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.

Compare and contrast these the case study with other cases or events in your own experience. What aspects of these incidents were similar? Which were different?

Building your knowledge base using case studies is enhanced by integrating this information with your existing knowledge of fire behavior. Often discussion of a case with others results in sharing of personal experience. Expand this discussion beyond simple "war stories" to consider commonalities and differences.

In addressing the first two questions, what happened and what were the contributing factors it might be useful to examine the fire development curve presented in Fire Development in a Compartment. What stage (incipient, growth, fully developed, or decay) and what burning regime (fuel controlled or ventilation controlled) is the fire in immediately prior to changes in fire behavior.

Case Study

This incident involved an early morning fire in a two-story, wood frame duplex that resulted in the deaths of three children and three firefighters. The fire occurred in the unit on Side Bravo of the structure (See Figure 2). This building was originally constructed in the 1870s as a single family dwelling and divided into two dwelling units in the 1970s. This case study will focus on fire behavior related aspects of this incident. However, this case provides an opportunity to learn a number of other important lessons (see the NIOSH and NIST reports for additional information on the incident).

Configuration: The unit involved in the fire had a kitchen, dining room, and living room on floor one and three bedrooms and a bathroom on floor two. Figures 3 and 4 show plan view of the first and second floor of the involved unit. A wall separated the first floor hallway and stairs to the second floor from the rooms on floor 1. There was a door leading from the floor one hallway into the living room (this door was open at the time of the fire). In addition, there was a door from the floor one hallway to the dining room (this door was closed at the time of the fire).

Fuel Profile: Contents were typical of a residential structure and included ordinary kitchen, dining, and living room furniture. Ceilings were covered with combustible wood fiber ceiling tile with the exception of the dining room, which had the original plaster and lath ceiling. Interior walls were covered with gypsum board. However, the walls of the first and second floor hallways, stairwell and bedrooms two and three (see Figure 4) were covered with wood paneling.

Ventilation Profile: At the time of ignition, there were no ventilation openings. The only air movement would have been due to normal building ventilation and leakage. Prior to the arrival of the fire department a building occupant opened a window in bedroom one on floor two (see figure 4). The front door was opened approximately two minutes after the fire department arrived on scene. The window in the kitchen was composed of small panes with wood framing and failed over a period of time (starting approximately when the front door was opened).

Fire Development: The fire originated in plastic materials on top of the stove in the kitchen that was located on floor one of the dwelling. The exact time of ignition and the speed with which the fire may have progressed from incipient to growth stages is unknown. The fire extended from the burning material on top of the stove to interior finish of the kitchen. Firefighters observed that there was smoke, but "no heat" at the first floor level shortly after beginning primary search. While smoke began to spread through the structure shortly after ignition, fire did not extend beyond the kitchen until eight minutes after flaming ignition (estimated to be six minutes after the arrival of the first company). The NIST fire model of this incident is consistent with this observation, showing near ambient temperature at floor level with temperatures between 570 degrees F and 840 degrees F at the ceiling in the living and dining rooms. Between six and eight minutes after the first company arrived on scene, conditions changed radically fire rapidly extending sequentially in the kitchen, dining room, living room, floor one hallway and stairway to floor two. Figure 5 illustrates the 12 critical minutes from the time the alarm was received by the dispatch center until 10 minutes after the arrival of the first company.