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Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 1 (1994) / Chapter Skim
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B7: Methane
Pages 143-148

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From page 143...
... James, Ph.D. Johnson Space Center Toxicology Group Biomedical Operations and Research Branch Houston, Texas PHYSICAL AND CHE1\IICAL PROPERTIES Methane is a colorless, odorless, nonpoisonous, flammable gas Hat burns wig a pale, faintly luminous flame.
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From page 144...
... Inhalation of commercial natural gas scented with 16.8 mg/m3 tert-buty~mercaptan and 7.2 mg/m3 of methyl acrylate by mice in a gas chamber for 2 h produced isopropanol, acetone, sec-buty! alcohol, and methyl ethyl ketone in the blooct and liver (Tsukamoto et al., 1985~.
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From page 145...
... TABLE 7-2 Spacecraft Maximum Allowable Concentrations _ Duration ppm mg/m3 Target Toxicity 1 h 5300 3800 0.1 x lower explosive limit 24 h 5300 3800 0.1 x lower explosive limit 7 d 5300 3800 0.1 x lower explosive limit 30d 5300 3800 0.1 x lower explosive limit 180 d 5300 3800 0.1 x lower explosive limit RATIONALE SMACs were set on the basis of methane s explosive properties rather than its toxicity with the following considerations. First, methane has no demonstrable toxicity and does not produce general systemic effects other Han being a simple asphyxiant.
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From page 146...
... A safety factor of lO-folci below the explosive limit was used to allow for some inhomogeneities in the local distribution of methane near Me site of leakage or generation of the methane, assuming that air circulation within the spacecraft produces moderately effective · ~ ~ ng.
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From page 147...
... Capable of forming explosive mixtures if diluted with air _ 1 1 +L I 14 16 18 20 FIGURE 7-1 The explosive limits of methalle~oward's Triangle. REFERENCES Bjorneklett, A
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From page 148...
... 1988. Breath methane and large bowel cancer risk in contrasting African populations.
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Key Terms

  • natural gas
  • simple asphyxiant
  • explosive limit
  • explosive mixtures
  • lower explosive

  • oxygen concentration
  • allowable concentrations
  • breath methane
  • spacecraft maximum
  • maximum allowable

  • systemic effects
  • exposure limit
  • diluted slightly
  • experimental study
  • simple asphyxiants

  • methane near
  • limits set
  • cancer studies
  • alveolar walls
  • rats exposed

  • chemical specificity
  • moderately effective
  • effects attributable
  • state produced
  • reach asphyxiating

  • quickly owing
  • ethyl ketone
  • healthy subjects
  • produces moderately
  • johnson space


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