Rank: Forum user 
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Can someone put me wise whether flash back arrestor is required in LPG gas cylinder ? If not why ?
Regards,
Pradeep
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Rank: Forum user
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Shouldn't be required.
FBS's required for Oxy / Fuel not LPG.
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Rank: Forum user
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We use propane cylinders for pre heating of welded joints. These have flash backs fitted at the cylinder valves because it is possible to have a leak in the pipe work that could result in having an air/propane mix in the system leading to a flash back situation. It is worth noting that flash back arresters have a 'use-by' date on them.
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Rank: Super forum user
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If using the LPG on its own, for heating, then it is not really necessary.
If using in conjunction with oxygen, for flame cutting, then I would recommend you do use one.
I note the comment above about oxy/fuel.....I also note that LPG is a fuel gas!
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Rank: Forum user
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Yes John,
My reply was a bit rushed I assumed the LPG was a single gas supply for heating and not as part of an Oxy - Propane set.
With LPG alone the requirement for FBA would not be there as it will only burn in a pretty narrow range of concentrations in air and critically there is no real mechanism or pressures which will introduce air (or O2) to the system upstream of the nozzle i.e. the cylinder is pressurised and positive displacement is taking place. In this scenario there should be no chance for flashback to occur.
Happy to be corrected on this one.
Cheers,
Davie
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Rank: Forum user
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JohnMurray wrote:If using the LPG on its own, for heating, then it is not really necessary.
If using in conjunction with oxygen, for flame cutting, then I would recommend you do use one.
I note the comment above about oxy/fuel.....I also note that LPG is a fuel gas! Wot E said.. cheap as chips anyway so why would you risk it?
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Rank: Super forum user
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it depends upon what purpose you are going to use it for.But most cases if you are using only LPG you FBA is not mandatory requirement.
but please do check with local regulations as well.
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Rank: New forum user
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No oxy/air present inside those LPG, there is no requirement of having it.
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Rank: Super forum user
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No oxy/air in acetylene either!
Show me someone stupid enough to operate using acetylene without a flashback arrester.
We operate with FBAs´ on oxygen, acetylene and propane (when used as fuel gas for flame cutting)
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Rank: New forum user
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For flash back we need to have mixture of oxygen and fuel. If only LPG cylinder is being used, there will be no flash back as the air will not be present due existance of LPG in tubing.
If the LPG or fule cylinder is coupled with oxygen cylinder, there is pressure difference which may cause flash back in any of the cylinder due to blockage of nozzels. Hence flash back arrestor is required.
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Rank: Super forum user
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Rank: Forum user 
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In addition to what John said (2 or 3 posts back)...
I'm pretty sure the flammability ranges for acetylene and propane come into play here. You would certainly have FBAs for acetylene as it will ignite in a range of mixtures with air between 2 (ish) to 82 (ish) percent, hence the likes of the Wolsingham explosion in 2007. It means that acetylene will ignite in air within that broad range of mixtures. So yes! entirely agree that FBAs are 100% required!
Propane meanwhile, the result of 2 failed terrorist attacks prior to the "John Smeaton" Glasgow airport attack has a flammability range of between 2 and 10 percent. If using propane by itself, even if you had a leak in the hose, the chances of reaching a 2-10% mix of propane with air in the hose would be very low - outside the hose is a different story!
Our guys use FBAs for oxy-acetylene and oxy-propane but not for the just propane rigs.
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Rank: Forum user
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If you're interested, the terrorist attacks failed because the (2) cars were left with a cranked open propane cylinder inside them. After a few minutes, the propane would have reached (an estimated) 80-100% propane which is well outside the flammability range for propane.
If you're that interested, one of the cars was left outside the "Tiger Tiger" nightclub, in Piccadilly Circus and it was around the time of the Glasgow airport attacks...
Plenty for you to Google on!
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