What your radon number means

What does your radon number mean?

Your result is in picocuries per liter, written pCi/L. EPA says fix your home if it's 4 pCi/L or higher. Consider fixing it if it's between 2 and 4 pCi/L.

PA DEP says to base the decision on one long-term test, or the average of two short-term tests.

What counts as normal?

PA DEP's guide gives these figures:

• About 0.4 pCi/L is normally found in outside air.
• The average indoor level is estimated at about 1.3 pCi/L.
• Most homes today can be reduced to 2 pCi/L or below.

DEP's own radon report says the average in Pennsylvania basements is about 7.1 pCi/L, and about 3.6 pCi/L on the first floor.

Is anything below 4 safe?

No level is completely safe. PA DEP's guide says EPA believes any radon exposure carries some risk, and levels below 4 pCi/L still pose some risk. The lower your level, the lower your risk.

What if your result is close to 4?

Short-term tests are less certain near 4 pCi/L. DEP's example: if two short-term tests average 4.1 pCi/L, there's about a 50 percent chance your year-round average is a little below 4. A long-term test gives a clearer answer.

How does the level relate to risk?

DEP's guide sets out EPA's lifetime estimates. For 1,000 people exposed to a level over a lifetime:

• At 4 pCi/L: about 7 people who never smoked could get lung cancer, and about 62 people who smoke.
• At 8 pCi/L: about 15 who never smoked, and about 120 who smoke.
• At 20 pCi/L: about 36 who never smoked, and about 260 who smoke.

That's why DEP says smoking and radon together are an especially serious risk.

What should you do next?

• 4 pCi/L or higher: confirm it with a follow-up test, then find a certified mitigation company.
• Between 2 and 4: consider fixing it. DEP says levels below 4 can often be reduced.
• Below 2: DEP suggests testing again some time in the future, and again if you start using a lower floor, like a basement.