Radon is a colorless, and odorless radioactive gas formed during the decay of uranium ore found in naturally occurring   de­posits in the earth.

Radon enters a building through dirt floors, cracks in concrete floors and walls, floor drains, sump pits, joints and tiny cracks or pores in hollow cinder block walls.  Radon also can enter water within private wells and be released into a home when the water is used.  In some unusual situations, radon may be released from materials used in the construction of a home.  For ex­ample, this may be a problem if a house has a large stone fireplace or has a solar heating system in which heat is stored in large beds of stone. 

Radon cannot enter the body through the skin; problems arise when radon is inhaled.  Radon particles travel throughout the lungs where they may damage the genetic material (DNA) of new (rapidly growing) cells, possibly creating damage that will cause a cell to become cancerous.

The need for establishing guidelines for exposure to radon is based upon studies of 4000 uranium miners routinely exposed to radon levels of 50 - 100 pCi/L within the mines.  Of these 4000 miners an extra 168 cases of lung cancer were observed above the number that would have been expected to develop in the normal population. 

The E.P.A. recommends every home be tested. If the results of the test are over 20 pCi/L, they recommend immediately having professionals mitigate the high Radon levels. If the results are below 20 pCi/L but above 4pCi/L they recommend a second long term test (longer that 3 months) to get a more accurate reading of the annual average Radon level in the building. A six month alpha track monitor is commonly employed for the long term test.

 Indoor radon levels can vary greatly depending on the season, humidity, frequency and amount of rainfall, time of day or the room in which the measurement is taken.  Typical 48 hour screening measurements only serve to indicate the potential for a radon problem. They are typically taken to reflect an estimate of the ‘worst case’ conditions in a building.  They are taken in basements under closed house conditions.  According to EPA estimates these screening measurements may vary from 2 to 6 times greater than the actual annual average radon value.    Using such screening procedures in a random sampling of 87 Dane County homes the EPA found that 75% had levels at or below 4 pCi/L, 21% had levels between 4pCi/L and 10 pCi/L and 4% had levels between 10 pCi/L and 20 pCi/L.  None of the homes screened had levels higher 20 pCi/L.

The present U.S. E.P.A. guidelines state that the annual average of 4 Pico Curies of radiation per liter of air (4 pCi/L) is the maximum level that should be toler­ated in a building.  If the average annual level exceeds this amount the E.P.A. recommends acting to ‘mitigate’ (reduce) the amount of radon that is entering the building to below their 4 pCi/L guideline. The Canadian level is slightly higher at 5.4 pCi/L.

Many states and organizations involved in health, safety or real estate concerns are using this 4 pCi/L level as an informal standard.  Homeowners, home builders, Realtors, and public health officials are under the impression that, if they can reduce radon levels in buildings to the magic number 4 then they are safe to live in.  The EPA has published a revised citizens guide containing a series of radon exposure risks and a series of action or guidance levels includ­ing levels below 4 pCi/L so members of the public can evaluate the health risk at each radon level. 

As you have noticed throughout this article the level of exposure and consequent health risk is determined by calculating the annual average levels in the living areas in a building.  The EPA guidelines are based upon an annual average exposure in the living areas of the home. The risk of contracting cancer from exposure to radon in these living areas is based upon the as­sumption that you will be exposed to the radon level found in your home for 70 years. Further these guidelines assume that the person exposed is an adult who is at home approximately 75% of the time.  Some studies have shown that children may be more sensitive to the effects of radiation exposure than adults.  If the length of time you and your family plan to live in your home and the amount of time you plan to spend indoors in your home is more or less than the figures that their assumptions are based on your risks will be different.   Remember other houses you have lived in-or will live in-may have the same or higher radon levels.

To relate the radon level in the home to the EPA guideline, it is necessary to measure the radon level in the home over at least a 6 month period to approximate the annual average radon level in the house.  The timing of radon testing and mitigation, if necessary, is something homeown­ers should consider carefully, especially if they are planning to sell the home in the future.  Testing a home for radon during the offer to purchase process of a home sale is poor timing because a long term test is not possible.  By testing well in advance of putting a home on the market, the owner has time to conduct long term tests should screening levels indicate the need for further tests. This need for advance testing is especially apparent when a relocation company becomes involved in a homes’ sale.  Most of the 40 national relocation companies in the U.S. will not purchase a home that has a radon value over 4 pCi/L.  Even though further testing is the next logical step the transferees typically do not have that option.  They must perform some type of mitigation.  Only after a second test performed after mitigation gives a reading of less than 4 pCi/L will the company purchase the house.


©Building Forensics 2013