InterNACHI Certified Radon Tester cheat sheet

Radon-222 is a colorless, odorless, tasteless noble gas produced by alpha decay of radium-226 in the uranium-238 decay chain; its own decay emits alpha particles and produces short-lived progeny (Po-218, Pb-214, Bi-214, Po-214).

Half-life of Rn-222 is 3.82 days; this permits measurable accumulation in a closed building while allowing decay after ventilation. Progeny half-lives range from ~0.0002 s (Po-214) to 26.8 min (Pb-214).

Health risk comes chiefly from inhaled short-lived progeny, not the gas itself: alpha-emitting progeny deposit in the bronchial epithelium; dose is governed by the working level (WL) of potential alpha energy, not gas concentration alone.

EPA action level is 4 pCi/L (148 Bq/m3); EPA also recommends considering mitigation in the 2-4 pCi/L range. WHO reference level is 100 Bq/m3 (~2.7 pCi/L).

Radon is the second leading cause of lung cancer after smoking and the leading cause among never-smokers; risk is multiplicative with smoking, not merely additive.

1 WL = 1.3 x 10^5 MeV of potential alpha energy per liter; 1 WLM = 1 WL for 170 working hours; 1 pCi/L at 50% equilibrium ≈ 0.02 WL.

Equilibrium ratio (F) = actual progeny concentration divided by the concentration at full secular equilibrium; typical indoor F is 0.3-0.7, so progeny-based and gas-based estimates can differ substantially.

Unit conversions: 1 pCi/L = 37 Bq/m3; 4 pCi/L = 148 Bq/m3; 200 Bq/m3 = 5.4 pCi/L; 100 Bq/m3 = 2.7 pCi/L.

Driving force for soil-gas entry is pressure-driven flow (typically a few pascals), not diffusion: stack effect, HVAC-induced depressurization, and wind create a small negative pressure in the lowest level relative to soil.

Stack effect strength rises with indoor-outdoor temperature difference and building height; cold-season testing therefore often yields higher readings in heating climates, while air-conditioning climates can invert seasonal patterns.

Principal entry routes: slab and foundation cracks, sump pits, floor drains, utility penetrations, hollow-block foundations, exposed soil (crawl spaces), and water supply degassing (minor in most homes).

Soil permeability and radium content, plus the house-to-soil pressure differential, govern entry rate; gravelly or fractured bedrock soils transport soil gas readily.

Diffusion through concrete is real but small; advective flow through penetrations dominates. Sealing alone is not a mitigation strategy unless paired with sub-slab depressurization.

Radon can migrate laterally from a neighbor's soil or from fill material; a house with no visible cracks can still test high.

Radon in water: 10,000 pCi/L in water contributes roughly 1 pCi/L to indoor air; well water is the usual concern, and aeration removes radon more effectively than GAC, which can build up radioactive solids.

Radon decays to progeny that plate out on surfaces and dust; HVAC operation, air filtration, and ceiling fans can shift the gas-to-progeny ratio, so test device type matters.

Passive devices: charcoal adsorption (short-term, 2-7 days, sensitive to humidity and temperature), charcoal liquid scintillation, alpha-track (long-term, 91 days to 1 year), and electret ion chambers.

Active devices: continuous radon monitors (CRM) using scintillation cells or ion chambers, often with tamper-detection features; CRM data can show diurnal patterns and require a documented placement period.

Device selection rule: short-term tests for real-estate transactions or quick screening; long-term (>=91 days) for reliable annual average. CRM use for real estate requires at least 48 hours of closed-house conditions.

Placement: lowest livable level of the home, in a room regularly used, 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.

Do not place devices in bathrooms, kitchens, laundry rooms, closets, crawl spaces, or hallways; avoid areas with drafts, high humidity, or direct sunlight.

Duplicate or blank devices are used for quality control: 10% duplicates and 5% blanks for large deployments; blanks detect shipping and handling contamination.

Device must remain undisturbed for the test duration; placement records include location sketch, serial number, start/end times, and environmental conditions.

CRM spike or calibration checks and cross-check measurements support measurement quality objectives; a device out of calibration invalidates the result.

Closed-house conditions: all exterior doors and windows closed, and window-mounted air conditioners set to recirculate, for at least 12 hours before and throughout a short-term test.

Short-term test duration: 2-7 days for passive devices; CRM minimum 48 hours. Long-term tests need at least 91 days and are not subject to closed-house conditions.

During the test, normal occupant entry and exit is allowed; HVAC can run normally, but do not operate whole-house fans, window fans, or open windows that would increase ventilation.

Post-mitigation testing waits at least 24 hours after mitigation system operation; re-testing after mitigation should occur within 30 days of system start-up.

Real-estate protocol: test in the lowest livable level, conduct a separate test in each distinct foundation type if multiple foundations exist, and document any deviations from closed-house conditions.

