Air "Purifiers" and Radon At the risk of steering this discussion off topic, I received a question asking if radon can build up in continuous radon monitors and become a radiation source within the home/office that they are stored in. Example being if there were 5 or 10 monitors in one spot. I understand background checks are important as part of the calibration process because of possible build up (of RDP I am guessing?) but I assume that cannot realistically build up to levels high enough to be a health concern? Taking this concept one step further, the discussion above brought up disposal of filters being a possible concern, so could RDPs build up enough in radon fan blades to a high enough degree that their disposal would ever become an issue, or at least something you wouldn't want sitting in your office/shop? Surely there would be plating out on those fan blades? I am pretty sure I was taught years ago that the pipe and fan would not be a health concern when modifying a very old system, so is it the surface area of the filter media that allows the HEPA filter disposal to be a possible concern? Any correction of my assumptions from the scientific folks in the audience would be appreciated.