Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants (1992)

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Historical Development of Limits for Toxicants in Spacecraft In 1968, at the request of NASA, the NRCs Space Science Board organized the Panel on Air Standards for Manned Space Flight to examine the likelihood of adverse effects from air contaminants on the health or performance of spacecraft crews on prolonged missions and to recommend limits for human exposure to spacecraft contaminants under emergency conditions. Approximately 200 potential contamin- ants of spacecraft atmosphere, identified from simulated spacecraft studies and off-gassing experiments, were reviewed. Some of these substances had already been examined by COT, and exposure limits had been recommended for submarine atmospheres. The Space Science Board panel recommended the acceptance of these limits for 90-day missions. From the 200 possible contaminants, the panel iden- tified compounds having significant hazard potential for which no submarine standards had been recommended and asked NASA to set priorities for chemicals of primary concern. NASA identified 11 compounds for which they desired long-term exposure limits; NASA also requested emergency limits for five compounds. The recommended exposure limits were based on exhaustive anal- yses of the toxicity literature on these compounds. The 90-day long- term limits recommended were chosen with the objective of avoiding (1) adverse health effects, either immediate or delayed, and (2) degra- dation of performance. The 1 -hr emergency limits were designed to avoid significant degradation in crew performance in emergencies and to avoid permanent injury; no safety factors were included, and tran- sitory effects were considered acceptable. The recommendations of this panel included (1) acceptance of the 90-day continuous exposure limits recommended by COT for 23 con- taminants for 90-day submarine missions (Table 1); (2) adoption of limits, as provisional guidelines for spaceflight, for 11 contaminants for 90-day and 1,000-day missions (Table 2); and (3) adoption of 60- min provisional emergency exposure limits (EELs) for five con- 13

14 GUIDELINES FOR DEVELOPING SMACS taminants in the event of a single accidental exposure during the mis- sion (Table 3) (NRC, 1968). It should be noted that many of the values in Tables 1-3 may be out of date because new toxicological data have become available since they were originally developed. TABLE 1 90-Day Contaminant Concentration Limits8 Contaminant 90-Day Limit, mg/m3 Acetone 71 Acetylene 2,700 Ammonia 17 Benzene 3 Carbon monoxide 29 Chlorine 03 Dichlorodifluoromethane 5,000 l,l,2>Tetrafluoro-l,2-dichloroethane 7,000 Ethyl alcohol 115 Hydrogen 245 Hydrogen chloride 15 Hydrogen fluoride 0.1 Methane 3300 Methyl alcohol 13 Methyl chloroform 3,000 Monoethanolamine 1 Nitrogen dioxide 1 Ozone 0.04 Phosgene 0.2 Sulfur dioxide 2.6 Toluene 188 1,1,1-Trichloroethane 1,100 Xylene 217 "Adapted from NRC (1968). In 1971, NASA requested that COT review the exposure limits es- tablished in 1968 by the Space Science Board (NRC, 1968) and set new limits where appropriate. The new limits were of primary importance to NASA in connection with providing engineering benchmarks to

HISTORICAL DEVELOPMENT OF LIMITS 15 TABLE 2 Provisional Limits for Space-Cabin Contaminants for 90 and 1,000 Days8 Air Limit in me 7m3 Contaminant 90 Days 1,000 Days n-Butanol 30 30 2-Butanone SB 59 Carbon monoxide 17 17 Chloroform 24 5 Dichloromethane 105 21 Dioxane 36 7 Ethyl acetate 144 144 Formaldehyde 0.12 0.12 2-Methylbutanone 82 82 Trichloroethylene 54 11 1,1,2-Trichloro, 1,2,2-trifluoroethane and related congeners 161 No recommendation "Adapted from NRC (1968). guide the development of advanced life-support systems for long-term missions. COT established the Panel on Air Quality in Manned Space- craft for this review, and provisional limits were recommended for 52 potential spacecraft contaminants for a variety of exposure durations (Table 4) (NRC, 1972). The panel emphasized that each limit value was provisional and subject to change as additional data became avail- able. The panel also emphasized that these limits represented a maxi- mum allowable concentration of a single contaminant without regard to its occurrence in mixtures of contaminants. For lexicological as- sessment of contaminant mixtures, the panel recommended the use of a group-limit concept (for greater detail, see pages 91-92).

