Radon Fundamentals, Health Risk, and Units
Radon Fundamentals, Health Risk, and Units
This domain tests the science that drives field decisions: how radon-222 is produced, how it enters a building, why its decay products matter, and how units and action levels shape reporting.
Core rules
- Radon-222 is a colorless, odorless noble gas in the uranium-238 decay chain. It forms from radium-226 and has a 3.82-day half-life.
- The health hazard is mainly alpha radiation from short-lived progeny-polonium-218, lead-214, bismuth-214, and polonium-214-deposited in the lung, not the gas alone.
- Soil gas is the dominant source. Water, building materials, and outdoor air can contribute. Stack effect, pressure differences, and HVAC operation change entry rates.
- US results use picocuries per liter (pCi/L); SI uses becquerels per cubic meter (Bq/m3). Conversion: 1 pCi/L = 37 Bq/m3.
- EPA's action level is 4 pCi/L. WHO's reference level is 100 Bq/m3 (about 2.7 pCi/L). These are action triggers, not a boundary between safe and unsafe.
Worked example
A lab reports 148 Bq/m3. Convert: 148 ÷ 37 = 4.0 pCi/L. That equals the EPA action level, so the client needs follow-up testing under the applicable protocol-not a blanket “safe” statement.
Traps
Confusing radon gas with its progeny; treating 4 pCi/L as “safe”; converting in the wrong direction; ignoring seasonal or pressure-driven variation; attributing all radon to soil without checking water or materials.