Radon Measurement: Standards, Placement, and QA
This domain tests the measurement professional's scope under ANSI/AARST measurement protocols: test design, closed-building conditions, device placement, quality assurance, and interpreting results against the U.S. EPA 4 pCi/L action level.
Closed-building and placement
- Maintain closed-building conditions for 12 hours before and throughout the test: exterior doors and windows closed; permanently installed HVAC operating normally; no temporary exhaust fans, window fans, or dryers venting outdoors.
- Sample the lowest livable level. Keep devices at least 20 inches above the floor and 4 inches from walls; avoid bathrooms, kitchens, closets, drafts, direct sunlight, and heat sources.
- Match device to duration: charcoal or electret short-term (2–7 days typical), CRM 48 hours minimum, alpha track long-term (more than 90 days).
QA and reporting
- Follow a QA plan: 10% duplicates, 10% blanks, and spikes for analytical labs; calibrate and cross-check CRMs.
- Report device type, serial number, dates, location, conditions, result, and any protocol deviation.
Worked example: A 48-hour CRM in a basement reads 4.6 pCi/L; a side-by-side duplicate reads 4.2 pCi/L. Both are at or above 4 pCi/L, so the action level is met. Do not average the pair down or dismiss the duplicate. Recommend mitigation or, if the decision can wait, confirmation with a long-term test; document both results.
Traps: starting the closed-building clock only when the device is deployed; placing a detector in a bathroom or closet; testing during unusual weather; failing to record deviations; treating 4 pCi/L as a "safe" line rather than an action level.