of gas of another "family". Any instrument used should be within its specified service life and most types require re-calibration at fixed intervals to ensure accuracy.

The probe of the instrument should be positioned to sample the part of the compartment likely to have the highest concentration of the type of gas that is involved. For a lighter than air gas, this will be at high level, whilst for heavier than air gases this will be at floor or basement level. It should be remembered that ceilings and floors are not usually designed to be gas tight, and if there are voids behind them concentrations of gas may be found in

that void or compartment.

Physical senses, such as smell and hearing, should not be ignored but must never be relied upon to declare an area safe. If the gas is stenched the concentration of the odorant is calculated to allow it to be smelt at very low concentrations, but the smell can be destroyed by combustion or by diluted sodium hypochlorite. Many people have a poor sense of smell, sometimes unknowingly. Additionally, where gas is leaking from pipes at pressures above 7 bars it is unlikely to be odorised and clearly the use of gas detection equipment is essential if an accurate assessment of the situation is to be made.

Escaping gas can often be heard, particularly at pressures above the low and medium pressure ranges. In the intermediate and high pressure ranges, the noise generated by a gas escape will often be sufficient to require the use of ear defenders by crews working in the vicinity of the leak.

3.4 Escapes of gas in open air

3.4.1 General

In general pipelines fail because of:

breaks (usually caused by mechanical damage) leaks (often from joints and flanges) malicious damage

Failure of the pipeline and the subsequent gas escape can result in one or more of the following:

(i) blast (ii) debris scatter of material from the

immediate area of the leak (iii) noise which can be extreme even from

medium pressure lines (iv) fire (v) asphyxiation risk (vi) gas cloud

In the gas industry, it is the size of the break in the pipeline that determines the difference between a

"leak" and a "break". A break will be a failure, which is at least the same size as the diameter of the pipe. If smaller it is considered to be a leak. In the event of a break or large leak in the NTS pipeline or the intermediate and high-pressure pipes of the LTS, debris from the area of the leak may be scattered with considerable force over a wide area. Fortunately very high-pressure mains are usually laid in predominately rural areas and the likelihood of personal injury is considered to be remote.

Whilst leaks and breaks in low and medium pressure lines are unlikely to carry a risk from debris scatter, the risks of fire and asphyxiation remains.

Gas from an escape can travel in any direction usually following the path of least resistance. Whilst natural gas is much lighter than air and its


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preferred route is upwards, underground fissures, ducts, voids and cellars can provide a conduit for it

to travel some distance from the point of origin. Sewers, service tunnels and railway installations, although usually deeper than the gas distribution system, could also become affected by gas from a break or leak.

3.4.2 Action by the Fire Service

In carrying out a risk assessment, in addition to testing for an explosive atmosphere, which should always be carried out in such circumstances, if suitable equipment is available, the oxygen level should also be established.

Extreme caution should be exercised by fire service personnel who are required to enter underground shafts or ducts in the vicinity of a gas leak.

Breathing apparatus must be worn. Other than to save life there is unlikely to be sufficient reason to justify the entry of fire-fighting crews into gas filled/oxygen deficient situations.

UNDER NO CIRCUMSTANCES ATTEMPT TO IGNITE ESCAPING GAS, EVEN IN OPEN AIR

N.B. There may be occasions, subject to a suitable risk assessment being carried out, when a low pressure leak can be effectively stopped using gaffa tape and Environmental Agency Plug and Dyke equipment, as a temporary measure.

The low vapour density of natural gas will aid its dispersal into the atmosphere and the speed with which this will happen is dependent on many factors including air turbulence. This a factor not only of wind strength, but also the nature of the terrain over which the wind blows with features such as trees or buildings increasing what is known as the "roughness factor". It is at its lowest on level

grassy plains and increases as air flows through areas of trees and hedges until the roughness factor is at its peak in city centres.

Insolation (exposure to sun rays) or lack of rays at night must also be included in the equation, which can predict gas cloud densities and dispersal distances in a set of known circumstances. Very often a plan giving risk contours for the area around a gas processing facility is included in the site safety report of COMAH sites.

3.4.3 Meteorological Forecasts

An expert and localised weather forecast can be obtained from the Meteorological Office by request from a fire brigade using the CHEMET procedure. On receipt of a CHEMET pro forma (usually from Brigade Control) a weather forecast- er will provide an immediate verbal assessment of wind speed and direction and also an estimate of the likely plume dispersion characteristics.

This will be followed, usually within twenty minutes, by fax giving further information and a map of the "area at risk". Met Office forecasters are not qualified to comment on the behaviour of individual chemicals and their report will assume a neu- trally buoyant gas, although other qualified experts may use the information provided by the Met Office to supply a more specific report.

3.4.4 Aides-Memoires

Points to be considered.

EVACUATE THE AREA (consider the likely dispersal route of the escaping gas) LIAISE WITH POLICE Maintain close contact throughout incident. REQUEST ISOLATION OF THE SUPPLY (it may be that the sophisticated control systems of the higher pressure mains have detected the leak/break and that supply has already been isolated but do not assume this. REMOVE SOURCES OF IGNITION Stop passing traffic. Sterilise the area. CONSIDER THE USE OF WATER SPRAY In still conditions this may provide turbulence to help disperse the gas. It may


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also help to insulate the gas from sources of ignition. LARGE ESCAPES OF GAS FROM THE NTS OR HIGH PRESSURE MAINS GENERATE NOISE. Consider the use of ear defenders.

REMEMBER GAS LEAKING FROM THE NTS OR FROM HIGH PRESSURE MAINS WILL NOT SMELL Only gas piped at pressures below 7 bar (intermediate, medium and low pressure mains) is odorised

Transco pipelines carry gas in the following pressure ranges.

LOW PRESSURE

Up to 75 mbar (about the same pressure required

to inflate a child's balloon)

Failure consequences: gas escape (minor through to major).

Material Polyethylene

Steel

Cast/Ductile Iron

These materials and operating pressures constitute the majority of the distribution system and are generally located beneath footpaths and roadways within population centres

MEDIUM PRESSURE

75 mbar - 2 bar (about the same pressure required to inflate a car tyre)

Failure consequences: (i) minor debris scatter; and (ii) gas escape (major)


Steel

Cast/Ductile Iron

Located in both population centres and rural areas

INTERMEDIATE PRESSURE 2 - 7 bar (about the same pressure as a mobile compressor)


Steel

Ductile Iron

Failure consequences: (i) minor blast; (ii) minor debris scatter; and (iii) gas escape (major)

Located in some suburban areas. However, the majority

are in rural areas.

HIGH PRESSURE

(includes all NTS and parts of the LTS)

over 7 bar

Material Steel

Failure consequences: (i) major blast: (ii) debris scatter; and (iii) gas escape (major)

Located in rural areas.

