InterNACHI Certified Radon Tester flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Radon-222 half-life

Radon-222 has a half-life of about 3.82 days, decaying by alpha emission into short-lived progeny such as polonium-218 and lead-214. This allows measurable buildup in closed buildings and natural decay after ventilation.

Radon progeny

Short-lived decay products including Po-218, Pb-214, Bi-214, and Po-214. They emit alpha particles and deliver most of the lung dose when inhaled and deposited in bronchial tissue.

EPA action level

The U.S. EPA action level is 4 pCi/L (148 Bq/m3). EPA also recommends considering mitigation when a long-term result falls between 2 and 4 pCi/L.

Working level

One working level equals 1.3 x 10^5 MeV of potential alpha energy per liter of air from short-lived radon progeny. One WLM equals one WL sustained for 170 working hours.

Equilibrium ratio

The ratio of actual progeny concentration to the concentration expected at full secular equilibrium. Typical indoor values are 0.3 to 0.7, so gas measurements overestimate progeny dose when equilibrium is low.

pCi/L to Bq/m3

Multiply picocuries per liter by 37 to obtain becquerels per cubic meter. Thus 4 pCi/L equals 148 Bq/m3, and 100 Bq/m3 equals about 2.7 pCi/L.

Stack effect

Warm indoor air rising and escaping high in the building lowers pressure at the lowest level. This small negative pressure draws radon-laden soil gas through slab cracks and penetrations.

Pressure-driven soil gas entry

Radon enters mainly by advective flow driven by a few pascals of pressure difference, not by diffusion. Stack effect, wind, and exhaust fans create that pressure differential.

Common radon entry routes

Slab and foundation cracks, sump pits, floor drains, utility penetrations, hollow-block walls, exposed crawl-space soil, and water degassing all admit radon into the lowest livable level.

Radon in well water

About 10,000 pCi/L in water adds roughly 1 pCi/L to indoor air. Aeration removes radon more effectively than granular activated carbon, which can accumulate radioactive solids.

Soil permeability effect

Highly permeable soils such as gravel or fractured bedrock transport soil gas readily, so entry rate depends on both radium content and how easily gas moves toward the foundation.

Charcoal adsorption device

A passive short-term device exposed for two to seven days. It is sensitive to humidity and temperature and is used for screening or real-estate transactions, not annual averages.

Alpha-track detector

A long-term passive device exposed for at least 91 days, typically up to one year. It integrates seasonal variation and gives a more reliable annual average than short-term devices.

Continuous radon monitor

An active electronic device using a scintillation cell or ion chamber that records hourly readings. It can reveal diurnal patterns and often includes tamper detection for real-estate testing.

Device placement height

Place the detector at least 20 inches (50 cm) above the floor, at least 4 inches (10 cm) from other objects, and at least 3 feet (0.9 m) from exterior walls, doors, or windows.

Unsuitable test locations

Avoid bathrooms, kitchens, laundry rooms, closets, crawl spaces, and hallways. Also avoid drafts, direct sunlight, high humidity, and areas near windows or exterior doors.

Duplicate and blank devices

Quality-control devices detect handling and shipping problems. Large deployments typically include about 10 percent duplicates and 5 percent blanks alongside the primary measurements.

Lowest livable level

The test location must be the lowest level of the home that could be occupied regularly. A basement or slab-on-grade room qualifies; a crawl space usually does not.

Closed-house conditions

All exterior doors and windows stay closed, and window air conditioners recirculate, for at least 12 hours before and throughout a short-term test. Normal occupant entry and exit is allowed.

Short-term test duration

Passive short-term devices remain in place two to seven days. Continuous monitors used for real-estate transactions require a minimum of 48 hours under closed-house conditions.

Long-term test duration

A long-term test lasts at least 91 days and is not subject to closed-house conditions. It better represents the annual average because it spans seasonal variation.

Post-mitigation testing wait

Wait at least 24 hours after the mitigation system begins operating before testing. Re-testing should generally occur within 30 days of system start-up.

Closed-house violation

If windows or doors were opened during the test, restart rather than adjust the result. If the test must continue, document the deviation in the report.

Follow-up test rule

A short-term result of 4 pCi/L or higher triggers a second short-term test or a long-term test before a mitigation decision is made.

Two-test averaging rule

In real-estate transactions, two short-term tests are averaged. If the average is 4 pCi/L or higher, mitigation is recommended; if the two differ widely, a third test may be needed.

Report required elements

A report states the measured value and units, test method, device serial number, test dates, placement location, and confirmation of closed-house conditions.

Result near action level

A value close to 4 pCi/L falls within measurement uncertainty. Report the number without rounding it down and recommend confirmatory testing before a final decision.

Seasonal variation

Indoor radon can differ by a factor of two or more between seasons because stack effect and ventilation change. A short-term test estimates conditions during the test, not the annual average.

Active soil depressurization

The standard mitigation method: a suction point through the slab, a sealed pit, PVC piping, and a continuously running in-line fan that discharges above the roofline.

Fan discharge requirements

Exhaust must terminate above the roofline and at least 10 feet from any window, door, or air intake. It must not discharge below the roof or into an attic.

System indicator

A u-tube manometer or similar gauge confirms that the fan is running and suction is present. The system should be labeled and inspected annually.

Sealing alone insufficient

Sealing cracks, sump lids, and penetrations supports mitigation but is not a stand-alone technique. It must be paired with sub-slab or sub-membrane depressurization to reduce radon.