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OCR for page 224
SESSION I: TOXICITY
SESSION OBJECTIVES
Characterize current fire-toxicity considerations and suggest how these considerations
should change in the future.
PARTICIPANTS
Chair: Stephanie Skaggs, New Mexico Engineering Research Institute
Committee: Barbara Levin, National Institute of Starboards arm Technology
Participants: Gary Burns, Dow Corning
Daniel Caidwell, U.S. Army
Marcelo Hirschler, Safety Engineering Labs
Thomas Murray, Boeing Commercial Airplane Group
David Purser, Fire Research Station
Henry Roux, Rowr International
Chuck Williamson, General Plastics Manufacturing Co.
SESSION REPORT
The following views and suggestions were presented by one or more participants in this
session. Although the workshop session focused on toxicity, several participants stressed that
toxicity is only one aspect of the total fire hazard. issues surrounding fire toxicity considerations
should be product-dnven (as opposed to materials-driven) and scenario-specific. New materials
should be designed such that toxicity of the product is never the limiting factor influencing
· · ~ .
survlva in a nre scenario.
The two key scenarios to consider include:
post-crash or external pool fires, and
concealed in-flight fires.
Excluded as major hazards were fires on unoccupied aircraft (not in revenue service) or visible
in-flight cabin fires.
There is a great deal of knowledge that currently exists as a result of previous
toxicological research. This information can be used to validate toxicity models.
224
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Part 11- Workshop Summary
225
Current Toxicity Criteria and Characterization Methods
There are currency no regulations establishing general toxicity critena for individual
products for aircraft. No general toxicity criteria are needed, rather a holistic "life-threat
cntenon" that includes the entire fire environment should be considered.
While many toxicity charactenzation methods exist, there is currency no one test that
adequately meets all needs.
Toxicity Goals for Long-Term Research
The primary cntenon for long-term research in toxicology is that toxic hazards in end
use should not be the limiting factor of any product. For aircraft interior applications, the
criteria require that toxicity not control escape time (i.e., the time available for escape is greater
than the time required for escape).
In order to facilitate evaluation of new matenals, it is important to develop small-scale
tests that have large-scale relevance.
Needed Development in Materials Evaluation and Characterization
Participants in this session suggested the following would be useful in evaluating and
characterizing new materials.
.
.
.
Design characterization methods that relate to real scenarios (post-crash or
concealed in-flight).
Consider lethality as the primary criterion. Also consider the possible effects of
incapacitation and long-term effects of acute one-time exposures, such as
immunological dysfunction, allergic reactions, teratogenicity, mutagenicity, and
· · ~
carcmogemclty .
· Validate small-scale tests against large-scale scenarios.
· Consider relevant toxic decomposition gases (narcotics, asphyxiants, irritants), as
well as smoke obscuration and heat.
· Include analytical characterization and model prediction, followed by a limited
bioassay proof test using animals that best represent human responses.
Incorporate heat, hot-water vapor, and particulates into predictive toxicity potency
models (e.g., N-gas and FED [fractional effective dosed.
Develop a toxicity profile for decomposition products that includes concentration,
effects, and interactions.
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226
research.
Improved Fire- arm Smoke-Resistant Materials
Long-Term Research
The participants in the Toxicity session had the following suggestions for long-term
.
.
.
Identify scenano-specific, product-driven characterization methods that are based
on performance requirements relevant to human survivability.
Validate that bench-scale characterization methods adequately represent larger-scale
tests of components or representative cabin areas (e.g., seats, row of seats, full
cabin).
· Enhance current models (N-gas and FED) to consider the toxicological effects of
heat, hot-water vapor, and particulates and free radicals.
Develop an overall life-threat analysis method that incorporates the effects of heat,
toxicity, and smoke obscuration.
· Investigate the factors that influence survivability. Determine physiological and
psychological considerations that may determine why some passengers survive.
Determine how people are actually affected by the fire environment using data from
post-crash survivors as well as fatalities.
· Review methods for assessing irritancy and determine if these methods are
meaningful.
Determine the relationship between physical exertion and adrenaline, alcohol, and
other agents on toxic-gas models.
· Examine the relationship between animal models and human responses. To
minimize the use of animals, investigate the use of in vitro (or cell culture) methods
that can be used instead of whole animals.
Determine the feasibility of new materials with additives that act as toxicant
suppressants.
Special Comments by Marcelo H~rschIer
Marcelo Hirschier, a participant in the Toxicity session, submitted the following
comments.
The major issue in fire toxicity is that the toxicity of the new materials, when
incorporated into the products they will be used in, must not become the limiting factor in the
fire hazard associated with the scenario under investigation. The toxic hazard must be assessed
as a part of an overall fire-hazard assessment.
The major fire scenarios of importance in aircraft are (~) a post-crash pool fire resulting
from ignition of aircraft fuel penetrating into the cabin following aircraft skin rupture; (2) a
concealed in-flight fire that is not detected for some time; and (3) an open in-flight fire, which
is likely to be detected rapidly and will be of little consequence.
In the pool-fire scenario, the incident flux vanes about 100-150 kW/m2 very close to the
rupture point and 10 kW/m2 within a relatively short distance from it, which is very different
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Part 11- Workshop Scary
227
from the approach of a typical flashover fire in ground fires. In aircraft fires, toxicity in a post-
flashover scenario is of no consequence, because after flashover aircraft egress is impossible.
Toxicity should be measured by exposing products (and not materials) in a scenario
representative of the way in which those products are likely to be exposed within the aircraft.
Any small-scale (or bench-scale3 tests to be used must be validated against tests conducted
in three over full-scale tests: testing of a complete product in isolation (for example, a chair)
or of an entire cabin. These large-scale tests should be the same ones conducted to assess all
other fire-performance issues.
There should be no prescriptive requirements for toxicity alone, since such requirements
may result in eliminating materials that would provide lower fire hazard once the overall fire-
hazard assessment is conducted.
There is, at present, no fire toxicity requirement by the Federal Aviation Administration,
and Mr. Hirschier does not recommend such a requirement. There are requirements set out for
some toxic gases, but he does not recommend this method.
None of the existing fire-toxicity test methods are fully acceptable (or capable of
achieving consensus). Whatever validated test method is chosen for use must expose products,
and determinations should include individual time profiles of indiviclual decomposition products
(asphyxiants, irritants, smoke obscuration and temperature). These should then be incorporated
(after consideration of the quantity of product present in the fire scenario and the time when the
product becomes involved in the fire) in the fire-hazard assessment model.
In order to ensure that products with unusual toxicity are not introduced, limited testing
of animals (of species for which the toxic effects are known to be relevant to human lethality)
should be conducted.
Incapacitation may occur before lethality but is difficult to characterize experimentally.
This should be understood and corrections may be needed.
If animal experiments have shown that no unusual toxic effects are present, mass-Ioss rate
may be a first-order approximation to fire toxicity.
Research should include the following:
investigation of effects on humans, both survivors and fatalities, from actual aircraft
Walrus;
development of a smoke toxicity test with proven validity for aircraft scenarios;
potential investigation of effects due to hot-water vapor, particulates, and free
radicals;
potential investigation of in vitro methods for toxicity targets; and
investigation of potential chronic effects of acute exposures to fire.
Representative terms from entire chapter:
fire toxicity