Internal distribution in domestic properties is generally in steel or copper pipes.

3.4.5 Dealing with gas escapes which are burning

The priorities when attending incidents at which escaping gas is alight are:

to effect any rescues and/or evacuation; to isolate the leak from its supply of gas; and to protect the surrounding area from radiated heat whilst this is being done.

In some instances, especially where high capacity mains are involved, it may be necessary for the supply of gas to be stopped both upstream and downstream of the escape. This principle of extinguishing the fire by stopping the supply of fuel applies to all burning gas incidents (not just natural gas).

Never extinguish a burning gas escape

Protect the surrounding risk from radiated heat

Have the gas supply stopped

Allow the flame to self-extinguish


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Once the supply of gas is stopped the flame will become increasingly "lazy" as the pressure in the pipeline falls. In large diameter mains this will take time and cooling must continue until the pipeline is cool and the area has been declared gas free following a survey with gas detection equipment.

Many lessons about dealing with incidents involving escaping burning gas can be learnt from a study of the actions taken by the crews who responded to reports of an "explosion and fire" at a site containing many gas installations including three large gasholders.

Gas distribution engineers principally use maps to locate gas mains. Marker plates, about the size of a hydrant plate, are used but not extensively. For historical reasons, the colour of the plates can vary throughout the country.

Figure 3.3 Gas pipeline marker. The pole is to aid identification of the site from the air.

(Photograph G. Cooper)

Figure 3.2 Gas valve marker (Photograph G. Cooper)


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cc. A Case Study Burning gas holder

On arrival at the scene, the Officer in Charge parked his appliances a little distance from the fire-ground and conducted his reconnaissance on foot. It appeared to him that all three gas-holders were alight and he immediately requested a make- up of ten pumps and two aerial appliances.

Minutes later the centre of the three gas-holders suffered a catastrophic failure at roof level. An enormous fireball of gas/air mixture rolled upwards into the night sky as the entire contents instantly escaped. As it emptied, the gas-holder rapidly deflated (as it was designed to) until when in its empty, housed, position the fire burnt itself out. The switchboard in Brigade Control was inun- dated with over seven hundred calls and clearly, despite it being 0400 hours, the fireball had been seen by many people across a wide area.

About this time it was learnt that terrorist action was considered to be the likely cause of the incident. With the fire in the central holder

Noteworthy points which led to a successful conclusion of this incident:

The initial reconnaissance and risk assessment was carried out by the initial incident commander while the PDA remained outside the immediate area of the incident.

Close co-operation was quickly established between the brigade and Transco engineers. This continued throughout the incident.

The surrounding area was efficiently evacuated.

The inner and outer cordon system of control worked well.

extinguished, it was possible to see that only one fire remained. Flame was issuing from a hole about 200mm in diameter 15m, from ground level in one of the remaining gas-holders and later examination showed that it had been punctured by shrapnel. The top of the third gas-holder was badly scorched probably by radiated heat from the fireball but fortunately it was not alight.

Liaison with the police confirmed that evacuation of the area surrounding the site was in hand. Close co-operation with gas engineers was established and arrangements were made for the gas-holders to be emptied although it was explained that this would take time. A five pump water relay was laid from a 300mm main to supply ground monitors which had been strategically placed at the scene.

Some thirteen hours after the initial call, the burning gas-holder came to rest on its base and shortly after the fire extinguished itself.

To avoid congestion on the fireground oncoming vehicles reported initially to a RVP close to the incident. They waited there until called forward.

The ability of Brigade Control to cope with a major incident and simultaneously handled many 999 calls.

The use of high capacity ground monitors (able to be remotely controlled or pre-set) reduced the time crews were exposed to risk.

The crews had visited the site for I (1)(d) visits and exercises and the benefit of these helped to bring the incident to its successful conclusion.


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4 Chapter 4 - Cylinders of compressed gas

4.1 General

4.1.1 Cylinders of Compressed Natural Gas (CNG) (excluding those used in conjunction with road vehicles)

Natural Gas is available from most commercial suppliers as a compressed gas in cylinders. Traditionally the cylinders are marked to conform to BS 349:1979 which requires CNG cylinders to be painted in a neutral colour with a red shoulder to indicate the primary nature of the contents as being flammable. Sometimes the secondary nature of CNG, its non-toxicity, is indicated by a green band below the red shoulder. The body of cylinders of methane gas are usually painted red.

The 1979 BS was replaced in 1997 by BS.EN 1089 part 3 which requires both methane and CNG cylinders to be provided with a red shoulder but it does not specify a colour for the body of the cylinder. Observance of the colour coding system is not mandatory and, to date, the compressed gas industry has made little progress towards implementing the 1997 standard.

Operational crews are advised to use the colour markings on cylinders as a guide only.

It is a legal requirement* that all cylinders of industrial compressed gas are labelled (which can include stencilling) to identify the contents and that safety information is provided. Such data should be regarded as the authoritative source of information regarding the contents of the cylinder.

(Carriage of Dangerous Goods by Road Regulations 1996. (CDG Road))

Figure 4.1 The British Standard which covers the marking of cylinders of compressed gases is not mandatory. The diagram illustrates the identification pattern used by the two largest suppliers of compressed gases: natural gas (left) and methane (right). (See text for a full explanation.)

Cylinders vary in exact size and pressure according to the supplier. Portable cylinders are about one metre high and standard cylinders are about 1.4m high. The pressure of a full cylinder is usually between 172-230 bar. Gas flow from the cylinder is controlled by a screw valve opened and shut by a hand wheel or a key (often square headed).

It is common practice for the main outlet of cylinders containing a flammable gas to be fitted with a left handed thread to reduce the risk of it being connected to an incorrect supply line. This important safety feature also includes the left hand threaded securing nut being notched at the edge of


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Indicates left-hand thread and that cylinder contains flammable gas

Figure 4.2 Drawing showing a left-hand threaded connector to cylinders containing a flammable gas.

the flats of the nut. In most cases a cylinder, when in use, will be fitted with a pressure regulator to reduce the pressure of the gas to suit the pipe work and equipment it is supplying. The regulator incorporates a safety relief valve to protect the final stage of the regulator and the pressure gauge. It will not protect the cylinder and cannot be relied on to protect the downstream pipe work.

For convenience of storage and handling, cylinders are sometimes delivered and kept in a cylinder bank frame and these can hold up to eighteen cylinders. Users of large quantities of CNG will often have gas delivered by "tube trailer" and up to eight cylinders, each to the length of the trailer of an articulated lorry, can be carried horizontally on the trailer.

4.1.2 Dealing with fire

The recognised advice that, other than when life is directly at risk, burning gas should not be extinguished applies equally to fires involving CNG. If the fire is fuelled from a cylinder some distance from the fire it will often be possible to turn off the cylinder valve or, if fitted, an intermediate valve safely. If this is not possible the flame should be left burning and fire-fighting concentrated on protecting the surrounding risk and if necessary cooling the cylinder.

