David E. Baker
Department of Agricultural Engineering

Indoor air can be polluted in a number of ways. Indoor pollutants include formaldehyde, carbon monoxide, respirable dust, nitrogen dioxide, radon and other gases. This guide focuses on just one of these pollutants — radon.

What is the risk level?

People exposed to radon or other pollutants face some uncertainty about the amount of health risk the radon poses. Radon risk estimates are based on scientific studies of miners exposed to varying levels of radon in their work underground. Consequently, scientists are considerably more certain of the radon risk estimates than they are the risk levels based totally on animal studies.

The Environmental Protection Agency's Science Advisory Board estimates that somewhere between 5,000 and 20,000 lung cancer deaths a year in the United States are caused by radon exposure. The American Cancer Society estimated that about 130,000 people would die of lung cancer in 1986. The U.S. Surgeon General estimated that about 85 percent of these lung cancer deaths were caused by smoking.

Despite some uncertainty in the risk estimates of radon, it is widely believed that the greater your exposure to radon, the greater your risk of developing lung cancer.

What is it?

Radon is an odorless, colorless, radioactive gas that is caused by the natural breakdown (radioactive decay) of materials that contain uranium. Radon can be found in high concentrations in soils and rocks containing uranium, granite, shale, phosphate and pitchblende. You can also find it in soils contaminated with certain types of industrial waste, such as the byproducts from uranium or phosphate mining.

In the outdoors, radon is diluted to such low levels that there is usually nothing to worry about. Once inside an enclosed space such as a home, however, radon can accumulate, depending upon the building's construction and the concentration of radon in underlying soil.


Radon in homes may come from many sources. The main route of entry is from the soil and rock underneath the home. Radon migrates from the soil and rock through the cracks and openings in walls and floors or through floor drains, sumps, joints and tiny cracks or pores in hollow-block walls. Earth-contact and solar-heated homes using rock-heat storage may have higher levels of radon because of the additional soil and rock used in such construction.

Radon can also enter water in private wells and be released into a home when the water is used. Usually, radon is not a problem with large community water supplies where it would probably be released into the outside air before the water reaches a home.

In some unusual situations, radon may be released from materials used in the construction of a home. For example, a problem might arise if a house has a large stone fireplace or has a solar heating system where heat is stored in large beds of stone. In general, however, building materials are not a major source of indoor radon.

Risk areas in Missouri

According to the State Geological Service, "There are more questions than answers as to where we expect high risks in Missouri." We have little scientific data where we might find high levels caused by specific geological formations. Areas of the state that might be suspect are:

  • Lamont sandstone areas.
  • Mountain areas in southeast Missouri.
  • Southwest Missouri — black shale (especially old mine areas).
  • Oil formation areas.
  • Northern half of Missouri — black or dark shale.

Detection techniques

The two most popular commercially available detectors for homeowners are Charcoal Canisters and Alpha Track detectors. Both are exposed to air in the home for a specific period of time and then sent to a laboratory for analysis.

Alpha Track detectors (AT)
Alpha Track detectors use a small sheet of special plastic material. The material is permanently marked by alpha particles. The units are installed in the home for up to three months for screening and for 12 months as a follow-up measure.


  • Relatively low cost per detector; cost of one unit may range from $20 to $60.
  • Convenient to handle and install.
  • Unobtrusive when installed.
  • No special skills required for deployment.
  • Can be distributed by mail.
  • Completely passive; need no external power.
  • Can measure the integrated average concentration over a 12-month period, which is the optimal measure of long-term concentration.


  • Relatively long measurement period necessary; three months are the recommended minimum for currently available detectors.
  • Large inherent variability (precision errors), particularly at low concentrations if the area counted is small.

Charcoal Canisters (CC)
Charcoal Canisters are containers filled with a pre-measured amount of activated charcoal. The homeowner unseals the airtight canisters and places them in the home according to manufacturer's guidelines for up to seven days. At the end of the test period, the canisters are re-sealed and returned to the laboratory or distribution point for analysis.


  • Low cost per canister; one canister may range from $10 to $25.
  • Convenient to handle and install.
  • Unobtrusive when installed.
  • No special skills needed for deployment.
  • Can be distributed by mail.
  • Completely passive; need no external power.
  • With proper analysis, can yield precise results.


