During a backdraft, (which is very rare I might add) the conditions are a VERY abundant amount of yellow-grayish smoke puffing out of every nook and cranny in the structure. Not just the bottom of the door when the victims just happend to drop they're keys. Also if you look in the window of the second backdraft scene, you'll notice a lamp that is not only undamaged from fire, but it's still lit! Not only would it be evaporated to ashes prior to a backdraft, the windows would be stained black and cracked (another sign of impending backdraft). Still a great movie, but lacking realism in some scenes.