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What radon level is dangerous?

By Radon411 Editorial TeamUpdated How we research

Short answer

EPA treats 4 pCi/L as the level at which to fix a home, and recommends considering a fix from 2 to 4 pCi/L, but there is no line where radon turns from safe to dangerous. The risk rises steadily with the level, with the years of exposure, and sharply with smoking.

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

EPA estimates that out of 1,000 people who never smoked and spent a lifetime at 4 , about 7 could get lung cancer; at 20 pCi/L, about 36. For people who smoked, the figures are about 62 and about 260. WHO estimates lung cancer risk increases by about 16 percent per 100 of long-term average radon.

Because a single short-term result can mislead, confirm a high result with a follow-up test before fixing, and take that second test immediately if the first is more than twice the 4 pCi/L .

What to do next: if your result is high, confirm it, then plan a fix; if you have not tested, test the lowest lived-in level first.

Where the line for action is drawn

Radon is not divided into safe and dangerous. The U.S. guidance uses one , 4 , where a fix is recommended, and a lower range, 2 to 4 pCi/L, where a fix is worth considering. Below that the risk is smaller but not zero; above it the risk keeps climbing with the level.

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.
The two guidance levels on a 0 to 10+ pCi/L scale, with becquerels per cubic meter.

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. The decision should rest on a confirmed number: one , or the average of two , at the action level or above.

How the danger grows with the 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 and its comparison to other risks.
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 1,000EPA's comparisonWhat to do
20 pCi/L740 Bq/m³Smoked: About 260Never smoked: About 36Smoked: 250 times the risk of drowningNever smoked: 35 times the risk of drowningFix your home
10 pCi/L370 Bq/m³Smoked: About 150Never smoked: About 18Smoked: 200 times the risk of dying in a home fireNever smoked: 20 times the risk of dying in a home fireFix your home
8 pCi/L300 Bq/m³Smoked: About 120Never smoked: About 15Smoked: 30 times the risk of dying in a fallNever smoked: 4 times the risk of dying in a fallFix your home
4 pCi/L150 Bq/m³Smoked: About 62Never smoked: About 7Smoked: 5 times the risk of dying in a car crashNever smoked: The risk of dying in a car crashFix your home
2 pCi/L75 Bq/m³Smoked: About 32Never smoked: About 4Smoked: 6 times the risk of dying from poisonNever smoked: The risk of dying from poisonConsider 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.
  • The risk comparisons are EPA's.
EPA's estimate of lifetime lung cancer risk at each radon level, out of 1,000 people, for people who smoked and people who never smoked, compared with other risks.
EPA's estimate: out of 1,000 people exposed over a lifetime, about how many could get lung cancer
Radon levelPeople who smokedPeople who never smoked
20 pCi/LAbout 260About 36
10 pCi/LAbout 150About 18
8 pCi/LAbout 120About 15
4 pCi/LAbout 62About 7
2 pCi/LAbout 32About 4

Each step up the scale adds risk; there is no cliff edge. Studies of homes put the increase at about 16 percent more lung cancer risk for every 100 of long-term average radon, WHO estimates, rising in proportion to exposure. Levels in homes, schools and offices range enormously, from 10 Bq/m3 to more than 10,000 Bq/m3.

What a high result changes

What to do as a first short-term result rises
First resultWhat to do
Below 2 pCi/LLower risk, not none; you may want to test again in the future
2 to 4 pCi/LConsider a fix; levels below 4 still carry some risk
4 to 8 pCi/LTake a follow-up test, long-term or a second short-term, before deciding
Above 8 pCi/LMore than twice the action level: take a second short-term test immediately
Very high readingsEven very high levels can be brought down to acceptable levels; some systems cut radon by up to 99 percent

A higher first result also makes the decision clearer: the higher your short-term results, the more certain you can be that the home needs fixing. A result near 4 is the least certain; two short-term tests averaging 4.1 pCi/L leave about a 50 percent chance the year-round average is below or above 4. Individual readings are explained on the level pages, such as 8 pCi/L and 10 pCi/L.

The level is only part of the danger

The chance of getting lung cancer from radon depends mostly on three things, and the level is only the first.

What sets the risk from a given radon level
FactorWhy it matters
How much radon is in the homeRisk rises with higher levels of radon
How long you spend thereLonger exposure means more risk
SmokingSmokers are about 25 times more at risk from radon than non-smokers, by WHO's estimate; radon combined with smoking is an especially serious risk

People who never smoked are not exempt. EPA estimates radon causes about 21,000 lung cancer deaths a year, about 2,900 of them among people who never smoked, which makes radon the leading cause of lung cancer among non-smokers by its estimate. The harm is slow: lung cancer takes many years to develop, and not everyone exposed to elevated radon gets it. The health evidence is in the radon lung cancer guide.

Questions about dangerous radon levels

What is a dangerously high level of radon?

The line for action is 4 pCi/L. There is no separate danger level above it; the risk keeps rising, to about 260 in 1,000 people who smoked and about 36 in 1,000 who never smoked for a lifetime at 20 pCi/L, by EPA's estimate.

At what level is radon harmful?

Any exposure carries some risk, so harm is a matter of degree. A fix is recommended at 4 pCi/L and worth considering from 2 to 4 pCi/L. See what is a safe level of radon.

Is 8 pCi/L of radon dangerous?

It is twice the action level. EPA estimates about 120 in 1,000 people who smoked, and about 15 in 1,000 who never smoked, could get lung cancer from a lifetime at 8 pCi/L. Confirm it with a follow-up test and plan a fix.

How dangerous is radon compared with other risks?

EPA's comparison puts a smoker's lifetime risk at 4 pCi/L at about 5 times the risk of dying in a car crash, and a never-smoker's at about the risk of dying in a car crash. At 20 pCi/L the smoker's risk is about 250 times the risk of drowning.

I have lived with a high level for years. Is it too late?

No. Reducing radon lowers the risk of lung cancer even after living with a radon problem for a long time.

Can very high radon levels be fixed?

Yes. Even very high levels can be brought down to acceptable levels, and most homes can reach 2 pCi/L or below. See how to reduce radon.

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