Understanding the factors affecting flashover of a fire in modern buildings

BRE (Building Research Establishment) is an independent, research-based consultancy, testing and training organisation, operating in the built environment and associated industries.

On 21 April 2017, BRE published; Understanding the factors affecting flashover of a fire in modern buildings (IP 2/17), written by Richard Chitty.

• The development of a fire in an enclosure can be categorised as:
• Ignition and growth.
• Fully developed.
• Decay and burnout.

The term ‘flashover’ refers to the transition of an enclosure or room fire from a localised fire to the ignition of all exposed flammable surfaces, creating conditions where life is no longer tenable. The time to flashover is important in determining the impact on; escaping occupants, firefighting tactics and the building structure.

Theoretical and experimental investigations involving flashover have been undertaken since the 1950s. Initially they involved small enclosures and scale models, used to identify the basic mechanisms of flashover in the context of domestic buildings, cellular offices and similar-sized enclosures. While this work is still relevant today for similar enclosures, different mechanisms may also be involved, or become dominant, in particular in very large or highly-insulated modern spaces.

This 12-page information paper explains the process of flashover and the factors that influence its occurrence and development. It is intended for fire risk assessors, fire safety managers, other safety managers and building managers with some responsibility for safety, as well as community fire safety officers, firefighters and fire investigators. It will also be useful for those who are new to fire safety engineering.

The contents of the information paper are:

• Introduction.
• Development of a fire.
• Fires in an enclosure.
• Thermal instability.
• Quantifying the conditions for flashover.
• Example calculations for time to flashover.
• Discussion and conclusions.
• References and further reading.

--BRE Group

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