Extreme Fire Behavior: Flashover

This is the first of three articles dealing with the extreme fire behavior phenomena, flashover, backdraft, and smoke explosion. Rapid fire progress presents a significant threat to firefighters during structural firefighting.


Editors Note: To view more detailed images of the figures displayed on the right, please click on the links to each figure in the body of the article.

Previous articles examined fire development in a compartment and the combustibility of smoke. This is the first of three articles dealing with the extreme fire behavior phenomena, flashover, backdraft, and smoke explosion. Rapid fire progress presents a significant threat to firefighters during structural firefighting. Figure 1 illustrates post-flashover conditions encountered by Lemley Fire Rescue firefighters during live fire training in an acquired structure. (see Figure 1.)

If firefighters do not have a high level of situational awareness this hazard is increased. It is difficult to develop proficiency in recognizing fire behavior indictors and developing an understanding of fire dynamics from fireground experience or classroom study alone.

This article examines flashover; the sudden transition from a developing to fully developed fire. This phenomenon involves a rapid transition to a state of total surface involvement of all combustible material within the compartment. If flashover occurs, the rate of heat release in the compartment as well as the temperature in the compartment increases rapidly. Flashover may occur as the fire develops in a compartment or additional air is provided to a ventilation controlled fire (that has insufficient temperature to backdraft).

Case Study Method

What is a case study? Cases are not simply narratives for entertainment. They are stories with an educational message. Each of the case studies in this article is based on an actual incident where Firefighters were injured or killed by rapid fire development or other extreme fire behavior. The purpose of these cases is not to lay blame or simply identify the mistakes of others; it is to develop an improved understanding of structural fire behavior.

How should you approach learning through the use of case studies? Read the questions to be answered first, this provides you with a framework for understanding the information presented. Second, read the case to get an overall understanding of the incident. Last, examine the incident in detail to answer the questions posed at the start of the case.

One excellent source for case studies are reports prepared by the National Institute for Occupational Safety and Health (NOSH) on firefighter fatalities. Particularly when fire behavior was a significant factor, the National Institute for Standards and Technology (NIST) Building and Fire Research Laboratory also prepares reports including fire test and modeling data. When using case studies as an element of fire behavior training, the following questions serve as a good starting point for your analysis:

Was extreme fire behavior involved in this incident? If so, what type of event happened?

Look at the reported conditions and observations of individuals involved in the incident. Was this a flashover, backdraft, or smoke explosion? Recognize that it may be difficult to determine based on limited information. If available, NIST fire test and modeling data can shed a great deal of light on the nature of extreme fire behavior phenomena.

How did the fire develop and what factors influenced the occurrence of the extreme fire behavior phenomenon?

As with the question of what happened, this question is complex. Many factors influence fire development and extreme fire behavior phenomena. Think about building factors such as fuel type, fuel load, and ventilation profile, changes in ventilation profile (may be caused by the fire or human action) and actions of firefighting forces.

What cues were present that may have indicated potential for rapid fire development?

Frequently there is limited information on exactly what was observed (particularly by the individuals most impacted by the incident). However, in some cases critical fire behavior indicators are mentioned and/or photographs of incident conditions are included in the reports.

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