NASA Conducts Autonomous Review of Hydrogen Sulfide (H2S)

NewsNASA Conducts Autonomous Review of Hydrogen Sulfide (H2S)

NASA’s Evaluation of Hydrogen Sulfide Exposure Limits for Space Missions

NASA’s Office of the Chief Health and Medical Officer (OCHMO) recently organized a specialized working group to meticulously assess and potentially revise the Spacecraft Maximum Allowable Concentration (SMAC) values for hydrogen sulfide (H2S). This initiative underscores NASA’s commitment to ensuring the safety and well-being of astronauts as they embark on increasingly complex missions, such as the upcoming Artemis missions aimed at returning humans to the Moon.

The working group convened virtually three times over the months of February and March 2023. During these sessions, panel members, who are experts in toxicology, provided their individual insights and opinions by April 2023. This panel was carefully selected to ensure a balanced representation of expertise in SMAC determinations, particularly from clinical and epidemiological viewpoints. Esteemed members of the panel included Dr. Terry Gordon, Dr. Tee Guidotti, and Dr. Joyce Tsuji. The discussions were facilitated by a dedicated OCHMO team comprising Dr. Doug Ebert, Dave Francisco, Sarah Childress, Kristin Coffey, and Kim Lowe.

Objectives of the Working Group

The primary goals of this working group were threefold:

  1. Endorse or Recommend Adjustments: The group was tasked with endorsing or recommending changes to the proposed H2S SMAC levels put forth by the Johnson Space Center (JSC) Toxicology Laboratory.
  2. Review of Draft Manuscript: Another key objective was to meticulously review a draft manuscript on H2S SMAC prepared by the JSC Toxicology Laboratory.
  3. Provide Additional Insights: The panel aimed to offer any further insights and considerations regarding the toxicity of H2S that should be factored into spaceflight programs.

    Understanding SMAC and its Importance

    The Spacecraft Maximum Allowable Concentrations (SMACs) are critical guidelines that define the maximum concentration of airborne contaminants that spaceflight crew can be safely exposed to over various durations. These durations include time spans of 1 hour, 24 hours, 7 days, 30 days, 180 days, and 1000 days. The NASA Spaceflight Human-System Standard (NASA-STD-3001) clearly stipulates that vehicle systems must limit atmospheric contamination below these established limits to ensure the safety and health of crew members.

    The JSC Toxicology Laboratory is responsible for maintaining the SMAC values document, which lists safe exposure limits for a range of chemicals, including carbon monoxide, ammonia, heavy metals, and various volatile organic compounds.

    The Need for Hydrogen Sulfide SMAC Values

    Historically, a SMAC value for hydrogen sulfide had not been established due to its negligible risk in spacecraft environments. However, with the advent of Artemis missions and the potential for lunar sample returns, there is a possibility of H2S being released within spacecraft. This is particularly concerning as H2S might be a constituent of lunar polar ice. Known for its distinctive rotten egg smell, hydrogen sulfide poses both psychological and physiological risks. At low concentrations, it acts as an irritant, while higher concentrations can lead to severe health effects, including neurological damage and unconsciousness.

    Establishing precise SMAC values for hydrogen sulfide is crucial for defining safe exposure limits for spaceflight crews on future missions. These values will also influence the development of new monitoring and mitigation strategies for this chemical during space missions.

    Key Findings from the Review

    The panel’s review highlighted several important points:

  4. Endorsement of Proposed SMAC Values: The SMAC values proposed for 1-hour, 24-hour, 7-day, 30-day, and 180-day exposures were deemed appropriate and received unanimous endorsement from the panel members.
  5. Challenge with 1000-day SMAC Value: The proposed 1000-day SMAC value was considered too low, with concerns that it may not be practically attainable due to human-generated sources. The panel suggested that this value should either be eliminated or reclassified as a guideline, as it does not represent a significant toxicological risk.
  6. SMAC Calculation Approach: The general approach to calculating SMAC values and the inclusion of safety factors were found to be logical. However, the panel recommended providing additional rationale to support these calculations.
  7. Negligible Interactive Effects: The panel concluded that interactive and additive effects with other substances are negligible at the proposed low concentrations.
  8. Impact of Microgravity: It was determined that physiological changes induced by microgravity are unlikely to exacerbate hydrogen sulfide exposure at these low concentrations.
  9. Considerations for Private Spaceflight Participants: Recognizing that SMACs are designed for pre-screened, healthy astronauts, the panel recommended that private spaceflight participants receive individual physician assessments and a review of all SMAC values, including those for hydrogen sulfide, to identify potential sensitivities in certain populations with existing health conditions.
  10. Use of Passive Dosimetry Technology: The panel advocated for the consideration of passive dosimetry technology for long-term monitoring at these low concentrations.

    Implementation of Recommendations

    After thorough consideration of the panel’s recommendations, the JSC toxicology group revised the NASA/TM-20240000101 Exposure Limits for Hydrogen Sulfide in Spaceflight document. The updated guidelines were released in January 2024, reflecting NASA’s proactive approach to ensuring the utmost safety for its crew members.

    Understanding the implications of hydrogen sulfide exposure and establishing appropriate SMAC values are essential steps in safeguarding the health of astronauts on future space missions. As space exploration continues to advance, these measures will play a pivotal role in ensuring that the challenges posed by exposure to potentially harmful substances are effectively managed.

    A Broader Perspective on Space Safety

    NASA’s meticulous approach to reviewing and setting SMAC values exemplifies the agency’s unwavering dedication to astronaut safety. It also underscores the broader challenges associated with human space exploration, where even seemingly minor details can have significant ramifications for crew health.

    As space missions become longer and more complex, the importance of stringent safety measures cannot be overstated. The proactive identification and mitigation of potential risks, such as hydrogen sulfide exposure, are fundamental to the success of these missions. Moreover, the collaboration with toxicology experts and the continuous refinement of safety standards highlight NASA’s commitment to fostering an environment where astronauts can perform their duties without compromising their health.

    In the evolving landscape of space exploration, NASA’s work in establishing and revising exposure limits serves as a critical foundation for future missions. By prioritizing the well-being of its crew members, NASA ensures that space exploration remains a safe and sustainable endeavor for generations to come.

    For more detailed information on the updated hydrogen sulfide exposure limits, you can refer to the NASA document.

For more Information, Refer to this article.

Neil S
Neil S
Neil is a highly qualified Technical Writer with an M.Sc(IT) degree and an impressive range of IT and Support certifications including MCSE, CCNA, ACA(Adobe Certified Associates), and PG Dip (IT). With over 10 years of hands-on experience as an IT support engineer across Windows, Mac, iOS, and Linux Server platforms, Neil possesses the expertise to create comprehensive and user-friendly documentation that simplifies complex technical concepts for a wide audience.
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