Posted By Ian G Hutchings
Take a look at this:

http://www.london-fire.g...inders.asp#safe_cylinder

Lots of information and resources re cylinders and a campaign by the London Fire Brigade.


Regards

Ian

Posted By Merv Newman
Any compressed flammable/oxygenating gas in a "fire" situation is extremely dangerous. First to the firemen and next to local residents. I think most people will accept that an oxygen, acetylene or hydrogen cylinder can go off in random directions and land anywhere. And I have no idea on what radius they can cover.

Best practice is to have all such weapons stored outside of the building at night. Somewhere securely locked but accessible to the fire brigade so that they can get them away from the fire.

The usual solid masonry wall between oxygen and flammables. But I have had to accept over the years that for welding trolleys, while they may be stored outside over night, the welders will not separate the bottles.

Risk assessment ? Low.

Merv

Posted By John Murgatroyd
Explain why a dissolved acetylene cylinder is a higher risk than, for instance, a 30kg propane tank ?
Or a 230 BAR hydrogen cyclinder ?
Is it more likely to explode ?
No.
The risk of explosion is low.
Even if heated in a fire, the risk is still low. The things have a LEAD plug in the bottom, they are low-pressure cyclinders, 15 BAR(ish) (depending on temperature)
The Oxygen cylinder, however, is a high risk in a fire...
Apart from acetylene instability at pressures higher than 25 PSI, what else ?
Over the 100 years of acetylene use it has propved itself a safe way to store a fuel gas....and it is hotter than propane, which is why it is still used for flame cutting...

http://www.aga.com/web/w...ages/History_Acetylene_1

I sometimes worry about the endless waste of time spent trying to invent the wheel again.
I've used oxy/acetylene for flame cutting for 40 years, never had a problem, not ONE.
Compare it with the storage of petrol and other flammable liquids.....like anything else, let an idiot loose near it and you've got trouble. The problem is with the idiot.

Posted By Phil Grace
I work for an insurer (so know soemthing of insurance but am I an insurance expert?) not am I an expert on acetylene.
But I recently attended London Brigade launch of their campaign on acetylene. Too much to reproduce in full but would comment:

Acetylene cylinders do NOT have a fusible (lead) plug
Fire Brigades are uncomfortable having to set up exclusion zones but are worried about consequences of not doing so (being sued?). They're also under pressure from councils/politicians etc about effects of this disruption.
Research by HSL reveals that the acetylene cylinders become dangerously unstable when subjected to heat. Decomposition of the acetylene takes place with generation of considerable heat and over pressure. Whilst decomp can be slowed by cooling any release of pressure e.g. by cracking the valve (traditional practice) can cause it to resume with "explosive" consequences.

As for liability for spread of fire: Any claim for consequences of fire must firstly pass test of negligence - in essence - was there negligence? did fire start because of negligence of site "owner/operator"? If not no liability.
Then there is the issue of whether someone who was simply evacuated from their premises due to Fire Brigade exclusion zone suffered any physical loss. Most Public Liability policies exclude what we in the insurance world call "economic/financial loss". If the neighbours property was damaged by spreading fire then there is a valid basis for a claim. If they were just evacuated on Fire Brigade orders - tough luck. They could claim but there would be no insurance, no deep pocket, so they could end up driving their neighbour into bankruptcy and getting next to nothing.

Posted By shaun mckeever
John Murgatroyd

the risk of an acetylene cylinder explosion are far greater than propane or hydrogen. The chemical bonds between the carbon and hydrogen atoms in acetylene are single bonds whereas in propane they are triple bonds. This makes the acetylene gase far more unstable. Mechanical shock or heat can cause decomposition within the gas cylinder with associated increase in the internl pressure which make s the cylinder more likely to rupture. As the flammability range of acetylene in air lies between 2.5% and 80% (very broad) it means that on contact with air their is likely to be an almost instantneous explosion. The flammability range for propane lies in the region of 6% - 15% (or is that methane?), the band is much, much lower. The ignition energy required for acetylene is far less than for propane or other flammable gases.

Take my word for it acetylene is an extremely dangerous gas by comparison to other gases.

