Appendix D
Toxicity Modeling Testing

The toxicity of the combustion products from new fire-safe materials will need to be determined. The terms ''fire safe'' or "fire resistant" are not the same as noncombustible. Unless new material is truly noncombustible, some thermal decomposition will occur when the material is exposed to fire conditions. Both the toxic gases and the irritants that are present in all smoke need to be considered as potential dangers. The toxic products can cause both acute and delayed toxicological effects. It is the acute and extremely short-term effects that prevent escape from an aircraft, causing faulty judgment, incapacitation, and death. The irritants in smoke can also interfere with passengers' ability to escape by causing severe coughing and choking and by preventing them from keeping their eyes open long enough to find the exits. In addition, the delayed effects, such as tissue or organ injury, mutagenicity, carcinogenicity, and teratogenicity need to be characterized since they may ultimately lead to permanent disability and post-exposure deaths.

TOXICITY MODELS

There is currently no national standard test method for evaluating smoke toxicity in the United States, although the American Society for Testing Materials is close to approving the Radiant Heat Method ASTM E-1678 (Babrauskas et el., 1991a; Levin, 1992a, b). The International Standards Organization, Technical Committee 92, Subcommittee 3 (ISO/TC92/SC3) on Toxic Hazards in Fire has approved an international standard for combustion toxicity. This standard (ISO/DIS 13344 "Determination of the Lethal Toxic Potency of Fire Effluents") describes the mathematical models available for predicting the toxic potency of fire atmospheres based on the toxicological interactions of the main combustion gases present (Hartzell, 1994; Levin et al., 1995; Purser, 1995). Rather than designate a specific combustion system, investigators have the flexibility of designing or choosing a system that will simulate conditions relevant to their fire scenario. One of the models, the N-gas model (included in ASTM E-1678 and ISO/DIS 13344) is an empirical mathematical relationship containing six gases—carbon monoxide (CO), carbon dioxide (CO2), low oxygen (O2), hydrogen cyanide (HCN), hydrogen chloride (HCI), and hydrogen bromide (HBr)—and is shown in Equation (1) (Levin et al., 1987a, b, 1995).

The numbers in parentheses indicate the time-integrated average atmospheric concentrations during a 30-minute (or other relevant time) exposure period ([ppm • min]/min) or for O2, the units are ([percent • min]/min). Although concentrations of CO2 generated in fires are not lethal, there is a synergistic effect between CO2 and each of the other tested gases. But the effect of CO2 can only be included in the model once. Therefore, it is included with the CO factor. Empirically, it was found that as the concentration of CO 2 increases (up to 5 percent), the toxicity of CO increases. In the presence of amounts of CO2 greater than 5 percent, the toxicity of CO starts to revert back toward the toxicity of CO by itself. The terms m and b in Equation (1) define this synergistic interaction. For example, in 30-minute exposures, m = –18 and b = 122,000 if the CO2 concentrations are 5 percent or less. For 30-minute studies in which the CO2 concentrations are above 5 percent, m = 23 and b = –38,600. The LC50 value of HCN is 200 ppm for 30-minute exposures or 150 ppm for 30-minute exposures plus the post-exposure observation period. The 30-minute LC50 of O2 is 5.4 percent which is subtracted from the normal concentration of O2 in air (i.e., 21 percent). The LC50 value of HC1 and HBr for 30-minute exposures plus post-exposures times is 3,700 ppm (Hartzell et al., 1990) and 3,000 ppm (W.G., Switzer, Southwest Research Institute. personal communication, 1995), respectively.

