Fire Dynamics, Firefighting

USFA: Recognizing Flashover

Firefighters stoking flames in the flashover can
Photo from FDIC International by Tim Olk

The U.S. Fire Administration (USFA) recently released a brief article dealing with the fire behavior phenomenon known as flashover.

Learning to recognize when flashover conditions exist can save a firefighter’s life. What is flashover? Flashover is a thermally-driven event during which every combustible surface exposed to thermal radiation in a compartment or enclosed space rapidly and simultaneously ignites.



Firefighter Training Bulletin: Flashover

Firefighter Safety: Understanding and Avoiding a Flashover


Differentiating the “Fireground Phenomena”

Flashover normally occurs when the upper portion of the compartment reaches a temperature of approximately 1,100 °F for ordinary combustibles. Building features like concealed spaces, lower ceiling heights, room partitions, and energy-efficient or hurricane windows are more likely to contribute to flashover conditions.

Wright McMeekan/YouTube

Factors that influence a flashover event

  • Location of fire.
  • Size, volume and shape of compartment.
  • Fire growth rate.
  • Contents and their exposed surfaces.
  • Compartment ventilation characteristics.

Factors that influence responder exposure

  • Arriving on the scene at a pre-flashover state.
  • Compartments are built tighter with fewer sources of air leakage.
  • Bunker gear provides a false sense of security.
  • Rooms filled with many more synthetics that flash at lower temperatures.

Signs of an impending flashover

  • Ambient temperatures quickly double and triple as hoselines are advanced.
  • Large volumes of heavy dark smoke.
  • Rollover: active flame circulation in the thermal layer.
  • Free burning fire in a ventilation-deficient environment.

The USFA report also linked off to the NIOSH report on a fire that killed Homewood (IL) Firefighter Brian Carey in 2010. You can find Joe Pronesti’s videos and podcast interview with Homewood Deputy Chief Steve Dejong here.