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At least 73 records · Page 4

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NASA NTRS2014

Development of Low-Toxicity Wastewater Stabilization for Spacecraft Water Recovery Systems

Wastewater stabilization was an essential component of the spacecraft water cycle. The purpose of stabilizing wastewater was two-fold. First, stabilization prevents the breakdown of urea into ammonia, a toxic gas at high concentrations. Second, it prevents the growth of microorganisms, thereby mitigating hardware and water quality issues due to due biofilm and planktonic growth. Current stabilization techniques involve oxidizers and strong acids (pH=2) such as chromic and sulfuric acid, which are highly toxic and pose a risk to crew health. The purpose of this effort was to explore less toxic stabilization techniques, such as food-grade and commercial care preservatives. Additionally, certain preservatives were tested in the presence of a low-toxicity organic acid. Triplicate 300-mL volumes of urine were dosed with a predetermined quantity of stabilizer and stored for two weeks. During that time, pH, total organic carbon (TOC), ammonia, and turbidity were monitored. Those preservatives that showed the lowest visible microbial growth and stable pH were further tested in a six-month stability study. The results of the six-month study are also included in this paper.

Adam, Niklas↗

NASA NTRS2015

Development of a Low Toxicity Urine Pretreatment for Water Recovery in Space

Adam, Niklas↗

NASA NTRS2015

Development of Low-Toxicity Wastewater Stabilization for Spacecraft Water Recovery Systems

Wastewater stabilization was an essential component of the spacecraft water cycle. The purpose of stabilizing wastewater was two-fold. First, stabilization prevents the breakdown of urea into ammonia, a toxic gas at high concentrations. Second, it prevents the growth of microorganisms, thereby mitigating hardware and water quality issues due to due biofilm and planktonic growth. Current stabilization techniques involve oxidizers and strong acids (pH=2) such as chromic and sulfuric acid, which are highly toxic and pose a risk to crew health. The purpose of this effort was to explore less toxic stabilization techniques, such as food-grade and commercial care preservatives. Additionally, certain preservatives were tested in the presence of a low-toxicity organic acid. Triplicate 300-milliliter volumes of urine were dosed with a predetermined quantity of stabilizer and stored for two weeks. During that time, pH, total organic carbon (TOC), ammonia, and turbidity were monitored. Those preservatives that showed the lowest visible microbial growth and stable pH were further tested in a six-month stability study. The results of the six-month study are also included in this paper.

Mitchell, Julie L.↗

NASA NTRS1972

A method for defining down-wind evacuation areas for transportation accidents involving toxic propellant spills

Evacuation areas for accidental spills of toxic propellants along rail and highway shipping routes are defined to help local authorities reduce risks to people from excessive vapor concentrations. These criteria along with other emergency information are shown in propellant spill cards. The evacuation areas are based on current best estimates of propellant evaporation rates from various areas of spill puddles. These rates are used together with a continuous point-source, bi-normal model of plume dispersion. The rate at which the toxic plume disperses is based on a neutral atmospheric condition. This condition, which results in slow plume dispersion, represents the widest range of weather parameters which could occur during the day and nighttime periods. Evacuation areas are defined by the ground level boundaries of the plume within which the concentrations exceed the toxic Threshold Limit Value (TLV) or in some cases the Emergency Exposure Limit (EEL).

Siewert, R. D.↗

NASA NTRS1974

Development of spacecraft toxic gas removal agents

The development of agents suitable for removal of CO, NH3, NO2 SO2, and other spacecraft contaminants was approached. An extensive technology review was conducted, yielding a large number of potentially useful materials and/or concepts. Because the two toxic gases of greatest interest, CO and NH3, suggested the use of catalysis principles emphasis was placed on the intestigation of transition metals on various supports. Forty-three materials were prepared or obtained and 25 were tested. Gas chromatographic techniques were used to find seven candidates that effectively managed various combinations of the four toxic gases: none managed all. These candidates included six transition metal-containing preparations and a supported LiOH material. Three commercial charcoals showed some efficiency for the toxic gases and may constitute candidates for enhancement by doping with transition metals.

Moore, R. S.↗

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.↗