firefighterjake
Minister of Fire
Capt Ron said:A "flash over" or "back draft" explosion usually occurs when there is inadequate venting above the fire to release the trapped super heated combustible gases... a structure fire needs to be vented above the fire before entry is made on the same level of the fire or below the fire to extinguish it...that's why you see firemen cutting a big hole in the roof...to vent those hot combustible gases...if entry is made before the proper venting above the fire the gases can flash or even explode with quite a force...I've seen many windows blown completely out due to this force...maybe there was a temporary venting problem in the flue when the door was shut and the accumulated heated gases ignited creating a small explosion of those gases...it takes very little pressure to blow out a tight structure or a soapstone stove...I've seen it happen even when the ventilation is done the proper way...It gets exciting for the guys on the hose lines when that flash over occurs and the flame rolls across the ceiling toward them!...it gets very hot very quickly!...Fire is not always an exact science...We use to say "every fire is different"...temps, fuel, air supply mix in many ways to create different chemical reactions...I think that's what makes fire so interesting to many people...That's my guess...
Check out the brick chimney...
http://youtu.be/aTQWNCeCBvQ
I believe that technically a flash over and backdraft are different . . . similar, but different . . . just being nitpicky I will admit.
A flashover generally is a fire that is freely burning away in one small area until it reaches the point in temp where all the combustibles in the room suddenly reach the ignititon temp and everything bursts into flame . . . typically the switch from free localized burn to flash over is fast and temps at the ceiling height are pretty darn hot.
A backdraft is often a fire that is oxygen starved . . . and when oxygen is reintroduced to this smoldering, oxygen starved fire the sudden explosion of fire results in . . . well . . . an explosion.
Either case is bad . . . bad for firefighters and bad for well anything in the general vicinity . . . and both can be prevented or alleviated by creating a vent hole above the fire to allow the super-heated and combustible gases to escape.
Like you said . . . I suspect what we saw here was a mini-backdraft of sorts . . . although many of us here call them backpuffs since generally the worse most of us have seen is a very small backdraft and some puffs of smoke leaking out the joints of the stove, stovepipe, etc. . . . but in some cases I have heard of stove pipes being rattled quite severely . . . hence the three screw requirement.
