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Further Development of the N-Gas Mathematical Model: An Approach for Predicting the Toxic Potency of Complex Combustion Mixtures.


pdf icon Further Development of the N-Gas Mathematical Model: An Approach for Predicting the Toxic Potency of Complex Combustion Mixtures. (986 K)
Levin, B. C.; Braun, E.; Navarro, M.; Paabo, M.

American Chemical Society. Fire and Polymers II: Materials and Tests for Hazard Prevention. National Meeting, 208th. Chapter 20. ACS Symposium Series No. 599. August 21-26, 1994, Washington, DC, American Chemical Society, Washington, DC, Nelson, G. L., Editor(s), 293-311 pp, 1995.

Keywords:

mathematical models; smoke; toxicity; toxicology; gas mixtures; methodology; animals; rats; nitrogen dioxide; carbon dioxide; carbon monoxide; oxygen; hydrogen cyanide

Abstract:

A methodology has been developed for predicting smoke toxicity based on the toxicological interactions of complex fire gas mixtures. This methodology consists of burning materials using a bench-scale method that simulates realistic fire conditions, measuring the concentrations of the following primary fire gases - CO, CO2, O2, HCN, HCl, HBr, and NO2 - and predicting the toxicity of the smoke using an empirical mathematical model called the N-Gas Model. The model currently in use is based on toxicological studies of the first six of the above listed primary gases both as individual gases and complex mixtures. The predicted toxic potency (based on this N-Gas Model) is checked with a small number of animal (Fischer 344 male rats) tests to assure that an unanticipated toxic gas was not generated. The results indicate whether the smoke from a material or product is extremely toxic (based on mass consumed at the predicted toxic level) or unusually toxic (based on mass consumed at the predicted toxic level) or unusually toxic (based on the gases deemed responsible). The predictions based on bench-scale laboratory tests have been verified with full-scale room burns of a limited number of materials of widely differing characteristics chosen to challenge the system. The advantages of this approach are: 1. The number of test animals is minimized by predicting the toxic potency from the chemical analysis of the smoke and only using a few animals to check the prediction; 2. Smoke may be produced under conditions that simulate the fire scenario of concern; 3. Fewer tests are needed, thereby reducing the overall cost of the testing; and 4. Information is obtained on both the toxic potency of the smoke and the responsible gases. These results have been used in computations of fire hazard, and this methodology is now part of a draft international standard that is currently being voted on by the member countries of the International Standards Organization (ISO), Technical Committee 92 (TC92). In this chapter, a new 7-Gas Model including NO2 and the data used in its development are presented.