Radon Levels
Radon level of 4 pCi/L: EPA's action level
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Move a reading around 4 pCi/L
The reading starts at 4 pCi/L. Slide it to see where EPA's guidance changes and how far this number is from each line.
Read a result for 4 pCi/L
Starts at 4.0 pCi/L, this page's reading
EPA’s own thresholds, as its guidance states them.
EPA’s reading of 4.0 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. That is EPA's action level exactly.
Short answer
A radon level of 4 pCi/L is EPA's action level: once a long-term test, or the average of two short-term tests, reaches it, EPA recommends fixing the home. It is about three times the U.S. indoor average, and EPA estimates that nearly one in 15 homes is at this level or higher.
Next step: pick the right test for your home. Which test to use
Key takeaways
- 4 pCi/L is exactly EPA's 4 pCi/L action level.
- At or above EPA's action level: fix once confirmed.
- EPA estimates the average U.S. home at about 1.3 pCi/L; 4 pCi/L is 3.08 times that.
- Confirm a short-term result with a second test; a long-term test shows the year-round average best.
Where it sits
Is a radon level of 4 pCi/L high?
4
- 150 Bq/m3
- 4 pCi/L in becquerels per cubic meter, the published figure.
- At the line
- 4 pCi/L is EPA's action level, where EPA recommends fixing a home.
- 3.08 times
- The U.S. indoor average of about 1.3 pCi/L (calculated).
Read moreThree paragraphs and a table, 1 min
A single short-term result of 4 pCi/L is a reason to test again first, with either a
4 pCi/L is about 148 Bq/m3, ten times the outdoor average, by our calculation, and EPA estimates that nearly 1 in 15 U.S. homes is at or above it. The line is drawn on two tests, not one: EPA recommends fixing when a long-term test, or the average of a short-term test and its follow-up, reaches 4 pCi/L.
Where 4 pCi/L sits against EPA's and WHO's reference points
Against outdoor air (about 0.4 pCi/L)
10 times the outdoor average (calculated)Against WHO's recommended reference level (100 Bq/m3, 2.7 pCi/L)
Above itEPA's band
At or above EPA's action level: fix once confirmed
Other readings explained: 1 pCi/L, 2 pCi/L, 3 pCi/L, 5 pCi/L, 6 pCi/L, 7 pCi/L, 8 pCi/L, 10 pCi/L, 12 pCi/L, 20 pCi/L, 30 pCi/L, 100 pCi/L.
What to do
What to do about a radon level of 4 pCi/L
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. For a reading of 4 pCi/L, the steps come to this:
Steps for a reading of 4 pCi/L
Confirm it
If 4 pCi/L was a first short-term result, take a follow-up test: a long-term test for the year-round average, or a second short-term test if you need results quickly.Decide on the confirmed number
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. The decision rests on one long-term test or the average of two short-term tests: two results averaging 4 pCi/L call for the fix.Hire a qualified contractor
Get more than one estimate and a written contract; see radon mitigation.Test after the fix
No sooner than 24 hours and within 30 days after the system starts, then at least every two years.
Read moreA paragraph, 1 min
The full sequence of tests, from a first result to the decision to fix, is drawn on radon testing.
Health risk
The lung cancer risk at 4 pCi/L
EPA's risk chart has a row for 4 pCi/L. It estimates how many people out of 1,000 could get lung cancer if exposed to that level over a lifetime, separately for people who smoked and people who never smoked.
| Radon level | People who smoked | People who never smoked | What to do |
|---|---|---|---|
| 4 pCi/L (150 Bq/m3) | About 62 in 1,000 | About 7 in 1,000 | Fix your home |
Read moreTwo paragraphs, 1 min
At 4 pCi/L, the chart's lifetime estimate is about 62 in 1,000 people who smoked (5 times the risk of dying in a car crash), and about 7 in 1,000 who never smoked (the risk of dying in a car crash). The comparisons in parentheses are the ones EPA prints beside the row.
