Revisions to Limits for 2-Propanol in Spacecraft Air

The original spacecraft maximum allowable concentrations (SMACs) for 2-propanol were established by NASA in 1996. 2-propanol is an irritant that may also cause central nervous system effects at high concentrations. Limits for 1 and 24 h were set at 400 and 100 ppm based on human exposure data. Limits for 7, 30, and 180 d were set at 60 ppm using the same human data but further accounting for the small number of subjects.

A literature search was conducted using keywords "isopropyl alcohol" and further narrowed with keywords "toxicity" and "inhalation." Additionally, studies cited in the development of occupational and acute exposure limits were assessed.

While no new toxicity studies were identified since the SMACs were established, a study that was not previously discussed in the existing documentation was identified. The data suggest that the original SMACs remain relevant, and we chose only to increase the 24-h limit from 100 to 200 ppm, the current occupational limit. We also determined that it is appropriate to apply the existing nominal SMAC of 60 ppm to missions of 1000 d.

NASA is committed to ensuring that spacecraft limits for chemicals in air and water are based on the most recent evidence and risk assessment methodologies. As such, we periodically review historical limits to ensure they are both adequately protective and not overly restrictive. For this compound, there is no new evidence to indicate significant change is required. Ryder VE. Revisions to limits for 2-propanol in spacecraft air. Aerosp Med Hum Perform. 2025; 96(4):360-362.