|A backdraft explosion from The Gray Monk|
As the smoldering fire sucks in oxygen, there is often a "puffing" effect as the fire gets a little, but not enough, oxygen. As the fire puffs, smoke produced by the fire is often sucked back into the burning area, giving rise to the term "backdraft." Firefighters are taught to avoid these dangerous situations, and to attempt to deal with it by ventilating the fire from the highest point. This allows the heat and smoke produced when the combustion reignites to escape through the highest point without exploding.
Wiki is full of all sorts of interesting trivia! There was a 1991 film "Backdraft" in which a serial arsonist was using backdrafts as a means for assassinating people! Also, if your house burns down and you've got papers stored in a safe--don't rush in to open it!! After the 1906 San Francisco earthquake and fire, business people who opened warm safes to recover their unburned papers exposed the hot gas of the interiors to an oxygen source, immediately and explosively setting the papers on fire!