Description of Driving Event:
Reduction in the Annual Limit for Radiation Exposure
Lesson(s) Learned:
In the ASAP Annual Report for 1997, the Panel expressed concern for the high doses of radiation recorded by the U.S. astronauts during extended Phase I missions in Mir. Subsequent and continuing review of this potential problem revalidates that unresolved concern. The current NASA limit for radiation exposure is 40 REM per year to the blood-forming organs, twice the limit for the U.S. airline pilots and four times the limit for Navy nuclear operators (see also Finding #23).
Recommendation(s):
In the ASAP Annual Report for 1997, the Panel expressed concern for the high doses of radiation recorded by the U.S. astronauts during extended Phase I missions in Mir. Subsequent and continuing review of this potential problem revalidates that unresolved concern. The current NASA limit for radiation exposure is 40 REM per year to the blood-forming organs, twice the limit for the U.S. airline pilots and four times the limit for Navy nuclear operators (see also Finding #23).
Evidence of Recurrence Control Effectiveness:
NASA concurs with the recommendation. However, in keeping with the "as low as reasonably achievable" (ALARA) radiation protection principle, NASA is proposing a set of administrative spaceflight exposure limits which are significantly below the NCRP recommended annual limits. The administrative limits are designed to improve the management of astronaut radiation exposures and ensure that any exposures are minimized. The proposed administrative BFO exposure limits range from 5 cSv (REM) for a one month exposure period to 16 cSv (REM) for a twelve month exposure period. These limits have been proposed for inclusion in section B14 of the Flight Rules and are currently awaiting concurrence from Energia and the Russian Space Agency. The National Council on Radiation Protection and Measurements (NCRP) developed these limits in 1989 for NASA. The NCRP is a congressionally chartered organization responsible for developing radiation protection limits. The NASA Administrator, OSHA, and the Department of Labor approved these limits. NASA has adapted 30 day and annual dose limits of 0.25 Sv and 0.5 Sv, respectively. The purpose of these limits is to prevent acute health effects, such as nausea, vomiting, etc. NASA also maintains career limits intended to limit the probability of cancer below 3% excess cancer mortality. These career limits are comparable to the US career limits for other radiation workers. Furthermore, the annual limits also serve to spread out career radiation exposure over time. The NCRP completed a re-evaluation of astronaut exposure limits in 1998 using the most recent results from longitudinal studies of Japanese atomic bomb survivors. Currently, the NCRP has a draft report undergoing full NCRP review and approval, which is expected to be released in the fall of 1999. When this report is released, NASA will consider its recommendations and, if appropriate, will proceed to implement any recommended reductions.
Documents Related to Lesson:
N/A
Mission Directorate(s):
- Exploration Systems
- Space Operations
- Aeronautics Research
Additional Key Phrase(s):
- Aerospace Safety Advisory Panel
- Medical
- Policy & Planning
- Research & Development
Additional Info:
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