  • Some canister types are more sensitive to temperature and humidity than others.
  • The charcoal absorption technique is inherently limited to a few days of sampling, which makes a longer term measurement impossible with a single detector.

Other techniques to measure radon are available, but they require trained personnel and special instrumentation. The techniques are also extremely expensive ($2,500 to $10,000).

They include

  • Continuous Radon Monitor or Continuous Working Level Monitor
  • Grab Sample
  • Radon Progeny Integrating Sampling Unit

The EPA conducts a Radon Measurement Proficiency Program. This voluntary program allows laboratories and businesses to demonstrate their capabilities in measuring indoor radon. For names of firms participating in the program, write or call:

  • The Bureau of Radiological Health
    1730 East Elm Plaza
    PO Box 570
    Jefferson City, MO, 65102

Measurement results

Radon risk evaluation chart.
Figure 1. Radon risk evaluation chart.

In most cases, the screening measurement is not a reliable measure of the potential for a radon problem. Depending upon the results of the screening measurement, a homeowner may need to have follow-up measurements to determine the average radon level in a home. The EPA strongly recommends that follow-up measurements be made before undertaking major efforts to permanently correct the problem.

Measurement results will be reported in one of two forms — working level (WL) or picocuries per liter (pCi per liter).

How to reduce risk

Lung cancer resulting from radon exposure depends upon the level and length of exposure.

The following measures can be taken to reduce exposure level. They are easy and inexpensive.

  • Stop smoking and discourage smoking in the leveling area. Scientific evidence indicates smoking may increase the risk of radon exposure.
  • Spend less time in areas with higher concentrations of radon, such as basements. Radon concentrations tend to be greater in lower levels of a home. Persons who spend a great deal of time in these areas, whether sleeping or working, will probably experience higher risk levels than persons with reduced exposure.
  • When practical, open all windows and turn on fans to increase the air flow into and through the house. This is especially important in basements.
  • If a home has a crawl space beneath it, keep the crawl space vents on all sides of the house fully open all year.

While the above actions help reduce risks occurring from radon, they generally do not offer a long-term solution. There are a number of permanent solutions that a homeowner may want to consider to alleviate a radon problem. The first is to seal all entry points, such as cracks, pipe openings and capped sumps. Another solution might be to use natural, fan-forced or heat-recovery ventilation to get rid of as much as 90 percent of the radon in the home. Table 1 is a comparison chart of various permanent, cost-effective solutions recommended by the EPA.

Table 1. Comparison of features.

Method Installation cost Operating cost Maximum possible reductions1 Comment
Natural ventilation:       Useful, immediate step to reduce high radon levels
Basement or lowest floor Minimal Very high Up to 90 percent  
Crawl space MInimal Moderate Up to 90 percent  
Forced ventilation:       More controlled than natural ventilation
Basement or lowest floor Low Very high Up to 90 percent  
Crawl space Low Moderate Up to 90 percent  
Air supply Low to moderate Low Site specific May be required to make other methods work
Heat recovery ventilation Moderate to high Moderate Up to 90+ percent Air intake and exhaust must be equal
Covering exposed earth Moderate Low Site specific Required to make most other methods work
Sealing cracks and spaces Minimal to moderate None Site specific Required to make most other methods work
Drain-tile suction Moderate to high Low Up to 97+ percent Works best when drain tiles are continuous, unblocked loop
Block-wall ventilation High to very high Low Up to 97+ percent Applies to block-wall basements sub-slab suction may be needed to supplement
Sub-slab suction High to very high Low Up to 97+ percent Important to have good aggregate or high permeable soil under slab
1. These represent the best reduction that a single method can accomplish. You may get higher or lower reductions depending on the unique characteristics of your house. It is likely that reductions in your house will not be as great as those shown. Especially with high initial radon levels, several methods may have to be combined to achieve acceptable results. Source: EPA Booklet OPA-86-005, Radon Reduction Methods — A Homeowner's Guide.

For more detailed explanations of techniques, see the EPA publication, Radon Reduction Methods — A Homeowner's Guide. You can obtain a copy of this booklet from:

  • The Kansas City EPA Regional Office
    Office of Public Affairs
    726 Minnesota Avenue
    Kansas City, Kansas 66101
Publication No. G1968