Measurement Devices and Test Placement
This domain tests device selection, calibration, and placement so that a reported number represents the occupied space rather than a convenient shelf.
Device types
Passive devices integrate exposure: charcoal canisters and charcoal liquid scintillation for short-term tests, alpha-track detectors for long-term tests, and electret ion chambers for either. Active continuous radon monitors (CRMs) record hourly values and can show tampering or unusual patterns. Devices must be from a calibrated production lot, handled per manufacturer instructions, and documented with chain of custody. CRMs need current calibration and anti-tamper features.
Placement
Test the lowest livable level-the lowest area that is regularly occupied or could be occupied. Place the device at least 20 inches (50 cm) above the floor, at least 4 inches (10 cm) from walls and other objects, and away from drafts, heat sources, direct sunlight, high humidity, and exterior doors. Do not place it in a bathroom, kitchen, closet, crawlspace, or near a sump opening, floor drain, or HVAC supply. Keep it out of dead-air pockets and away from vibration.
Worked example
A basement has a finished family room, an open sump pit, a bathroom, and a supply register. A device on the bathroom shelf is wrong because of humidity and placement height. A device beside the sump is wrong because it samples a concentrated entry stream. The defensible location is the family room, about 20 inches above the floor, 4 inches from a wall, and several feet from the sump and register.
Traps
Testing a crawlspace instead of the lowest livable level; placing a CRM where it can be moved; putting a charcoal canister in a bathroom; skipping duplicate or blank QA samples; and accepting a device without calibration or chain-of-custody records.