Radon in Arizona
Radon is a radioactive gas that is as natural as air and water, but it cannot be detected by our senses. You cannot see, smell or taste radon. Radon gas is formed by the natural decay of radium, which results from the decay of uranium. Both radium and uranium are very common elements present in Arizona soils and rock.
The only way to know how much radon is in a home is to test.
The presence of uranium in Arizona is not surprising to geologists. In fact, uranium mining was practiced in many parts of the state from the 1950s to the 1980s. Some Arizona residents mistakenly assume their home will not have a radon concern unless the home is located near the site of a uranium mine. However, the amount of uranium in soil needed to cause a concern for residential radon is far less than the amount needed to support uranium mining.
For more detailed information about radon as a geologic hazard in Arizona, plus links to other radon information sites on the Internet you can visit the Arizona Geological Survey's radon information page.
Radon incidence in Arizona is similar to the national average.
Results from the state indoor radon sampling survey conducted 1987-89 by the Arizona Radiation Regulatory Agency suggest that about 1 out of 15 Arizona homes may contain radon concentrations in excess of the EPA recommended action level of 4.0 picocuries per liter of air (4.0pCi/L). That rate is similar to the national average. However, Arizona's warm temperate climate can result in a lower thermal suction on the soil beneath homes than is typically found beneath houses situated in a more northward latitude. Thus, even though radon is present, less may be drawn into a home here than in a comparable home in many other states.
Evaporative coolers can help.
Indoor radon concentrations can also be reduced by the use of evaporative coolers, sometimes called "swamp" coolers, because they push cooled outdoor air into a building. This dilutes indoor radon levels and can offset the air-pressure differences that typically bring radon into a home from the soil below.
Sub floor air ducts can allow radon entry.
Some Arizona homes have forced air conditioning systems that include a feature not often found in colder climates; return air ducts located in the soil below slab floors. If these ducts are not airtight, radon-laden air from the surrounding soil can be drawn into the house through the ducts, resulting in higher indoor radon and increased mitigation cost.
Residential usage patterns can impact average indoor radon levels.
Over time, the way residents actually use a home can strongly affect the level of indoor radon. For example, if the windows remain closed year-round, the home's average radon level will usually be higher than if occupants frequently ventilate the home when weather permits.
Arizona Radon Facts
- Elevated levels of radon are found in both new and old buildings.
- Radon can be found in buildings other than homes.
- Radon can be found in homes built on all types of foundations, including crawlspaces and slab-on-grade basements.
- The percentage of Arizona homes that contain radon above recommended levels is similar to U.S. average.
- The average radon level found in homes in the U.S. is about 1.4 pCi/L. In Arizona, the median of radon levels found in 4000+ homes during the state indoor radon survey (1987-89) was about 1.6 pCi/L.
- Radon can vary from house to house. The only way to know the level of radon in the house you are buying or selling is to have it tested.
- Sub-floor ductwork for forced air furnaces and air conditioners can draw radon-laden soil gas into a home.
- Radon levels in Arizona can often be higher in the summer air conditioning months than during months with milder temperatures.
What Makes Some Areas Higher in Radon Than Others?
The amount of radon in a building is dependent upon:
The amount of uranium found in the soil beneath the building. The existing radon potential depends partly upon the amount of uranium and radium found in the soil.
The way a building literally pulls radon from the soil beneath it, and the ease with which radon moves through the soil and into a building. The amount of radon that actually enters a building is dependent upon the force that draws in the radon, as well as the ease with which it can move through the soil and into a building.
Ventilation rate of building:
How well radon is diluted with air. Once radon gets into a building, the final radon concentration is dependent upon the amount of ventilation that will dilute the radon. Low ventilation rates can affect indoor radon levels, but are not the cause of a radon problem.
Residential usage patterns can also have an impact on average indoor radon levels:
Over time, the typical usage patterns of a home's residents can also greatly affect the radon levels in a home. For instance, occupants who ventilate a home often when weather permits may be exposed to lower radon concentrations, on average, than if the same home were occupied by persons who keep the windows closed year-round.