Report on the Environment https://www.epa.
gov/roe/
Radon: Homes At or Above EPA's Action Level
Radon is a radioactive gas. It comes from the decay of uranium that is naturally occurring and
commonly present in rocks and soils. It typically moves up through the ground to the air above and
into a home through pathways in ground contact floors and walls. Picocuries per liter of air (pCi/L)
is the unit of measure for radon in air (the metric equivalent is becquerels per cubic meter of air).
Each year, radon is believed to be responsible for an estimated 21,100 lung cancer deaths in the U.S.
(U.S. EPA, 2003). Smokers exposed to radon have a significantly higher risk of lung cancer; radon
is the second leading cause of lung cancer after cigarette smoking. Radon-related lung cancer is the
leading cause of lung cancer in non-smokers. An estimated 13.4 percent of lung cancer deaths in the
U.S. are believed to be radon-related (U.S. EPA, 2003). To reduce the risk of lung cancer, EPA has
set a recommended "action level" of 4 pCi/L for homes. At that level, it is cost-effective for
occupants to reduce their exposure by implementing preventive measures in their homes.
This indicator presents (1) the number of U.S. homes estimated to be at or above the EPA
recommended radon action level of 4 pCi/L and without an operating radon mitigation system (i.e.,
the estimated number of homes needing mitigation) and (2) the number of homes with an operating
radon mitigation system. The difference between the homes in these two categories is the number of
homes that have not yet been mitigated (generally, homes are only mitigated if the EPA
recommended radon action level of 4 pCi/L or more is measured). The data for this indicator were
extracted from the National Residential Radon Survey (U.S. EPA, 1992a), which estimated radon
levels in the U.S. housing stock. The number of homes at or above 4 pCi/L was estimated by
applying the results of the Radon Survey (U.S. EPA, 1992a) to 2000 U.S. Census data on the number
of U.S. households. The 1992 National Residential Radon Survey was based on the housing stock
that would be covered by EPA's radon testing policy (i.e., homes that should test). This included
only homes intended for regular (year-round) use and covers single-family homes, mobile homes on
permanent foundations, and multi-unit and group quarters (U.S. EPA, 1992b). The 1992 residential
survey estimated that about one in 15 homes in EPA's "should test" category would have a radon
level of 4 pCi/L or more. The measure of the number of homes with operating mitigation systems
was developed from radon vent fan sales data provided voluntarily by fan manufacturers (U.S. EPA,
2014).
What the Data Show
There was a 611 percent increase in the number of homes with operating mitigation systems from
1990 to 2013, going from 175,000 to 1,244,000 homes over 24 years. During the same period, there
has been a 14 percent increase in the estimated number of homes needing mitigation (i.e., having
radon levels at or above 4 pCi/L and no mitigation system); that number increased from about 6.2
million to 7.1 million homes (Exhibit 1). Exhibit 2 shows radon potential in homes at the county
level based on indoor radon measurements, geology, aerial radioactivity, soil permeability, and
foundation type. Zone 1 is the highest radon potential area, followed by Zone 2 (medium), and Zone
3 (low).
It has been reported anecdotally that radon vent fans and mitigation systems are also being used to
control for soil gases and vapor intrusion in homes in the vicinity of Superfund sites, underground or
aboveground storage tank sites, and similar sites as an element of corrective action plans. While
radon vent fans and mitigation systems used in this way may provide a radon reduction benefit, they
radon vent fans and mitigation systems used in this way may provide a radon reduction benefit, they
could be considered a subtraction from the number of homes with operating mitigation systems, thus
slightly reducing the slope of the trend line.
Limitations
The indicator presumes that radon vent fans are used for their intended purpose; the available
information supports this premise. Even if fans are used for managing vapor intrusion, a radon
risk reduction benefit still occurs.
A home with an operating mitigation system is presumed to have a vent fan with an average
useful life of 10 years. Each year the total number of homes with operating mitigation systems
is adjusted to reflect new additions and subtractions (i.e., vent fans installed 11 years earlier).
The number of homes with radon levels at or above 4 pCi/L is an estimate based on one year
of measurement data extrapolated for subsequent years based on population data, rather than
on continuing measurements.
This indicator does not track the number of homes designed and built with radon-reducing
features, and without a vent fan (passive systems). These features can help diminish radon
entry in homes. Thus, more people are likely to have a reduced risk from exposure to radon in
indoor air than suggested by the trends in operating radon mitigation systems alone. However,
homes with passive systems only should be tested to determine if they are at or above EPA's
radon action level.
Data Sources
Summary data in this indicator were provided by EPA's Office of Radiation and Indoor Air, based
on two types of information. The estimated number of homes with estimated indoor air
concentrations at or above EPA's radon action level and without mitigation systems was originally
derived from the National Residential Radon Survey (U.S. EPA, 1992a) and is updated with U.S.
Census data; and the number of homes with radon mitigation systems was developed from
unpublished sales data provided by U.S. radon vent fan manufacturers (U.S. EPA, 2014).
References
U.S. EPA (United States Environmental Protection Agency). 2014. Unpublished sales data provided
by radon vent manufacturers.
U.S. EPA. 2003. EPA assessment of risks from radon in homes. EPA/402/R-03/003. Washington,
DC. June. https://www.epa.gov/sites/production/files/2015-05/documents/402-r-03-003.pdf (PDF)
(98 pp, 526K).
U.S. EPA. 1992a. National residential radon survey: Summary report. EPA/402/R-92/011.
Washington, DC. October.
U.S. EPA. 1992b. Technical support document for the 1992 Citizen's Guide to Radon.
EPA/400/R-92/011. Washington, DC. May.
