Fires in Mass Transit Vehicles Guide for the Evaluation of Toxic Hazards (1991) / Chapter Skim
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5. Toxic Hazard Assessment
5. Toxic Hazard Assessment
Pages 41-50
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From page 41... ...
HAZARD ASSESSMENT ENGINEERING MODELS The most widely used approach to hazard models involves incremental exposure doses (Cidt) of a toxic species ~i.
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From page 42... ...
The mass loss curve for the fire is then used in conjunction with toxic potency data derived from laboratory-scale smoke toxicity tests. The tests, operated under conditions relevant to those in the fire, supply the lethal mass loss exposure dose (LCt50)
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Computer programs using a Variety of fire scenarios and material input data have been developed for assessing potential toxic hazard for fires involving several materials simultaneously. Purser Mass Loss FED Mode!
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From page 44... ...
To the extent that lethal exposure doses in the rat are similar to those in humans, an approximation that is considered to be appropriate, it is also possible to make some predictions about the possible human lethal exposure hazard in large-scale fires in which measurements of the major toxicant concentrations have been made. HartzelI-Emmons Toxic Gas FED Mode!
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From page 45... ...
It is designed to predict to~cic hazard in terms of exposure dose and time to incapacitation for humans in fires and is intended for use in fire engineering calculations of modeled fire scenarios, full-scale fire tests, and data related to actual fire victims. As with all the multiple toxicant models, it relies on measured or calculated concentration-time data for the important toxic fire gases.
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From page 46... ...
For the majority of fire atmospheres, which contain a mixture of organic and acid gas irritants, irritancy is modeled in terms of mass toss exposure concentration and dose. A mass loss concentration of 1.0 gums is considered to produce a degree of incapacitation due to sensory irritation, and an accumulated exposure dose of 300 gums.
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From page 47... ...
The total exposure is the sum of the exposure doses accumulated in each room until the occupant exits the building. SELECTION OF HAZARD ENGINEERING MODELS Methodology for calculating the toxic effects of fire effluents has made considerable progress.
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From page 48... ...
Although modeling methodology has advanced significantly, considerable judgment is still required in the current state of the art of predicting the toxic hazards of fire effluents, and the models are not substitutes for testing. CONCLUSIONS Hazard assessment engineering calculations provide the capability to analyze the hazards, including toxic hazard, associated with specific fire scenarios.
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From page 49... ...
1988. Further Studies of the Toxicological Effects of Different Time Exposures to the Individual and Combined Fire Gases: Carbon Monoxide, Hydrogen Cyanide, Carbon Dioxide, and Reduced Oxygen, Polvurethanes 'S8, Proceedings of the SPI 31st Annual Technical/Marketing Conference, Philadelphia, PA, October 18-21; Technomic Publishing Company, Inc., Lancaster, PA, pp.
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