Invalid 48-Hour CRM Test Before a Friday Closing
A real estate agent orders a 48-hour continuous radon monitor (CRM) test on a 1978 split-level before a Friday closing. You place the CRM in the finished basement - the lowest livable level - on a shelf 22 inches above the floor and 3 feet from the exterior wall. The test starts Tuesday at 9:00 a.m., and the homeowner signs the closed-house agreement. At the Wednesday afternoon visit you download the data: hourly values average 9.4 pCi/L for the first 24 hours, then fall steeply - hour 26 is 4.1, hour 28 is 3.0 - and the final 48-hour average is 5.6 pCi/L. The CRM's motion sensor logged a disturbance at 1:10 p.m. Wednesday, and the homeowner's text admits they opened a stairwell window "for about two hours because the house felt stuffy." Outdoor temperature is 18°F. The agent wants the 5.6 pCi/L result delivered Friday to keep the closing on schedule.
1. Is the 5.6 pCi/L result reportable as a valid 48-hour test? Explain your reasoning and state what you do next.
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The result is not reportable as a valid 48-hour test. Closed-house conditions must be maintained for at least 12 hours before the test starts and throughout the entire exposure period. Opening a stairwell window for two hours breaks that condition, and the CRM data show the expected dilution signature: a 9.4 pCi/L average before the disturbance, then 4.1 and 3.0 pCi/L within hours, pulling the 48-hour average down to 5.6 pCi/L. You cannot attribute the drop to weather or stack effect when the motion sensor and the homeowner's own statement place an open window at the same time. Correct action: stop treating the run as valid, notify the agent and client in writing, and restart after 12 hours of closed-house conditions, or switch to a long-term test if the decision can wait. Do not truncate, correct, or reinterpret the data to produce a passing number.
2. The agent insists the closing cannot slip. What alternatives can you offer, and what must you refuse to do?
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You can offer a new 48-hour test that begins after 12 hours of closed-house conditions - for example, start Thursday evening and retrieve Saturday evening - and you can offer to expedite the lab or use a second calibrated CRM if one is available. You can also explain a long-term test (90+ days) if the buyer can decide on that timeline. What you must refuse: editing or truncating the hourly file, deleting the disturbed hours, applying a "ventilation correction," or representing the 5.6 pCi/L average as a valid result. A closing deadline is a business constraint, not a measurement protocol. If the agent or seller pressures you, state the rule in writing and copy the client. Some relocation or lending programs have their own acceptance rules, but they do not authorize you to certify an invalid test.
3. What should you document in the final report about the disturbance, and why does the CRM's sensor log matter?
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Document the device ID, serial number, calibration date, placement, start and stop times, and the full hourly file with the disturbance time annotated. Include the motion-sensor log, the homeowner's written statement, outdoor temperature, HVAC status, and any photos. The report should state plainly that closed-house conditions were broken and that the test is invalid, not simply omit the disturbance. Sensor logs matter because they are time-stamped and objective; they corroborate or contradict occupant accounts and protect both the technician and the client if the result is later challenged. Keep the raw data and communications for the retention period your program requires, and attach the invalidation notice to the file.