Radon limits

In the United States, the figures people call radon EPA limits are two recommendations. 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 Map of Radon Zones page gives the same marks in both units: 4 pCi/L (150 Bq/m3) for fixing, and 2 to 4 pCi/L (75 to 150 Bq/m3) for considering a fix.

EPA radon action level

The action level is where EPA recommends fixing a home, once a result is confirmed. EPA's testing steps make the confirmation explicit: after a long-term follow-up test, fix the home if the result is at or above 4 pCi/L; after a second short-term test, consider fixing if the average of the two is at or above 4 pCi/L. The Surgeon General's 2005 health advisory, as EPA reports it, urged Americans to test their homes and stressed remedying the problem as soon as possible when the level is 4 pCi/L (150 Bq/m3) or more. EPA and the Surgeon General recommend testing all homes below the third floor, and EPA also recommends testing in schools.

Why is EPA's action level 4 pCi/L?

EPA's action level page ties its health estimate to the average home, not to the action level: the average indoor radon concentration for America's homes is about 1.3 pCi/L, and it is upon this national average indoor level that the EPA based its estimate of 21,000 radon-related lung cancers a year. The 4 pCi/L mark is where EPA recommends fixing; the 2 to 4 pCi/L range exists, EPA says, because there is no known safe level of exposure to radon. The page adds that countries worldwide have adopted action levels for radon exposures, and most are similar to the 4 pCi/L (150 Bq/m3) action level recommended in the United States.

Radon exposure limits: homes, schools and workplaces

EPA's action level is guidance for homes. For schools, daycare and childcare facilities and workplaces, CDC says to contact your state radon office for information about testing and reduction strategies in your area. WHO notes that for most people the greatest exposure occurs in the home, though indoor workplaces may also be a source, and says its recommendations are consistent with the International Basic Safety Standards (2014). EPA's own page is clear that the figure to apply depends on where the test is done:

Mines use a different measure. ATSDR reports that the Mine Safety and Health Administration (MSHA) has adopted an exposure limit of 4 Working Level Months (WLM) per year for people who work in mines; in ATSDR's words, WLMs basically combine the concentration of radon progeny in mine air with length of exposure inside the mine. That is a different unit from the pCi/L of a home test.

No, according to all three agencies. CDC says there is no known safe level of radon and that you should always aim to have the lowest level. EPA's Citizen's Guide says that since there is no known safe level of radon, there can always be some risk, but the risk can be reduced by lowering the radon level in your home. WHO says the dose-response relation is assumed to be linear, with the risk of lung cancer rising by about 16% per 100 Bq/m3 increase in long-term average radon concentration.

Safe levels of radon: why the agencies avoid the word

The action level marks where EPA recommends fixing a home, not where risk starts. EPA says radon levels less than 4 pCi/L still pose a risk and, in many cases, may be reduced. EPA's own risk chart shows why: it estimates that if 1,000 people who never smoked were exposed to 2 pCi/L over a lifetime, about 4 could get lung cancer, and for 1,000 people who smoked, about 32. A result under the action level is a lower risk, not no risk. The chart in full is in radon and lung cancer.

At what level is radon harmful?

There is no known level at which harm starts. EPA's page on WHO's 2009 handbook says there is significant risk at levels below 4 pCi/L (150 Bq/m3) and there is no known safe level of radon exposure; ATSDR reports that EPA also notes radon levels less than 4 pCi/L still pose a health risk and can be reduced in many cases. CDC's testing page says you should always aim to have the lowest radon levels to reduce the risk of lung cancer. For what counts as a high reading, see high radon levels.

Radon safe limit versus acceptable level

EPA does use the word acceptable, in a practical sense. It says even very high levels can be reduced to acceptable levels, and that a qualified mitigation contractor should make sure the finished system effectively reduces radon levels to acceptable levels. That is a statement about what a fix can achieve, not a safe limit, and EPA does not attach a separate number to it beyond its two guidance marks.

EPA's guidance points to what can be reached rather than to a number that is acceptable in itself. The U.S. Congress has set a long-term goal that indoor radon levels be no more than outdoor levels. EPA says that goal is not yet technologically achievable in all cases, but that most homes today can be reduced to 2 pCi/L or below. EPA's risk chart adds a caution at the other end: reducing radon levels below 2 pCi/L is difficult.

Read together, EPA's and CDC's statements point the same way: a fix aims below the action level, EPA says most homes can reach 2 pCi/L or below, and CDC says any further reduction still helps. The levels guide explains each band, and 4 pCi/L explained covers the action level in detail.

Acceptable levels of radon after mitigation

After a system is installed, EPA says to test again to confirm that the elevated level has been reduced, and recommends an independent, qualified radon tester for that test. EPA also suggests retesting every two years to be sure levels remain low. If a result stays high after mitigation, high radon levels covers what to check.

Acceptable radon levels in water

Water is handled differently. WHO's Guidelines for drinking-water quality (2011) recommend that screening levels for radon in drinking water be set based on the national reference level for radon in air, and WHO says it is prudent to measure where high concentrations might be expected. EPA says to test the air in the home first; if your water comes from a public system that uses ground water, call your water supplier, and if the home has a private well, have the water tested. No single water figure applies everywhere. See radon in water.

A radon level chart is the quickest way to place a number. The bands below use EPA's own marks and EPA's and CDC's words for each; they describe guidance for a home, not a verdict on anyone's health.

