804 - natural gas & CO (28/09/15) Flashcards Preview

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Flashcards in 804 - natural gas & CO (28/09/15) Deck (48)
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1
Q

1.2 Natural gas is distributed throughout the UK in a system of

to local distribution zones (LDZ) called the

and then to distribution sites where the gas supply is staged down to a much lower pressure for domestic use. It is at this point that

A

high pressure (85 bar) pipelines called the national transmission system (NTS)

medium pressure system (25 bar)

the stenching agent, ethyl mercaptan, is added to the natural gas so that leaks can be readily detected. Traditionally, gas holders were used to store gas and to maintain the pressure in the local distribution network at times of peak usage and many local distribution centres can be identified by gas holders although more modern centres may not have gas holders. Natural gas is considerably lighter than air and will readily disperse in open air, especially in windy conditions.

2
Q

1.3 The legal responsibility for dealing with natural gas leaks including carbon monoxide and natural
gas safety rests with

A

the Gas Authority (GA) who operate a 24 hour emergency response service. Gas safety (management regulations) 1996HSE guide paragraph 40.

3
Q

2.1 A jet of gas at between 25 - 85 bar pressure will cause

A

physical mechanical damage to its

surroundings and people and will generate a loud jet like noise.

4
Q

2.2 Ignition of natural gas under 25 - 85 bar pressure is likely to result in

A

a large fire ball and jet flame that would cause localised oxygen starvation and could lead to asphyxiation in the local vicinity.

5
Q

2.4 Large un-ignited release of natural gas could present a risk of detonation where there is

A

confinement or congestion see Appendix 1.These processes can in exceptional circumstances
lead to a detonation of natural gas in the open air.

6
Q

Gas distribution sites
2.5 These sites will have a system of valves that stage the natural gas supply down from high pressure
to low pressure of

  1. 6 The high pressure system can take up to
  2. 7 Large storage facilities such as natural gas holders are often associated with these sites.
A

approximately 1 bar for distribution to domestic customers.

an hour to turn off as the natural gas has to be staged
down to prevent rupture in the system from sudden shock of the valves being closed.

7
Q

2.10 Ethyl mercaptan is added to the natural gas supply at the local distribution centres so that natural
gas leaks can quickly be identified by smell. It is added to natural gas in very small concentrations
and is detectable to the human nose at a few parts per million. As Ethyl mercaptan is considerably

A

heavier than natural gas it will drop while the natural gas rises. Therefore the smell of ethyl mercaptan in the open air should only be considered as a possible indicator of the presence of a natural gas leak. There are occasions when the gas national grid infrastructure is undergoing maintenance that sections of pipe work are deliberately vented to the air which can lead to false indication of natural gas leaks. The only true indicator of the presence of natural gas is the use of
detection identification and monitoring equipment(DIM)

8
Q

2.11 Where present in quantity, such as at gas distribution centres, ethyl mercaptan should be treated
with caution. It is naturally a colourless to yellow liquid but may be dyed by the manufacturer for
use. The vapour has an explosive range of between

A

2.8% to 18.2% and it is extremely harmful to

the environment and should not be allowed to enter water courses or drains

9
Q

2.12 Carbon monoxide (CO) is a

A

by-product burning of natural gas and other fuels . It is very toxic in
small doses.

10
Q

2.13 CO is flammable however, a faulty natural gas appliance would

A

not generate sufficient CO to
reach the flammable limits before the flame went out and the appliance failed to work. This could
lead to unburnt gas filling the compartment.

11
Q

2.14 CO is approximately the same density as air and will mix in the room. Therefore

A

all adjoining rooms have the potential to be contaminated with CO.

12
Q

3.6 WIND DIRECTIONS ARE ALWAYS QUOTED AS

A

WHERE THE WIND IS COMING FROM. To
avoid confusion, whenever discussing wind direction, use the term ‘from’ as in “the wind
direction is from the north”. Beware of placing too much emphasis on wind directions in built up
areas. The presence of tall buildings can create turbulence where the wind appears to be blowing
in different directions at the same time.

13
Q

3.8 If no wind is forecasted there may be limited or no

A

dispersion above COMAH sites. IC must be
cautious of highly concentrated localised gas/vapour clouds.

3.9 The situation mentioned as above will be worse at night or during foggy days when vertical
dispersion could be less effective.

14
Q

4.1 An initial ? attendance is dispatched to investigate the report of a natural gas leak and assess the risk of that gas leak to the public.

A

one pump

15
Q

4.2 Appliances should be positioned a minimum of ? from the suspected leak. Unless the nature of the risk or pre-planning dictate otherwise.

A

25 metres

16
Q

4.3 Do not position crews or equipment in

A

direct line of sight of a building suspected of having a

natural gas leak. Position crews at an angle greater than 45 degrees to the front and rear of the building.

