Flashover / Backdraft

Wikipedia:
Dangers of flashovers

Flashover is one of the most-feared phenomena among firefighters. Firefighters are taught to recognize flashovers and avoid backdrafts. For example, they have certain routines for opening a closed door in a building on fire, such as sitting beside the door instead of in front of it, and to be ready to fight shooting flames.

Despite superior protective gear, a firefighter has less than two seconds to evacuate a room that has a flashover.