Extreme Fire Behavior: Smoke Explosion

In the case of both backdraft and smoke explosion, smoke is the fuel. However, the other sides of the fire triangle are quite different.


Configuration: This 1600 ft2, tri-level, wood frame apartment building had two levels above ground and a daylight basement (partially above grade on Side C). The first floor was comprised of a single room, divided into living and kitchen areas. A single bedroom and bathroom were located on the second floor.

Due to the roofline of the structure (see Figure 3), there were substantial void spaces behind knee walls on the Alpha and Charlie sides of the second floor (see Figure 4). While NIOSH Report F2005-13 emphasizes the void space hazards of this type of truss, similar voids are likely any time a finished room is located directly beneath a pitched roof.The area of fire origin was behind a knee wall (storage area) on floor two (see Figures 4 and 5). The interconnected void spaces behind the knee walls and above the ceiling permitted the fire and hot smoke to surround the rooms on floor two.

Fuel Profile: Contents were typical of a residential structure. NIOSH report F2005-13 made no specific mention of the contents of the attic storage areas.

Ventilation Profile: While not specified in NIOSH report F2005-13, truss spaces are equipped with roof vents, typically providing 1 ft2 of vent area for each 150 ft2 of attic floor area. These building vents would have potentially provided limited air supply for fire development within the storage area and void spaces.

It is unknown if either exterior door on floor one was open before the arrival of the fire department. However, Engine 1 the first arriving company opened the door and made entry through the doorway on Side C with a hoseline. At approximately the same time, the Incident Commander observed a small amount of flame from the roof above the door on Side C (see Figure 6).

The Captain from Engine 1 tasked a place a positive pressure blower at the door on Side A. Engine 2 stretched a line to this doorway, creating a second opening on floor one. NIOSH Report 2005-3 also discusses the Captain's intention to establish a horizontal exhaust opening on floor two, Side Delta, but found no windows at this location. The report mentions that he observed a skylight on Side Charlie (see Figures 5 and 6). The report did not specify if the Captain vented the skylight.

Fire Development: From its point of origin in the storage area on Side Charlie (Bravo/Charlie corner of the unit), the fire extended throughout the storage area and void spaces on Side C, above the ceiling, and on Side Alpha. Even with the limited ventilation provided by the attic vents, the high wind (30+ mph blowing from Side Charlie) may have accelerated fire development. Fire behavior indicators observed by the first arriving companies included a small amount of flame from the roof peak near the chimney on Side Delta (see Figures 3 and 6) and light colored smoke seeping from the roof shingles and the attic of Exposure Bravo. A short time later flames were observe above the door on Side Charlie (intersection of the involved unit and Exposure Bravo). Engine 2 observed heavy brown smoke filtering down the stairwell as they extended a backup line to the door on Side Alpha. Approximately eight minutes after Engine 1 arrived on scene, an explosion blew the crew from Engine 2 out the door on Side Alpha and caused the window on floor one, Side Delta to fail. Fire and black smoke was blowing out the door on Side Alpha and window on Side Delta. Crews entering the building to attempt a rescue of the crew from Engine 1 encountered fully developed fire conditions on floors 1 and 2.

Initial Tactical Operations: Initial response to this incident was two engines (one with a a Captain and two firefighters and the other a Lieutenant and three firefighters), a truck (Lieutenant and two firefighters), and three additional personnel (Lieutenants) arriving in personally owned vehicles (POV). One of the Lieutenants arrived in his POV and assumed Command just as Engine 1 arrived on scene. Initial reports from bystanders were that children were trapped on floor two. A firefighter (company not specified in NIOSH report F2005-13) placed a PPV fan at the door on Side Alpha. Engine 1 deployed a 1-3/4-inch hoseline through the doorway on Side Charlie to support primary search. Engine 2 stretched a second 1-3/4-inch line through the door on Side Alpha and onto the stairwell to back up the crew from Engine 1 while Truck 1 was setting up (tactical assignment not specified in NIOSH report F2005-13). (Figure 7: 12 Minutes on the Fireground)