Natural Gas and Carbon Monoxide (PN 804)

Question 1

Name one ‘by product’ of the Natural Gas supply system

Answer 1

Carbon Monoxide

Question 2

What does NTS stand for?

Answer 2

National Transmission System

Question 3

The main pipelines that form the NTS contain gas pumped at high pressure. What pressure in bar can this reach?

Answer 3

85 bar

Question 4

What does LDZ stand for?

Answer 4

Local Distribution Zone

Question 5

LDZ pipelines are part of the medium pressure system. What bar pressure can these pipes run up to?

Answer 5

25 bar

Question 6

The natural gas is odourless and so a stenching agent is added but at what point is that done?

Answer 6

At the Distribution Center where the gas supply is staged down to a much lower pressure for domestic use

Question 7

How might you identify a local Distribution Center?

Answer 7

The presence of Gas Holders though more modern centres may not have them

Question 8

What is the name of the stenching agent used to ensure that leaks can be readily detected?

Answer 8

Ethyl Mercaptan

Question 9

Is natural gas lighter or heavier than air?

Answer 9

Considerably LIGHTER which means it will readily disperse in open air

Question 10

Who is legally responsible for dealing with gas leaks?
A) The Fire Service
B) The Gas Authority
C) The Health and Safety Executive

Answer 10

B) The Gas Authority (GA)
They are required to provide a 24 hour emergency response by paragraph 40 of the Gas Safety (management regulations) 1996

Question 11

Ethyl Mercaptan is naturally colourless but may be dyed by the manufacturer, it is extremely harmful to the environment and the vapour has an explosive range between 2.8 and 18.2% but is it lighter or heavier than air?

Answer 11

HEAVIER and it will therefore separate and drop away from the natural gas when released

Question 12

At approximately what bar pressure does a domestic gas supply run at?
A) 1 bar
B) 3 bar
C) 5 bar

Answer 12

1 bar

Question 13

Name 3 of the 4 ‘Hazards’ listed in the note associated with a leak in the NTS (high pressure network)?

Answer 13

1) Mechanical damage caused by the jet of gas
2) Asphyxiation through local oxygen starvation should ignition occur
3) Radiated heat from ignited jet of gas
4) Detonation/explosion where Un-ignited gas becomes confined

Question 14

Why might it take up to an hour to turn off the high pressure gas pipe?

Answer 14

Shut off has to be staged to prevent further ruptures in the system from the sudden shock of closing valves

Question 15

What are the circumstances in which natural gas might be an asphyxiant?

Answer 15

In confined spaces or in close proximity to a very large gas release

Question 16

Is Carbon monoxide (CO) toxic in small doses?

Answer 16

YES

Toxic at 9+ ppm with long exposure
0-70 ppm probably no visible effects unless exposed for hours
70-150 ppm headache,fatigue, shortness of breath, nausea, dizziness within a few hours
150-200 loss of consciousness
400+ effects will take less than 5 minutes

Note Gas Authority engineers may deem it safe to work at levels that we would deem dangerous but this is based on short exposure times

This Q is not in note

Question 17

Is Carbon Monoxide (CO) lighter or heavier than air?

Answer 17

It is approximately the same density

(Slightly lighter CO is 1.14 kg/m3 Air is 1.225 kg/m3) which is why detectors should not be positioned either high or low but at head height

Question 18

Why does CO poisoning give people a ‘rosey complexion’?

Answer 18

The CO make bonds to red blood cells. The attraction of CO and hemoglobin is approximately 250 times greater than the attraction between oxygen and hemoglobin. This prevents the body from collecting oxygen and as the brain and heart require large amounts of oxygen they quickly suffer from any shortage

Question 19

Which is the Act of parliament contains section 7.2(d)?
Fire and Rescue Services Act 
2004
2006
2008

Answer 19

2004

Question 20

Is wind direction quoted as where the wind is coming from or where the wind is going to?

Answer 20

Where it is coming from

Eg ‘the wind direction is from the north’ avoid northerly/southerly etc

Use of FireMet via control may be a consideration

Question 21

What is the minimum distance that an appliance should be positioned from a suspected gas leak?

Answer 21

25 meters

Question 22

Where possible crews should be positioned at what angle (or greater) from the front and rear of the building involved?

Answer 22

45 degrees

Question 23

What will be the clearest indication that a high pressure pipeline has been ruptured?

Answer 23

The noise

Question 24

Where a high pressure pipeline is ruptured in a congested area the distance for a hazard zone should be 600 meters and crews must wear Full PPE and BA to effect rescues. Under non congested conditions a hazard zone of how many meters must be established?

Answer 24

200 meters

Question 25

‘No attempt is to be made to….’ do what 2 things by fire crews?

Answer 25

1) Control the leak (High Presure)

2) Extinguish the fire where the leak has ignited (any pressure)

Question 26

Where there is an uncontrolled leak from a ‘massed storage site’ crews should withdraw to what distance?

Answer 26

1000 meters

Question 27

After establishing a 25 metre cordon at a domestic leak what is the next priority? (3)

Answer 27

1) Removal of ignition sources (can the electrical supply be isolated externally)
2) Shutting off the gas supply from the outside
3) Ventilating before entry

Question 28

As well as full PPE and BA what 2 pieces of equipment should be used at a low pressure or domestic gas leak incident?

Answer 28

1) DIM equipment (detection, identification and monitoring equipment)
2) Intrinsically Safe radios (B.A.R.I.E sets)

Question 29

Does the fire service have ‘powers of entry’ at gas leak incidents for the purpose of securing the gas supply?

Answer 29

No, however the GA does.

Question 30

Can a single BA crew be committed to ventilate at an Incident where a Carbon Monoxide alarm is actuating?

Answer 30

Yes