InterNACHI Certified Radon Tester key terms

The standard U.S. unit for radon concentration in air, meaning one trillionth of a curie of radioactive decay activity per liter of air. Outdoor air averages about 0.4 pCi/L.

The metric SI unit of radon activity concentration, equal to one radioactive decay per second in a cubic meter of air. One pCi/L equals 37 Bq/m3.

A measure of the potential alpha energy from short-lived radon decay products in one liter of air. Used mainly in mining and occupational settings rather than residential testing.

Cumulative occupational exposure equal to breathing one working level for 170 hours. Historically linked to lung cancer risk in uranium miners.

Short-lived solid progeny such as polonium-218, lead-214, and bismuth-214 that emit alpha and beta radiation. These charged particles attach to dust and deliver most of the lung dose.

A helium nucleus emitted during radioactive decay. Alpha radiation travels only a few centimeters in air and cannot penetrate skin, but is highly damaging when inhaled.

The most common radon isotope, a colorless, odorless, radioactive noble gas with a 3.8-day half-life produced by radium-226 decay in soil and rock.

A radioactive metal in the uranium-238 decay chain that decays into radon gas. Its concentration in soil and rock largely determines a region's radon potential.

The time required for half the atoms of a radioactive substance to decay. Radon-222's 3.8-day half-life means concentrations respond to changes in entry rate within weeks.

The radon concentration at which remediation is recommended. U.S. EPA guidance sets 4 pCi/L as the action level and 2 pCi/L as a consider-fixing level.

A mapped estimate of the likelihood that a building in a given area will exceed a threshold concentration, based on geology, soil permeability, and indoor test data.

Air occupying pore spaces in soil, often enriched in radon from surrounding rock and radium. It is the dominant source of indoor radon in most buildings.

Upward air movement caused by warm indoor air rising and exiting high in a building while replacement air enters low. It draws soil gas inward through foundation openings.

A difference in air pressure between indoor and outdoor or soil environments. Even small negative indoor pressure can pull radon-laden soil gas through cracks and gaps.

A reduction of indoor air pressure relative to soil or outdoors, caused by exhaust fans, combustion appliances, or stack effect. It increases radon entry.

A membrane or sheet placed under a slab or crawlspace to limit soil gas movement into the building. Alone it is not a substitute for an active mitigation system.

An active mitigation method using a fan and piping to draw soil gas from beneath a slab and vent it above the roof, keeping soil gas pressure below indoor pressure.

A specialized inline fan rated for continuous duty and outdoor use that maintains negative pressure under a slab or in a sump pit. It must be installed outside living space.

A visual device such as a U-tube manometer or labeled fan that shows whether a mitigation system is operating. Testers should confirm it shows normal operation.

Test conditions requiring exterior doors and windows closed, typically 12 hours before and throughout the test, with normal heating or cooling operating.

A radon measurement lasting from 2 to 90 days, most commonly 48 hours. It provides a quick screening result but is more affected by weather and seasonal variation.

A radon measurement lasting more than 90 days, often 3 to 12 months. It better represents average annual exposure and reduces the influence of short-term fluctuations.

Changes in indoor radon concentration across the year due to temperature, soil moisture, and building operation. Winter values often exceed summer values in cold climates.

Choosing a location in the lowest livable level, away from exterior walls, drafts, heat sources, and moisture. Placement errors are a common cause of invalid results.

The lowest floor of a building suitable for occupancy, such as a basement or ground floor, where radon concentrations are typically highest and testing is performed.

A passive device using activated charcoal to collect radon over a short exposure period. It is inexpensive but sensitive to humidity and requires prompt analysis.

A passive device that records alpha particle tracks in a plastic film over weeks to months. It is well suited to long-term testing and is unaffected by humidity.

A passive detector using a charged electret whose voltage drops as radon decay products ionize the air inside the chamber. Exposure duration depends on the electret type.

An electronic device that measures radon hourly and can record temperature and pressure. Its time-stamped data help verify closed-house conditions and detect tampering.

A quality assurance check in which a detector is exposed to a known radon concentration and the reported result is compared with the expected value.

Two detectors deployed side by side for the same period to assess precision. Results should agree within a stated tolerance to confirm reliable measurement.

A periodic comparison of a tester's device results with those from a reference laboratory or another device to verify accuracy over time.

The range within which a true radon concentration likely falls, given device precision, counting statistics, and environmental variation. Results near 4 pCi/L warrant confirmatory testing.

Building modifications that reduce indoor radon concentrations, such as sub-slab depressurization, sealing, or ventilation. A qualified professional should design and install the system.

A radon test conducted after a mitigation system is installed to confirm it lowers concentrations below the action level. It should follow the same closed-house protocol.

A plastic sheet used in crawlspaces or over exposed soil to block soil gas and moisture. It must be sealed and combined with depressurization for effective radon control.

A mitigation technique that draws air from a sealed crawlspace and vents it outdoors, lowering pressure so soil gas does not enter the living space above.

Dissolved radon released from well water when used for showering or washing. It contributes to indoor air concentrations and may require aeration or granular activated carbon treatment.