A new N-gas model was needed to move from the six-gas model (containing CO, CO2, HCN, O2 concentrations. HCI, and HBr) to a seven-gas model which also includes NO2 (Levin, 1994; Levin et al., 1995). NO2 primarily produces pulmonary edema and post-exposure deaths. In binary gas studies, NO2 increased the toxicity of all the tested within-exposure toxic gases except HCN with which an antagonistic effect was observed. The reverse was also seen; that is, the post-exposure effects of NO2 were more toxic if the animals



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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft Appendix D Toxicity Modeling Testing The toxicity of the combustion products from new fire-safe materials will need to be determined. The terms ''fire safe'' or "fire resistant" are not the same as noncombustible. Unless new material is truly noncombustible, some thermal decomposition will occur when the material is exposed to fire conditions. Both the toxic gases and the irritants that are present in all smoke need to be considered as potential dangers. The toxic products can cause both acute and delayed toxicological effects. It is the acute and extremely short-term effects that prevent escape from an aircraft, causing faulty judgment, incapacitation, and death. The irritants in smoke can also interfere with passengers' ability to escape by causing severe coughing and choking and by preventing them from keeping their eyes open long enough to find the exits. In addition, the delayed effects, such as tissue or organ injury, mutagenicity, carcinogenicity, and teratogenicity need to be characterized since they may ultimately lead to permanent disability and post-exposure deaths. TOXICITY MODELS There is currently no national standard test method for evaluating smoke toxicity in the United States, although the American Society for Testing Materials is close to approving the Radiant Heat Method ASTM E-1678 (Babrauskas et el., 1991a; Levin, 1992a, b). The International Standards Organization, Technical Committee 92, Subcommittee 3 (ISO/TC92/SC3) on Toxic Hazards in Fire has approved an international standard for combustion toxicity. This standard (ISO/DIS 13344 "Determination of the Lethal Toxic Potency of Fire Effluents") describes the mathematical models available for predicting the toxic potency of fire atmospheres based on the toxicological interactions of the main combustion gases present (Hartzell, 1994; Levin et al., 1995; Purser, 1995). Rather than designate a specific combustion system, investigators have the flexibility of designing or choosing a system that will simulate conditions relevant to their fire scenario. One of the models, the N-gas model (included in ASTM E-1678 and ISO/DIS 13344) is an empirical mathematical relationship containing six gases—carbon monoxide (CO), carbon dioxide (CO2), low oxygen (O2), hydrogen cyanide (HCN), hydrogen chloride (HCI), and hydrogen bromide (HBr)—and is shown in Equation (1) (Levin et al., 1987a, b, 1995). The numbers in parentheses indicate the time-integrated average atmospheric concentrations during a 30-minute (or other relevant time) exposure period ([ppm • min]/min) or for O2, the units are ([percent • min]/min). Although concentrations of CO2 generated in fires are not lethal, there is a synergistic effect between CO2 and each of the other tested gases. But the effect of CO2 can only be included in the model once. Therefore, it is included with the CO factor. Empirically, it was found that as the concentration of CO 2 increases (up to 5 percent), the toxicity of CO increases. In the presence of amounts of CO2 greater than 5 percent, the toxicity of CO starts to revert back toward the toxicity of CO by itself. The terms m and b in Equation (1) define this synergistic interaction. For example, in 30-minute exposures, m = –18 and b = 122,000 if the CO2 concentrations are 5 percent or less. For 30-minute studies in which the CO2 concentrations are above 5 percent, m = 23 and b = –38,600. The LC50 value of HCN is 200 ppm for 30-minute exposures or 150 ppm for 30-minute exposures plus the post-exposure observation period. The 30-minute LC50 of O2 is 5.4 percent which is subtracted from the normal concentration of O2 in air (i.e., 21 percent). The LC50 value of HC1 and HBr for 30-minute exposures plus post-exposures times is 3,700 ppm (Hartzell et al., 1990) and 3,000 ppm (W.G., Switzer, Southwest Research Institute. personal communication, 1995), respectively. A new N-gas model was needed to move from the six-gas model (containing CO, CO2, HCN, O2 concentrations. HCI, and HBr) to a seven-gas model which also includes NO2 (Levin, 1994; Levin et al., 1995). NO2 primarily produces pulmonary edema and post-exposure deaths. In binary gas studies, NO2 increased the toxicity of all the tested within-exposure toxic gases except HCN with which an antagonistic effect was observed. The reverse was also seen; that is, the post-exposure effects of NO2 were more toxic if the animals

