Answer to Question #3092 Submitted to "Ask the Experts"

Thank you for visiting the Health Physics Society website and using the Ask the Experts feature. I hope the following answers your question about radiation exposure limits for emergency operations like conducting life-saving operations or defusing an improvised nuclear/radiation dispersal device. I know the answer is a little complicated, but that is the nature of radiation regulations in the United States, and of decision making in emergency situations.

The examples you have given in your question fall into two different categories that can involve radiation exposure. These categories are "occupational" exposure and "emergency worker" exposure. If the radiation exposure is "occupational" exposure, specific dose limits apply. However, if the radiation exposure is "emergency worker" exposure involving a one-time dose received in responding to an emergency, the radiation dose is covered by guidance that takes into account the circumstances of the emergency and the person who will receive the radiation exposure.

If radiation exposure is received by federal SWAT (Special Weapons and Tactics) team members as they search for a radiological device or apprehend terrorists who have a radiological device, or if bomb technicians receive radiation exposure while defusing an explosive radiological device, the radiation exposure is being received while they do their jobs. That qualifies as "occupational" exposure and they should be limited to the occupational dose limits. The Environmental Protection Agency (EPA) has the responsibility for issuing Federal Guidance to federal agencies for radiation safety standards. However, it is the responsibility of each federal agency that has responsibilities for regulating worker's safety to set the standards. Therefore, the specific occupational dose limits can vary depending on the federal agency that is responsible for the person's safety.

Essentially all federal agencies have the same basic occupational dose limit, which is 5 rem in any calendar year. (A rem is a unit of radiation dose. A more detailed definition can be found on the website "Fact Sheet" page under "Equivalent Dose."  However, for perspective the average person in the United States receives about 0.3 rem each year from natural radiation, medical exams, and consumer products.) There are also provisions in the regulations if a worker needs to exceed 5 rem in a year. The requirements and provisions for getting this special occupational exposure may vary between agencies, but it allows up to a total of 10 to 12 rem per year.

For the "emergency worker" exposure, there is no specific dose limit because there needs to be flexibility in an emergency that accounts for what the action is that needs to be done and who is doing it. The EPA Federal Guidance for emergency-worker exposure is contained in a Federal Guidance report titled "Manual of Protective Action Guides and Protective Actions For Nuclear Incidents," which was issued in 1992. The report's guidance is that workers can receive up to 10 rem to protect valuable property and up to 25 rem for saving a life. They also recommend greater than 25 rem can be received for life saving if the persons volunteer, are nonpregnant adults, and are fully aware of the risks involved. These emergency doses for a once-in-a-lifetime exposure are not added to occupational dose.

The National Council on Radiation Protection and Measurements (NCRP), which is a scientific nonprofit organization chartered by Congress to develop recommendations for radiation protection standards, issued its latest recommendations in 1993, which is later than the EPA emergency guidance. The NCRP recommendation for emergency occupational exposure is that exposures that do not involve life saving be limited to occupational dose limits. However, for life saving the dose may approach 50 rem provided the workers understand the risks from this amount of exposure. They also state that the use of volunteers is desirable and that older workers with low lifetime exposure should be chosen, whenever possible.

One final note—these dose limits and levels are applicable if the entire body is exposed to penetrating radiation. If only small parts of the body are exposed, or the radiation is not penetrating, higher doses may be received depending on what organs are exposed and the nature of the radiation.

Keith Dinger, CHP