Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 1 (1994) / Chapter Skim
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B3: Carbon Monoxide
B3: Carbon Monoxide
Pages 61-90
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From page 61... ...
Other Han an endogenous source, CO can also be produced in He thermodegradation of materials containing carbon in an atmosphere containing oxygen, so gas stoves and furnaces can be sources of CO indoors. A COHb level of 0.6I.0% has been reported in nonsmokers in an indoor environment (Raciford etal., 1981~.
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From page 62... ...
A second common source of CO is cigarette smoke. Most smokers who smoke a pack a day have a COHb level of 5-6% (Stewart, 1975~.
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From page 63... ...
A COHb level of 6% increases He frequency of ventricular premature depolarization in patients wig coronary artery diseases (Sheps et al., 19904. There are contradictory reports on the neurological effects of low-level CO exposures in humans (Laties and Merigan, 1979~.
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From page 64... ...
In rats, the sciatic nerve conduction velocity is reduced 4 w after an acute CO intoxication in which the COHb level of 19% was reached (Pankow et al., 1975~. CO is known to affect oxidative drug metabolism.
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From page 65... ...
CO exposure reduced the builclup rate of COHb during an acute CO challenge, He final COHb level achieveci during the acute challenge was not affected by die repeated exposure. There is also evidence of adaptation to He depression effects of CO on He central nervous system (CNS)
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From page 66... ...
, so its toxicity in animals is discussed below mainly in terms of COHb levels rather than its concentradons. Subchronic or chronic CO exposures have been shown to increase the hemoglobin level and hematocrit in several animal species.
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From page 67... ...
These effects, however, were absent at generally lower COHb levels, for instance in continuous exposures at 20 ppm (3.4% COHb) for 2 y in monkeys (Eckardt et al., 1972)
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From page 69... ...
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From page 70... ...
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From page 71... ...
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From page 73... ...
73 o o ~ rat ~rat ` ~to C
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From page 76... ...
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From page 77... ...
FAA = Federal Aviation Administration. TABLE 3-4 Spacecraft Maximum Allowable Concentrations Target Duration ppm mg/m3 COHb, % Target Toxicity 1 ha 55 63 3 Heart, CNS 24 h 20 23 3 Heart, CNS 7db 10 11 1.6 Heart, CNS 30d 10 11 1.6 Heart, CNS 180 d 10 11 1.6 _ Heart, CNS aRefer to "Rationale" section for a discussion of lowering the 1-h SMAC in the unlikely event that the 1-h exposure immecliately follows a 24-h exposure at the ;24-h or 7~ SMAC.
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From page 78... ...
. Even though there are conflicting reports on the effects of COHb levels higher than 5% on reaction time and hancl-eye
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From page 79... ...
A higher minute volume was not used, even though He crew is expected to exercise more than ~ in/cl, because NASA will issue a flight rule Hat disallows exercise when the CO level in the spacecraft approaches the I-h SMAC. In addition, a pre-exposure COHb level of 0.6% and the inflight hemoglobin concentration measured in Skylabs were used (Kimzey, 1977)
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From page 80... ...
, 1.6% is selected to be the target COHb level for the 7-d SMAC. With the use of the Coburn-Forster-Kane equation (Peterson ant!
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From page 81... ...
So using the COHb levels achievable in an exposure to the EPA's NAAQS usually will provide enough protection in setting the SMACs of CO. On the other hand, based on the carcliotoxicity of CO, the astronauts could be considered a hypersusceptible population.
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From page 82... ...
The target COHb level of I.6% for 7-d SMAC would also be appropriate for the 30- and 180-d SMACs because the same rationale for the 7-d SMAC should apply for a 30- or 180-d CO exposure. With 1.6% being lower Han He COHb levels commonly cletected in smokers anti the possibility of tolerance, I.6% COHb should provide a sufficient margin of safety toward the neurological and cardiac effects of CO in a continuous 3~ or I80~ exposure.
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From page 83... ...
. Because the COHb level reaches equilibrium 24 h into a CO exposure (Peterson and Stewart, 1975)
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From page 84... ...
1987. Effect of low level carbon monoxide on compensatory tracking and event monitoring.
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From page 85... ...
1985. Review of the National Ambient Air Quality Standards for carbon monoxide.
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From page 86... ...
1948. The nature of the acclimatization occurring during repeated exposure of the human subject to atmospheres containing low concentrations of carbon monoxide.
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From page 87... ...
1959. Continuous exposure of laboratory animals to low concentration of carbon monoxide.
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From page 88... ...
1990. Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants.
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From page 89... ...
1970. An exploratory study of automobile driving performance under the influence of low levels of carboxyhemogIobin.
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From page 90... ...
1986. The effect of carbon monoxide on hormone levels and organ weights in rats.
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