Revisions to Spacecraft Maximum Allowable Concentrations for 2-Butanone

At high concentrations 2-butanone is an irritant that may cause central nervous system effects. In 1996, NASA established spacecraft maximum allowable concentrations (SMACs) for short-duration, off-nominal scenarios at 50 ppm based on human exposure data from the 1940s. Limits for 7, 30, and 180 d were set at 10 ppm using the same data, but accounting for the small number of volunteers and extrapolation from mild effects to no effects for nominal operations. Limits were not established for missions of 1000 d.

A literature search was conducted of toxicity studies of inhalation exposure to 2-butanone published since the original SMACs were developed. Additionally, studies cited in the development of existing occupational limits, acute exposure guidelines, and state permitting and monitoring limits were assessed.

Several toxicity studies published after SMACs were established in 1996 are summarized here. Many of the studies evaluated whether the existing occupational limit of 200 ppm is adequate to protect workers.

As part of a periodic review of historical limits, SMACs were revised for all durations for 2-butanone. Acute SMACs were increased from 50 ppm to 200 ppm. The SMAC for 7 d was increased from 10 ppm to 67 ppm, and the SMACs for 30 and 180 d were increased from 10 ppm to 22 ppm. A SMAC for 1000 d has now been set at 22 ppm. Limits based on the most recent evidence and risk assessment methodologies will ensure the appropriate degree of conservatism in future spacecraft design. Ryder VE. Revisions to spacecraft maximum allowable concentrations for 2-butanone. Aerosp Med Hum Perform. 2025; 96(12):1094-1097.