Passive and Active Radon test results

A question, if
Inspector “A” does a passive radon test, he sets his test kit 18 inches away from a wall and 30 inches off the floor. 48 inches away is an active A/C return vent. Inspector “A” has a high radon reading. Inspector “B” is asked to do a follow up test (time is limited) Inspector"B" sets up a CRM in the same position, distance from the wall and height off the floor and 48 inches from the active A/C return vent

I am inspector “B” , is this comment true?

“As with a typical follow-up measurement I placed a CRM in the same location as I was advised the initial screening was taken from, for a comparison this may work, however the actual measurements I believe to be in error due to the proximity of the measuring devices and the return air vent for the HVAC system. I believe that[FONT=‘Helvetica’,‘sans-serif’] Charcoal Liquid Scintillation, a passive radon measurement device such as the one I am led to believe was used for the original screening placed in close proximity (48 inches) to an active vent may yield a higher Radon Measurement than is actually present. These same conditions may cause a CRM or active Radon Measurement device to yield a higher Radon Measurement as well, however it being an active test device I believe it to be influenced less by the above stated conditions. I suggest a properly done retest to obtain accurate measurements.”[/FONT]

or, would these conditions effect a CRM differently than I am thinking?

Test A was a short term test and yielded a different results than Test B conducted on different days, time and weather conditions.

The tests yielded different results. Period…

Not only that, each test device is going to yield different results, but “similar” due to each device being different and in this case, under different environmental circumstances (not taken at the same time).

I may need to rephrase the question: in the above situation was the active test flawed in the same way as the passive test or would the effects of the vent on the active test be more, less or opposite. I believe it would be less flawed but may be missinformed


What leads you to believe that your equipment would differ?

Some testing devices are more prone to error.
But because they are reactive to other environmental factors, not because of how the Radon by-products are moving around the room.

What’s the stated accuracy of the CRM?

What’s the stated accuracy of the canisters?

David thanks for your input, I’m just trying to get a better understanding of what to me was a gray area in a recent course I have taken.

I am wondering if a passive test, subjected to more air movement in a confined space would obsorb more particles than one subjected to less air movement in the same confined space or would it only be effected by fresh air being introduced? and would the same be true for an active test?

I’m not keeping up with you, I’ve been out in the hot sun too long today! :wink:

More air movement, same tester, will read higher.

More fresh air movement will dilute radon concentration, lower readings.

I see not difference between active and passive testing subject to the same environment.

If this means anything, a ceiling fan is a great radon mitigation machine because Radon By-products are statically charged and plate out on anything they come in contact with in the room. More air movement can reduce radon in the room, thus a lower reading. But… if the tester is in the “wind” it will get more radon to test for the same reason.

David, thanks, that was the the information I was looking for. My second train of thought is that a active test device used under the same conditions (with more air flow, compared to a passive device) would yield a more realistic result due to the mechanical action of a pump of sorts drawing a metered volume of air through a tube of sorts. would you think this train of thought correct?