4.2 Direct or indirect heating of cylinders of CNG

4.2.1 General

When heated, the contents of a cylinder of gas will expand and the pressure within the cylinder will rise. Safety devices such as pressure relief valves, fusible plugs and bursting discs are not normally fitted to industrial cylinders of CNG or methane and it is inevitable that if heating continues the internal pressure of the gas will rise until the cylinder bursts. This will happen with considerable force and debris and remains of the cylinder will be scattered over a wide area.

Where cylinders are directly involved in fire, set up an initial 200m hazard zone. Every effort should be made from a safe distance to cool them. If necessary, a cooling branch should be lashed to a secure object or a ground monitor employed and left to cool the cylinder. When the source of heat has been extinguished and when the cylinder is cool it can be approached. A wetting test could be used to check if the cylinder is hot.

An indication that it is not cool could be the presence of steam from cylinder when the cooling jet is briefly "knocked off" or that the cylinder dries off quickly when cooling water supply is stopped. If available, a thermal imaging camera may be used to give an indication of the temperature of the cylinder. (See Appendix 1.)

4.2.2 Failure of CNG cylinders (RIDDOR)

The failure of any closed vessel operating above atmospheric pressure (e.g. a gas cylinder) consti- tutes a failure as described in Part 1 (2) of Regulation 2 (1) Dangerous Occurrences of the Reporting of Injury Diseases and Dangerous Occurrences Regulation 1995 (RIDDOR). It is a requirement that such a failure is reported to the Health and Safety Executive, by the person in control of the premises or in connection with the work going on at which the dangerous occurrence happened.

Where a cylinder has been exposed to fire, but has not failed and has undergone an adequate period of


cooling, it should be removed from service, labelled and placed to one side in a secure compound. The owner of the cylinder, who is usually the supplier of the gas should be informed, and arrangements made for its collection.


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5 Chapter 5 - Landfill site and spoil tips

5.1 General

Lives have been lost and explosions have been caused by gases, which are naturally generated in landfill sites and spoil tips. The sites, which often contain huge quantities of domestic and industrial waste, can appear to be innocuous especially when they have been grassed over.

As decomposition takes place within the tip, air trapped underground is replaced by carbon dioxide (up to 80%) and hydrogen (up to 20%). With time, microbial activity increases and the gas content changes, with methane becoming the major gas present (up to 65%). Carbon dioxide may make up the remainder although the exact composition will vary according to the contents of the tip.

The decomposition process can continue for decades and the hazards that may result can include:

a build-up of flammable gases

Figure 5.1 Drawing showing use of a "French Trench " to

protect the basement of a propertyfrom explosive gases migrating from a nearby source.

Soil

danger of asphyxiation especially where gases collect in low lying areas, trenches or shafts.

production of hydrogen sulphide (H2S), a highly toxic gas which smells of rotten eggs and is often associated with decaying animal matter.

Gases produced in these sites can travel underground considerable distances to beyond the boundaries of the site and often the first indication of this are reports of a bad smell. Explosions in properties normally in the basement or void beneath the ground floor, can follow. To prevent dangerous concentrations of gas building up in vulnerable properties ventilation equipment is often installed and a porous "French trench", filled with porous shingle, may surround the building allowing gases that are lighter than air to vent before they reach the footings of the building.

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Figure 5.2 "Porous pipes " ready to be buried in a tip to

transport flammable gases of decomposition to a vent stack. The

pipes are made from plastic and the inlet holes can be seen at the base of the ridges. (Photograph: G. Cooper)

Figure 5.3 A typical flame stack used to

discharge flammable gases collected from a tip. The gas can be automatically ignited and burns with a pale blue flame which can be difficult to see in

daylight. The incoming pipes

from the tip can be seen on the right. (Photograph: G. Cooper)


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A longer-term solution to the problem of gas migration is for porous pipes to be laid throughout the tip, which is then covered with a layer of clay. The pipes gather the gas from the site and it is moved by fans 'connected to one end of the pipework to a flue provided at the other end from where it is discharged to open air. Should the amount of gas being discharged fall within its flammable limits, it is ignited and burns with a characteristic pale blue flame which often can only be seen in dark conditions. Developments in the future may lead to the gas being used more pro- ductively (see Figures 5.2 and 5.3).

Despite great improvement in the management of waste sites, numerous abandoned tips remain together with the hazards they present. Operational crews should respond with care to incidents on such sites, especially if there are reports of people or animals being overcome. Clearly, toxic and/or asphyxiant gases could have been responsible for the casualties and brigade and civilian fatalities have occurred in just such circumstances.

A Case Study Black Damp

Operational crews responded to a report of "young girls overcome in a shaft". On arrival at the scene it was found that the girls had gained entrance to the drift shaft+ from the roof of a building, which blocked the shaft. Firefighters subsequently became aware of fumes and rigged in BA. The girls were found in a small cavity in the shaft which had been filled with spoil and rubbish from the disused colliery. A firefighter working in the shaft collapsed, and as he slumped to the ground his face-mask became dislodged.

He and three young girls perished in the "black damp"* fumes.

+ passage following a seam of coal * carbon dioxide in mines, shafts, etc. also

known as "choke damp"

5.2 Fires in rubbish tips

Modern methods of waste tip management have resulted in a dramatic reduction in the number of incidents Brigades attend at these sites. When fires do occur, they are usually deep seated and extensive, although they rarely present a direct hazard to third parties.

It is likely that the initial actions of the first attendance will be to contain the fire whilst discussions take place with the site's manager. Deep-seated fires in rubbish tips are difficult to extinguish without the co-operation of other agencies.

Use of a thermal imaging camera may reveal the extent of the fire although the sheer depth of rubbish can influence the effectiveness of the camera. Fire-fighting will require large quantities of water and for this to be applied effectively, the burning material must be exposed. Mechanical plant will be needed to expose the fire.

Consideration may need to be given to allowing the fire to burn under controlled conditions.

Environmental issues must be considered. Run off water from fire-fighting jets will inevitably find its way into water courses, as only the most modern sites are sealed at the bottom and sides of the tip (usually with a layer of clay or plastic) to prevent the contents of the tip leaking into the subsoil.

In many cases there is no alternative to protracted and crew intensive fire-fighting operations aided by mechanical diggers. The longer term and expensive option is for the tip to be capped with an impervious layer in an attempt to reduce the amount of air available to fire.

At all times during firefighting operations, crews must be aware of the possible presence of Fire Damp and/or Black Damp as well as other gases, depending on the contents of the tip.


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Monitoring with suitable portable gas detection equipment should be carried out before and during firefighting operations.


