Fire and Smoke Understanding the Hazards (1986) / Chapter Skim
Currently Skimming:
5 Laboratory Methods for Evaluation of Toxic Potency of Smoke
5 Laboratory Methods for Evaluation of Toxic Potency of Smoke
Pages 78-104
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 78... ...
After contrasting chemical and biologic analyses, we discuss animal test methods that use death as an end point and then methods that use nonlethal end points, including factors that can impede escape from fires and nonlethal pulmonary effects that can be extrapolated to human exposures. USE OF COMBUSTION-PRODUCT TOXICITY TESTS: TO SCREEN OR NOT TO SCREEN A screening test should be simple, inexpensive, and valid.
|
From page 79... ...
The Committee takes issue with the assumption that any regulatory pass/fail judgment can be made on the basis of toxicity screening test data alone. The more complex evaluation of fire properties (fire hazard analysis)
|
From page 80... ...
The product was first detected by its acute effects on laboratory animals, which included grand mal seizures; it also produced observable psychomotor effects on several of the human investigators. This incident is often cited as evidence of chemical tests' potential failure to detect unanticipated, and in this case unusually toxic, combustion products.
|
From page 81... ...
Chemical tests often do not discriminate among the physical forms of a toxicant, such as its adsorption on particles and its occurrence as an aerosol, even though toxicity might depend on form. Correlations between human health response and combustion-product mixture dosage are poorly understood, so the health consequences of exposure to a fire gas at a given concentration over a given duration are poorly predicted.
|
From page 82... ...
are rare. the application of data derived solely from chemical tests to fire hazard models is that most current models are designed to accommodate toxicity data in units of concentration.
|
From page 83... ...
Any exposure system used for evaluation of toxic potency must be considered representational, because actual human exposures vary widely and cannot be fully modeled in a test system. The major categories of exposure that have been incorporated in smoke toxicity tests can be described as static, in which smoke collects in a closed compartment, and dynamic, in which smoke streams from its source past the test subjects.4 ~ 07 Whether these differences are important is not known.
|
From page 84... ...
Integration of data from any toxicity test into a currently available numerical fire hazard model requires the expression of the test results as concentrations of smoke at which a specific end point is attained. Examples of end points might be change in attention span, lacrimation, loss of postural bonus, or, at the extreme, death.
|
From page 85... ...
(The routine measurement of CO in smoke or of carboxyhemoglobin, COHb, in the blood of exposed animals, however useful such measures are for research purposes, provides no information of utility to hazard assessment efforts that is not provided with more certainty by the LC50 itself.) Because of the requirement for data expressed in units of concentration, only three test methods are candidates for use with current numerical models of fire hazard: the National Bureau of Standards (NBS)
|
From page 86... ...
LC50 is defined as the concentration of a toxicant that causes death in 50% of the exposed animals in a specified period; concentration is defined as the relative content of a substance, e.g., milligrams per milliliter or milligrams per kilogram. The "concentration" as NBS uses it is grams of sample charged relative to the volume of the exposure chamber (200 L)
|
From page 87... ...
UNIVERSITY OF PITTSBURGH METHOD The combustion system of the Pittsburgh methods 6 19 2 0 is a box furnace that is heated at 20°C/min. The exposure chamber is a 2.2-L glass box with ports to allow monitoring of the test atmosphere and placement of mice for head-only exposure.
|
From page 88... ...
2 0 CO, CO2, and O2 are monitored in air pulled from the exhaust line immediately after animal exposure; this air is not recycled. COMPARISON OF TEST METHODS Acute Toxicity The LC50 protocols from the NBS and Pittsburgh tests are similar in several respects.
|
From page 89... ...
4 It is necessary to remain alert to this potential problem Physical Test Characteristics The physical characteristics of these two tests need to be carefully compared and contrasted to identify differences in the fire and exposure models used and artifacts to be encountered. The impact of physical characteristics on smoke potency remains mostly unknown.
|
From page 90... ...
