Skip Navigation LinksSkip Navigation Links
Centers for Disease Control and Prevention
Safer Healthier People
Blue White
Blue White
bottom curve
CDC Home Search Health Topics A-Z spacer spacer
Blue curve MMWR spacer

Health Hazards Associated with Elevated Levels of Indoor Radon -- Pennsylvania

As a part of the safety program at the Limerick Nuclear Power Plant in Pennsylvania, personnel entering the plant must pass through a radiation monitoring area. In December 1984, the monitoring device detected an abnormally high level of radiation in one construction worker. When an investigation was made to determine how and where this worker was being exposed to excessive radiation, investigators found that the air in the man's home contained extremely high levels of "radon daughters," the short-lived decay products of radon-222. Radon is an inert, radioactive gas formed in the decay chain of uranium-238. For each year the worker and his family lived in this house, they were exposed to over 50 times the annual occupational limit of exposure for uranium miners. The family relocated until remedial actions to lower the indoor radon levels could be completed.

As a result of this incident, in January 1985 state officials in Pennsylvania began a sampling program in which over 2,000 homes around the construction worker's house were examined. The homes are in an area of natural uranium deposits. Approximately 40% of the homes had radon levels exceeding the U.S. Environmental Protection Agency (EPA) guideline for indoor radon of 0.02 "working levels." A working level is a measure of radon daughter concentrations and is defined as any combination of radon daughters in 1 liter of air that results in 1.3 x 10((5)) million electron volts of potential alpha energy. About 7% of the homes tested had radon levels at or above the 0.1 working level. If residents in these homes spend 75% of their time indoors exposed to 0.1 working level, their yearly exposure would equal 4 working level months, the annual occupational limit of exposure. A working level month is a measure of exposure and is a function of the time of exposure and the level of radon daughters, given in working levels. Reported by J Logue, DrPH, J Fox, MD, Pennsylvania Dept of Health; Cancer Br, Div of Chronic Disease Control, Center for Environmental Health, CDC.

Editorial Note

Editorial Note: The elevated radon levels near the eastern border of Pennsylvania are associated with natural uranium deposits that extend into northern New Jersey and southern New York. Since similar geologic deposits are found throughout the country, the elevated radon levels in Pennsylvania may indicate a much broader national problem. Radon enters a building through cracks, such as those in a basement floor, and through openings around pipes and wiring. Once inside, the radon builds up in the air, particularly in poorly ventilated houses. As radon daughters are formed, they attach to airborne particulates. When inhaled, these particulates can deliver a substantial dose of radiation to the bronchial epithelium.

No exposure limit has been established for indoor levels of radon from natural sources; however, EPA is now developing guidelines that will define action levels concerning houses with high concentrations of radon and is developing and evaluating mitigation strategies.

Exposure to radon daughters increases a person's lifetime risk of lung cancer. The risk rises in direct relationship with the length of exposure and with radon daughter levels.

The two risk estimates in Table 1 are derived from studies of uranium miners and have been extrapolated from relatively high occupational exposures to environmental levels. The highest lifetime risk calculated from studies of uranium miners is 7.3 x 10))-4)) deaths per working level month, and the lowest generally accepted risk is 3.0 x 10))-4)) deaths per working level month (1,2). These estimates are for the general population, including smokers. The risks for nonsmokers are approximately six times less than those given in the upper portion of the table (1).

Each year, approximately 5,000-30,000 deaths may be attributed to background levels of indoor radon. The health threat from radon can be addressed by identifying geographic areas that could produce elevated levels of indoor radon, developing strategies to reduce exposure, conducting research on effective remedial measures to be taken in buildings, and providing educational programs for health officials and the public. Changes in usage patterns of high-radon areas in a home, such as the basement, and the control of future construction in geographic areas high in uranium deposits can reduce exposure. Effective remedial measures for individual dwellings can also be used to lower radon exposure. Research in these areas should be coordinated with other agencies active in this field. The educational programs can be used to inform health officials and the public about the health threat from radon and about associated risk factors, such as smoking.


  1. National Research Council. The effects on populations of exposure to low levels of ionizing radiation. Washington, D.C.: National Academy Press, 1980.

  2. International Commission on Radiological Protection. Limits for intakes of radionuclides by workers. ICRP report no. 32, part 3, 1981.

Disclaimer   All MMWR HTML documents published before January 1993 are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to

Page converted: 08/05/98


Safer, Healthier People

Morbidity and Mortality Weekly Report
Centers for Disease Control and Prevention
1600 Clifton Rd, MailStop E-90, Atlanta, GA 30333, U.S.A


Department of Health
and Human Services

This page last reviewed 5/2/01