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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft had simultaneously been exposed to binary mixtures plus NO2, plus CO, CO2, or O2. The new seven-gas model including NO2 is presented in Equation (2). where terms are defined as for Equation (1). The LC50 for NO2 is 200 ppm following 30-minute exposures. Either the six-gas (Equation 1) or the seven-gas (Equation 2) model can be used to predict deaths that will occur only during the smoke exposure or those that will occur during and following the exposure. The seven-gas model is used if NO2 predict the lethal toxicity of atmospheres that do not include NO2, Equation (1) is used. The N-gas model has been developed into an N-gas method. This method reduces the time necessary to evaluate a material and the number of test animals needed for the toxic potency determination. It also indicates whether the toxicity is usual (i.e., the toxicity can be explained by the measured gases) or is unusual (additional gases are needed to explain the toxicity). To measure the toxic potency of a given material with this N-gas method, a sample is combusted under the conditions of concern, and the concentration of gases considered in the model are measured. Based on the results of the chemical analytical tests and the knowledge of the interactions of the measured gases, an approximate LC50 value is predicted. In just two additional tests, six rats are exposed to the smoke from a material sample size estimated to produce an atmosphere equivalent to the approximate LC50 level (this can be for exposure or exposure plus post-exposure). Since the concentration-response curves for animal lethalities from smoke are very steep, it is assumed that if some percentage (not 0 or 100 percent) of animals die, the experimental loading based on the predicted LC50 value is close to the actual LC50. No deaths may indicate an antagonistic interaction of the combustion gases. The deaths of all of the animals may indicate the presence of unknown toxicants or other adverse factors. If more accuracy is needed, then a detailed LC50 can be determined. Results using the N-gas method have shown the good predictability of this approach,1 Validation studies looking at a series of materials and products under conditions ranging from laboratory bench-scale to full-scale room burns indicated that, in all cases, the six-gas model was able to predict deaths correctly (Braun et al., 1988, 1990. 1991; Babrauskas et al., 1990, 1991a, b). The seven-gas model works when the animals are exposed to various concentrations and combinations of the tested gases (Levin et al., 1995). Studies need to be done to ensure that the seven-gas model predicts the outcome when nitrogen-containing materials and products are thermally decomposed. TOXICITY TESTING Toxicity screening tests for both acute and delayed effects are needed to evaluate the combustion products, including irritant gases of any newly proposed aircraft interior materials and products. It is imperative that the materials and products be tested under experimental conditions that simulate the realistic fire scenarios of concern in aircraft interiors as described earlier in this appendix. Tests should be simple, rapid, inexpensive, use the least amount of sample possible (since, in many cases, only small amounts of the developmental material may be available), use a minimum number of test animals, and have a definitive toxicological endpoint for comparison with other material candidates. While faulty judgment and incapacitation of passengers in an aircraft fire are significant causes of worry since they can prevent escape and cause death, they are complex endpoints that cannot be directly measured. Death of experimental animals (e.g., rats) is a more definitive and easily determined endpoint and can be used to compare the relative toxicities of alternative materials. Using lethality as the sole endpoint assumes that materials with greater toxicity based on a lethality endpoint will also cause more severe incapacitation and impairment. The number of experimental animals can be significantly reduced by utilizing one of the predictive mathematical models developed for combustion toxicology (Hartzell, 1994; Levin et al., 1995; Purser, 1995). Many test methods for the determination of the acute toxicity of combustion products from materials and products have been developed over the last two decades and continue to be developed and improved (Kaplan et al., 1983; Norris, 1988; Caldwell and Alarie, 1991; Levin, 1992a, b). Two methods that are well known and have been used to generate much toxicity data are University of Pittsburgh I, a flow-through smoke toxicity method (Alarie and Anderson. 1979, 1981) and the closed-system cup furnace smoke toxicity method developed at the National Institute of Standards and Technology (NIST) (Levin et al., 1982, 1991). More recently, 1   The LC50 values given for use in equations (1) and (2) are dependent on the test protocol, on the source of test animals, and on the rat strain. It is important to verify the above values whenever different conditions prevail and if necessary, to determine the values that would be applicable under the new conditions.