In the Pittsburgh test, the material is heated at a constant rate. Heating continues well beyond the ignition temperature; after ignition, therefore, the sample receives energy both from its own flame radiation and from the oven.
|
From page 91... ...
Douglas fir, for example, loses about 80% of its weight in this relatively high-energy environment. 6 The NBS test provides no such high-energy period.
|
From page 92... ...
Exposure System The static exposure chamber of the NBS test is representative of conditions in which smoke accumulates and mixes as the fire progresses, and it allows interactions among products that might be given off sequentially. The dynamic exposure system of the Pittsburgh test can be considered representative of human exposure to a moving stream of fire gas.
|
From page 93... ...
Considering the substantial differences in the test characteristics, lack of agreement should not be surprising. A published range of LC50 values obtained with the Pittsburgh test for a wide variety of end products is 126 g (starting weight)
|
From page 94... ...
Values obtained by Alexeeff and Packham are compared with those obtained with the NBS test in Table 5-1. With two exceptions (cotton fabric and Douglas fir)
|
From page 95... ...
The Committee believes that toxicity data alone -- e.g., data from screening tests -- are not sufficient for the complete and accurate assessment of fire hazard. The first guideline recommended the use of both pyrolysis and flaming decomposition conditions.
|
From page 96... ...
The 2-week observation period is incorporated in the NBS test; the Pittsburgh test calls for a 10-min postexposure recovery time. The fourth guideline pertained to evaluation of the test atmosphere.
|
From page 97... ...
As a result, the earlier National Research Council Committee on Fire Toxico~ogy~64 recommended that small-scale animal test protocols include a measure of the loss of ability to escape, termed n incapacitation." "Incapacitation," however, was not defined, and the methods later developed for measuring incapacitation, some of which are described in this chapter, have reflected the various investigators' interpretations. The characteristics of smoke that might impede or prevent escape cover a wide range of effects, from relatively minor to severe, including: · Blocking of visibility, which makes escape routes more difficult to find and use.
|
From page 98... ...
Thus, the two end points apparently would provide similar information for ranking materials. Motorized Activity Wheels Several investigators have used motorized activity wheels to measure the capacity of rats or mice to perform a motor act during exposure to products of thermal degradation 6 0 ~ 5 9 ~ ~ 4 6 ~ 9 3 2 JO Crane et al 6 0 tested rats in motor-driven exercise wheels housed in an exposure chamber.
|
From page 99... ...
Sensory Irritation and Physiologic Stress The use of plethysmography to measure sensory irritation in laboratory animals was developed by Alarie and co-workers 2 3 5 2 ~ ~ ~ 2 A mouse is exposed to the products of thermal decomposition of a material in a chamber into which its head protrudes (described earlier as the Pittsburgh method)
|
From page 100... ...
They proposed that the RD50 is equivalent to an intolerable degree of sensory irritation for humans and would probably cause incapacitation within 3-5 min.3 28 ll2 They also proposed that use of 10 times the RD50 would be lethal or cause severe injury to the respiratory tract. This prediction has been verified.
|
From page 101... ...
Russo et al.l9 6 compared the effects of the smoke from polyimide and flexible polyurethane foams. The thermally less stable polyurethane foam caused greater performance decrements at the lower heating temperature at which greater amounts of CO were evolved.
|
From page 102... ...
The authors suggested that the temporary decrease in licking behavior was caused by irritant components of the smoke to which the rats had adapted by the end of the exposure period. Rotorod with Electrified Grill Floor .
|
From page 103... ...
fluid from the lungs of exposed animals to detect lung damage. Many investigators have used this technique to evaluate the potential chronic lung toxicity of inhaled materials, on the basis of the hypothesis that animals exposed by inhalation to a pulmonary toxin will suffer subtle acute lung damage that can be measured by various biochemical and cytologic changes.
|
From page 104... ...
Not only do analyses of BAL fluid potentially provide information on the development of chronic lung disease, but these techniques might provide a highly sensitive method for ranking the acute toxicity of inhaled combustion products. SUMMARY Efforts have been made to use analytic chemistry to predict the toxic potency of smoke.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.