16 GUIDELINES FOR DEVELOPING SMACS TABLE 3 Provisional Emergency Limits for Space-Cabin Contaminants"'1' Contaminant Air Limit in mg/m3 for 60 min 2-Butanone 294 Carbonyl fluoride 67 Ethylene gtycol 253 2-Methylbutanone 409 1,1,2-Trichloro, 1,612 1,2,2-trifluoroethane and related congeners "Adapted from NRC (1968). bApplies to a single exposure during the mission.

HISTORICAL DEVELOPMENT OF LIMITS 17 TABLE 4 Maximum Allowable Concentrations for Manned Spacecraft8 ppm (mg/m3) Compound (Molecular Weight) lOMin, Special 60 Area Min 90 6 ALCOHOLS Days Mon Notes Methyl alcohol (32.04) - 200 (260) 40 (52) 40 (52) Ethyl alcohol (46.07) 2,000 2,000 (3,800) (3,800) 50 (95) 50 b (95) N-Butyl alcohol (74.12) - 200 (600) 40 (120) 40 (120) Isobutyl alcohol (74.12) - 200 (600) 40 (120) 40 (120) Sec butyl alcohol (74.12) - 200 (600) 40 (120) 40 (120) Tertbutyl alcohol (74.12) - 200 (600) 40 (120) 40 (120) «-Propyl alcohol (60.11) - 200 (500) 40 40 (120) (120) Isopropyl alcohol (60.11) 400 200 (1,000) (500) 40 (100) 40 (100) ESTERS Methyl acetate (74.0) - 200 (600) 40 (120) 40 (120) Ethyl acetate (88.10) - 300 (1,080) 50 (180) 50 (180) Butyl acetate (116.16) - 200 (940) 40 (188) 40 (188) Propyl acetate (102.1) - 200 (840) 40 (168) 40 (168)

18 GUIDELINES FOR DEVELOPING SMACS TABLE 4 (Continued) ppm (mg/m3) Compound (Molecular Weight) lOMin, Special 60 Area Min 90 * Mon KETONES Days Notes Acetone (58.08) - 1,000 (2,400) 300 (720) 300 (720) b Methylethylketone (72.1) - 100 (290) 20 (58) 20 (58) Methyl isobutylketone — 100 20 20 Methylisopropylketone (86.77) - 100* (350) 20* (70) 20* (70) c ALDEHYDES Acetaldehyde (44.05) - 50 (90) 10 (18) 10 (18) d Acrolein (56.06) - 0.2 (0.5) 0.1 (0.2) 0.1 (0•2) Formaldehyde (30.03) - 1.0 (1.0) 0.1 (0.1) 0.1 (0.1) ALICYCLICS Cyclohexane (82.14) - 300 (1,020) 60 60 (204) (204) Cyclopentane (70.13) - 300 (870) 60 60 (204) (204) Methyl cyclohexane (98.14) - 500 (2,000) 15* (60) • (60) c Methyl cyclopentane (84.1) - 300 (1,029) 15* (51) 15* e (51)

