Flashover

Fire doesn't burn things, it burns the gases that super heated things give off. Through a process known as pyrolosis, things give off gases which catch on fire. Most of those gases do not reach their ignition point and end up floating around in the atmosphere of the fire room. If the oxygen that feeds that fire is somehow cut off, the fire will try to suck in more. It will begin sucking the smoke back toward itself in search of the oxygen it craves. The smoke will actually run backwards.
And you are in trouble.
The room gets very hot, almost blindingly hot because the fire is smoldering and searching for oxygen to allow it to burn. The smoke roils and bubbles like a turbulent sea. Even with turnout gear you can feel the heat, smothering you. Its only a matter of time before the fire finds oxygen and flares up enough to ignite one of the gases trapped below the ceiling.
When that happens, theres a brilliant flash, so hot and so powerful that everything bursts into flames. Anyone in a room when it flashes will not survive, turnout gear will burn readily, tissue paper would be just as usefull in that situation.
In order to be able to recognize the signs of a coming flashover, a Swedish fire safety company developed a trailer that simulates the flashober. Well, simulates is the wrong word, because it actually is a flashover. The only reason that its survivable is because the firefighters are placed three feet below the floor of the room that is flashing over. The trailer is two levels, with two doors and a vent hole, an instructor mans a charged hoseline to control the flashover.
The effect is absolutely mind blowing. Snakes of fire, jellyfish like explosions of flames and smoke expolode over my head as I repeat "Holy shit," again and again. Smoke boils so thick you can take handfuls of it and play with it like a sort of black mercury. The heat goes down through your body, cooking you. When I got out my hands, arms and chest were covered in red, sunburn like splotches, the result of radiant heat burns. I was litterally getting cooked like a hot dog in the microwave.
And thats with turn out gear and an SCBA on. My whole body was drenched in sweat, my eyes burned as I watched hell explode six inches above my facepiece.
To allow the flashover to occur again and again, the instructor would spray short stacatto bursts of a hoseline into the ceiling of the trailer. The water, close to freezing from being pumped through icy hoselines, converted to steam instaneously. All the while, the gases above our heads burst into flames from the intense heat, an occurence know as auto ignition.
A pre flashover produces dark yellowish brown smoke in breath like puffs that give the appearance of breathing. The smoke tries to escape and gets sucked back, the fire dampens to a fierce orange glow as it sucks futily for oxygen. Then someone opens the door and it explodes again, flames ripple the length of the trailer and lick the top of my tin foil covered helmet. Its not really tin foil, but a silver shield that reflects radiant heat. At least its supposed to, but with that much heat, some warmth is bound to get through. But thats what aloe vera burn lotion is for.
Now, I just enjoy the show and try to remember everything I see. In a real fire, I won't be able to sit back and watch, I'll have to get out before my facepiece explodes and I inhale superheated gases. Its something to think about as the world around me burns.