Measurement Devices and Protocols
What you must understand
Devices divide into passive (no power, integrating) and active (pumped, often continuous). Passive: charcoal canisters and liquid scintillation (2–7 days), alpha-track (1–12 months), electret ion chambers. Active: continuous radon monitors (CRM), which record hourly data and can detect tampering and diurnal patterns. Protocols specify placement: lowest livable level, 20 inches (50 cm) above the floor, at least 12 inches (30 cm) from exterior walls, 4 inches (10 cm) from other objects, and away from drafts, heat, and humidity. Closed-house conditions: 12 hours before and during a short-term test; doors and windows closed except for normal entry/exit. Short-term tests are 2–90 days; long-term exceed 90 days. Duplicate and blank devices support QA. Follow device-specific exposure times and retrieval windows exactly.
Traps
Questions place detectors in bedrooms on upper floors when the lowest livable level is required, or apply long-term closed-house rules to a short-term test. Don't confuse the 12-hour pre-test closure with the duration of the test. Remember CRMs need power and can be unplugged - check the data.
Worked example
A 48-hour charcoal test requires closed-house conditions starting 12 hours before deployment and continuing through retrieval. Rule of thumb: 20 inches up, 12 inches from exterior walls, 4 inches from objects, lowest livable level.