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6 Chapter 6 - Natural gas and the generation of electricity 6.1 General

One significant advantage that natural gas has over other fossil fuels is that its products of combustion contain lower amounts of many of the substances which are considered to be harmful to the environment. Boilers in some existing power stations are being converted from other fuels to burn natural gas, and gas turbines have long been used to provide, almost instantly, large quantities of electricity at times of peak national demand. The turbine, often an industrialised aircraft jet engine, is coupled directly to the generator and the exhaust gases from the engine are vented to atmosphere.

Gas turbines are generating increasing amounts of electricity and many new power stations now operate combined cycle gas turbines (CCGT) to produce electricity with high levels of efficiency.

6.1.1 A typical CCGT station

Natural gas from the National Transmission system (NTS) reaches the power station through a 600mm diameter pipeline 17km long. As it enters the station, which covers an area of about 11

hectares, it passes into a "slam shut" valve, which can be remotely operated to isolate the site from the gas supply. Additionally, it will automatically operate should conditions within the pipeline or at key areas of the plant vary from pre-determined parameters.

The gas is warmed to 137°C to improve its combustion characteristics, is cleaned, and supplied to two (some plants have three or four) industrial gas turbines. Each gas turbine is directly coupled to a generator. The jet engine produces vast amounts of exhaust gases at a temperature of 550°C and this is taken to a heat recovery boiler to produce steam at a temperature of 512°C. The steam from each

boiler is collected to power a single steam turbine and generator. The combined output of the three generators (two gas turbine and a steam turbine) is 688MW but, with favourable air temperature and pressure which improves combustion, it can be as high as 700MW. The output is sufficient for a town of about one million people and it is fed into the National Grid at 400kV level.

Generators with an output in excess of 200MW at both CCGT and the more traditional power stations are usually cooled by hydrogen gas. Despite its well known hazards this gas is used because its high specific heat capacity and thermal conductivity make it a particularly effective cooling agent. Generators with an output of less than 200MW output are usually air cooled.

Hydrogen is stored in bulk as a compressed gas in cylinders and typically kept in an isolated brick built roofless compound. The gas flows in a closed loop cooling circuit built to the highest mechanical and electrical standards.

6.1.2 Alternative fuel supplies

The contract between the gas supplier and the operator of the power station often stipulates that the supply of gas can be interrupted at short notice. This usually happens in winter and, to allow the plant to continue operating, an alternative fuel, gas oil, is kept on site. A bunded 3.7 million litre tank stores enough gas oil to supply the station for 24 hours and this can be replenished from a nearby fuel storage depot.

CCGT stations achieve efficiency levels of about 55%, which can be as much as 20% higher than many older stations. Forty people work at the site although at night is it operated by a shift of four.


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Flow diagram of a typical small scale combined heat and power unit

Low pressure outlet to boiler

Low pressure inlet from radiators etc

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120°C

Heat exchange

Lubricating oil tank

Engine coolant 95°C

Gas inlet with emergency stop valve often in a vandal-resistant box

Air inlet filter

Gas supply N

A Gas engine and cooling manifolds

Fuel/air supply

Pressure regulator

Valve

Exhaust gases 500°C

Electricity generator

Control unit

With telemetry to remote control room

Figure 6.1 Flow diagram of a typical small scale combined heat and power (CHP) unit.

6.1.3 Firefighting on CCGT sites (many points will apply equally to CHP operations)

As with any technically advanced plant, firefighting can only be enhanced if it is undertaken with the help and co-operation of the management of the plant. The value of regular exercises and/or 1(i)(d) visits to such sites cannot be overempha- sised.

Typical features of such sites include:

Many sections of the plant can be isolated from the gas supply. Operation of the "slam shut" valve will isolate the site. Gas is not stored on site. Many parts of the plant are individually enclosed and protected by automatic

is 2

Exhaust outlet Silencer

fire/gas detection and a CO2 fire suppression system. Water for firefighting is often stored on site. Gas oil storage tanks are usually protected by a fixed foam pourer with an associated foam generating system. Many CCGT sites are remotely located. Much of the site is automatically and/or remotely operated.

6.1.4 Combined Heat and Power plants (CHP)

Users of large amounts of power and heat are increasingly operating gas turbines to generate electricity for their plant. Sometimes surplus capacity is supplied to the National Grid. As with a CCGT plant the huge amount of exhaust heat is


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used to produce steam but a CHP station uses the of installation external shut down valves are not steam for industrial processes or to heat buildings provided and the emergency shut down valve will or even districts. Users of CHP plants include be found on the normal incoming gas supply route. paper mills and chemical works, and one plant serving a board mill produces 49MK of electricity and 82MW of process steam. Efficiency levels of a typical small scale CHP

6.1.5 Small Scale CHP systems

Public buildings, hospitals, housing estates, hotels and retail outlets are among the increasing number of users of small scale combined heat and power installations to economically provide heat and/or electricity for on site use. Efficiency levels can exceed 80% and the heat/power ratio is usually 1.7:1. A system will typically consist of a natural gas powered spark ignition engine driving a generator with a heat exchanger recovering heat from

%

Energy Input 100

Electricity produced 30

Heat recovered 50

Flue Losses 15

Radiated heat lost 5

TOTAL 100

the exhaust gases and another recovering heat from Other fuels used to power small scale CHP include the engine cooling water and oil. Outputs vary LPG diesel, biogas and methane gas from landfill from as little as 15kWe/25kWth (kilowatt electric- sites. ity - kilowatt thermal energy) to 5MWe/8.5MWth (megawatt electricity - megawatt thermal energy). Economics will decide the exact operating pattern of the plant but this is usually about 17 hours a day. Heat recovered by the heat exchangers is used to raise the temperature of feed water to the hot water boilers by as much as 15°C.

6.1.6 Operational considerations

Stand-alone CHP units are invariably placed close to the building they serve. The engine with its generator is housed within an acoustic enclosure in a lightly clad building. It will be unattended, automatic in operation, and remotely controlled and monitored by sophisticated telemetry. It is unusual for the building to have a fixed firefighting system but on the outside, in a vandal resistant box, crews will often find an emergency control valve for the gas supply to the engine. Once operated this will stop the engine and generator.

With the fuel supply isolated, electricity will not be generated, but the building will not be electrically isolated and normal precautions must be taken.

Where a CHP is installed within the building, perhaps as an addition to an existing boiler house, it will be protected by fire detection and firefighting equipment similar to the existing plant. In this type


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Chapter 7 - Natural gas as a fuel for vehicles

7.1 Introduction

Since the earliest days, gas has been used as a fuel for vehicle engines and, perhaps more successfully, for stationary industrial engines. But not until the 1980's, prompted by the increasing availability of natural gas, and ever more stringent demands for cleaner exhaust emissions, did a development programme of any size start in this country. Abroad, many countries already have tens of thousands of natural gas powered vehicles on the road.