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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft the University of Pittsburgh II radiant furnace method (Caldwell and Alarie, 1991), a radiant furnace smoke toxicity protocol (Babrauskas et al., 1991a, Levin, 1992a, b) by NIST and Southwest Research Institute, and the National Institute of Building Sciences (NIBS) toxic hazard test method (Norris, 1988; Roux, 1988) have been developed. The NIST radiant test and the NIBS toxic hazard test use the same apparatus—consisting of a radiant furnace, a chemical analysis system, and an animal exposure chamber—although the methods have different toxicological endpoints. The NIST method uses an approximate LC50, based on the mass of material needed to cause lethality in 50 percent of the test animals during a 30-minute exposure or the 30-minute exposure plus a 14-day post-exposure period, as the determinant of toxicity. The number of animals needed to run the test is substantially reduced by first estimating the LC50 using the N-gas model as described above. The toxicological endpoint of the NIBS toxic hazard test is the IT50, the irradiation time that is required to kill 50 percent of the animals within a 30-minute exposure or during a 14-day post-exposure time. The actual results of the NIBS test with 20 materials indicated that the test animals died in very short periods of time, and the test was unable to discriminate definitively among materials. These test results indicate that the use of mass was a better discriminator among materials and thus was a better indicator of acute toxicity than time (i.e., the smaller the mass necessary for an LC50, the more toxic the material). In their current form, both the NIST and NIBS radiant test methods are unsuitable for the purpose of acute toxicity testing of materials for aircraft interiors because they are designed to simulate a post-flashover scenario which is not relevant to the fires of concern in aircraft interiors. The premise for simulating a post-flashover fire is that most people that die from inhalation of toxic gases in residential fires are affected in areas away from the room of fire origin. Smoke and toxic gases are more likely to reach these distant areas following flashover. In aircraft interior fires, however, tests need to be designed to specifically address the relevant scenarios discussed in Chapter 3. In addition, tests need to be designed to address the issues of delayed effects such as tissue or organ injury, mutagenicity, carcinogenicity, and teratogenicity. REFERENCES Alarie, Y.C., and R.C. Anderson. 1979. Toxicologic and acute lethal hazard evaluation of thermal decomposition products of synthetic and natural polymers. Toxicology & Applied Pharmacology 51:341–362. Alarie, Y.C., and R.C. Anderson. 1981. Toxicologic classification of thermal decomposition products of synthetic and natural polymers. Toxicology & Applied Pharmacology 57:181–188. Babrauskas, V., R.H. Harris, Jr., E. Braun, B.C. Levin, M. Paabo, and R.G. Gann. 1990. Large-scale validation of bench-scale fire toxicity tests. Pp. 3–12 in Interflam '90 Fire Safety, C.A. Franks, ed. London: Interscience Communications Ltd. Babrauskas, V., R.H. Hams, Jr., E. Braun, B.C. Levin, M. Paabo, and R.G. Gann. 1991 a. Large-scale validation of bench-scale fire toxicity tests . Journal of Fire Sciences 9:125–148. Babrauskas, V., R.H. Harris, Jr., E. Braun, B.C. Levin, M. Paabo, and R.G. Gann. 1991b. The Role of Bench-Scale Test Data in Assessing Real-Scale Fire Toxicity. NIST Technical Note 1284. Gaithersburg, Md.: National Institute of Standards and Technology. Braun, E., B.C. Levin, M. Paabo, J.L. Gurman, H.M. Clark, and M.F. Yoklavich. 1988. Large-Scale Compartment Fire Toxicity Study: Comparison With Small-Scale Toxicity Test Results. NBSIR 88-3764. Gaithersburg, Md.: National Institute of Standards and Technology. Braun, E., S. Davis, J.H. Klote, B.C. Levin, and M. Paabo. 