NASA’s Office of the Chief Health and Medical Officer (OCHMO) assembled a small working group to review hydrogen sulfide (H2S) Spacecraft Maximum Allowable Concentration (SMAC) values. The group met virtually three times during February and March 2023, and panel members submitted individual opinion statements in April 2023. Toxicology subject matter experts were chosen to result in a balanced panel with respect to expertise in SMAC determinations and specific H2S considerations, from both clinical and epidemiological perspectives. Panel members were Dr. Terry Gordon, Dr. Tee Guidotti, and Dr. Joyce Tsuji; OCHMO team members who facilitated the discussions were Dr. Doug Ebert, Dave Francisco, Sarah Childress, Kristin Coffey, and Kim Lowe.