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According to the EPA, at what level does radon become a health concern requiring mitigation?

By Radon411 Editorial TeamUpdated How we research

Short answer

EPA's action level is 4 pCi/L: at a confirmed result of 4 pCi/L or more, EPA recommends fixing the home, usually with a vent pipe and fan system. Between 2 and 4 pCi/L, EPA recommends considering a fix, and it says any radon exposure carries some risk, so the line is a decision point rather than a safe limit.

Next step: pick the right test for your home. Which test to use

The is a decision point, not a line between safe and unsafe. The lower the radon level, the lower the risk, and EPA says no level of radon is safe. The 2 to 4 range is where EPA asks people to consider a fix even though it is below the action level.

The level applies to a confirmed result: one , or the average of two . A first short-term result at or above the action level is followed up before anything is installed, with a long-term test for a better picture of the year-round average, or a second short-term test when time is short.

Other bodies set their marks differently. WHO's advice is a national reference level of 100 for homes, and no more than 300 where 100 cannot be reached. EPA's 4 pCi/L is 148 becquerels per cubic meter.

What to do next: read your result with the interpreter, and if a confirmed level calls for a fix, find a certified professional.

EPA's two levels: fix, and consider fixing

EPA gives two numbers, not one. EPA recommends fixing a home when the radon level is 4 or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Below 2 pCi/L there is no recommendation to fix, but there is no all-clear either: EPA's position is that any radon exposure carries some risk, and that the lower the level, the lower the risk.

Scale of radon levels from 0 to 10 pCi/L marking EPA's 2 pCi/L level, where EPA says to consider fixing, and its 4 pCi/L action level, where EPA says to fix the home, with each mark also in Bq/m³.
Read this figure as text
  • 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 two guidance levels on one scale: consider fixing from 2 pCi/L, fix from 4 pCi/L.

For scale, EPA estimates the average indoor radon level at about 1.3 pCi/L and puts outdoor air at about 0.4 pCi/L. Congress has set a long-term goal that indoor radon be no higher than outdoor levels. That goal is not yet technologically achievable in every case, and getting below 2 pCi/L is difficult, but most homes today can be brought down to 2 pCi/L or below.

The result the decision rests on

EPA's level applies to a confirmed result, not to a single quick test. Because radon levels vary from day to day and season to season, a is less likely than a to show the year-round average. So a first short-term result at or above the is followed up before anyone installs anything.

How a test result becomes a decision under EPA's testing steps
What you testedWhat decides it
One short-term testNot enough on its own. If it is at or above 4 pCi/L, take a follow-up test.
First short-term result more than twice the action levelTake a second short-term test right away.
Follow-up long-term test (more than 90 days)Fix the home if the long-term result is 4 pCi/L or more.
Follow-up second short-term testConsider fixing if the average of the two is 4 pCi/L or more; the higher the results, the more certain you can be.
Home saleAny of three short-term options: two tests at once, two in a row, or a continuous monitor, each run at least 48 hours.

Why 4 pCi/L: the risk at and below the action level

The action level is a point on a sliding scale of risk. EPA's risk chart estimates how many people out of 1,000 could get lung cancer if exposed to a given level over a lifetime, and the numbers fall with the level but do not reach zero at 4, at 2 or even at the average indoor level.

Bar chart of EPA's radon risk estimates for people who smoked and people who never smoked: out of 1,000 people exposed over a lifetime, about how many could get lung cancer at 20, 10, 8, 4, 2, 1.3 and 0.4 pCi/L, from about 260 smokers at 20 pCi/L to about 3 at 0.4 pCi/L, with EPA's advice at each level.
Read this figure as text

EPA estimate, lifetime exposure

  • Out of 1,000 people who smoked
  • Out of 1,000 people who never smoked
About how many people out of 1,000 exposed over a lifetime could get lung cancer, by radon level
Radon levelCould get lung cancer, per 1,000What to do
20 pCi/L740 Bq/m³Smoked: About 260Never smoked: About 36Fix your home
10 pCi/L370 Bq/m³Smoked: About 150Never smoked: About 18Fix your home
8 pCi/L300 Bq/m³Smoked: About 120Never smoked: About 15Fix your home
4 pCi/L150 Bq/m³Smoked: About 62Never smoked: About 7Fix your home
2 pCi/L75 Bq/m³Smoked: About 32Never smoked: About 4Consider fixing between 2 and 4 pCi/L
1.3 pCi/L50 Bq/m³Smoked: About 20Never smoked: About 2Average indoor radon level
0.4 pCi/L15 Bq/m³Smoked: About 3Never smoked: No figure givenAverage outdoor radon level
  • Smoked: If you are a former smoker, your risk may be lower.
  • Never smoked: If you are a former smoker, your risk may be higher.
  • Reducing radon levels below 2 pCi/L (75 Bq/m3) is difficult.
  • Lifetime risk of lung cancer deaths, as EPA estimates it.
EPA's estimates of lifetime lung cancer risk at each radon level, for people who smoke and people who never smoked.