17
Q

4.4 The IC must conduct a RA. For most domestic situations this will mean contacting the caller and
ensuring that a gas leak is likely. Where it is suspected that there is a gas leak,

A

the GA must be requested via control. If it is apparent that crews will be required to perform rescues, any
additional resources that are required to maintain a safe system of work should be requested in a
priority assistance message

18
Q

NTS and LDZ and local distribution sites

5.1 It will be very obvious from ? that a high pressure natural gas pipeline has been ruptured.

A

the noise

19
Q

NTS and LDZ and local distribution sites

5.2 The IC must establish a minimum

A

200 metres hazard zone. Crews working within this zone to affect rescues must have full PPE and BA.

20
Q

NTS and LDZ and local distribution sites

5.3 Under “congested” conditions a hazard zone of a minimum of

A

600-1000m

21
Q

NTS and LDZ and local distribution sites
5.4 The IC must inform the National grid and request that the supply is shut down via control;
however,

A

it will take a considerable time to shut the supply down.

22
Q

NTS and LDZ and local distribution sites

5.5 No attempt is to be made to

A

control the leak by fire crews or to extinguish the fire where the leak has ignited.

23
Q

NTS and LDZ and local distribution sites

5.7 Surrounding risks may be protected from flame and heat impingement only when

A

crew are not

placed in undue danger.

24
Q

NTS and LDZ and local distribution sites
5.8 Where there is an uncontrolled leak from a massed storage site, crew should withdraw to outside
of a

A

1000metres hazard zone and await the advice of the hazardous materials and environmental protection officer (HMEPO).

25
Q

NTS and LDZ and local distribution sites

5.9 At this point the IC may have sufficient information to initiate

A

any special operational procedures

based upon the scale of the gas leak, see Policy number 263 - Major incident procedure.

26
Q

NTS and LDZ and local distribution sites
5.10 Rendezvous points(RVPs) or marshalling areas must be considered so as to avoid being
overwhelmed by appliances. These RVPs may need to be

A

some distance from the incident to
avoid crew and appliances being placed in the hazard zone. Once determined, their locations
should be sent to Brigade Control using the appropriate message, see Policy number 518 –
Messages from incidents.

27
Q

Low pressure and domestic network

5.11 Where a leak in the natural gas supply is suspected, a cordon to ensure public safety of a minimum of

A

25 metres is to be maintained and advice sought from the GA. Consideration should
be given to whether additional resources are required.

28
Q

Low pressure and domestic network

5.13 Crews may be committed to shut off the gas supply only

A

where they are not put at risk from a gas explosion and must have donned BA and full structural PPE to mitigate the effects of any sudden flaming from ignited natural gas. This should only be undertaken where there is a risk to life in surrounding buildings or critical infrastructure. The responsibility for the safety of the gas supply rests with the GA

29
Q

Low pressure and domestic network
5.14 Before entering a building suspected of having a natural gas leak the following must be
considered:

A

• Removal of ignition sources, e.g. can the electrical supply be isolated externally.
• Shutting off the natural gas supply from the outside.
• Ventilating to property prior to entry to remove explosive atmospheres.
• Personal protective equipment full structural firefighting kit with BA.
• Detection identification and monitoring equipment carried on the fire rescue units to
alert crew of the presents of and explosive atmosphere. Policy number 797 – Detection
identification and monitoring instrumentsrefers.
• Intrinsically safe equipment.
• Communications: B.A.R.I.E. must be used as fire ground radios are not intrinsically safe
and must not be carried into these environments. Please see Policy number 592 –
Breathing apparatus radio interface equipment.

30
Q

Low pressure and domestic network

5.15 Where a natural gas leak has ignited, the flames should

A

not be extinguished but surrounding
risks should be protected by lashing jets in place and evacuating the area until the gas supply has
been isolated.

31
Q

Low pressure and domestic network

5.16 The fire service does not have powers of entry at gas leak incidents for the purpose of

A

securing the gas supply. However, the GA does. Crews should not make an entry on behalf of the gas
authority unless there is an exceptional public safety issue, see Appendix 3.

32
Q

Low pressure and domestic network
5.17 Following a fire consideration must be given to the possibility that gas apparatus may have been
affected by radiated heat or temperatures above normal which, if excessive, could affect the
integrity of the sealants within the apparatus and may result in a leakage of gas. Where the IC has
reason to suspect that damage to gas apparatus has been caused

A

a request for the attendance
gas authority should be made in accordance with Policy number 518 - Messages from incidents,
see Appendix 3.

33
Q

5.18 A single breathing apparatus (BA) crew may be committed to ventilate when responding to a
domestic carbon monoxide detector actuating having regard to the following points:

A

• Calls to domestic CO detector actuating are level 1 incidents and the GA must be requested simultaneously as part of the level 1 attendance;
• CO is lighter than air when heated and will accumulate at the highest point in the building. As it cools it will potentially dissipate through all rooms adjoining the room of origin therefore all room must be ventilated not just the compartment of origin.
• Turn off and isolate the natural gas supply to all gas appliances in the premises.
• Leave the duty with the GA or their representative.
• BA must be worn even though this may appear to be unnecessary as small doses of CO can accumulate over time and crews may become ill if exposed to repeated small doses.
• A single pumping appliance should be sufficient as BA is required only to prevent accumulation of small doses of CO. Where larger concentrations are involved the
incident may need additional resources.