Three fuelling systems are being evaluated.

(i) Vehicles which carry both petrol and natural gas either of which can be used at the flick of a switch. Engines for this method operate on the spark ignition cycle.

(ii) Vehicles which carry both diesel fuel and natural gas. The engine operates on the compression ignition cycle with diesel being used to start the engine and provide the heat to ignite natural gas as it is gradually introduced to the engine in ratios which vary according to the operating parameters. When conditions are at their optimal the fuel mixture consists of about 80% natural gas and 20% diesel.

(iii) Dedicated Natural Gas Vehicles which operate only on natural gas, carried either compressed (CNG) or liquified (LNG).

The auto ignition temperature of natural gas is in the region of 538°C (which is very high compared to diesel at 250°C) and such a temperature is difficult to achieve in an engine by compression alone, consequently all dedicated NGV engines use spark ignition to provide the high temperature required to ignite the fuel.

Chapter

Engines suitable for vehicles up to 44 tonnes have been developed.

7.2 Fuel storage on Natural Gas Vehicles (NGVs)

Dual fuel vehicles carry petrol or diesel in the normal way often using exactly the same fuel system as the vehicle on which they were based prior to conversion. Natural gas for these vehicles and for dedicated vehicles is carried either as compressed gas (CNG) or liquified natural gas (LNG).

7.2.1 Cylinders of CNG (for use on vehicles powered by natural gas Chapter 4 covers industrial cylinders of CNG)

These are usually charged to a pressure of 200 bar and are made from steel, a composite of steel or aluminium wrapped with carbon fibre, or a composite of plastic and carbon fibre wrap. Cylinder size varies with cars, light vans, estate cars and forklift trucks using a cylinder of between 60 to 90 litre water capacity (wc) which is the equivalent to 15 to 25 litres of petrol. Vans normally carry more than one cylinder to give a total capacity of typically 90 to 180 litres (wc) and this is equivalent to 25 to 50 litres of petrol.

Lorries and buses usually carry a number of cylinders and the total capacity can vary widely from 350 litres (wc) to in excess of 1,000 litres (wc). A large vehicle could conceivably have a CNG capacity in excess of the equivalent of 250 litres of petrol.

All cylinders are secured to be crashworthy, able to resist the huge g forces of an impact and the standard of engineering throughout the gas fuel system is high. Pipework is fabricated from stainless steel

Natural Gas Incidentss 35

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which is attached only to the structural members of the vehicle. Each cylinder incorporates a manually or electrically operated (or both) isolation valve and is protected by a pressure relief device which is likely to include a temperature sensitive fusible plug. In the event of a fire heating the cylinder and causing the pressure of the gas to rise the pressure relief device will open and release the contents of the cylinder to atmosphere outside the vehicle. The escaping gas is likely to be ignited as it leaves the vent line and a flame several metres in length could result.

Other safety devices fitted to NGVs include a deceleration switch, which will stop the flow of gas and, if the cylinder is fitted with an electrically operated cylinder valve, isolate the cylinder if the vehicle suffers a substantial impact. A vehicle may also be fitted with an excess flow device which will prevent the excessive flow of gas from the storage container in the event of a ruptured pipe or if the regulator pressure relief device is venting.

Lorries fuelled by natural gas usually carry their fuel containers secured externally to the vehicle

chassis, whilst on buses they are likely (but not always) to be carried at roof level screened by light bodywork. Safety devices similar to those found on smaller vehicles will be found.

7.2.2 Tanks of LNG

Natural gas can be liquified to enable the greatest quantity of fuel to be carried in a given volume. One litre of liquified natural gas (LNG) will vapor- ise to give 630 litres of gas and to keep it in its liquid state the fuel is kept at a temperature of 160°C and a pressure of 7 bar. To maintain these conditions the cryogenic (very low temperatures) storage tank incorporates both vacuum and super insulation and is pressure resistant. Despite this some "boil off" will convert the liquid to gas rais- ing the pressure within the tank. Normal use of the vehicle will relieve this pressure, but if the vehicle is not used (and perhaps for as much as ten days) the gas will be automatically vented to atmosphere to keep the contents of the tank at a pressure between 7 and 16 bar. It is important, therefore, if LNG vehicles are left for long periods of time without use that they are kept in a well ventilated area, particularly at roof level.

Super Insulation

Inner Vessel

Outer Vacuum Jacket

Excess Flow Check Valve

Fuel Delivery Connection

Fill Check Valve

Figure 7.1 Features of an LNG storage tank. (Diagram courtesy of ERF)


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The LNG storage tank(s) is usually secured to the chassis of the vehicle, in the case of an articulated lorry, usually between the front and rear axles of the tractor unit. As a general rule to achieve the same range of an equivalent diesel lorry LNG vehicles require twice as much fuel storage capacity, whilst LNG vehicles require five times as much.

7.2.3 Refuelling CNG vehicles

CNG vehicles can be refuelled overnight from a slow fill dispenser or, in much the same time as conventionally fuelled vehicles, by a fast fill dispenser. It is a design requirement of CNG refuelling systems that "the driver shall be dissuaded" from driving the vehicle away during refuelling operations. In early vehicles this was ensured by placing the fuel inlet under the bonnet in a position which required it to remain open during refuelling. More recently sensors have been used to detect an open refuelling flap and as a result immobilise the vehicles ignition. The filling connections are unique to CNG vehicles and are identical in both fast and slow fill systems. When connected, the nozzle maintains electrical continuity between the vehicle and the dispensing unit and need not be held whilst refuelling. Should it become dislodged when in use, it will self seal (as will the fuel system on the vehicle) to prevent natural gas escaping to atmosphere.

(a) Slow Fill or Trickle Charge system

This option which can be connected to a domestic natural gas outlet via a small compressor about the size of a domestic fridge is aimed mainly at small businesses, and depot based fleets who want their own facilities. Bus and truck operators use the CNG slow fill system with a larger compressor(s) to top up the fleet overnight. Once connected and switched on the system is automatic in operation switching itself off when the CNG cylinder is full. (See Figure 7.2.)

(b) Fast Fill Stations

These will be increasingly found at public commercial refuelling stations as well as at the depots of fleets using large numbers of NGVs. The fast fill station consists of a gas compressor often with

a large electric motor in an acoustic enclosure. The output from the compressor is kept in transportable cylinders or similar vessels to act as buffer storage for supply to the fuel dispenser with its associated hose and nozzle. Excess flow sensors are incorporated into the system and these will stop the flow of gas should a large leak occur in the pipework or the fuel dispenser and hose. The dispenser unit will be separate from the compressor and the storage part of the installation and it will be clearly marked to identify it as a source of natural gas. (See Figure 7.3.)

