What is Flashover?

Flashover is generally understood to be the moment in the development of a room fire in which all exposed surfaces pyrolise and reach ignition temperatures more or less simultaneously, and it transitions from a fire in a room to a room on fire. It is the tipping point between the growth stage and the fire becoming fully developed.

In other words, the fire now becomes a blaze, transitioning from controllable to uncontrollable. This typically occurs when a fire in a room has enough energy to reach a temperature of approx. 500- 600°C, which can happen within a few minutes depending on the rate of fire growth.

When a fire reaches flashover, the blaze poses an existential threat to building occupants, property assets and stored contents. Taking steps to reduce the chances of flashover through active fire protection such as sprinkler systems, or ensuring compartmentation to contain flashover through passive fire protection measures such as using building elements with high levels of fire resistance, can significantly reduce the chances of injury and minimise damage.

Effective compartmentation will help to contain a flashover, preventing the fire from spreading throughout the building to allow time for safe evacuation of occupants and to reduce the risk of significant property damage. In terms of business continuity, Forrer says "Compartmentation is really important in cases of flashover - by keeping the fire to one area, losses can be kept to a minimum and businesses can even continue to run."

How does a Fire reach Flashover?

Merl Forrer, Fire Engineer, explains the science behind flashover and how a fire in a room can quickly develop into a room on fire.

A flashover is the point when there is so much thermal energy being radiated from the fire and hot gasses back onto the contents of the room that everything ignites and burns. Essentially, flashover is the point when we move from a fire in a room to a room on fire.

Merlyn Forrer, Fire Engineer

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