Radon gas

Yes. ATSDR describes radon as a naturally occurring, radioactive, noble gas that is odorless, colorless, and tasteless, formed as part of three radioactive decay chains that begin with uranium or thorium. PubChem's periodic table lists it as a gas in the noble gas group, and lists its density as 0.00973, against 0.0012506 for nitrogen and 0.001429 for oxygen in the same table.

Is radon heavier than air? Does radon gas rise?

Radon is several times denser than nitrogen or oxygen, by PubChem's figures, but weight is not what decides where it collects. It enters from the soil, so levels are usually higher in basements, cellars and living spaces in contact with the ground, as WHO says, and WHO adds that considerable radon concentration can also be found above the ground floor. See is radon heavier than air and does radon gas rise.

How long does radon gas last?

Each atom decays quickly by human standards: EPA gives radon's half-life as 3.8 days. But the supply does not run out. EPA says that because radon comes naturally from the earth, people are always exposed to it, and the soil under a house keeps producing it. The radon element guide covers the chemistry and the decay chain.

EPA's Citizen's Guide names two main sources for the radon in a home's indoor air: the soil and the water supply. Building materials are a third, minor source. The table below sets out how EPA weighs each one.

The main source of radon: soil gas

EPA explains that radon typically moves up through the ground to the air above and into a home through cracks and other holes in the foundation. WHO adds that radon escapes from the ground into the air, where it decays and produces further radioactive particles.

Water as a source

According to EPA, a radon in water problem is more likely when the water comes from ground water, such as a private well or a public system that uses ground water, and is not usually a problem when the source is surface water. Most of the risk from radon in water comes from radon released into the air when water is used for showering and other household purposes. EPA's advice is to test the air first; if the air shows a radon problem and the water comes from a well, have the water tested too. The radon in water guide covers that path.

Building materials

EPA's Consumer's Guide names granite and certain concrete products as building materials that can give off radon in a small number of homes, and repeats that building materials rarely cause radon problems by themselves.

A building changes what happens to radon. Outdoors, WHO says, radon quickly dilutes to very low concentrations. Indoors, EPA says, your home traps radon inside, where it can build up. EPA's Consumer's Guide explains the mechanism: air pressure inside a home is usually lower than the pressure in the soil around its foundation, so the house acts like a vacuum, drawing radon in through foundation cracks and other openings.

• Cracks in solid floors
• Construction joints
• Cracks in walls
• Gaps in suspended floors
• Gaps around service pipes
• Cavities inside walls
• The water supply

WHO lists what decides how much radon builds up in a particular building: the local geology, such as the uranium content and permeability of the rocks and soils underneath; the routes available for radon to pass from the soil into the building; radon given off by building materials; and the rate of exchange between indoor and outdoor air, which depends on how the building is constructed, how the occupants ventilate it and how airtight it is.

Radon gas in basements and lower floors

CDC notes that radon levels are often higher in basements and lower levels. WHO says the same of basements, cellars and living spaces in contact with the ground, and adds that considerable radon concentrations can also be found above the ground floor. The radon in homes guide goes through basements, slabs and crawlspaces in detail.

Everywhere, to some degree. EPA's Radionuclide Basics page says elevated radon levels have been found in every state, and the Surgeon General's 2005 advisory says millions of homes have an elevated radon level. EPA made its Map of Radon Zones to identify areas of the U.S. with the greatest potential for elevated indoor radon levels, and says the map should not be used to determine if individual homes need to be tested. The figure counts the counties in each zone, from the zone data on this site.

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Predicted potential

Counties per EPA radon zone

Zone	Bar	Counties	Share of all counties
Zone 1Highest predicted potential		1,071	33.1%
Zone 2Moderate predicted potential		1,034	32.0%
Zone 3Lower predicted potential		1,033	32.0%
No zoneNo EPA zone on file		93	2.9%

3,231 counties in all.

An EPA radon zone describes predicted potential across a whole county. It is not intended to determine whether any individual home should be tested, and homes with elevated levels occur in all three zones. EPA recommends testing every home regardless of zone, and testing is the only way to know the radon level in a specific building.

The radon zone map shows the zones by county, and each state report, such as Colorado, adds the testing data reported for that area.

ATSDR says radon and radon progeny are normally found at higher levels in indoor air in homes, schools, and office buildings. EPA says people are exposed to radon primarily from breathing radon in air that comes through cracks and gaps in buildings and homes. WHO says that for most people the greatest exposure occurs at home, though indoor workplaces may also be a source of exposure, and that the highest levels are found in places like mines, caves and water treatment facilities.