7.2.4 Fire involving CNG refuelling facilities

The refuelling equipment for both systems is usually in open air with only the compressor and its motor housed in an acoustic enclosure. Should gas escape it will rapidly disperse vertically and if a canopy is provided it will be designed so as not to inhibit natural ventilation and to prevent the accu- mulation of any potential gas release.

The procedure to follow for an "emergency shut down" (ESDP) will be clearly displayed throughout the filling station and emergency switches will be clearly identified. Once the ESDP has been activated the system shall be reset only by an authorised person.

When the ESDP is actuated, the supply of gas to the filling station will be stopped, the compressor will be isolated and the storage facilities will be closed (or at a low fill facility, the outlet from the compressor).

The strategy for firefighting will concentrate on cooling the surrounding risk whilst, unless life is at risk, allowing any escaping burning gas to continue to burn until the supply of gas is exhausted and the fire self extinguishes.

Increasingly fast fill gas dispensers will be found alongside liquid fuel dispensers and in the event of an incident involving either type of fuel the hazards presented by all the fire risks will need to be considered by the incident commander.


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Slow Fill Refuelling system configurations

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Figure 7.2 Diagram of a Slow Fill system. (Diagram courtesy of British Gas Vehicles Fuels)

7.3 Incidents involving Natural Gas Powered Vehicles (NGVs)

7.3.1 General Information

Schedule 5A(12 -(i)) of The Motor Vehicles (Authorisation of special Types) (Amendment) (No2) Order 1998 requires "Every vehicle which is equipped to be fuelled by natural gas shall be fitted with a metal identification plate, located in a readily visible and accessible position, that is marked clearly and permanently to identify - (a) that the vehicle has been constructed or

adapted to run on natural gas, and

L Single hose to serve a bus or truck

Double or triple connecting manifold

(b) the maximum system filling pressure"

and

"The filling point for natural gas shall be identified adjacent to the point by the words NATURAL GAS or other suitable word."

A European (CEN) committee has been set up to consider regulations and harmonisation.

It is not surprising with so few NGVs on the road (at present) in this country there is little operational experience of fires involving these vehicles.


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Solenoid Manual valve valve

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Figure 7.3 Diagram of a Fast Fill Compressed Natural Gas refuelling station. (Diagram courtesy of British Gas Vehicle Fuels)

Abroad, where there are often many more NGVs, there is no evidence to suggest that NGVs or their refuelling facilities are involved in fire more fre- quently than traditionally fuelled vehicles.

In the absence of information from the driver of the vehicle or markings about its fuel it may be difficult to identify if a vehicle is gas powered. The filling point may be labelled "natural gas" but this sign may be indistinct in a fire situation or sited behind the filler flap and invisible if the flap is shut. Other clues need to be sought.

It may be possible to see if the vehicle has two filling points (if bi fuelled or dual fuelled) or to see the cylinder occupying some of the load space. In a saloon car the cylinder will normally be in the boot and if it is safe and possible to open the boot this can be checked. Most cylinders fitted in the boot are protected by a cylinder cover but their outline usually remains obvious.

Most lorries powered by natural gas carry cylinders (CNG) or flasks (LNG) bolted to the vehicle chassis often either side and clearly visible.

Storage

The CNG used as a vehicle fuel is odourised and a smell of gas in the vicinity of an incident could well indicate a leak of gas from the vehicle. The odour given to gas is destroyed by combustion. LNG is not odourised.

At any incident involving a NGV it should be established if an alternative fuel system is fitted to the vehicle and if so the alternative fuel should be treated in the same way as a conventional vehicle powered by that fuel.

An experiment in France where an aluminium 127 litre cylinder containing natural gas at 190 bar pressure was suspended immediately above a fire consisting of many rubber tyres shows a protective fusible plug rupturing after only 2 min 40 sec. Immediately the cylinder pressure dropped from 190 bar to 79 bar and a few seconds later when a second fusible plug actuated it fell to 74 bar. Both gas discharges ignited to give flames about 3m long. Nine minutes after ignition the cylinder pressure was 1 bar and shortly afterwards the gas flames self extinguished.


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7.3.2 Action at Incidents

Many safety devices are incorporated into the fuel system of NGVs and it is not inevitable that an NGV involved in an accident will leak or catch fire. Nevertheless, gas presents a similar hazard to other spilt fuels. A measured approach to a vehicle involved in an RTA must always be adopted. Risk management requires there must be a justification if firefighters are to be exposed to risk. A risk assessment of an incident involving an abandoned vehicle on a country lane will result in a different outcome from the assessment reached if the same vehicle was burning in a crowded town centre. This philosophy which is applied to all operational incidents, not just those referred to in this manual, can be summed up as `if after implementing all available control measures, the cost of proceeding with a task still outweighs the benefits, DO NOT PRO- CEED but consider viable alternatives' (Dynamic management of risk at operational incidents. A Fire Service guide ISBN 0-11-341221-5).

Upon arrival at the scene of an incident crews are likely to find one of the following situations:

(a) THE VEHICLE IS NOT ALIGHT AND A GAS LEAK IS NOT IMMEDIATELY APPARENT

It may be difficult, particularly from a distance, to determine if a vehicle is leaking gas but if the vehicle is damaged it should be assumed that it is

and at risk from fire until it has been established otherwise. A likely course of action for the above scenario will be:

Assess the condition and location of any casualties. Assess the risk to them and the surrounding area. If possible contact the driver of the vehicle and establish the nature of its fuels. If there is a secondary fuel it is likely to be petrol or diesel and if these are leaking they should be dealt with in the normal manner. It will be helpful if the driver can recall if the vehicle's ignition has been switched off. Some cylinder isolation valves are solenoid operated and switching

off the ignition will isolate the cylinder/s. Evacuate the area immediately around the NGV extending further downwind. Eliminate potential sources of ignition. (Many simple operations, such as opening a car door which actuates an interior light switch or turning on or off the ignition, can create a spark which has the potential to ignite a fuel/air mixture). Layout firefighting jets. If cutting is to be undertaken, take care not to sever gas pipes. Cold cutting equipment only should be used in the vicinity of a gas leak.

IF IT IS NECESSARY to investigate the vehicle, wear full firefighting clothing and approach the vehicle from upwind paying particular attention for:

A possible smell of gas. Unlike CNG, LNG is not odourised and the resulting gas from LNG will not have the characteristic `gas' smell. The sound of gas escaping. A mist of LNG indicating the vicinity of a leak. A pool of rapidly evaporating LNG below the leak. Consider the presence of other types of fuel if there are no obvious signs of a serious gas leak (or the spillage of other fuels), and it is necessary and safe to do so, close the cylinder isolation valve/s. If it is safe to do so switch off the ignition if this has not been done. In many cases this will close the cylinder/s isolation valve/s by the actuation of solenoids. The manually operable part of such valves is not always obvious. A further safety precaution that can be undertaken in the absence of a gas/air mixture is the disconnection of the vehicle battery.