Posted By shaun mckeever
Thanks Jane, I knew my chemistry was a little rusty but I still think I am correct that the bonding between the atoms is the principle reason why acetylene is so unstable.

Posted By Jane Blunt
Yes, the bonding is the reason for the reactivity. However, chemical bonding is responsible for most things in life, the universe and almost everything! ;o)

My two-penn'orth on this topic is that the key difference between acetylene and other compressed/stored gases/LPG or whatever is that the risk from acetylene persists for a period after the fire because the material may still be reacting inside its cylinder. Other cylinders will either fail during the fire or, once the fire is extinguished, the risk subsides.

The key danger inside the 200 metres cordon is projectiles from failed cylinders, unless you can be shielded by a substantial piece of masonry.

Posted By Jane Blunt
We have strayed off topic. Acetylene cannot be replaced by another fuel gas for most of the welding applications for which it is used. It has unique properties.

There may be some applications for which it could be substituted, but we have to guard against getting into a situation where we need to have two fuel gases in the workshop because we have decided that for some applications we can use another gas.

Jane

Posted By Pete48
John, but what if the untrained idiot is not yours but starts the fire that causes the issue with your cylinders?
You clearly have a lifetime of experience of working with industrial gases so, in the original context of this thread, I would be interested to hear your view of the appropriate level of emergency response if your "safe" cylinders were involved in an emergency caused by someone else's idiot?

Posted By Aidan Toner
As we speak, the main dual carriage way between Belfast and Dublin is closed (with no small impact on traffic flow)and will not be opened until midday tomorrow (Thursday)- All due to fire in roadside metal workshop and hence related acetylene concerns.
Local cinema closed 6 weeks ago due to fire in 'nearby'?? foundry and once again acetylene concerns.
Certainly appears that acetylene has been given a raised profile in terms of 'extended' safety cordon.

Posted By Tabs
We are looking at alternatives here in the City based on the fact that the Brigade has a clear and non-changeable policy of 200m cordon evacuation, from 24 to 48 hours.

Incidents involving acetylene is running at more than one per month.

Regardless of the chemistry, the advantages or disadvantages, being denied access to our buildings because of a cordon is very expensive. This is the primary incentive to change.

Posted By Geoff Parkinson
The fundamental difference between acetylene and other gases is this:

When heated, the contens of the cyliner expands - very dangerous. However, when cooled the gases (with the EXCEPTION of acetylene) contract and the risk goes away. Acetylene has the unpleasant capability to thermally decompose after heat has been removed. This 'self-sustaining' decomposition will continue to pressurise the vessel until it is either subjected to cooling or, in the worst scenario, ruptures the container.

My first Watch Officer (old firefighter!) told me that if a propane cylinder hasn't ruptured by the time you start cooling it, it won't. As the temperature is reduced, so is the internal pressure. Something to do with the Gas Laws.

I attended many 'cylinders involved' incidents over the years and always found his rule of thumb to be correct.

To prevent the thermal decomposition, the brigade applies water for 24 hours (this timescale is NOT set by the fire service, they are guided by others on the matter).

Ignoring the damage the cylinder might produce, imagine the water damage that will be produced by the cooling jets! 24 hours is a lot of water!!!! Anyone got major flooding in their risk assessment?

Posted By Crim
When I was a young firefighter in the 60's we would make a dam, fill it with water and carry the affected acetylene cylinder and place it in the water. The extra PPE we had at the time to deal with such incident was an asbestos (yes asbestos) hood and asbestos gloves (to protect from a flash burn), these were worn with our basic fire fighting uniform.

We also fought fires in prefabricated bungalows made with asbestos cement without wearing breathing apparatus, and tackled chimney fires from the roof tops in freezing weather without any fall protection.

Then there was the rescue of persons from upper floors of buildings by hook ladder?

Ah the good old days!

Nowadays fire services pay a lot of heed to health and safety in an effort to protect firefighters from harm, and why should'nt they. They are employees just like us and deserve the same protection.

They are getting a lot of bad press regarding this exclusion zone issue but it's all in the interest of safety.