This is the second part of a report about a fire that occurred on Nov. 21, 2009, in which two firefighters from the Wheat Ridge, CO, Fire Department became trapped and initiated a Mayday while operating on the interior of a working fire in a single-family dwelling. The Mayday was transmitted...
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Examination of the area under the bed revealed a rug/carpet remnant and miscellaneous items that had evidence of heat exposure. The rug directly under the bunk bed and rug/carpet remnant was pristine in nature, after being cleared of debris, as was the area to the west of the bed and showed no signs of exposure to radiant heat or direct flame impingement. Based on these observations, the lower-level bunk bed is determined to be the fire's area of origin. It is further determined that the area of origin and the vicinity surrounding the area of origin are void of all potential ignition sources.
While excavating debris from the northeast area of bedroom 1, a disposable cigarette lighter was found along the north wall adjacent to the hinged side of the closet door. The female occupant said in her interview that all lighters in her residence should be secure and there was no legitimate reason a disposable lighter should be in a child's bedroom.
The investigation concludes that the fire was set in the lower-level bunk bed with an unknown external ignition source as no ignition or heat sources were in the area of fire origin. Furthermore, after a complete, thorough and extensive site analysis and excavation, the only identifiable source of ignition noted in the room was the disposable lighter.
Investigators hypothesize that the fire was set by the 5-year-old male occupant in the lower level of the bunk bed with the cigarette lighter that was discovered in the room of origin. The fire developed slowly and was controlled while in its early growth phase by the limited amount of oxygen available. The room is very small and the door to it was closed. Both factors would contribute to the limited availability of oxygen to the fire. Once the door to bedroom 1 was opened by the interior crew, additional oxygen was rapidly introduced into the room and significantly enhanced the conditions necessary for rapid fire development. Further enhancing the conditions necessary for rapid fire growth was the fuel package and arrangement. The combustible nature of the fibrous composition of the mattresses, combined with the upper mattress being exposed to heat on the underside from the fire below, created ideal conditions for rapid fire growth.
National Fire Protection Association (NFPA) 921, Guide for Fire and Explosion Investigations, defines a flashover as "a transitional phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously and fire spreads rapidly throughout the space, resulting in full room involvement of the compartment or closed space." Based on this definition, the fire contained in bedroom 1, while intense, did not likely experience flashover.
Contributing factors leading to and resulting in the Mayday: