[NASA] Exposure Guidelines (SMACs and SWEGs)

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Preparations for Next Moonwalk Simulations Underway (and Underwater)

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NASA astronaut Steve Swanson, Expedition 40 commander, holds the Carbon Dioxide Removal Assembly (CDRA) in the Kibo laboratory of the International Space Station. (30 June 2014)

NASA

The JSC toxicologists establish guidelines for safe and acceptable levels of individual chemical contaminants in spacecraft air (SMACs) and drinking water (SWEGs) in collaboration with the National Research Council’s Committee on Toxicology (NRC COT) and through peer-reviewed publication.  The framework for establishing these levels is documented for 

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 and 

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, and recent refinements to the 

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 reflect current risk assessment practices.

In addition to official SMACs used for the evaluation of spacecraft air, JSC toxicologists set interim 7-day SMAC values that are listed in NASA Marshall Space Flight Center’s Materials and Processes Technical Information System (“MAPTIS”), which is used to evaluate materials and hardware off-gassing data.  

Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants

A table listing the official NASA SMAC values is published in 

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 (Last revised – June 2024). References for the published values are provided below:

• NRC (1994) Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, 
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  , National Academy Press, Washington, D.C.
• NRC (1996) Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, 
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  , National Academy Press, Washington, D.C.
• NRC (1996) Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, 
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  , National Academy Press, Washington, D.C.
• NRC (2000) Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, 
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  , National Academy Press, Washington, D.C.
• NRC (2008) Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, 
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  , National Academy Press, Washington, D.C.
• Meyers VE, Garcia HD, James JT. Safe Human Exposure Limits for Airborne Linear Siloxanes during Spaceflight. 
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   2013; 25(13):735-46.
• Romoser AA, Ryder VE, McCoy JT. Spacecraft Maximum Allowable Concentrations for Manganese Compounds in Mars Dust. 
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   2019; 90(8):709-719.
• Scully RR, Garcia H, McCoy JT, Ryder VE. Revisions to Limits for Methanol in the Air of Spacecraft. 
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  . 2019; 90(9):807-812.
• Garcia, H.D, Acceptable Limits for n-Hexane in Spacecraft Atmospheres. 
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  . 2021;92(12);956-961. 
• Ryder, V.E. and Williams, E.S. Revisions to Limits for Propylene Glycol in Spacecraft Air. 
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  . 2022; 93(5);467-469. 
• Lam CW, Ryder VE. Spacecraft Maximum Allowable Concentrations for Hydrogen Fluoride. 
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  . 2022; 93(10)746-748.
• Williams ES, Ryder VE. Spaceflight Maximum Allowable Concentrations for Ethyl Acetate. 
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  . 2023; 94(1):25–33.
• Ryder VE and Williams ES. Revisions to Acute/Off-Nominal Limits for Benzene in Spacecraft Air. 
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  . 2023; 94(7):544–545.
• Wimberly, AA and Ryder VE.
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  . NASA/TM-20240000101, NASA Johnson Space Center, 2024.
• Tapia CM, Langford SD, Ryder VE. 
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  . Aerosp Med Hum Perform. 2024; 95(7):399-402.
• Ryder VE.
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  . Aerosp Med Hum Perform. 2025; 96(4):360–362.
• Williams ES, Tapia CM, Ryder V.
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  . Aerosp Med Hum Perform. 2025; 96(11):1019–1023.
• Ryder VE.
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  Aerosp Med Hum Perform. 2025 Dec;96(12):1094-1097.

Spacecraft Water Exposure Guidelines for Selected Waterborne Contaminants

A table listing the official NASA SWEG values is published in

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(Last revised – November 2023). References for the published values are provided below:

• NRC (2004) Spacecraft Water Exposure Guidelines for Selected Contaminants, 
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  , National Academy Press, Washington, D.C.
• NRC (2006) Spacecraft Water Exposure Guidelines for Selected Contaminants, 
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  , National Academy Press, Washington, D.C.
• NRC (2008) Spacecraft Water Exposure Guidelines for Selected Contaminants, 
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  , National Academy Press, Washington, D.C.
• Ramanathan R, James JT, McCoy T. (2012) Acceptable levels for ingestion of dimethylsilanediol in water on the International Space Station. 
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  . 83(6):598-603.
• Garcia, HD, Tsuji, JS, James, JT. (2014) Establishment of exposure guidelines for lead in spacecraft drinking water. 
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  . 85:715-20.

Toxicology and Environmental Chemistry

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Last Updated

Dec 16, 2025

Editor

Robert E. Lewis

Location

Johnson Space Center

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