Answer to Question #1152 Submitted to "Ask the Experts"

Category: Policy, Guidelines, and Regulations — Guidance Documents

The following question was answered by an expert in the appropriate field:

What are considered "safe" exposure levels to gamma radiation, including guidelines recommended by the Environmental Protection Agency, the Department of Energy, Occupational Safety and Health Administration, etc.?

The term "safe" is a value judgement and is difficult to define. Some people consider safe to mean no risk, while others consider safe to carry risks that they consider negligible, but that others would consider unacceptable. In connection with radiation exposure, there is no safe radiation dose if by safe is meant no risk. This is a consequence of the linear, no-threshold (LN-T) model of radiation carcinogenesis that is currently the basis of radiological protection practices in all countries. As you may be aware, the LN-T model assumes that the risk of radiogenic cancer increases in direct proportion to the dose, with no threshold below which there is no effect. Thus, even very low levels of radiation are assumed to carry some low risk of cancer. Because of this, regulatory agencies and standard-setting organizations do not speak of safe levels of radiation, but rather of acceptable levels.

The dose limits are set at levels that are considered to be roughly at the dividing line between what would be considered an acceptable level of risk and an unacceptable level, assuming continuous exposure at these dose levels. However, because there are no "safe" levels of radiation, meaning there are no levels that carry no risk, licensees are expected, in addition to operating at all times below the dose limits, to also maintain exposures as low as reasonably achievable (ALARA).

The application of ALARA has led to occupational and public doses that are far below the limits and that now currently stand at levels considered by most people to carry quite acceptable, or even negligible, levels of risk, or, as some may say loosely, safe levels.

Sami Sherbini

Nuclear Regulatory Commission

Answer posted on August 31, 2001. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.