InterNACHI Certified Radon Tester common mistakes
InterNACHI Certified Radon Tester · Understand the traps and how to avoid them.
Treating radon as a chemical toxin or 'poison' rather than a radioactive gas, and describing health risk as direct chemical damage to lung tissue.
Candidates carry over general indoor-air-pollutant intuition from other certifications; the exam instead tests the decay-chain model (Ra-222 to Po-218, Pb-214, Bi-214, Po-214) and the fact that alpha-emitting progeny deposited in the lung deliver the dose.
What to do instead
Study the U-238 decay chain explicitly: which parent produces radon, radon's 3.8-day half-life, which progeny are alpha emitters, and that risk is from inhaled alpha-emitting solids, not from radon's own chemistry. Practice explaining the mechanism in one paragraph without using the word 'toxic'.
Confusing picocuries per liter (pCi/L) with becquerels per cubic meter (Bq/m3) or working level (WL), and mis-stating the numeric action level and EPA-recommended maximum.
Unit conversions and the 4 pCi/L action level appear across measurement, reporting, and mitigation questions; candidates memorize '4' without attaching it to a unit, a threshold type, or the 1 pCi/L conversion factor to Bq/m3 (37 Bq/m3 per pCi/L).
What to do instead
Build a one-page unit card: 1 pCi/L = 37 Bq/m3; 4 pCi/L action level; ~0.02 WL correspondence; and the distinction between the action level and the World Health Organization's 100 Bq/m3 reference level. Drill conversion arithmetic until it is automatic.
Assuming radon enters mainly through cracks in the slab and ignoring the pressure-driven soil-gas mechanism, the stack effect, and the role of HVAC-induced depressurization.
Candidates picture a simple 'gas leaks in through holes' model and miss that the dominant driver is a pressure differential (typically a few pascals) between soil and indoor air, which means entry rate depends on building operation, not just on crack area.
What to do instead
Learn the entry pathway list (cracks, sump openings, slab penetrations, block-wall voids, water supply, building materials) alongside the driving forces (stack effect, exhaust appliances, HVAC balance, wind). Practice predicting how opening a window, running a bath fan, or sealing a sump changes the soil-to-indoor pressure difference.
Treating closed-house conditions as 'windows shut' only, and starting the test without verifying the 12-hour pre-test closure or the 48-hour (or longer) exposure period required for the chosen device.
The protocol has multiple time windows that candidates collapse into one; they also forget that the closure period begins before device deployment and that normal entry/exit is allowed while windows stay closed.
What to do instead
Memorize the timeline as a checklist: at least 12 hours of closed-house conditions before the start of the test, and for short-term tests generally 48 hours minimum of closed conditions (longer for some devices). Record the closure start time and verify it at placement and retrieval. Practice writing the client instruction sheet from memory.
Placing a test device in a bathroom, kitchen, laundry room, closet, crawlspace, or near a sump opening or exterior door, instead of in the lowest livable level's normal living space.
Candidates optimize for convenience and quiet rather than for representativeness; they also misread 'lowest livable level' as 'any room on the lowest floor' and forget that high-moisture or high-air-exchange rooms distort results.
What to do instead
Apply placement rules mechanically: lowest level that is used regularly, interior wall, at least 20 inches above the floor, at least 12 inches from exterior walls, at least 3 feet from windows and doors, away from heat sources, drafts, and moisture. Write out the exclusion list and check each candidate location against it before deploying.
Reporting a single short-term result as a definitive annual average, or failing to recommend follow-up testing when a first short-term result is near or above the action level.
Candidates want to give a clean yes/no answer; the exam tests the statistical nature of radon variability and the follow-up decision rules, including confirmatory short-term tests and long-term testing options.
What to do instead
Learn the decision tree: below 4 pCi/L, consider retesting or long-term testing if between 2 and 4; at or above 4 pCi/L, confirm with a second short-term test (or a long-term test) before committing to mitigation, and report the range and test conditions with every result. Practice writing a report conclusion that states uncertainty explicitly.
Deploying or retrieving a device without documenting device serial number, placement location, start and end times, and the closed-house verification, then being unable to defend the result.
Candidates treat paperwork as secondary to the measurement; the exam and professional standards treat chain-of-custody and field documentation as part of the test itself, and missing data invalidates results.
What to do instead
Use a fixed field form covering device ID, location sketch, height and distance measurements, closure start, deployment and retrieval timestamps, HVAC status, weather, and any protocol deviations. Rehearse completing it as part of the test, not after.
Recommending a specific mitigation contractor, price, or system design as part of the test report, or implying the tester is affiliated with a certification body or government agency.
Candidates conflate 'helping the client' with giving design advice; the tester's role is measurement and reporting, and mitigation design belongs to a qualified mitigator under separate standards.
What to do instead
Learn the boundary: report results, explain health context, and refer clients to qualified mitigation professionals without endorsing individuals. Include a disclaimer that the report is not a mitigation design and that the tester holds no official government affiliation.
Describing a mitigation system as 'just a fan and a pipe' and failing to explain the sub-slab depressurization principle, the need for a post-mitigation test, or the requirement to maintain and retest the system.
Candidates focus on the diagnostic side and skim mitigation basics; the exam checks whether they understand that the system creates a pressure field under the slab, that sealing alone is not a mitigation strategy, and that verification testing is required.
What to do instead
Study the active soil depressurization model: suction point, collection piping, fan sizing, discharge location above the roofline, and pressure-field extension. Memorize the sequence: diagnose, design, install, verify with a post-mitigation test, and retest periodically and after major renovations.
Ignoring quality-assurance elements such as duplicate and blank samples, device calibration and cross-checking, and the difference between a measurement error and a real change in radon concentration.
Candidates treat QA as optional overhead and cannot distinguish device precision from building variability, so they misread small differences between two tests as meaningful.
What to do instead
Learn the QA toolkit: duplicate measurements, field blanks, spike or calibration checks, and the expected variability of short-term tests. Practice interpreting two results that differ by 1 pCi/L and deciding whether that is within measurement uncertainty or warrants further testing.