Acetylene Procedures

[Dragon]

Overthe last few years my Brigade, and most in UK, have taken steps to ensure strict procedures are in place at any incident where acetylene cylinders are involved (and rightly so).

Given that Carbon Monoxide has a flammability range of 12.5% - 74% and is the major constituent of smoke (actual make-up depends on what is burning/smouldering) it worries me somewhat that OIC's at incidents still send BA teams into smoke filled buildings after the fire is extinguished without any extinguising medium.

Do any other Brigades have specific procedures re extinguishing medium? Especially as cold smoke explosions are now recognised as being a danger in such instances.

[burgermuncher999]

NO BA TEAM SHOULD EVER UNDER ANY CIRCUMSTANCES BE COMMITTED INTO A SMOKE FILLED ENVIRONMENT WITHOUT TAKING WITH THEM AS A MINIMUM A HrJ CHARGED TO 24 BAR.
It is also important that they are made aware of the need to continually gas cool (dilute the fire gases by the use of a fine pulse spray) even in cold smoke.

[Dragon]

Burgermuncher, I agree entirely but it is, worryingly, common practice to send BA teams in to ventilate tenements and high rise which can be, at times, heavily smoke logged without any protection.

Personally speaking, having been caught in a dust explosion, I wouldn't either put myself in, or send anyone else in, to any smoke filled atmosphere (whether the fire was out or not) without protection.

My point was that a lot of attention is given to acetylene because of its flammability range but not to carbon monoxide which has a very wide range too.

[messy]

The issue of CO's explosive range being similar to acetylene is a fair point with regards to BA/extinguishing medium etc, furthermore it's easier to predict and detect acetylene in an atmosphere than CO, making CO a very risky gas to deal with.

However, the vast majority of the revised acetylene procedure relates to it's inherent instability and the fact that cooling has only a minimal effect.

[guest28]

cold smoke explosions? anyone care to expand on that ?? its not a term we use in avon.

[guest28]

cold smoke  explosion same as  delayed backdraught??  embers ingniting residual Co/smoke ?

[rips]

a cold smoke explosion is not the same as a delayed backdraught. A delayed backdraught involves very hot gases. They are certainly far from "cold".
A delayed backdraught might occur like this:
Fire in a compartment with limited ventilation. The fire has used all available oxygen within that compartment. Fire fighters make an entry and begin to move through the compartment. The gases within are now starting to dilute towards their ideal mix. For example a mattress might be turned over, causing a spark to ignite the gases. This could occur several minutes after the firefighters have entered the compartment.

This might not occur at all but it is possible if all conditions are ideal

[buffalosid]

thanks for the reply...... rips
my last post should have read --is a cold smoke explosion the same as  etc.....?
i havent actually heard a delayed backdraught described as a cold smoke explosion and didnt actually consider them to be the same thing, in fact never even heard the term "cold smoke explosion"  before but thanks for clearing that up.

but again what actually is a cold smoke explosion???

[rips]

are people getting mixed up with a dust explosion?

[Paul]

Just because gases with a compartment have been allowed to cool does not mean thay are no longer flammable.

A delayed backdraught means exactly that.  If the door of the compartment is opened and the oxygen allowed to enter, it may not react in the noraml manner as there may not be an immediate ignition point, therefore, the gases have cooled. Enter into the room and stir the embers and boom, backdraught!!

A typical scenario would be in a compartment fire where old types of  foam filled furniture has been allowed to smolder for some time.  Because it has been allowed to do this, the temperature within the compartment has dropped significantly.  However, the gases within this compartment remain flammable and as dangerous as ever.  mix them with the now O2 starved room and introduce an ignition source, and there goes your backdraught, possibley into other areas of the premises as party trick.

[fireftrm]

I have always understood the cold smoke to be that in the areas outside the compartment on fire. Those that escape into the corridor, for example, and which tend to look grey/white. These are flammable gases with water vapour (hence the colouring) and are cool. They are as flammable as those in the room, where the delayed backdraught is a possibility. The manual on compartment fires expalins the reasons for ventilating the areas outside the compartment as does the video on compartment fire fighting tactics. These should be on every fire station in the UK, they were issued.

Rips - dust explosions, as their name suggests, are expolsions in flammable dusts; for example flour, custard powder (highly dangerous stuff) and sawdust. Apart from the rapid flame spread being the same type of exposion - defalgration (as opposed to detonation) - they are completely different examples of fires.

[rips]

firetrm, i understand dust explosions are different, but was just asking the question if there was some confusion over certain phonomenen.

As I have found out over the last few years, different brigades both in this country and abroad have different explanations for most fire behaviour and tactical ventilation scenarios. Something else we can't agree on!

[fireftrm]

Sorry Rips, hope no offence taken. You are right about differing definitions of terms too!

[burgermuncher999]

The term cold smoke explosion is an age old term given to what is in effect a backdraught. It's just that back when the term cold smoke explosion was first coined little or nothing was known about the flammability of CO in fire gases. As has been stated a backdraught need not rely on the presence of heat. If the CO in the fire gases and the O2 introduced as the under ventilated compartment is opened up combine in the correct proportions then the presence of any ignition source may result in a backdraught situation.
The comparison between fire gases and acetylene is excellent for acetylene like CO doesn't need to be hot in order for it to go bang.
Keep gas cooling. Even in cold smoke filled compartments REMEMBER 'It ain't cold smoke, its potentially explosive CO'.

[rips]

None taken at all firetrm.