Radon Levels
Radon level of 100 pCi/L: what to do
Short answer
A radon level of 100 pCi/L is extremely high, 25 times the action level and far above EPA's risk chart. The guidance does not change at this level: confirm it with a second short-term test right away, check that the test was run properly, and fix the home, which is possible even at very high levels.
Next step: pick the right test for your home. Which test to use
Key takeaways
- 100 pCi/L is 25 times EPA's 4 pCi/L action level.
- More than twice the action level: confirm right away, then fix.
- EPA estimates the average U.S. home at about 1.3 pCi/L; 100 pCi/L is 76.92 times that.
- Confirm a first short-term result this high with a second short-term test immediately.
Where it sits
Is a radon level of 100 pCi/L high?
- About 3700 Bq/m3
- 100 pCi/L in becquerels per cubic meter, at about 37 Bq/m3 per pCi/L (calculated).
- 25 times
- EPA's 4 pCi/L action level (calculated).
- 76.92 times
- The U.S. indoor average of about 1.3 pCi/L (calculated).
Check how the test was done. Improper testing may yield inaccurate results and require another test, and interfering with the device or with may invalidate the result.
The risk chart tops out at 20 , about 260 lung cancers per 1,000 people who smoked and about 36 per 1,000 who never smoked over a lifetime; at 100 pCi/L the risk is higher still. WHO estimates the risk of lung cancer rises by about 16% per 100 of long-term average radon, and 100 pCi/L is roughly 3,700 Bq/m3 by our calculation.
Where 100 pCi/L sits against EPA's and WHO's reference points
Against outdoor air (about 0.4 pCi/L)
250 times the outdoor average (calculated)Against WHO's recommended reference level (100 Bq/m3, 2.7 pCi/L)
Above itEPA's band
More than twice the action level: confirm right away, then fix
What to do
What to do about a radon level of 100 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 100 pCi/L, the steps come to this:
Steps for a reading of 100 pCi/L
Retest right away
100 pCi/L is more than twice the action level, so take a second short-term test immediately rather than wait for a long-term test.Check the first test
Improper testing may give inaccurate results; confirm the device, its placement and closed-house conditions.Fix the home
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Get estimates from qualified contractors; 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 100 pCi/L
EPA's risk chart stops at 20 pCi/L, so 100 pCi/L is above its highest row. The table shows that top row; the risk at 100 pCi/L is higher.
The chart's top row, 20 pCi/L, gives about 260 in 1,000 people who smoked (250 times the risk of drowning), and about 36 in 1,000 who never smoked (35 times the risk of drowning). 100 pCi/L is 5 times that row's level (our calculation), so the risk at 100 pCi/L is higher than the top row shows.
| Radon level | People who smoked | People who never smoked | What to do |
|---|---|---|---|
| 20 pCi/L (740 Bq/m3) | About 260 in 1,000 | About 36 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 100 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 is less likely than a to show the year-round average, and levels can change from hour to hour. A single short-term result of 100 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 closed-house conditions are on radon testing.
With a system
How much a radon system would lower 100 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 100 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 100 pCi/L, about |
|---|---|---|
| Active sub-slab suction (the usual system) | 50 to 99 percent | 50 pCi/L or lower |
| Sump-hole suction | 50 to 99 percent | 50 pCi/L or lower |
| Drain-tile suction | 50 to 99 percent | 50 pCi/L or lower |
| Submembrane suction (crawl spaces) | 50 to 99 percent | 50 pCi/L or lower |
| Passive sub-slab suction (no fan) | 30 to 70 percent | 70 to 30 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 100 pCi/L
100 pCi/L in three common situations
Was the test disturbed?
Improper testing may yield inaccurate results and require another test, and interfering with the device or the closed-house conditions may invalidate the result.100 pCi/L confirmed
Even very high levels can be reduced to acceptable levels. The contractor may need to run diagnostic tests during the first phase of the installation to design the best system for the house.100 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.
Retest
When to retest after 100 pCi/L
At 100 pCi/L, retest right away with a second short-term test, and check how the first test was run before anything else. A reading five times the chart's top row of 20 pCi/L (our calculation) is worth confirming quickly.
| When | What to do |
|---|---|
| To confirm the first result | Immediately, with a second short-term test |
| 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 100 pCi/L: questions
Is 100 pCi/L of radon safe?
No. 100 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 100 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 100 pCi/L in Bq/m3?
It is about 3700 Bq/m3, at about 37 Bq/m3 per pCi/L (our calculation).
Should I buy a house with a radon level of 100 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 100 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 100 pCi/L?
Do not wait: a first short-term result more than twice the action level calls for a second short-term test immediately.
Can 100 pCi/L be fixed?
Yes. Even very high levels can be reduced to acceptable levels, and a contractor may run diagnostic tests first to design the system for a source this strong.