Empirical models for flashover

Flashover is a pivotal phase in the development of an enclosed fire. It is not a totally sudden event, but rather a gradual transition where an initially localized fire evolves into a fully-developed fire, affecting all combustible materials in a volume. This phase is marked by a rapid intensification of pyrolysis of materials under the combined effect of thermal radiation from the hot smoke layer and increased internal heat flows.

Flashover is the result of the accumulation of energy and combustible gases in an enclosed or semi-enclosed space, creating the critical conditions necessary for near-simultaneous ignition. This process depends on a number of factors, including the thermal properties of materials, ventilation and the geometric configuration of the burning compartment.

Understanding flashover is essential, as it marks the transition from a controllable growth phase to a fully developed fire, featuring extreme temperatures and heat flows capable of compromising surrounding structures. For occupants, this transition severely limits evacuation possibilities, while for responders it increases the risk of involvement and calls for specific anticipation and fire-fighting strategies.

In this article, we propose to examine empirical models for characterizing and predicting flashover. After introducing the physical and thermal principles governing this transition, we will present the main qualitative and quantitative models, emphasizing their practical applications and limitations in real-life situations.