(b) A SERIOUS GAS LEAK IS DETECTED OR SUSPECTED

If there is a serious gas leak it must be assumed that the resulting gas cloud could ignite.


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Re-assess the system of work. The risk is greatly increased and only if the benefit of continuing with the task remains greater than the risk it entails should the vehicle be approached:

It is likely, in the event of a serious gas leak from an NGV, that the only justification there can be to work in the immediate vicinity of the vehicle will be the preservation of life. BA should be worn and most of the actions listed previously should be implemented. Water sprays may help to disperse the gas clouds (which will rapidly ascend) and only cold cutting gear should be used to cut metal in order to release a casualty. Where life is not threatened, allow the CNG (or LNG) to disperse to atmosphere while, if necessary, protecting the surrounding area. When sufficient time has elapsed for the gas to escape, approach the vehicle again employing all the precautions previously listed.

NB. After the incident the NGV should be inspect- ed and made safe by a suitably competent person before it is taken away.

(c) THE VEHICLE IS ALIGHT

A fire in an NGV may not be the result of a gas leak. It could follow from a fault in the secondary fuel system (if it is so fitted) or may have resulted from the usual causes of fire in vehicles (arson, electrical, carelessness etc). Whatever the cause, any major fire in an NGV could result in the gas cylinder/s being weakened by the heat before the pressure release device/s (prd) have actuated and a risk of explosion exists.

The standard advice that burning gas should not be extinguished unless it directly threatens life remains.

Set up initial 200m Hazard Zone. Consider evacuation. Assess the condition and location of any casualties. Use jet/sprays from a safe distance to cool the cylinder/s. This may be difficult as they are often shrouded by trim and bodywork. Do not extinguish the burning gas. A flame from an open pipe carrying CNG may be several metres long. Protect the surrounding risk and, particularly, in the case of large vehicles, any part of the vehicle not effected by fire. IF IT IS SAFE TO DO SO, turn off the gas cylinder/s. This action will not prevent the prd from actuating and releasing CNG. The flame from a prd vent pipe will be several metres in length and should not be extinguished. Wear full firefighting clothing and additionally, in the immediate vicinity of the fire, breathing apparatus. Consider the possible involvement of a secondary fuel. A thermal imaging camera may be able to assist in providing an indication of the relative temperature of the fuel cylinder/s.


A Case Study One of the first incidents of fire in a CNG powered vehicle in the UK

Just six minutes after a call to a "refuse truck alight" two pumps arrived on a bright still after- noon to find the front and centre of the lorry to be well alight. Two jets one on either side of the truck and a hose reel were used to attack the fire which at this time was thought to involve a diesel powered vehicle.

After about a further ten minutes the flames from the cylinders (two banks one on either side) sub- dued with the rapidity which later reports suggested they had appeared. A `stop' message was sent seventy five minutes after the initial call and not surprisingly the incident was investigated by the brigade and other interested parties.

Through the intense flame a Junior Officer spotted a cylinder beneath the lower compartment and close to the chassis, and he immediately informed the Incident Commander, who moved the crews away from what was thought to be a disused cylinder which had been collected by the bin men. The Officer's suspicions were raised by the nature of the flames which were strong, noisy and clean and made him suspect that this was not a usual truck fire. He noted more cylinders on the other side of the lorry and at about that time he was approached by a dustman who told him the vehicle was powered by CNG.

The Incident Commander maintained the jets, not to extinguish the fire but to minimize the effects of radiated heat and to protect the rear of the truck which had been little affected by the flames.

It was established that the jets of flame issued from the pressure release plug incorporated in each of the eight cylinders, four on each side, carried by the lorry. The cylinders were each of 80 litre capacity and as the vehicle was approaching the end of its working day would not have been full. It probably took about fifteen minutes for them to empty.

The vehicle was extensively damaged at the front and in the centre but the rear including the rubbish compactor and the load was only slightly damaged by fire.

Investigations have revealed the most likely cause to be a failure in a hydraulic pipe which allowed fluid at high pressure to escape. The resulting mist may have been ignited by either a hot exhaust or a spark.



Appendices

1 Considerations for Incident Commander (Gas cylinders heated or involved in fire)


3 Some significant dates in the development of gas as a fuel

4 Glossary of Terms

Appendices


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APPENDIX 1

Considerations for Incident Commander (Gas cylinders heated or involved in fire)

Considerations for Incident Commander

Actions on arrival Siting of appliances

Gather information to determine likelihood of cylinders being involved and heated

Assess potential risk in order to determine operational actions

Operation of pressure release devices

Determine 200m hazard zone

Consider shielding

Establish Inner Cordons

Consider evacuation

Key Actions

ACTION

Identify initial 200m hazard zone

Carry out Dynamic Risk Assessment within hazard zone

4 Establish Cordons

y 40

Apply Water

4 4 40

Re-assess risk and reduce hazard zone/cordons

+

4 Fire Brigade Incident Closed

As the incident develops Appoint safety officers

If possible apply cooling water

Determine tactical mode, any firefighting should be undertaken from behind shielding

Use of ground monitors and/or lashed branches

Wetting test

When cylinder is cool reduce hazard zone

CONSIDER

Type of structure Topography

Public safety Firefighter safety Liaise with Police

Accessibility of cylinder Public safety Firefighter safety. Environmental impact Operational restraints

Cylinder remains wetted Cylinder leaking? Contents burning off? Shielding


(fl

(fl

a))

APPENDIX 2

Basic Risk Assessment

Operational Activity Hazards dealing with incidents involving natural gas cylinder(s)

Task Hazard/ Level Risk Control Measures Risk of Risk Groups

Firefighting Death from catastrophic High All Pre-planning. failure of cylinder.

Projectile Hazards.

Secondary Projectiles. Thermal Radiation.

I Id information.

Intelligence Gathering i.e. liaison with local authority planning depts etc.

Where information is not available assess premise likelihood of cylinders being present. Based on the nature of processes.

Structural damage. High All Development Programme to identify correct procedures to be followed during incidences of structural damage

Signs and Symptoms.

Safe Areas.

Vehicle Marshalling.

Establishing Death from catastrophic High All Maintain hazard Zone. hazard zone. failure of cylinder.

Evaluation of projectile travel distance Projectile Hazards. Secondary Projectiles. PPE.

Shielding.

Maintaining Assault on personnel. Med A Confrontation Management. the cordon.

Police Attendance.

Public Campaigns led by local authority.

Public injury. Med B, C Insufficient resources to undertake a safe and expedient evacuation.

Provide information to public.

Use of premise owners building to act as shielding in instances of potential explosions e.g. Move occupiers to a

safer part of building with sufficient distance between incident and them.


