Exposure Limits for Hydrogen Sulfide in Spaceflight

Hydrogen sulfide (H2S) has not historically been detected in spacecraft, but the possible evolution of volatile components from polar ice on the lunar surface is a potential concern for NASA’s planned Artemis missions. Numerous case reports and occupational epidemiological studies document that exposure to H2S at high concentrations has effects on the respiratory system, potentially leading to unconsciousness followed by debilitating neurological effects. Studies in rodents demonstrate sensitivity of the respiratory system to lower concentrations of H2S. Adverse respiratory effects have also been indicated in workers chronically exposed to H2S. The objective of the present publication is to develop Spacecraft Maximum Allowable Concentrations (SMACs) for H2S for all current standard durations of exposure for spaceflight (1-hour, 24-hours, 7-days, 30-days, 180-days, and 1000-days). Summary sources and literature review were used to identify relevant studies to inform SMAC development. Space flight mission specific activities and most probable exposure scenarios were used to determine the relevant toxicity endpoints and supporting studies. SMACs were established for hydrogen sulfide of 5 ppm for 1-hour, 1.3 ppm for 24-hours, 1.3 ppm for 7-days, 1.3 ppm for 30-days, and 0.3 ppm for 180-days. Data are not sufficient currently to establish a 1000-day SMAC value. SMACs for H2S will support development of handling protocols and proper containment for lunar sample collection.