Radon Levels
Radon level of 4 pCi/L: EPA's action level
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?
- 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).
4 is not a line between safe and unsafe. Any radon exposure carries some risk, and the risk chart puts 4 pCi/L at about 62 lung cancers per 1,000 people who smoked and about 7 per 1,000 who never smoked, over a lifetime. It is about 150 , and most countries' action levels are similar.
A single short-term result of 4 pCi/L is a reason to test again first, with either a or a second . Results just over the line are the least certain; see is a radon level of 4.1 considered high.
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
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. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. 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.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.
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.
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.
| 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 |
These are population estimates from EPA's 2003 assessment of radon risk in homes, not a forecast for any one person. Your own chances depend mostly on how much radon is in your home, how much time you spend there, and whether you smoke or have ever smoked; a former smoker's risk may sit between the two columns. Lung cancer risk is estimated to rise by about 16% per 100 Bq/m3 of long-term average radon.
EPA's whole chart, from outdoor air to 20 pCi/L, is drawn on radon levels.
How sure
How certain is a reading of 4 pCi/L?
One test is a sample of a level that moves. Radon levels tend to vary from day to day and season to season, so a short-term test is less likely than a long-term test to show the year-round average, and levels can change from hour to hour. A single short-term result of 4 pCi/L is a reading for those days.
Where the test sat matters as much. A test belongs in the lowest lived-in level, and levels are usually higher in basements and rooms in contact with the ground. Testing is the only way to know the radon level in a specific building. Placement and are on radon testing.
With a system
How much a radon system would lower 4 pCi/L
Each technique has a typical reduction range, and with today's technology radon levels in most homes can be reduced to 2 pCi/L or below. Applied to 4 pCi/L, the low end of each range gives the figures below: our arithmetic on the published ranges, not a prediction for your house. Only a test after installation shows what a system achieved.
| Technique | Typical reduction | From 4 pCi/L, about |
|---|---|---|
| Active sub-slab suction (the usual system) | 50 to 99 percent | 2 pCi/L or lower |
| Sump-hole suction | 50 to 99 percent | 2 pCi/L or lower |
| Drain-tile suction | 50 to 99 percent | 2 pCi/L or lower |
| Submembrane suction (crawl spaces) | 50 to 99 percent | 2 pCi/L or lower |
| Passive sub-slab suction (no fan) | 30 to 70 percent | 2.8 to 1.2 pCi/L |
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 , 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 |
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.
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. 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. Levels are usually highest in basements and rooms in contact with the ground, though considerable levels can occur above the ground floor too. 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.
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.