If closed-house conditions are violated, restart the test rather than adjusting the result. Document the violation if the test must continue.

Test documentation includes start and stop times, device type, serial number, placement location, weather, and any events affecting the result.

Follow-up testing: if a short-term result is 4 pCi/L or higher, conduct a second short-term test (or a long-term test) before deciding on mitigation.

Decision rule for real estate: two short-term tests averaged; if the average is >=4 pCi/L, mitigation is recommended. A single test >=4 pCi/L triggers a follow-up test.

Report the measured value with units (pCi/L or Bq/m3), the test method, device serial number, test dates, and the statement of closed-house conditions.

Do not round a result down to avoid action: report the numeric value and the action level comparison without editorializing.

Measurement uncertainty: CRM and passive devices have a stated precision; report the value and note that results near the action level warrant confirmatory testing.

EPA action level is 4 pCi/L; WHO reference level is 100 Bq/m3. State which benchmark is being used.

Post-mitigation result below 4 pCi/L is the usual goal; EPA also suggests considering further reduction if the result remains between 2 and 4 pCi/L.

Report should include limitations: short-term tests estimate, they do not predict annual average; seasonal variation can change results by a factor of two or more.

Retain raw data (CRM hourly readings, chain of custody) for at least the period required by the applicable state program; the report should be reproducible from the file.

Active soil depressurization (ASD) is the standard method: a suction point through the slab, a sealed pit, PVC piping, and a continuously running in-line fan discharging above the roof edge.

Sub-slab depressurization requires a suction field; multiple suction points may be needed for large or compartmentalized slabs. Drain-tile or block-wall depressurization is used where slab access is impractical.

Fan discharge must be above the roofline and at least 10 feet from any window, door, or air intake; exhaust must not terminate below the roof or in an attic.

System indicator (manometer or u-tube) confirms fan operation; a post-installation test verifies radon reduction, and the system should be labeled and inspected annually.

Sealing of cracks, sump lids, and penetrations is a supporting measure, not a stand-alone mitigation technique.

Crawl-space mitigation uses a vapor barrier with depressurization beneath it; water mitigation uses aeration or GAC with proper permitting.

Professional standards: follow EPA radon mitigation standards and state licensing; provide a written contract, warranty, and post-mitigation test; disclose system presence at resale.

Mitigation contractors should not perform the post-mitigation measurement if independence is required by the state or client; third-party testing is preferred.

Radon-222 is a colorless, odorless, tasteless noble gas produced by alpha decay of radium-226 in the uranium-238 decay chain; its own decay emits alpha particles and produces short-lived progeny (Po-218, Pb-214, Bi-214, Po-214).

Half-life of Rn-222 is 3.82 days; this permits measurable accumulation in a closed building while allowing decay after ventilation. Progeny half-lives range from ~0.0002 s (Po-214) to 26.8 min (Pb-214).

Health risk comes chiefly from inhaled short-lived progeny, not the gas itself: alpha-emitting progeny deposit in the bronchial epithelium; dose is governed by the working level (WL) of potential alpha energy, not gas concentration alone.

EPA action level is 4 pCi/L (148 Bq/m3); EPA also recommends considering mitigation in the 2-4 pCi/L range. WHO reference level is 100 Bq/m3 (~2.7 pCi/L).

Radon is the second leading cause of lung cancer after smoking and the leading cause among never-smokers; risk is multiplicative with smoking, not merely additive.

1 WL = 1.3 x 10^5 MeV of potential alpha energy per liter; 1 WLM = 1 WL for 170 working hours; 1 pCi/L at 50% equilibrium ≈ 0.02 WL.

Equilibrium ratio (F) = actual progeny concentration divided by the concentration at full secular equilibrium; typical indoor F is 0.3-0.7, so progeny-based and gas-based estimates can differ substantially.

Unit conversions: 1 pCi/L = 37 Bq/m3; 4 pCi/L = 148 Bq/m3; 200 Bq/m3 = 5.4 pCi/L; 100 Bq/m3 = 2.7 pCi/L.

Driving force for soil-gas entry is pressure-driven flow (typically a few pascals), not diffusion: stack effect, HVAC-induced depressurization, and wind create a small negative pressure in the lowest level relative to soil.

Stack effect strength rises with indoor-outdoor temperature difference and building height; cold-season testing therefore often yields higher readings in heating climates, while air-conditioning climates can invert seasonal patterns.

Principal entry routes: slab and foundation cracks, sump pits, floor drains, utility penetrations, hollow-block foundations, exposed soil (crawl spaces), and water supply degassing (minor in most homes).

Soil permeability and radium content, plus the house-to-soil pressure differential, govern entry rate; gravelly or fractured bedrock soils transport soil gas readily.

