Radon Levels
Radon level of 100 pCi/L: what to do
Try it
Move a reading around 100 pCi/L
The reading starts at 100 pCi/L. Slide it to see where EPA's guidance changes and how far this number is from each line.
Read a result for 100 pCi/L
Starts at 100.0 pCi/L, this page's reading
EPA’s own thresholds, as its guidance states them.
EPA’s reading of 100.0 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 96.0 pCi/L above EPA's action level, 25 times it.
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?
Check how the test was done. Improper testing may yield inaccurate results and require another test, and interfering with the device or with
- 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).
Read moreThree paragraphs and a table, 1 min
The risk chart tops out at 20
100 pCi/L is 250 times the outdoor average and about 77 times EPA's estimate of the average U.S. home, by our calculation. Bringing it to 2 pCi/L would take a 98% reduction, at the edge of the up to 99 percent EPA cites for some radon reduction systems, so the first question is whether the test was run properly and the second is a follow-up test; if the reading holds, the fix is the same work as at lower levels, sized to the source.
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
Other readings explained: 1 pCi/L, 2 pCi/L, 3 pCi/L, 4 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.
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. 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 25 times the action level, more than twice it, 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.
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 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.
| 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 |
Read moreTwo paragraphs, 1 min
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.
These are population estimates from EPA's 2003 assessment, and at 100 pCi/L (about 3,700 Bq/m3) a home is 5 times past the chart's last row: the chart gives no figure that high, and fixing the home comes first.
How sure
How certain is a reading of 100 pCi/L?
At 100 pCi/L the question is not whether the home is high but how high, since a day-to-day or seasonal swing cannot explain a reading this far above the
Read moreA note, 1 min
With a system
How much a radon system would lower 100 pCi/L
From 100 pCi/L, an active system at the low end of its typical range would leave about 50 pCi/L, still at or above the action level, so the test after installation decides whether the system is enough; at the high end, about 1 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 100 pCi/L, about |
|---|---|---|
| Active suction: sub-slab, sump hole, drain tile, or a crawl-space membrane | 50 to 99 percent | 50 to 1 pCi/L |
| Passive sub-slab suction (no fan) | 30 to 70 percent | 70 to 30 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 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
| 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 |
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 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; 100 pCi/L is 25 times that line.
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: from 100 pCi/L, an active system's typical reduction would leave 50 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 100 pCi/L in a basement different from upstairs?
Usually the basement reads higher. If 100 pCi/L came from a room upstairs, a basement half again as high would read 150 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 100 pCi/L?
Do not wait: 100 pCi/L is more than twice the action level, and a first short-term result that high 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.