At 4 pCi/L, EPA estimates that about 62 of 1,000 people who smoke and about 7 of 1,000 who never smoked could get lung cancer from a lifetime of exposure. At 2 pCi/L the estimates are about 32 and about 4. Smoking and radon together are an especially serious risk, which is why EPA's advice to people who smoke is to stop smoking as well as fix the home.

How EPA's level compares with WHO's

The two agencies use different units and set their marks differently. EPA's 4 pCi/L is 148 (Bq/m3). WHO's policy advice is a national reference level of 100 Bq/m3 for the annual average in homes, and where a country cannot reach that, a reference level that should not exceed 300 Bq/m3.

Chart of radon levels on one Bq/m³ scale: EPA's average indoor level of 48.1 Bq/m³, EPA's 2 pCi/L, WHO's 100 Bq/m³ reference level, EPA's 148 Bq/m³ (4 pCi/L) action level and WHO's 300 Bq/m³ upper limit.
Read this figure as text
  • U.S. EPA
  • World Health Organization
  • EPA: average indoor air48.1 Bq/m³ (1.3 pCi/L)The average for indoor air is 48.1 Bq/m3 (1.3 pCi/L).
  • EPA: consider fixing2 pCi/L (74 Bq/m³, calculated)Consider fixing between 2 and 4 pCi/L.
  • WHO: reference level100 Bq/m³ (2.7 pCi/L, calculated)A national annual average residential radon concentration reference level of 100 Bq/m3.
  • EPA: fix your home148 Bq/m³ (4 pCi/L)EPA recommends fixing your home when the radon level is at or above 148 Bq/m3 (4 pCi/L).
  • WHO: upper limit for a reference level300 Bq/m³ (8.1 pCi/L, calculated)If 100 Bq/m3 cannot be reached under the prevailing country-specific conditions, the reference level should not exceed 300 Bq/m3.

Calculated by Radon411: figures marked calculated convert the publisher's unit at 37 Bq/m³ per pCi/L, EPA's factor: “1 pCi/L corresponds to 37 Bq/m3”. A becquerel is one atomic nucleus transforming each second. WHO sets reference levels for countries; EPA's level is a recommendation to fix a home.

EPA's levels and WHO's reference levels on one becquerel scale.

Both rest on the same evidence about long-term exposure: WHO puts the rise in lung cancer risk at about 16 percent per 100 Bq/m3 increase in the long-term average, and treats the relationship as linear. EPA's 2 to 4 pCi/L range for considering a fix works out to about 74 to 148 Bq/m3 (our conversion, at 37 Bq/m3 per pCi/L), so WHO's 100 falls inside it.

Is mitigation required?

EPA's levels are recommendations to homeowners, not a law that forces a fix. What can be required depends on where you live: any measures taken or system installed must conform to your state's regulations, some states require radon testers to follow a specific protocol, and some require disclosure of radon information to buyers.

Where rules can apply
SituationWhat applies
Fixing your own homeEPA's guidance. Any system installed must meet your state's regulations; where a state has none, EPA recommends following its current voluntary consensus standards.
Hiring a contractorMany states require radon professionals to be licensed, certified or registered.
Selling a homeYour state or local government may require disclosure of radon information to buyers.
New constructionBuilding codes in your state or local area may require radon-resistant construction features.

State rules are summarized on our state radon programs page.

Questions about EPA's action level

When should you mitigate radon?

When a confirmed result reaches EPA's action level: one long-term test, or the average of two short-term tests, at 4 pCi/L or more. Between 2 and 4 pCi/L, EPA recommends considering a fix. Don't wait to act on a high result.

Should I mitigate a radon level of 3?

EPA recommends considering it: 3 pCi/L is inside the 2 to 4 range where EPA asks people to consider a fix, and EPA's position is that any exposure carries some risk. See what radon level is dangerous.

Is radon remediation necessary below 2 pCi/L?

EPA does not recommend a fix below 2 pCi/L, and getting below 2 is difficult. The average indoor level is about 1.3 pCi/L.

Is the action level 4.0 exactly?

Yes: EPA's action level is 4 pCi/L, and its guidance applies at 4 or more. A result of exactly 4.0, confirmed, is at the action level.

Does EPA require radon mitigation?

No. EPA recommends it; it does not order homeowners to fix. State and local rules may cover licensing, disclosure in a sale, building codes and how a system must be installed.

What level does WHO recommend?

A national reference level of 100 Bq/m3, about 2.7 pCi/L, and no more than 300 Bq/m3, about 8.1 pCi/L, where 100 cannot be reached. Those conversions are ours, at 37 Bq/m3 per pCi/L.

How much does a fix lower the level?

Some radon reduction systems can lower levels by up to 99 percent, and most homes can be brought to 2 pCi/L or below. See does radon mitigation work.

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