Diffusion through concrete is real but small; advective flow through penetrations dominates. Sealing alone is not a mitigation strategy unless paired with sub-slab depressurization.

Radon can migrate laterally from a neighbor's soil or from fill material; a house with no visible cracks can still test high.

Radon in water: 10,000 pCi/L in water contributes roughly 1 pCi/L to indoor air; well water is the usual concern, and aeration removes radon more effectively than GAC, which can build up radioactive solids.

Radon decays to progeny that plate out on surfaces and dust; HVAC operation, air filtration, and ceiling fans can shift the gas-to-progeny ratio, so test device type matters.

Passive devices: charcoal adsorption (short-term, 2-7 days, sensitive to humidity and temperature), charcoal liquid scintillation, alpha-track (long-term, 91 days to 1 year), and electret ion chambers.

Active devices: continuous radon monitors (CRM) using scintillation cells or ion chambers, often with tamper-detection features; CRM data can show diurnal patterns and require a documented placement period.

Device selection rule: short-term tests for real-estate transactions or quick screening; long-term (>=91 days) for reliable annual average. CRM use for real estate requires at least 48 hours of closed-house conditions.

Placement: lowest livable level of the home, in a room regularly used, 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.

Do not place devices in bathrooms, kitchens, laundry rooms, closets, crawl spaces, or hallways; avoid areas with drafts, high humidity, or direct sunlight.

Duplicate or blank devices are used for quality control: 10% duplicates and 5% blanks for large deployments; blanks detect shipping and handling contamination.

Device must remain undisturbed for the test duration; placement records include location sketch, serial number, start/end times, and environmental conditions.

CRM spike or calibration checks and cross-check measurements support measurement quality objectives; a device out of calibration invalidates the result.

Closed-house conditions: all exterior doors and windows closed, and window-mounted air conditioners set to recirculate, for at least 12 hours before and throughout a short-term test.

Short-term test duration: 2-7 days for passive devices; CRM minimum 48 hours. Long-term tests need at least 91 days and are not subject to closed-house conditions.

During the test, normal occupant entry and exit is allowed; HVAC can run normally, but do not operate whole-house fans, window fans, or open windows that would increase ventilation.

Post-mitigation testing waits at least 24 hours after mitigation system operation; re-testing after mitigation should occur within 30 days of system start-up.

Real-estate protocol: test in the lowest livable level, conduct a separate test in each distinct foundation type if multiple foundations exist, and document any deviations from closed-house conditions.

If closed-house conditions are violated, restart the test rather than adjusting the result. Document the violation if the test must continue.

Test documentation includes start and stop times, device type, serial number, placement location, weather, and any events affecting the result.

Follow-up testing: if a short-term result is 4 pCi/L or higher, conduct a second short-term test (or a long-term test) before deciding on mitigation.

Decision rule for real estate: two short-term tests averaged; if the average is >=4 pCi/L, mitigation is recommended. A single test >=4 pCi/L triggers a follow-up test.

Report the measured value with units (pCi/L or Bq/m3), the test method, device serial number, test dates, and the statement of closed-house conditions.

Do not round a result down to avoid action: report the numeric value and the action level comparison without editorializing.

Measurement uncertainty: CRM and passive devices have a stated precision; report the value and note that results near the action level warrant confirmatory testing.

EPA action level is 4 pCi/L; WHO reference level is 100 Bq/m3. State which benchmark is being used.

Post-mitigation result below 4 pCi/L is the usual goal; EPA also suggests considering further reduction if the result remains between 2 and 4 pCi/L.

Report should include limitations: short-term tests estimate, they do not predict annual average; seasonal variation can change results by a factor of two or more.

Retain raw data (CRM hourly readings, chain of custody) for at least the period required by the applicable state program; the report should be reproducible from the file.

Active soil depressurization (ASD) is the standard method: a suction point through the slab, a sealed pit, PVC piping, and a continuously running in-line fan discharging above the roof edge.

Sub-slab depressurization requires a suction field; multiple suction points may be needed for large or compartmentalized slabs. Drain-tile or block-wall depressurization is used where slab access is impractical.

Fan discharge must be above the roofline and at least 10 feet from any window, door, or air intake; exhaust must not terminate below the roof or in an attic.

System indicator (manometer or u-tube) confirms fan operation; a post-installation test verifies radon reduction, and the system should be labeled and inspected annually.

Sealing of cracks, sump lids, and penetrations is a supporting measure, not a stand-alone mitigation technique.

Crawl-space mitigation uses a vapor barrier with depressurization beneath it; water mitigation uses aeration or GAC with proper permitting.

Professional standards: follow EPA radon mitigation standards and state licensing; provide a written contract, warranty, and post-mitigation test; disclose system presence at resale.

Mitigation contractors should not perform the post-mitigation measurement if independence is required by the state or client; third-party testing is preferred.