Backdraght Vs Flashover.....

Some might find this boring but I've seen a few fire videos on here and just wanted to put my two penneth in on the difference between a flashover and a backdraght as there's so much confusion between LL'ers

What the instructors are do is get the fire hot enough inside so it becomes "fully involved"... everything inside reaches its Auto Ignition temperature and basically everything in there sets on fire, even all the smoke is now just fire... this transition between a fire and a fully involved fire is what is known as the "FLASHOVER". It's not a state of a fire itself, or a sustained event, but the transition from one state to the next. A fire doesn't have to reach this state to make a backdraght occur, but it's what the instructors have done to get the best result.

They then close the doors to the compartment and the fire very quickly uses up all the available oxygen inside and drops below the LFL (lower flammable limit) and the fire snuffs out. But due to the extreme temperatures the materials are still pyrolising (giving of all the highly flammable gasses).

When the door is opened, the gasses/smoke vent out and as oxygen is reintroduced to the compartment the mixture of the gasses come back into the flammable range and are just looking for any ignition source. As soon as it finds one everything explosively ignites in a sudden fireball..... this is the BACKDRAUGHT (because I spell like that)... or Backdraft for the US readers...

Here's a vid or two where you can see backdraghts in training and in real life plus one on flashover (skip to 1:20 on last vid)