What is FLASHOVER? Flashover is a very rapid transition from local burning of the contents within a compartment to widespread burning of all exposed fuels with that compartment. Flashover occurs because all the combustible material in the room have been heated to their ignition temperature and there is an almost simultaneous ignition. A flashover can occur in as little as 90 seconds from the ignition of a residential fire. Not every fire results in a flashover occuring nor is a flashover predict