School Screening Plan With a Failing Classroom Duplicate
A K-8 school district asks you to screen its building for radon during winter break. The building has 28 frequently occupied ground-contact rooms on slab, 12 second-floor classrooms, and a gym with a concrete slab and floor drains. The district wants results before a board meeting in three weeks and has budget for 40 charcoal canisters. Outdoor temperatures are below freezing, the HVAC runs with a small outside-air fraction, and only custodial staff will be in the building during the break. One first-floor classroom has a window air conditioner and a floor sink; another shares a wall with the mechanical room that houses the boiler. The facilities director asks whether testing only the basement-level rooms nearest the soil would be sufficient and faster.
1. Which rooms should be tested, and how do you allocate the 40 canisters?
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Test every frequently occupied ground-contact room - all 28 - because radon varies room to room and you cannot predict which slab section communicates with a source. Add a few second-floor rooms as controls to show the vertical gradient; typically 3 are enough. The gym should be tested if it is occupied and ground-contact, and the floor drains make it more important, not less. With 40 canisters: 28 ground-floor rooms + 3 upper-floor controls + 1 gym = 32; add 3 duplicates (about 10%) and 2 blanks (5%) = 37, leaving room for a repeat if a device is damaged. The facilities director's proposal to test only the rooms nearest the soil is not sufficient - radon can enter through any slab crack, sump, or utility penetration, and screening only "likely" rooms can miss the worst room.
2. How do you place devices in the room with the window air conditioner, the room with the floor sink, and the room sharing a wall with the boiler room?
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In the room with the window air conditioner, turn the unit off for the test, keep the window closed, and place the canister at least 3 feet from the unit and away from the window, at 20 inches above the floor in the breathing zone. In the room with the floor sink, place the device at least 3 feet from the sink and note the sink in the sketch; do not seal it for the test unless the district has already sealed it as part of normal operations. In the room sharing a wall with the boiler room, avoid mounting on or immediately beside that wall; heat and vibration can affect the device and the wall may be warmer. Keep devices out of closets, off shelves near exterior walls, and away from supply and return registers.
3. A first-grade classroom returns 7.4 pCi/L and its duplicate returns 3.9 pCi/L. What is your next step?
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RPE = |7.4 − 3.9| ÷ [(7.4 + 3.9) ÷ 2] × 100 = 3.5 ÷ 5.65 × 100 = 62%, far above the 25% criterion, so that room's result is not reliable. Do not average them and do not report 5.65 pCi/L. Look for a placement problem first - were both devices really in the same breathing zone, away from the sink, window, and air streams? Then repeat the room with a new duplicate pair or a 48-hour CRM after confirming closed-house conditions. If either repeat result is 4 pCi/L or higher, treat the room as elevated, do follow-up testing, and schedule a mitigation evaluation. Also check whether the same technician or lab batch produced other failing pairs in the building.