..C

Operational Activity Hazards dealing with incidents involving natural gas cylinder(s)

Task Hazard/Risk

Applying Death from catastrophic cooling failure of cylinder. water.

Environmental damage.

Level Risk Control Measures of Risk Groups

High All Time.

Distance.

Shielding.

Med None Prohibit water run off from entering watercourse.

Develop environmental impact assessment programme.

Closing the Breakdown In Med B, C Establish clear lines of communication incident. Communications. with all relevant agencies, within the

area of responsibility e.g. railway companies, local government etc.

Risk Groups

A Firefighters

B Non-Service

C Public


APPENDIX 3 Some significant dates in the development of gas as a fuel

1272 Marco Polo observes natural gas burning in Baku near the Caspian Sea.

1659 Thomes Shirley observes natural gas emanating from a coal seam near Wigan.

1684 John Clayton makes a "flammable gas" by carbonising coal.

1733 John Lowther extracts fire damp (methane) from a mine and burns it continuously on the surface.

1780 The ninth Earl of Dundonald builds a tar oven to obtain tar from coal and produces gas.

1799 Patent issued for the use of gas for heating and lighting.

1826 First telescopic gasholder erected in Leeds.

1844 Dry gas meter patented.

1850 Cooking by gas begins to attract public attention, James Sharp cooks dinner for 120 people in Southampton.

1876 Compressed gas used to light railway carriages.

1917 An explosion in a munitions factory causes a nearby gasholder to collapse. Eight million cubic feet of gas destroyed in a single flame.

1937 Substantial quantities of natural gas encountered in a trial bore at Eskdale (Yorks).

1948 Gas Act passed: industry nationalised.

1959 First trial import of liquid natural gas from Louisiana.

1963 Regular shipments of LNG start to arrive from Algeria.

1969 National programme of conversion to natural gas started in Burton-on-Trent. First polyethylene pipes laid to distribute gas.

1976 Production of coal gas falls to negligible quantities.

1979 Conversion of nation to natural gas completed.

1986 Gas Act 1986 passed to introduce a new structure for the gas industry in the private sector. British Gas plc floated on the stock market.

1998 Interconnector to link the UK gas system with the European system opened. The pipeline runs between Bacton (Norfolk) and Zeebrugge (Belgium).


F°'

APPENDIX 4 Glossary of Terms

Term

Ambient

Bar

Barg

Baseload

Calorific Value (CV)

Coal Gas

Combined Heat and Power (CHP)

Closed Circuit Gas Turbine (CCGT)

Cubic Metre (M3)

Downstream

Fossil fuel

Gasholder

Gas Processing Facility

Gas Production Facility

Interconnector

Interuptable Service

Meaning

Surrounding

A unit of pressure which is approximately equal to atmosphere pressure (0.987 standard atmospheres).

Shortened form of "bar gauge". A unit of pressure in a pipe when measured relative to the pressure surrounding the pipe.

The permanent load on a power supply system

A measure of the ratio of energy to volume measured in Megajoules per cubic metre (MJm3). For a gas this is expressed under standard conditions of temperature and pressure.

Mixed gases extracted from coal and used for heating and lighting. Last produced in the UK in any significant amount in 1976.

The simultaneous generation of electricity and heat for use within buildings or processes by the recovery of heat used in the generation process.

The generation of electricity utilising the power of the gas turbine and steam made from its exhaust gases.

The unit of volume approximately equal to 35.34 cubic feet.

In the direction of flow of a stream etc.

A natural fuel such as coal or gas formed in the geological past from the remains of living organisms.

A vessel used to store gas for diurnal use.

Any site which blends or purifies gas, removes from gas any of its constituent gas or separates any oil or water and is situated at a terminal which receives gas directly or indirectly from a gas production facility.

A facility for the production of gas from strata or for the manufacture of gas.

A pipeline which transports gas for another country. The Irish interconnectors takes gas from the UK to Ballylumford and Dublin, the European to Zeebrugge (Belgium).

A service which supplies gas at a lower price, but which can be shut off by Transco at times of high demand.


-CD

f1. S.,

0-2

Kilowatt hour(kWh)

Liquidfied Natural Gas (LNG)

Local Distribution Zone (LDZ)

National Transmission System (NTS)

Offtake

Odourisation

Public Gas Transporter (PGT)

OFGAS

Producer

Shippers

Supplier

Service Pipe

T.B.M.

Telemetry

Therm

The unit of energy used by the gas industry. Approximately equal to 0.0341 therm.

Natural gas in its liquid state.

A defined geographic area supplied by one or more NTS offtakes. Consists of a LTS and Distribution system pipelines.

A high pressure system consisting of terminals, compressor stations, pipelines and offtakes. Operates at pressures up to 85 bar. NTS pipelines take the gas from terminal to the NTS offtakes.

An installation defining the boundary between the NTS and LTS (or very large consumer). The installation will include equipment for metering pressure regulation etc.

The addition of the distinctive odour given to natural gas to make the detection of leaks simpler.

A company licensed by OFGAS to transport gas to consumers. Transco is the largest PGT.

The Office of Gas Supply. A non ministerial government department and regulator of the UK onshore gas industry. It grants licences to PGTs shippers etc.

Operators who explore for gas (for the UK invariably in off shore waters) and deliver the gas to gas processing facilities.

A company with a licence to buy gas from a producer and who sells it to suppliers using a PGT to transport it to the customer.

A company with a Supplier's Licence contracts with a shipper to buy gas which is then sold to the customer. A supplier may also be licensed as a shipper.

A service pipe connects the distribution main to an individual premise and terminates at the outlet of the emergency control valve (often close to the meter). It is upstream of the installation pipework and other fittings.

Tertiary butyl mercaptan - a sulphur based liquid used to give natural gas its distinctive smell.

The transmission of readings etc to a distant receiving set, station, or control.

The imperial unit of energy now largely replaced by the metric unit the kilowatt hour (kWh). 1 therm equals 29.3071 kWh.


Town Gas A manufactured gas for domestic and commercial use. Almost totally replaced in the late 1970's by natural gas.

Watt The SI unit of power equivalent to I joule per second.

Watt-hour The energy used when one watt is applied for one hour.


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Acknowledgements

HM Fire Service Inspectorate is indebted to all who helped with the provision of information and expertise to assist the production of this Manual, in particular:

Geof Cooper

Mark Wheeldon Transco

Dr Norman D'Urso British Gas Vehicle Fuels

SDO Graham Maltby Kent Fire Brigade

Paul Fagan

Hannaford Forensic Ltd

Stephen Elliott British Compressed Gases Association

Small Scale CHPs Nedalo (UK) Ltd

'' rry llf Fire Service Operations · OR EXPLOSION Further reading 1 Fire Service Manual - Volume 1...

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