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Estimating Reduced Fire Risk Resulting From an Improved Mattress Flammability Standard.


pdf icon Estimating Reduced Fire Risk Resulting From an Improved Mattress Flammability Standard. (1346 K)
Ohlemiller, T. J.; Gann, R. G.

NIST TN 1446; 80 p. August 2002.

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Keywords:

mattresses; fire risk; flammability; standards; ignition; cone calorimeters; heat release rate; heat flux; heat transport; smoke transport; thermal ignition

Abstract:

This study addresses the hazards posed by bed fires of varied sizes in an effort to relate potential fire size reduction to decreased risk of bed fire fatalities. For this purpose, a "bed" refers to a mattress, a foundation and bedclothes. There are three hazards: (I) the potential for a bed fire, by itself, to cause flashover in a bedroom; (2) the probability that a bed fire will ignite additional objects in the same room as a result of the fire's radiated heat; possibly leading to flashover and (3) the heat and toxic gas threat, in the room of fire origin and beyond, due to the bed fire alone. To address the first two issues, twin and king-size beds of three designs (always using the same bedclothes) were burned in duplicate both under an open hood and in a room. The three designs (termed MI, M3 and M5, consistent with previous usage) produced widely different peak heat !'j. release rates; open hood peaks ranged from 160 kW (M3 twin fire) to 3850 kW (MI king fire). . The radiant heat flux distribution around the fires was measured using up to two arrays of five flux gages each. These radiant flux reach data were translated into piloted ignition reach outward from the edge of the burning bed by means of ignitability results for seven materials. IN These materials are viewed as surrogates for the surfaces of other potentially significant combustible objects such as chairs or drapes which, if ignited by the bed fire, could push the room to a flashover condition. The results were then cast into a form that should be related to the probability of ignition in the overall population of bedrooms, i.e., the fraction of the room area (beyond the bed) that is at risk of piloted ignition of a second object by a bed fire. This fraction, is strongly influenced by the size of the bed fire and of the size of the room. Both MI and M5 \ fires are inferred to present substantial threats of second object ignition. The threat for an M3 fire is localized to the bed periphery but could be problematical in small bedrooms. To address the third hazard, heat and toxic gases, CF AST was run using the measured heat release rate curves from the room tests as input. This program predicts the spread of hot, toxic smoke in the room of fire origin and beyond. Here the context was a single story house consisting of four monitored spaces. The MI and M5 fires presented a substantial lethal threat due to heat exposure in the room of fire origin and some spaces beyond. The M3 fire (consisting mainly of the bedclothes with little contribution from the mattress/foundation) was substantially less threatening but not innocuous, especially with a king size bed. Minimizing the occurrence of flashover and its attendant fatalities would require limiting the heat release rate peak from a mattress/foundation to less than that of an M5 fire. Localizing the fire to the bed would save significantly more lives but would require limiting the mattress/foundation heat release rate to near zero as with the M3 design. Even this case presents some threat of heat lethality away from the bed (in addition to the localized threat) since the bedclothes set used here yielded a 400 kW fire atop a king-size M3 mattress. Overall the study suggests that beds with fire performance similar to the M3 design would achieve very significant reduction in fire risk. Since the bedclothes contributed the bulk of the heat release seen with the M3 beds, further reduction in fire fatalities would probably have to address the bedclothes flammability as well.