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What is a safe level of radon?

By Radon411 Editorial TeamUpdated How we research

Short answer

No level of radon is known to be safe: any exposure carries some risk, and lowering the level lowers the risk. EPA recommends fixing a home at 4 pCi/L, its action level, and considering a fix between 2 and 4 pCi/L, while WHO's reference level is 100 Bq/m3, about 2.7 pCi/L.

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

Any radon exposure carries some risk, and no level of radon is known to be safe; even levels below 4 pose some risk. The aim is always the lowest level you can reach.

A home cannot be brought to zero either. Outdoor air holds about 0.4 pCi/L of radon, and EPA estimates the average U.S. home at about 1.3 pCi/L. Radon in many homes can be reduced to 2 pCi/L or less.

What to do next: test the lowest lived-in level of your home, and read the result as a point on a scale of risk rather than a pass or a fail.

Is any level of radon safe?

No level of radon is known to be safe. Any exposure carries some risk, and the goal is always the lowest level you can reach. That goal has a floor, though: radon cannot be reduced to zero, because the outdoor air itself contains some.

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 estimate of how many people out of 1,000 could get lung cancer from a lifetime of exposure at each level, for people who smoked and people who never smoked.

The chart shows why no safe line exists. Risk falls with the level but never reaches zero. At 2 , EPA estimates about 32 of 1,000 people who smoked, and about 4 of 1,000 who never smoked, could get lung cancer over a lifetime; at the national indoor average of 1.3 pCi/L, about 20 and about 2. The relation is treated as linear: risk rises in proportion to exposure, and even the low concentrations common in homes carry some risk.

Safe and acceptable are not the same thing

When people ask for a safe level they usually mean the point at which to act. There are several such marks, and none of them is a safe level; each is a line for deciding what to do.

The guidance levels in use
LevelWhoseWhat it means
4 pCi/L (150 Bq/m3)EPA action levelFix the home at or above it
2 to 4 pCi/L (75 to 150 Bq/m3)EPAConsider a fix, because no level is known to be safe
100 Bq/m3 (2.7 pCi/L)WHO reference levelThe national reference level WHO recommends for homes
300 Bq/m3 (8.1 pCi/L)WHO ceilingWhere 100 Bq/m3 cannot be reached, a reference level should not go above 300
About 0.4 pCi/LCongress's long-term goalIndoor levels no higher than outdoor levels, not yet achievable in every home
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.

The U.S. and WHO levels on one becquerel scale. A converted value is marked as calculated.

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. WHO's lower reference level does not change the U.S. , because the 2 to 4 pCi/L range already calls for considering a fix, given the significant risk below 4. Most countries' action levels sit close to the U.S. figure. National and workplace limits are covered in the radon limits guide.

How your number compares with average levels

Average radon levels, for context
WhereAverage levelBasis
U.S. homesAbout 1.3 pCi/L (50 Bq/m3)EPA's estimate of the national indoor average
Outdoor air, U.S.About 0.4 pCi/L (15 Bq/m3), one-tenth of the action levelEPA's estimate
Outdoor air, worldwide5 to 15 Bq/m3WHO's range

An average is not a safe level either: EPA based its estimate of 21,000 radon-related lung cancers a year on the 1.3 pCi/L national average. What the averages do show is how low a home can usually go. Radon in many homes can be brought to 2 pCi/L or less, and going below 2 pCi/L is difficult.

Basements and the floors you live on

There is no separate safe level for a basement. The same guidance applies wherever people spend time, and the basement is often where the level is highest, because radon is usually higher in basements, cellars and rooms in contact with the ground. Upper floors can still carry considerable radon.

Which floor's result to go by
SituationWhat to do
You live in or use the basementTest the lowest lived-in level, which is the basement if it is used often
You start using a lower floor, for example a basement bedroom or home officeRetest on that level
Your result is below 2 pCi/LNo action is needed, but test again if you start living on a lower level

Questions about safe radon levels

What are acceptable radon levels?

No level is called acceptable in the sense of risk-free. The U.S. guidance is to fix at the 4 pCi/L action level and consider a fix from 2 to 4 pCi/L; lowering the level lowers the risk. WHO recommends a reference level of 100 Bq/m3, about 2.7 pCi/L.

Is 2 pCi/L safe?

It is lower risk, not no risk. EPA estimates about 4 in 1,000 people who never smoked, and about 32 in 1,000 who smoked, could get lung cancer from a lifetime at 2 pCi/L. Getting much below 2 pCi/L is difficult. See the 2 pCi/L explainer.

What is the maximum safe radon level?

There is none, because no level is called safe. The highest guidance level in use is WHO's ceiling for a national reference level, 300 Bq/m3 (about 8.1 pCi/L). The U.S. action level is lower, at 4 pCi/L.

Is a result of 4.1 pCi/L basically safe?

No. A result that close to 4 is uncertain: if two short-term tests average 4.1 pCi/L, there is about a 50 percent chance the year-round average is somewhat below 4. A long-term test gives a better picture of the year-round average. See is a radon level of 4.1 considered high.

What level of radon in water is safe?

No safe level for water is set in the guidance here. Most of the risk from radon in water comes from radon released into the air when water is used, and the lung cancer risk from breathing radon is much larger than the stomach cancer risk from swallowing it. Test the air first; see radon in water.

Should I fix a home below 4 pCi/L?

You may. A fix is worth considering between 2 and 4 pCi/L, and reducing radon always lowers the risk of lung cancer, even below 4 pCi/L.

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