as 7-, 30-, and 180-day SMACs for the C3 to C8 straight-chain, aliphatic aldehydes. Table 2-2 presents the SMACs NASA established for these compounds. Respiratory irritation potential threshold data from rats and mice indicate similar properties (sensory irritation) within this group of compounds and the closely related acetaldehydes (Sim and Pattle 1957; Steinhagen and Barrow 1984; Babiuk et al. 1985). Because the C3 to C8 aldehydes exhibited similar toxicities for this particular end point, the Committee on Spacecraft Exposure Guidelines chose to establish SMACs for these compounds as a group instead of setting a separate SMAC for each compound. The toxicological end points of concern identified previously include mucosal irritation, nasal-cavity injury, nausea and vomiting, and liver damage. SMACs for each exposure time were selected based on the most conservative acceptable concentration (AC) for each toxicological end point.

An early study reported that exposure to propanal at 134 parts per million (ppm) for 30 min was mildly irritating to mucosal surfaces in humans (Sim and Pattle 1957). The same study found that exposure to 230 ppm butanal and 207 ppm isobutanal for 30 min was not irritating to human subjects. Human data were available only for the three aldehydes propanal, butanal, and isobutanal. However, animal data available at the time indicated the possibility that other aldehydes in the group may be two to three times more irritating than propanal (Salem and Cullumbine 1960; Abdo et al. 1998). Thus, ACs for the 1- and 24-h SMACs based on mucosal irritation were set at 50 ppm (Equation 1).