The committee chose not to use Occupational Safety and Health Administration (OSHA) exposure limits since those limits are based on working periods only (8 hours per day, 5 days per week). Once the astronaut living area on Mars is contaminated with soil or airborne dust, the astronauts may be exposed to low levels of Martian airborne particulates on a continuing basis for up to 1.5 to 2 years. Therefore using the risk estimates discussed above for continuous (24-hour) exposure represents a conservative approach for health protection.

The committee understands certain risks may over-shadow others. For instance, as discussed, the committee assumes the allowable risk for astronauts getting cancer (not necessarily fatal cancer) as a result of exposure to toxic trace elements is the range between 1 in 10,000 and 1 in 100,000. For low Earth orbit, NASA has established the limit of 3 percent excess risk of fatal cancer from radiation exposure, or 1 in 33.

Regardless of the large difference between the risk of fatal cancer from radiation and the risk of getting cancer from toxic metal exposure, it is prudent to reduce risk in all areas that are amenable to such reductions. It is important to reduce risks in areas that are reasonably achievable, as there can be synergistic effects of combined hazards. For instance, radiation exposure may weaken the human immune system and make a person more susceptible to other hazards. Balancing risks from various hazards will be necessary to allow NASA to make informed decisions regarding risk.

REFERENCES

Cucinotta, F., W. Schimmerling, J. Wilson, L. Peterson, G. Badhwar, P. Saganti, and J. Dicello. 2001. Space Radiation Cancer Risk Projections for Exploration Missions: Uncertainty Reduction and Mitigation. JSC 29295, January. Johnson Space Center, Houston, Tex.

Institute of Medicine (IOM). 2001. Safe Passage: Astronaut Care for Exploration Missions. National Academy Press, Washington, D.C.

National Aeronautics and Space Administration (NASA). 1998. Human Rating Requirements, JSC 29354. Johnson Space Center, Houston, Tex.

National Research Council (NRC). 1972. Atmospheric Contaminants in Manned Spacecraft. National Academy Press, Washington, D.C.

NRC. 1992a. Biological Contamination of Mars: Issues and Recommendations. National Academy Press, Washington, D.C.

NRC. 1992b. Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants. National Academy Press, Washington, D.C.

NRC. 1994. Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Vol. 1. National Academy Press, Washington, D.C.

NRC. 1996. Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Vol. 2. National Academy Press, Washington, D.C.

NRC. 1997. Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Vol. 3. National Academy Press, Washington, D.C.

NRC. 2000. Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Vol. 4. National Academy Press, Washington, D.C.

NRC. 2002. Signs of Life: A Report Based on the April 2000 Workshop on Life Detection Techniques. National Academy Press, Washington, D.C., in press.

Travis, C.C., S.A. Richter, E.A.C. Crouch, R. Wilson, and E.D. Klema. 1987. “Cancer Risk Management.” Environmental Science and Technology 21(5):415.

U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health (NIOSH). 1997. Pocket Guide to Chemical Hazards. Also available at <http://www.cdc.gov/niosh>.



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