HISTORICAL DEVELOPMENT OF LIMITS 19 TABLE 4 (Continued) ppm (mg/m3) lOMin, Compound Special (Molecular Weight) Area 60 90 6 HALOGENATED ALIPATHICS Min Days Mon Notes Chloroform — (11939) 100 (490) 5 (24.5) 5 (24.5) 1,2-dicnloroethane — (98.97) 200 (800) 10 (40) 10 (40) Dichloromethane — (84.94) 100 (340) 25 (87.5) 25 (87.5) Methyl chloroform — (133.4) 300 (1,620) 50 50 (270) (270) Tetrachloroethylene — (165.85) 100 (680) 5 (34) 5 (34) R-ll. Trichloroflouro- — methane (140.5) 5,000 (28,500) 100 (570) 100 (570) R-12. Dichlorodiflouro- — methane (124.0) 5,000 (25,500) 100 (510) 100 (510) R-113. Trichlorotriflouro- — ethane (192.5) 500 (3,950) 50 50 (395) AROMATICS (395) Benzene — (78.11) 100 (320) 1.0 (?) 1.0 <3) Ethyl benzene — (106.16) 200 (860) 20 (86) 20 e (86) Styrene — (104.1) 50 (215) 10» (43) 10* c (43) Toluene — (92.1) 200 (760) 20 20 (76) (76)

20 GUIDELINES FOR DEVELOPING SMACS TABLE 4 (Continued) ppm (mg/m3) Compound (Molecular Weight) lOMin, Special Area 60 90 6 AROMAT1CS (continued) Min Days Mon Notes 1,3,5-Trimethylbenzene (120.12) "• 25 (123) 3* (15) 3* (15) Xylene (o,m,p) (106.12) - 100 (430) 20 20 (86) HALOGENATED AROMATICS (86) Dichlorobenzene, mixed o- and p- — 50 (300) 5 (30) 5 (30) HETEROCYCLICS 1,4-Dioxane (88.0) — 100 (360) 5 (18) 5 (18) f Furan (68.07) — 2 (5) 0.04 (0.1) 0.04 (0.1) Indole (117.15) 1.0 (4.8) 1.0 (4.8) 0.1 (0.5) 0.1 (0.5) e Skatole (131.1) 1.0 (5) LO (5) 0.1 (0.5) 0.1 (0.5) e INORGANICS Ammonia (17.03) 100 100 (70) 25 (17.5) 25 (17.5) (70) Carbon dioxide (44.01) 40,000 (72,000) 30,000 (54,000) 10,000 (18,000) 10,000 (18,000) Carbon monoxide (28.01) — 125 (144) 15 (17) 15 (17) g,h Hydrogen chloride, gas (36.46) — 5.0 (7.5) 1.0 1.0 (1.5) (1.5)

HISTORICAL DEVELOPMENT OF LIMITS 21 TABLE 4 (Continued) ppm fmg/m3) lOMin, Compound Special 60 90 6 (Molecular Weight) Area Min Days Mon Notes INORGANICS (continued) Hydrogen fluoride, gas — 5.0 0.1 0.1 (20.0) (4) (0.08) (0.08) Nitrogen dioxide — 2.0 0.5 0.5 (46.01) (4) (1.0) (1.0) Phosgene — 0.5 0.05 0.05 (98.92) (2.0) (0.2) (0.2) Sulfur dioxide — 5.0 1.0 1.0 (64.1) (13) (3) (3) MISCELLANEOUS Acetronitrile — 40 4.0 4.0 (41.05) (68) (6.8) (6.8) Methylmercaptan 1.0 1.0 0.1 0.1 e (48.11) (2) (2) (0.2) (0.2) "Adapted from NRC (1972). ''Not to be included in group limits. 'Estimated levels bear an asterisk; more inhalation data with animal models would be desirable. dBased on eye irritation. "Long-term limits based principally on odor. *These levels for dioxane are subject to drastic revision downward (< 1 ppm) if future research proves that the compound is carcinogenic in animal models at low (< 100 ppm) inhalation concentrations. *The 60-min limit is based on a requirement that the carboxyhemoglobin level not exceed 10%, assuming heavy-work activity (30 L/rnin respiration) and conformity to Coburn's equation. If the assumption of heavy-work activity in the weightless situation proves unreal, then a value of 300 ppm (330 mg/m3) is recommended. hThe mg/m3 limits are also specified for the 70% O2, 30% N2 atmosphere at Spsia.