34
Q

5.19 Where calls to CO incidents indicate there is a suspected large release or persons are reported
trapped,

A

a minimum level 2 attendance will be required.

35
Q

5.21 The RA must take account of the possible presence of irrespirable and or flammable atmospheres
and the environment must be monitored using the appropriate detection and monitoring equipment carried on the fire rescue units, rapid response team (RRT) and fire investigation team (FIT). The IC must not rely on the GA or other agencies detection equipment, if

A

crews are to be

committed to a risk area.

36
Q

6 Evacuation or shelter in place

  1. 1 When considering whether to evacuate the IC should undertake a RA and consider the following:
    (a) Can the public remain in a place of safety?

6.2 If evacuation is considered necessary. The IC must take into account.

A
  • Indoors with doors and windows shut.
  • With ventilation and air conditioning systems shut down.
  • With naked flames extinguished when appropriate.

• The prevailing weather conditions and wind direction.
• Minimum distances required by the pertinent procedure or through RA.
• The IC will need to carry out a RA where premises such as hospitals or a significant risk fall within the actual HZ. Close liaison with the police and premises managers will ensure that maximum risk reduction is implemented. ICs will, for instance in the case of hospitals, need to decide whether the evacuation of patients will pose a greater risk to individuals than
leaving them in situ.
• Where a person refuses to leave their premises, the IC should pass the details over to the Police

37
Q

7 End of the incident

7.1 The responsibility for the incident should be handed to

A

the GA or their representatives.

38
Q

7.2 The LFB is not responsible for arranging the recovery of hazardous materials waste. The
responsibility for any waste should be

A

clearly transferred to a relevant person before leaving. The HMEPO may be able to liaise with other authorities such as the police, LAS, LA, health protection authority, and the environment agency (EA) to assist in the resolution of an incident. LFB vehicles must not be used to transport hazardous waste.

39
Q

7.3 It is the responsibility of the owner or relevant person to assess if their premises are safe; the ICs
may assist by

A

giving an opinion using outputs from appropriate instruments and specialist advice
where available.

40
Q

7.4 Where the gas supply has been shut off before the arrival of the Brigade or it has been safe for crews to shut off the supply (e.g. from the consumer unit outside of the property), the occupier should be advised to open all the doors and windows to ventilate the property. A Tag Form 5288 should be attached to the valve and

A

the GA authority must be informed via control that the duty is passed to them. This is advice consistent with that detailed in the gas safety regulations

41
Q

7.5 The main role of the fire and rescue service at this type of incident is to

A

ensure public safety as far

as is reasonably possible. Rectifying the gas leak is the responsibility of the gas authority

42
Q

7.6 Crews should only remain on site to ensure public safety. A request to remain on site to provide cover for the gas authority workforce should be authorised by

A

the duty DAC and may be a chargeable special service, see Policy number 402 – Charging for special service incidents.

43
Q

• The word “fittings” has a special significance in the gas industry and denotes pipes and
connections, valves, siphons, etc. In the electrical industry the word “service” denotes the
cables which enter buildings, cut-outs at the ends of cables, meters and fuse boards. The
terms “fittings” and “service” are not to be used by members of the Brigade when sending
messages and for this purpose the general description

• If safety considerations prevent gas personnel from immediately getting on with their
duties they will maintain liaison until such action is possible.

A

“gas(or electrical) apparatus” is to be used as appropriate.

44
Q

• When Control have to notify a GA that gas apparatus is involved at an incident the following information has to be included:-

A

(a) whether the incident is inside or outside premises (this is important as the GA send different teams for inside and outside incidents);
(b) the size of the fire;
(c) whether any injuries have been sustained by members of the public

45
Q

• Upon arrival at an incident the GA’s official will report to the incident commander or the control unit if in attendance. They will want to establish

A

the name of the manager to whom he has reported and will await instructions to proceed. All GA’s employees or representatives will adopt this reporting procedure when attending incidents.

46
Q

• The IC should remember that whilst the incident is still in progress the LFB is responsible

A

for the safety of anyone working at the incident.

47
Q

• The GA’s official will want to try and establish if any gas apparatus is at fault and may have caused the incident or contributed towards its development. The IC should

A

make every practical effort to preserve the scene.

• Where an investigation of this nature is likely the Fire Investigation Team should be requested.

48
Q

• Cordons:
• for public safety at a domestic
natural gas leak;

• from a ruptured high/medium
pressure pipeline or building filled with natural
gas;

• from ruptured high/medium
where the gas jet is directed through a
congested region;

• from a mass release of bulk
storage of natural gas;

A

25 metres

200 metres

600 metres

1000 metres