NRPP RMI common mistakes
NRPP RMI · Understand the traps and how to avoid them.
Treating the closed-house condition as a suggestion and letting occupants open doors or run exhaust fans during the test, or starting the 12-hour pre-test period without confirming it was actually maintained.
Candidates memorize the number '12 hours' but not the operational meaning: windows and doors closed except for normal entry/exit, and no permanent-operation fans or combustion appliances that affect pressure. They assume the client's word is enough and skip documenting or verifying conditions.
What to do instead
Build a pre-test checklist you recite and record: confirm and document the 12-hour closed-house interval, note any exhaust fans, fireplaces, or HVAC settings that could alter pressure, and record the start time in the field log. Practice explaining the requirement to a client in plain language so it becomes part of your test-day routine, not an afterthought.
Placing detectors at heights or locations that violate protocol - on the floor, near exterior walls, in closets, bathrooms, kitchens, or within the restricted distance of windows and exterior doors - because the site was convenient.
Candidates remember 'livable space' but not the specific placement rules for height and proximity to openings, or they defer to whatever spot the homeowner offers. Placement errors are invisible on the report and only surface as a failed audit or invalid result.
What to do instead
Memorize the placement criteria as a short rule set (typical detector height in the breathing zone, minimum distance from exterior openings, away from heat, moisture, and drafts) and carry a tape measure. Do a walkthrough first, mark acceptable locations, then deploy. Photograph or sketch each location for the record.
Deploying the wrong device type for the test objective - using a short-term activated charcoal device for a long-term question, or an alpha-track device for a quick pre-sale screening - and reporting the result as if it answered the client's question.
Candidates learn device names but not the time-integration tradeoff. Charcoal adsorbs and gives a short-term snapshot; alpha-track integrates over months. Mixing them up produces a technically valid number that misrepresents the exposure period.
What to do instead
Anchor each device to its intended exposure window and state that window in the report. Before the site visit, write one sentence linking the client's question to the device and duration. If the client's goal does not match the device, reschedule rather than substitute.
Skipping or fumbling duplicate and blank measurements, or failing to deploy the required number of detectors for the size and configuration of the home.
Candidates treat duplicates, blanks, and detector counts as paperwork. In practice they are the quality-assurance backbone that lets you detect field error and lab bias, and the required count scales with square footage and foundation type.
What to do instead
Make a deployment plan keyed to the home's footprint and foundation before you arrive. Label every detector and its duplicate pair, and record blank placement. Treat the count as a hard gate: no plan, no deployment.
Handling detectors with bare hands, opening the exposure chamber, or storing devices in a hot vehicle or near solvents before and after deployment.
Candidates focus on the measurement and forget the device is a passive sampler whose accuracy depends on uncontaminated adsorbent and intact housing. Skin oils, cross-contamination between sites, and heat degrade the result silently.
What to do instead
Adopt a handling sequence: gloves, no opening of the chamber, sealed transport container, cool storage, and chain-of-custody documentation at every handoff. Rehearse the sequence until it is automatic, and include it in your field kit checklist.
Misreading or mis-recording the deployment and retrieval times, so the exposure duration used in the calculation does not match the actual interval.
Candidates calculate correctly from the numbers they wrote down, but the numbers were transcribed from memory or rounded. Because the reported concentration is inversely proportional to exposure time, a small timing error shifts the result.
What to do instead
Record exact clock times at deployment and retrieval, with a second person or a photo of the time source. Compute duration from those recorded times, not from planned times. Keep the raw field sheet and reconcile it against the lab submission before reporting.
Reporting a single short-term result as a definitive statement about the home's annual average, or omitting the measurement conditions, duration, and uncertainty from the report.
Candidates conflate 'the number I measured' with 'the exposure the occupants have.' Radon varies seasonally and with weather and operation of the home, so a short-term result is an estimate under stated conditions, not a verdict.
What to do instead
Write reports that state device type, exposure start and end, conditions during the test, and the appropriate interpretation for that duration. Where the result is near a decision threshold, recommend confirmatory testing rather than declaring the home safe or unsafe.
Failing to recognize and control interference from radon in water, combustion appliances, or backdrafting that changes the pressure field during the test, and not documenting those sources.
Candidates study soil gas and forget that the indoor concentration is shaped by pressure-driven entry and by other sources. An exhaust fan or a running well pump can move the number without any change in the soil.
What to do instead
During the pre-test walkthrough, inventory pressure-affecting systems and water sources, document them, and either control them per protocol or note them as a limitation. Learn to explain pressure-driven entry so you can justify why the conditions matter.
Ignoring the laboratory's reporting units and detection limits, or comparing a result to an action level without converting units or accounting for uncertainty.
Candidates plug numbers into a formula without checking whether the lab reports in the units the threshold uses, or they treat a result at the detection limit as a precise value.
What to do instead
Before any comparison, write the unit, the detection limit, and the uncertainty next to the value. Convert explicitly and show the conversion in the report. Where the result is at or below the detection limit, report it as such rather than as a point estimate.
Letting the quality-assurance results (duplicates, blanks, spikes) sit unexamined, or reporting a result that the QA data show is out of control.
Candidates view QA samples as a compliance box and never close the loop. If duplicates disagree beyond the acceptance criterion or a blank shows contamination, the measurement is not defensible and must not be reported as valid.
What to do instead
Set acceptance criteria in advance, review QA results before releasing any report, and have a documented corrective-action path for out-of-control batches. Practice a worked example where a duplicate pair fails so the decision rule is familiar before it happens on a real job.