Time indoors is why the indoor level matters. The Surgeon General's advisory cites a study finding that Americans spend between 85 and 95 percent of their time indoors. For buildings other than homes, CDC says EPA provides guidance and resources for reducing radon in schools, and to contact your state radon office for information about testing and reduction strategies in schools, daycare and childcare facilities, and workplaces in your area.

Radon is measured by how much of it is in a volume of air. In the United States the unit is picocuries per liter of air (pCi/L); WHO and many other countries use becquerels per cubic metre (Bq/m3). EPA's figures give a sense of scale.

WHO puts the average outdoor level at between 5 and 15 Bq/m3, and says levels in buildings such as homes, schools and offices can vary substantially, from 10 Bq/m3 to more than 10 000 Bq/m3. The highest levels, WHO notes, are found in places like mines, caves and water treatment facilities. That spread is the reason a national average says little about a single house.

pCi/L

Picocuries per liter of air, the unit EPA uses for radon in air and the unit U.S. guidance is written in.

Bq/m3

Becquerels per cubic metre. WHO explains that one becquerel corresponds to the transformation of one atomic nucleus per second, and that radon in air is measured by the number of transformations per second in a cubic metre of air.

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2 pCi/L

4 pCi/L

00 Bq/m³274 Bq/m³4148 Bq/m³6222 Bq/m³8296 Bq/m³10+370 Bq/m³

• Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
• 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
• At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.

EPA's guidance turns a number into a decision. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Neither mark is a line between safe and unsafe: EPA's Citizen's Guide says any radon exposure carries some risk and that even levels below 4 pCi/L pose some risk. Put a result in context with the radon level interpreter.

The gas matters because of what it turns into. WHO explains that as we breathe, the radioactive particles radon produces are deposited on the cells lining the airways, where they can damage DNA and potentially cause lung cancer. EPA's Citizen's Guide describes the same process: the particles get trapped in the lungs and, as they break down further, release small bursts of energy that can damage lung tissue over a lifetime.

EPA is equally clear about the limits of that risk. Not everyone exposed to elevated radon will develop lung cancer, and the time between exposure and the disease may be many years. Your chances depend mostly on how much radon is in your home, how much time you spend there, and whether you smoke or have ever smoked. The radon and lung cancer guide covers the evidence in depth.

Testing is the only way to know the radon level in a specific building. EPA and the Surgeon General recommend testing all homes below the third floor, and EPA's Citizen's Guide says testing should only take a few minutes of your time. These are the steps EPA gives for a do-it-yourself short-term test; the radon testing guide goes through devices and placement in more depth.

1. 1

   Choose a test

   Short-term tests stay in the home for two to 90 days, depending on the device. EPA's Home Buyer's and Seller's Guide says all radon tests should be taken for a minimum of 48 hours. Long-term tests stay for more than 90 days and are more likely to reflect your year-round average.

2. 2

   Close the house first

   For a short-term test of less than four days, close windows and outside doors at least 12 hours before the test begins, and keep them closed except for normal entry and exit during it.

3. 3

   Place it in the right room

   Use the lowest lived-in level: the basement if it is used regularly, otherwise the first floor. Avoid the kitchen and bathroom, and set the kit at least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls.

4. 4

   Send it to the lab promptly

   Leave the kit in place for as long as the package says, reseal it and send it to the lab named on the package right away.

5. 5

   Follow up a high first result

   If a first short-term result is at or above 4 pCi/L, EPA recommends a follow-up test: a long-term test for a better picture of the year-round average, or a second short-term test if you need results quickly.

Radon gas test kits and detectors: where to get one

CDC lists three places to get a kit, below. On length, CDC says the longer the test, the better the results will reflect your home radon levels and your lifestyle, and that long-term kits tell you your home's year-round average level. See radon test kits.

EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. EPA's Citizen's Guide says the method primarily used is a vent pipe system and fan that pulls radon from beneath the house and vents it to the outside, known as a soil suction radon reduction system, and that some radon reduction systems can reduce radon levels by up to 99%.

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1. 1Soil gas drawn from beneath the slab
2. 2Suction point through the slab
3. 3Vent pipe
4. 4Fan, outside the living space
5. 5Discharge above the roofline

EPA advises using a contractor trained to fix radon problems, because lowering high radon levels requires technical knowledge and special skills. Your state radon office can supply names of qualified or state-certified contractors, and the radon professionals directory lists measurement and mitigation providers separately. The radon mitigation guide explains how systems work. After any fix, test again: EPA says to test after the system is installed, and to retest every two years to be sure levels stay low.

For context before you test, the radon zone map and the state and county radon reports show predicted potential and reported testing data by area. EPA says elevated radon levels have been found in every state, so an area report, such as the one for Colorado, is background for a decision and never a reading for your building.