Lung cancer risk is estimated to rise by about 16% per 100 Bq/m3 of long-term average radon. At 150 Bq/m3, a long-term average of 4 pCi/L, that comes to about 24% above the risk with no radon at all (our calculation, a population estimate, not a forecast for one person); a former smoker's risk may sit between the chart's two columns.
How sure
How certain is a reading of 4 pCi/L?
A first short-term result of 4 pCi/L is enough to act on only once a second test agrees: radon varies from day to day and season to season, and a long-term test is likelier to show the year-round average. At 4 pCi/L, a year-round average a third lower would be 2.67 pCi/L, just under the
Read moreA note, 1 min
With a system
How much a radon system would lower 4 pCi/L
From 4 pCi/L, an active system at the low end of its typical range would leave about 2 pCi/L, inside the 2 to 4 pCi/L range; at the high end, about 0.04 pCi/L. Our arithmetic on the published ranges, not a prediction for your house: radon levels in most homes can be reduced to 2 pCi/L or below.
| Technique | Typical reduction | From 4 pCi/L, about |
|---|---|---|
| Active suction: sub-slab, sump hole, drain tile, or a crawl-space membrane | 50 to 99 percent | 2 to 0.04 pCi/L |
| Passive sub-slab suction (no fan) | 30 to 70 percent | 2.8 to 1.2 pCi/L |
Read moreA paragraph, 1 min
Which technique fits depends on the foundation; see radon mitigation systems, and for cost, radon mitigation cost.
Situations
Where people meet a reading of 4 pCi/L
4 pCi/L in three common situations
Exactly 4 on a first short-term test
Results close to 4 are the least definitive: two short-term tests averaging 4.1 pCi/L carry about a 50 percent chance that the year-round average is somewhat below, or above, 4. Follow up before deciding.4 pCi/L after a mitigation system
As a post-mitigation result, 4.0 pCi/L or greater means fix the building, and with a system already installed, more work may be needed to lower the radon further.4 pCi/L in a home sale
The buyer and seller should discuss the timing and costs of radon reduction, and the contract can say when mitigation will be done and who will pay for it.
Retest
When to retest after 4 pCi/L
4 pCi/L is exactly the action level, so the follow-up decides it. Take a long-term test, or a second short-term test if you need results quickly. EPA recommends fixing when one long-term test, or the average of two short-term tests, shows 4 pCi/L or more.
| When | What to do |
|---|---|
| To confirm the first result | With a long-term test, or a second short-term test if you need results quickly |
| After a system is installed | No sooner than 24 hours and within 30 days, with a two- to seven-day test |
| With a system in place | At least every two years |
| After a remodel | In the lowest lived-in area |
Show all 4 rows
Read moreA paragraph, 1 min
The general answer is on how often should I test for radon.
Questions
Radon level of 4 pCi/L: questions
Is 4 pCi/L of radon safe?
No. 4 pCi/L is at or above EPA's 4 pCi/L action level, where EPA recommends fixing the home once the result is confirmed.
Do I need radon mitigation at 4 pCi/L?
Yes, by EPA's guidance, once a long-term test or the average of two short-term tests confirms the level is 4 pCi/L or more; 4 pCi/L is 1 times that line.
What is 4 pCi/L in Bq/m3?
It is 150 Bq/m3, the figure EPA prints for it.
Should I buy a house with a radon level of 4 pCi/L?
A high level is fixable: from 4 pCi/L, an active system's typical reduction would leave 2 pCi/L or less. Buyers and sellers should discuss the timing and costs of radon reduction, and the contract can say when mitigation happens and who pays. See should I buy a house with radon.
Is 4 pCi/L in a basement different from upstairs?
Usually the basement reads higher. If 4 pCi/L came from a room upstairs, a basement half again as high would read 6 pCi/L, at or above the action level; a test belongs in the lowest lived-in level.
How long should I wait to retest after 4 pCi/L?
Follow up soon, with a long-term test if you have time or a second short-term test if you need results quickly: 4 pCi/L is exactly at the line.
How many homes are at 4 pCi/L or more?
Nearly one in 15 U.S. homes is estimated to have an elevated radon level, 4 pCi/L or more.