Each band is about the level in the room that was tested, over the time the test ran. Radon levels vary from day to day and season to season, EPA says, which is why EPA's steps call for a follow-up test before a decision to fix. For readings well above the line, see high radon levels; to place your own number, use the result interpreter.

All outdoor and indoor air has some radon in it, CDC says, and CDC's testing page repeats that according to EPA, the average radon level in American homes is about 1.3 pCi/L. EPA's Radionuclide Basics page gives the same averages in becquerels: 48.1 Bq/m3 (1.3 pCi/L) indoors and 14.8 becquerel/m3 outdoors. EPA's estimates give the U.S. baseline:

Normal radon levels in home: what the average does and does not tell you

An average is not a target and not a forecast for any one house. EPA estimates that nearly one out of every 15 homes in the United States has an elevated level of 4 pCi/L or more, and says homes next to each other can have different indoor radon levels. A county's predicted potential on the radon map, or a neighbor's result, cannot stand in for your own test.

Radon gas normal range, indoors and out

WHO describes the range. Outdoors, radon quickly dilutes to very low concentrations and is generally not a problem; the average outdoor level varies from 5 Bq/m3 to 15 Bq/m3. In buildings such as homes, schools and offices, levels can vary substantially, from 10 Bq/m3 to more than 10 000 Bq/m3. WHO adds that radon concentrations vary considerably between adjacent buildings, and within a building from day to day and hour to hour.

WHO's figure is lower than EPA's, and EPA has explained why it keeps its own. EPA's page on the 2009 WHO Handbook on Indoor Radon says the handbook's most noteworthy recommendation is that country reference levels for radon should be set at 2.7 pCi/L (100 Bq/m3), if possible, or as-low-as-reasonably-achievable, but should not exceed 8.1 pCi/L (300 Bq/m3).

EPA calls the handbook the FIRST Global Call to Action on indoor radon. In practice the two sets of advice point the same way for a household: EPA already recommends considering a fix from 2 pCi/L, which is below WHO's 100 Bq/m3 (2.7 pCi/L).

Outside the United States, the common starting point is WHO's recommendation. The WHO handbook on indoor radon sets out policy options for countries, which the WHO fact sheet lists:

• Providing information on radon levels indoors and the associated health risks.
• A national radon programme aimed at reducing both the overall population risk and the individual risk for people living with high radon concentrations.
• A national annual average residential reference level of 100 Bq/m3, or, if that cannot be reached under the country's conditions, one that does not exceed 300 Bq/m3.
• Measurement protocols to ensure quality and consistency in radon testing.
• Radon prevention in building codes, and programmes to keep levels below national reference levels.
• Education for building professionals, and financial support to remove radon from existing buildings.
• Including radon as a risk factor in national strategies on cancer control, tobacco control, indoor air quality and energy conservation.

Acceptable radon levels in Europe

WHO notes that in many countries of Europe, as in the United States and China, protective measures for new buildings are included in building codes. Each country sets its own reference level and rules, and WHO tracks them in a radon database on national policies and regulations in its Global Health Observatory. For a home in Europe, the national radon authority's reference level is the figure to compare with; this guide covers the EPA and WHO figures only.

Acceptable radon levels by state

Within the United States, EPA's figures are the federal guidance, and EPA says the action level should comply with the guidance of the state or local jurisdiction where the test is done. EPA's Home Buyer's and Seller's Guide adds that state requirements or guidance may be more stringent than EPA's, and that any mitigation system installed must conform to your state's regulations. Some states run credentialing programs for radon professionals. Your state radon program is the place to check local rules.

1. 1

   Check the unit

   U.S. results are in pCi/L, the unit EPA uses; WHO's figures are in Bq/m3. To convert, multiply pCi/L by 37 or divide Bq/m3 by 37 (Radon411's conversion; EPA rounds, printing 4 pCi/L as 150 Bq/m3).

2. 2

   Check the test

   Short-term tests run 2 to 90 days, and EPA says all radon tests should be taken for a minimum of 48 hours, under closed-house conditions. A long-term test runs more than 90 days and is more likely to tell you your year-round average.

3. 3

   Compare with EPA's marks

   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.

4. 4

   Confirm before fixing

   Follow a high short-term result with a long-term test, or with a second short-term test if you need results quickly.

5. 5

   Outside the U.S., use the national figure

   EPA says the action level should follow the guidance of the country or jurisdiction where the test is done.

Read this figure as textHide the text version

1. 1Step 1: Take a short-term test.

   • Below 4 pCi/LEven if your test result is below 4 pCi/L, you may want to test again sometime in the future.
   • At or above 4 pCi/LIf your result is at or above 4 pCi/L, take a followup test to be sure.

2. 2Step 2: Follow up with either a long-term test or a second short-term test.

   • Long-term testFor a better understanding of your year-round average radon level, take a long-term test.
   • Second short-term testIf you need results quickly, take a second short-term test. If your first short-term test result is more than twice EPA's 4 pCi/L action level, you should take a second short-term test immediately.

3. 3Step 3: Decide whether to fix your home.

   • After a long-term testFix your home if your long-term test result is 4 pCi/L or more.
   • After a second short-term testConsider fixing your home if the average of your first and second test is at or above 4 pCi/L.

Testing is the only way to know the radon level in a specific building. If you have not tested yet, start with how to test for radon. If you have a number, the result interpreter places it against these limits, and the directory lists measurement and mitigation professionals.