1990. Assessment of the Fire Performance of School Bus Interior Components. NISTIR 4347. Gaithersburg, Md.: National Institute of Standards and Technology. Braun, E., J.H. Klote, S. Davis, B.C. Levin, M. Paabo, and R.G. Gann. 1991. An assessment methodology for the fire performance of school bus interior components. Pp. 855–864 in Fire Safety Science—Proceedings of the Third International Symposium , G. Cox and B. Langford, eds. New York: Elsevier. Caldwell, D.J., and Y.C. Alarie. 1991. A method to determine the potential toxicity of smoke from burning polymers: III. Comparison of synthetic polymers to Douglas Fir using the UPitt II Flaming Combustion/Toxicity of Smoke Apparatus. Journal of Fire Sciences 9:470–518. Hartzell, G.E. 1994. Smoke toxicity and toxic hazards in fires. ASTM Standardization News 22:38–44. Hartzell, G.E., A.F. Grand, and W.G. Switzer. 1990. Toxicity of smoke containing HCI. Pp 12–20 in Fire and Polymers: Hazards Identification and Prevention. ACS Symposium Series 425, G.L. Nelson, ed. Washington, D.C.: American Chemical Society. Kaplan, H.L., A.F. Grand, and G.E. Hartzell. 1983. Combustion Toxicology Principles and Test Methods. Lancaster, Pa.: Technomic Publishing Company, Inc. Levin, B.C. 1992a. The development of a new small-scale smoke toxicity test method and its comparison with real-scale fire test. Pp. 257–264 in Toxicology from Discovery and Experimentation to the Human Perspective, P.L. Chambers, C.M. Chambers, H.M. Bolt, and P. Preziosi, eds. New York: Elsevier Press. Levin, B.C. 1992b. 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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft Levin, B.C. 1994. A new approach for predicting the toxic potency of complex combustion mixtures. Proceedings of the American Chemical Society Division of Polymeric Materials: Science and Engineering 71:173–174. Levin, B.C., A.J. Fowell, M.M. Birky, M. Paabo, A. Stolte, and D. Malek. 1982. Further Development of a Test Method for the Assessment of the Acute Inhalation Toxicity of Combustion Products. NBSIR 82-2532. Gaithersburg, Md.: National Institute of Standards and Technology. Levin, B.C., M. Paabo, J.L. Gurman, and S.E. Harris. 1987a. Effects of exposure to single or multiple combinations of the predominant toxic gases and low oxygen atmospheres produced in fires. Fundamental and Applied Toxicology 9:236–250. Levin, B.C., M. Paabo, J.L. Gurman, S.E. Harris, and E. Braun. 1987b. Toxicology interactions between carbon monoxide and carbon dioxide. Toxicology 47:135–164. Levin, B.C., M. Paabo, and S.B. Schiller. 1991. A standard reference material for calibration of the cup furnace toxicity method for assessing the acute inhalation toxicity of combustion products. Journal of Research of the National Institute of Standards and Technology 96:741–755. Levin, B.C., E. Braun, M. Navarro, and M. Paabo. 1995. Further development of the n-gas model: an approach for predicting the toxic potency of complex combustion mixtures. In Fire and Polymers, G. Nelson, ed. ACS Symposium Series. Washington, D.C.: American Chemical Society. Norris, J.C. 1988. National Institute of Building Sciences Combustion Toxicity Hazard Test. Pp. 146–155 in Proceedings of the Joint Meeting of the Fire Retardant Chemicals Association and the Society of Plastics Engineers. Purser, D. 1995. Smoke toxicity. Pp. 175–195 in Improved Fire- and Smoke-Resistant Materials for Commercial Aircraft Interiors: A Proceedings. National Materials Advisory Board report NMAB-477-2. Washington, D.C.: National Academy Press. Roux, H.J. 1988. The NIBS SNITIX WG Program (for toxicity testing). Pp. 543–545 in Proceedings of the 37th International Wire and Cable Symposium, Reno, Nevada, November 15–17. Fort Monmouth, N.J.: U.S. Army Communications Electronic Command.