Natural Gas and Carbon Monoxide (PN 804) Flashcards
Name one ‘by product’ of the Natural Gas supply system
Carbon Monoxide
What does NTS stand for?
National Transmission System
The main pipelines that form the NTS contain gas pumped at high pressure. What pressure in bar can this reach?
85 bar
What does LDZ stand for?
Local Distribution Zone
LDZ pipelines are part of the medium pressure system. What bar pressure can these pipes run up to?
25 bar
The natural gas is odourless and so a stenching agent is added but at what point is that done?
At the Distribution Center where the gas supply is staged down to a much lower pressure for domestic use
How might you identify a local Distribution Center?
The presence of Gas Holders though more modern centres may not have them
What is the name of the stenching agent used to ensure that leaks can be readily detected?
Ethyl Mercaptan
Is natural gas lighter or heavier than air?
Considerably LIGHTER which means it will readily disperse in open air
Who is legally responsible for dealing with gas leaks?
A) The Fire Service
B) The Gas Authority
C) The Health and Safety Executive
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
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?
HEAVIER and it will therefore separate and drop away from the natural gas when released
At approximately what bar pressure does a domestic gas supply run at?
A) 1 bar
B) 3 bar
C) 5 bar
1 bar
Name 3 of the 4 ‘Hazards’ listed in the note associated with a leak in the NTS (high pressure network)?
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
Why might it take up to an hour to turn off the high pressure gas pipe?
Shut off has to be staged to prevent further ruptures in the system from the sudden shock of closing valves
What are the circumstances in which natural gas might be an asphyxiant?
In confined spaces or in close proximity to a very large gas release
Is Carbon monoxide (CO) toxic in small doses?
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
Is Carbon Monoxide (CO) lighter or heavier than air?
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
Why does CO poisoning give people a ‘rosey complexion’?
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
Which is the Act of parliament contains section 7.2(d)? Fire and Rescue Services Act 2004 2006 2008
2004
Is wind direction quoted as where the wind is coming from or where the wind is going to?
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
What is the minimum distance that an appliance should be positioned from a suspected gas leak?
25 meters
Where possible crews should be positioned at what angle (or greater) from the front and rear of the building involved?
45 degrees
What will be the clearest indication that a high pressure pipeline has been ruptured?
The noise
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?
200 meters
‘No attempt is to be made to….’ do what 2 things by fire crews?
1) Control the leak (High Presure)
2) Extinguish the fire where the leak has ignited (any pressure)
Where there is an uncontrolled leak from a ‘massed storage site’ crews should withdraw to what distance?
1000 meters
After establishing a 25 metre cordon at a domestic leak what is the next priority? (3)
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
As well as full PPE and BA what 2 pieces of equipment should be used at a low pressure or domestic gas leak incident?
1) DIM equipment (detection, identification and monitoring equipment)
2) Intrinsically Safe radios (B.A.R.I.E sets)
Does the fire service have ‘powers of entry’ at gas leak incidents for the purpose of securing the gas supply?
No, however the GA does.
Can a single BA crew be committed to ventilate at an Incident where a Carbon Monoxide alarm is actuating?
Yes
