Further Development of the N-Gas Mathematical Model: An Approach for Predicting the Toxic Potency of Complex Combustion Mixtures.
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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899