Extreme Fire Behavior: Backdraft

A backdraft involves deflagration or rapid combustion of hot pyrolysis products and flammable products of combustion upon mixing with air. Several conditions are necessary in order for a backdraft to occur within a compartment. The fire must have...


 

Configuration: The unit involved in the fire had a kitchen and living room on floor one and two bedrooms, bathroom (sink and shower) and water closet (toilet) on floor two. Figure 4 shows a plot plan and plan view of the first and second floor of the involved unit.

 

Fuel Profile: Contents were typical of a residential structure and included ordinary kitchen, and living room furniture. The fire originated in clothing located in the kitchen. In addition, all rooms were carpeted. Research conducted by the British Fire College Fire Experimental Unit (FEU) indicated that carpet can contribute significantly to fire load and can have a significant impact on fire development and intensity. This finding is independently supported by research conducted by the National Institute of Standards and Technology (NIST) examining fire development in the deaths of two firefighters during a training exercise in Osceola, Florida in 2002 (Hollenbach, 2002).

 

Ventilation Profile: At the time of ignition there were not ventilation openings to the exterior of the structure and the door between the kitchen and living room was open. The occupant discovered the fire at approximately 0548 and reportedly closed the door between the kitchen and living room and exited the structure, leaving the front door open. At approximately 0605 (five minutes prior to the arrival of the first company) the kitchen window failed (at least partially) with flames exiting the widow. Smoke pushing from the front door raises the possibility that a gravity current had developed at this opening as well as at the kitchen window (See Figure 4).

 

The FBU investigative report indicates that the fire breached the ceiling/floor between the kitchen and bedroom two (See Figure 4) at 0615, changing the ventilation profile and related air track. However, subsequent analysis (Grimwood, 2002; personal communication P. Grimwood, Febrary 2006) indicates that the ceiling/floor may not have failed until later in the incident.

 

Fire Development: The fire originated clothing located in the kitchen (See Figure 4). The exact time of ignition is estimated at 0537. The speed with which the fire may have progressed from incipient to growth stages is unknown. However, the occupant discovered the fire at approximately 0548 and was able to close (partially?) the door between the kitchen and living room prior to escape. This indicates that the fire had not yet reached flashover. Sufficient heat was developed within the kitchen to cause failure of the kitchen window. This could have occurred fairly early in fire growth, as the melting temperature of CPVC can be as low as 150o C (302o F). This provided an additional, but limited supply of air to support fire growth to flashover within the kitchen. Dr. Martin Thomas of the FEU estimated that post flashover ceiling temperatures in the kitchen were as high as 1000o C (1832o F).

 

Flaming combustion was not observed from the doorway on Side A at the time firefighters entered the structure. However, it is possible that combustion was occurring above the neutral plane and the dense smoke obscured it from the firefighters view. Shortly after 0615 (five minutes after arrival of the first company) there was a deflagration resulting in an immediate transition to flaming combustion on both floors one and two.

 

Initial Tactical Operations: Initial response to this incident was a single pump (six personnel) and Station Officer. Upon receipt of additional information that there were persons reported in the building, a second pump (five personnel) was added to the incident. As the first company (B031) arrived on scene, they observed thick, dense smoke from the house drifting across the road. Initial size-up showed a large volume of black smoke from the open front door as well as smoke showing from the eaves. The windows on Side A were intact and showed evidence of condensed smoke (staining of the window glazing). It was apparent that both floors one and two were smoke logged (substantial smoke accumulation within the compartments on each floor).