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At least 91 records · Page 5

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NASA NTRS1976

Relative toxicity of pyrolysis products of some foams and fabrics

A limited number of foams and fabrics was evaluated in the course of developing test procedures for determining the relative toxicity of materials. The principal variable studied, heating rate, did not affect the relative ranking of the materials tested. Two pyrolysis test procedures using the same basic approach but employing different sample weights, chamber volumes, laboratory animals, heating rates, and upper temperature limits, resulted in identical rankings of relative toxicity. The data obtained show that modification of conventional flexible polyurethane foams with flame retardants to comply with California upholstered furniture flammability regulations seems to consistently reduce toxicity under pyrolysis conditions.

Hilado, C. J.↗

NASA NTRS1976

Evaluation of the smoke density chamber as an apparatus for fire toxicity screening tests

The smoke density chamber is perhaps the most widely used apparatus for smoke measurements. Because of its availability, it has been proposed as an apparatus for evaluating fire toxicity. The standard apparatus and procedure were not found suitable for toxicity screening tests using laboratory animals, because not enough materials of interest produced animal mortality or even incapacitation under standard test conditions. With modifications, the chamber offers greater promise as a screening tool, but other tests specifically designed to measure relative toxicity may be more cost-effective. Where one-dimensional heat flux is a requirement, the chamber is the most suitable apparatus available. It should be improved in regard to visibility of animals and ease of cleaning.

Hilado, C. J.↗

NASA NTRS1976

The sensitivity of relative toxicity rankings by the USF/NASA test method to some test variables

Pyrolysis temperature and the distance between the source and sensor of effluents are two important variables in tests for relative toxicity. Modifications of the USF/NASA toxicity screening test method to increase the upper temperature limit of pyrolysis, reduce the distance between the sample and the test animals, and increase the chamber volume available for animal occupancy, did not significantly alter rankings of relative toxicity of four representative materials. The changes rendered some differences no longer significant, but did not reverse any rankings. The materials studied were cotton, wool, aromatic polyamide, and polybenzimidazole.

Hilado, C. J.↗

NASA NTRS1976

The effect of changes in the USF/NASA toxicity screening test method on data from some cellular polymers

Rankings of relative toxicity can be markedly affected by changes in test variables. Revision of the USF/NASA toxicity screening test procedure to eliminate the connecting tube and supporting floor and incorporate a 1.0 g sample weight, 200 C starting temperature, and 800 C upper limit temperature for pyrolysis, reversed the rankings of flexible polyurethane and polychloroprene foams, not only in relation to each other, but also in relation to cotton and red oak. Much of the change is attributed to reduction of the distance between the sample and the test animals, and reduction of the sample weight charged. Elimination of the connecting tube increased the relative toxicity of the polyurethane foams. The materials tested were flexible polyurethane foam, without and with fire retardant; rigid polyurethane foam with fire retardant; flexible polychloroprene foam; cotton, Douglas fir, red oak, hemlock, hardboard, particle board, polystyrene, and polymethyl methacrylate.

Hilado, C. J.↗

NASA NTRS1976

Relative toxicity of products of pyrolysis and combustion of polymeric materials using various test conditions

Relative toxicity data for a large number of natural and synthetic polymeric materials are presented which were obtained by 11 pyrolysis and three flaming-combustion test methods. The materials tested include flexible and rigid polyurethane foams, different kinds of fabrics and woods, and a variety of commodity polymers such as polyethylene. Animal exposure chambers of different volumes containing mice, rats, or rabbits were used in the tests, which were performed over the temperature range from ambient to 800 C with and without air flow or recirculation. The test results are found to be sensitive to such variables as exposure mode, temperature, air flow and dilution, material concentration, and animal species, but relative toxicity rankings appear to be similar for many methods and materials. It is concluded that times to incapacitance and to death provide a more suitable basis for relative toxicity rankings than percent mortality alone, that temperature is the most important variable in the tests reported, and that variables such as chamber volume and animal species may not significantly affect the rankings.

Hilado, C. J.↗

NASA NTRS1977

Relative toxicity of pyrolysis products of some polyurethane and polychloroprene foams

Results of toxicity screening tests on some polyurethane and polychloroprene flexible foams are presented. The test method involves the exposure of four Swiss albino male mice in a 4.2-liter hemispherical chamber to the pyrolysis effluents from 1 g of sample exposed to temperatures rising from 200 to 800 C at a rate of 40 C/min. Mortality and times to incapacitation and to death are recorded. Comparisons indicate that flexible polyurethane foams without fire retardant are more toxic than the corresponding foams containing fire retardant, and polychloroprene foams are least toxic.

Hilado, C. J.↗

NASA NTRS1977

Relative toxicity of pyrolysis products of some elastomers

Ten samples comprising seven generic types of elastomers were evaluated for relative toxicity using the USF/NASA toxicity screening test method. The nitrile rubber samples appeared to generally exhibit greater toxicity than the samples of polyisoprene, styrene butadiene, and chlorinated polyethylene rubber. Carbon monoxide was present in sufficient concentration in the blood of the test animals to be the principal cause of death in the case of polyisoprene and styrene butadiene rubber.

