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What is radon?
Radon is a radioactive gas. It is has no color, odor, or taste. Unless you test for it, there is no way of telling how much is present.
Radon is formed by the natural radioactive decay of uranium in rock, soil, and water. Low levels of uranium occur naturally in Earth's crust and can be found in all 50 states; thus, radon can be found throughout the United States as well. Once produced, some of the radon gas moves up through the ground into the air above and some remains below the surface where it dissolves in the water that collects and flows under the ground.
Radon has a half-life of about four days—that is, half of a given quantity of it breaks down every four days. When radon undergoes radioactive decay, it emits ionizing radiation in the form of alpha particles. It also produces short-lived decay products, often called progeny or daughters. Some of these are also radioactive.
Unlike radon, the progeny are not gases and can easily attach to dust and other particles. Those particles can be transported by air and inhaled. The decay of progeny continues until stable, nonradioactive progeny are formed. At each step in the decay process, radiation is released.
Sometimes, the term radon is used in a broad sense, referring to both radon and its radioactive progeny. When testing radiation from the progeny, the measurements are usually expressed in working level (WL) units. When testing radiation from radon, the amount is usually expressed in picocuries per liter of air (pCi/L).
Is radon common in Montana?
Radon can be found in every state, including Montana. The geology of an area typically determines the concentrations of radon found. Radon in air is measured in a variety of units, i.e. Becquerels per cubic meter of air (Bq/m3), picocuries per liter of air (pic/L), etc. In Montana, we refer to radon levels in homes using picocuries. The U.S. EPA has documented the radon potential of Montana and defines the zones as follows.
What is a "picocurie" (pCi)?
A pCi is a measure of the rate of radioactive decay. One pCi is one trillionth of a curie, 0.037 disintegrations per second or 2.22 disintegrations per minute. Therefore, at 4 pCi/L (picocuries per liter, the EPA's recommended radon action level), there will be approximately 12,672 radioactive disintegrations in one liter of air during a 24-hour period.
The U.S. EPA defines Montana’s radon potential as follows:
Zone 1 counties have a predicted average indoor radon screening level greater than 4 pCi/L (picocuries per liter) (red zones)
Zone 2 counties have a predicted average indoor radon screening level between 2 and 4 pCi/L (orange zones)
Zone 3 counties have a predicted average indoor radon screening level less than 2 pCi/L (yellow zones)
What health effects are associated with radon exposure?
Radon is identified as the second leading cause of lung cancer in the United States, behind smoking. Like other indoor air contaminants, it appears that children are at greater risk than adults from radon exposure because their metabolism is higher and they have more years ahead of them in which to contract negative long-term effects.
Only smoking causes more cases of lung cancer. If you smoke and are exposed to elevated radon levels, your risk of lung cancer is especially high.
Radon gas decays into radioactive particles that can get trapped in your lungs when you breathe. As they break down or decay, these particles release small bursts of energy that can damage lung tissue and lead to cancer over the course of your lifetime. Not everyone exposed to elevated levels of radon will develop lung cancer, and the amount of time between exposure and the onset of the disease may be many years.
Breathing radon does not cause any short-term health effects such as shortness of breath, coughing, headaches, or fever.
Why is 4 pCi/L the recommended action level for radon?
The EPA recommended this mitigation action level in 1986 for several reasons. First, at lower levels (2 pCi/L) false negative errors increase threefold, and false positive errors increase twofold. Secondly, research indicates that, 95 percent of the time, elevated levels can be reduced to 4 pCi/L and that 2 pCi/L can be achieved 70 percent of the time. Further, today’s mitigation technology can reduce radon levels to between 2 and 4 pCi/L most of the time.
Finally, a cost-benefit analysis performed in 1986 indicated that an action level of 4 pCi/L results in a cost of about $700,000 per lung cancer death saved. If the action level was set at 3 pCi/L, the cost would be $1.7 million, and if set at 2 pCi/L, the cost would be $2.4 million per lung cancer death saved.
Homeowners can further reduce their potential risk by mitigating homes that are below 4 pCi/L.
What is the "acceptable" level of radon in air?
The EPA states that any radon exposure carries some risk. However, the EPA recommends that radon be mitigated in homes if an occupant's long-term exposure will average 4 picocuries per liter (pCi/L) or higher.
How often is indoor radon a problem?
Nearly one out of every fifteen homes has radon concentrations at the level the EPA considers to be elevated, 4 pCi/L or greater. The U.S. average radon-in-air level in single family homes is 1.3 pCi/L. Because most people spend as much as 90 percent of their time indoors, indoor exposure to radon is an important concern.
How does radon get into a building?
Most indoor radon comes from the soil or rock beneath the building. When radon, or other gases. rise through the soil, it gets trapped under the building and builds up pressure. Because air pressure inside a home is usually lower than the pressure in the soil, the higher pressure under the building forces the gas though floors and walls, and into the building. Most of the gas moves through cracks and other openings. Once inside, the radon can become trapped and concentrated.
Openings that are common pathways for the gas include:
- Cracks in floors and walls
- Gaps in suspended floors
- Openings around sump pumps and drains
- Cavities in walls
- Joints in construction materials
- Gaps around utility penetrations (pipes and wires)
- Crawlspaces that open directly into the building
Radon may also enter a building dissolved in water, particularly well water. Typically, about 1/10,000 of the radon in water coming from a faucet is released into the air. The more radon in the water, the more it can contribute to the indoor radon level.
Trace amounts of uranium are sometimes incorporated into materials used in construction. These include, but are not limited to, concrete, brick, granite, and drywall. Though these materials have the potential to produce radon, they are rarely the main cause of an elevated radon level in a building.
Outdoor air that is drawn into a building can also contribute to the indoor radon level. The average outdoor air level is about 0.4 pCi/L, but it can be higher in some areas.
While high levels of radon may be more common in some geographic areas, any home might have an elevated radon level. New and old homes, well-sealed and drafty homes, and homes with or without basements all can have a radon problem. Homes below the third floor of a multi-family building are particularly at risk.
Can the radon level in a building's air be predicted?
No. The only way to determine the level is to test. The EPA and the Surgeon General recommend testing all homes below the third floor for radon.
A map of radon zones has been created to help national, state, and local organizations target their resources and implement radon-resistant building codes. However, the map is not intended to be used for determining if a home in a given zone should be tested for radon. Homes with elevated levels have been found in all three zones.
In addition, indoor radon levels vary from building to building. Do not rely on radon test results from other buildings in your neighborhood—even ones next door—to estimate the radon level in your building.
I just found out my house has elevated radon gas levels. Should I see my physician?
Many homeowners who perform their first radon test after several years of occupancy will learn that their homes have radon values of 4 pCi/L or more. This often raises medical questions for them. There is no standard medical screening test at this time to determine if an individual has incurred tissue damage that might increase the risk of lung cancer.
Inform your family physician of your radon exposure. Normally, a chest x-ray is not recommended for radon exposure alone, but your physician will determine the correct course of action for your situation.
Do radon levels increase with the age of a home?
No. Elevated radon has been found in brand new homes and homes over 150 years old. The only way to know the radon level in any home, regardless of its age, foundation type, heating system, air tightness, or building materials, is to conduct a test.