Hilado, C. J.↗

NASA NTRS1977

Toxicity studies of a polyurethane rigid foam

Relative toxicity tests were performed on a polyurethane foam containing a trimethylopropane-based polyol and an organophosphate flame retardant. The routine screening procedure involved the exposure of four Swiss albino male mice in a 4.2 liter hemispherical chamber to the products generated by pyrolyzing a 1.00 g sample at a heating rate of 40 deg C/min from 200 to 800 C in the absence of air flow. In addition to the routine screening, experiments were performed with a very rapid rise to 800 C, with nominal 16 and 48 ml/sec air flow and with varying sample rates. No unusual toxicity was observed with either gradual or rapid pyrolysis to 800 C. Convulsions and seizures similar to those previously reported were observed when the materials were essentially flash pyrolyzed at 800 C in the presence of air flow, and the toxicity appeared unusual because of low sample weights required to produce death.

Hilado, C. J.↗

NASA NTRS1977

Hydrocarbon concentrations in fire toxicity tests as an indication of flash fire propensity

The concentrations of hydrocarbons in the gases from fire toxicity tests are often determined to obtain an indication of their contribution to toxic effects and of the mechanisms of thermal decomposition. Because the gas compositions produced in the University of San Francisco/NASA toxicity screening test are generated under identical pyrolysis conditions, they offer the potential of comparing the flash-fire propensity of various materials.

Hilado, C. J.↗

NASA NTRS1977

The possibility of flash fires in toxicity tests

The concentrations of combustible compounds in the gases generated in toxicity tests may together result in a flammable mixture which could be ignited by accident or by a deficiency in procedure. The principal hazard stems from the increase in the concentrations of combustible non-toxic gases which may result from efforts to increase the concentrations of toxic gases to obtain desired physiological responses.

Hilado, C. J.↗

NASA NTRS1977

Relative toxicity of pyrolysis products of some building materials

Fourteen samples of building materials were evaluated for relative toxicity using the USF/NASA toxicity screening test method. There appeared to be no major differences in relative toxicity under these conditions between different samples of cellulosic board products and roofing felts.

Hilado, C. J.↗

NASA NTRS1977

Effect of test conditions on relative toxicity rankings of fifteen materials

Fifteen materials were evaluated for relative toxicity of pyrolysis effluents, using different test conditions in the USF methodology. Wool fabrics were consistently among the most toxic materials, and polystyrene and polychloroprene flexible foam were consistently among the least toxic materials.

Hilado, C. J.↗

NASA NTRS1978

Toxicity of pyrolysis gases from some cellular polymers

Various samples of cellular polymers were evaluated for toxicity of pyrolysis gases, using the screening test method developed at the University of San Francisco. The cellular polymer samples included polyimide, polymethacrylimide, polybismaleimide, polyurethane, polyisocyanurate, polyethylene, polychloroprene, polyvinyl chloride, polystyrene, polysiloxane, and polyphosphazene. The cellular polymers exhibited varying levels of toxicity under these test conditions. Among the rigid cellular polymers, times to death were shortest with the imide type foams and longest with polyvinyl chloride and polystyrene. Among the flexible cellular polymers, times to death were shortest with polyimide and polyester, and longest with polychloroprene and polysiloxane. Increased char yield was not necessarily associated with reduced toxicity.

Hilado, C. J.↗

NASA NTRS1979

A comparative study of the toxicity of the combustion products of Tedlar and a fluorenone-polyester film

The relative toxicity in rats resulting from a 30 minute exposure to the combustion products of two materials, Tedlar and fluorenone-polyester film was assessed. The combustion products were generated into a static exposure system using a laboratory-scale furnace. The toxicity was assessed using the primary measurements employed in a more detailed overall toxicity evaluation. The toxicological events observed during the 30 minute exposure are reported.

Farrar, D. G.↗

NASA NTRS1978

Effect of pyrolysis temperature and air flow on toxicity of gases from a polycarbonate polymer

A polycarbonate polymer was evaluated for toxicity of pyrolysis gases generated at various temperatures without forced air flow and with 1 L/min air flow, using the toxicity screening test method developed at the University of San Francisco. Time to various animal responses decreased with increasing pyrolysis temperature over the range from 500 C to 800 C. There appeared to be no significant toxic effects at 400 C and lower temperatures.

Hilado, C. J.↗

NASA NTRS1979

Toxicity of pyrolysis gases from polyoxymethylene

A sample of polyoxymethylene was evaluated for toxicity of pyrolysis gases, using the toxicity screening test method developed at the University of San Francisco. Under several test conditions, this material gave shorter times to death than many other synthetic polymers. Carbon monoxide appeared to be the principal toxicant in the pyrolysis gases.

Hilado, C. J.↗

NASA NTRS1979

Toxicity of pyrolysis gases from polytetrafluoroethylene

A sample of polytetrafluoroethylene was evaluated for toxicity of pyrolysis gases, using various test conditions of the toxicity screening test method developed at the University of San Francisco. Time to death appears to be affected by the material of which the pyrolysis tube is made, with Monel tending to give longer times to death than quartz. When quartz tubes are used, time to death seems to be related to carbon monoxide concentration. When Monel tubes are used, carbon monoxide does not appear to be the principal toxicant.

Hilado, C. J.↗

NASA NTRS1979

Toxicity of pyrolysis gases from polyether sulfone

A sample of polyether sulfone was evaluated for toxicity of pyrolysis gases, using the toxicity screening test method developed at the University of San Francisco. Animal response times were relatively short at pyrolysis temperatures of 600 to 800 C, with death occurring within 6 min. The principal toxicant appeared to be a compound other than carbon monoxide.

Hilado, C. J.↗