One High Clearance Sample and a Contractor's Average
You are the project monitor for abatement of 1,200 square feet of acoustical ceiling tile in a single-story office building in Dickinson. The contractor completed removal, cleaned the containment, and passed the visual inspection. You collected five PCM clearance samples inside the containment using aggressive sampling: 0.004, 0.006, 0.005, 0.012, and 0.003 f/cc. A background sample outside the containment reads 0.002 f/cc. The contractor's project manager calculates the average as 0.006 f/cc and says the job passes because the average is below 0.01 f/cc. The 0.012 sample was collected near the return-air grille; the contractor calls it an outlier. The building owner wants to reopen tomorrow. The contract specifies AHERA clearance criteria and requires five samples minimum.
1. Does the project pass clearance? Explain the standard you are applying.
Read the worked answer
No. AHERA clearance is not based on the average of the samples. The criterion is that each sample must be below 0.01 f/cc; a single sample at 0.012 f/cc fails. The contractor's average of 0.006 f/cc is mathematically correct but legally irrelevant. The background of 0.002 f/cc does not explain away the 0.012 result, and labeling it an outlier does not change the clearance decision. The location near the return-air grille is actually a reason for concern, because it may indicate residual dust in a pathway that can redistribute fibers. The monitor should document the sample locations, the aggressive sampling method, the calibration records, and the failed result, and should not sign a clearance report.
2. What should happen before the building is reopened?
Read the worked answer
The containment must be recleaned and re-sampled. The contractor should HEPA-vacuum and wet-wipe all surfaces, especially the return-air grille and nearby ledges, and the monitor should verify that the cleaning is thorough. Then collect a new set of aggressive clearance samples using the same accepted protocol and at least the required minimum number. Do not reopen until every sample is below 0.01 f/cc and the visual inspection passes again. If the return grille continues to produce elevated results, investigate whether dust has entered the HVAC system or whether the containment boundary was compromised. The monitor should notify the owner and contractor in writing that clearance failed and that the reopening date is contingent on a passing re-sample.
3. The owner pressures you to accept the average because the office lease starts tomorrow. How do you respond?
Read the worked answer
Explain that accepting the average would misapply the clearance standard and could expose occupants to asbestos. The monitor's role is to protect the public and document the true result, not to accommodate a lease date. Offer a rapid but compliant path: immediate recleaning, re-sampling, and expedited laboratory turnaround if available, while making clear that reopening before a pass is not an option. Put the failed result and the owner's request in the project record. If the owner directs the contractor to reopen anyway, the monitor should document the direction and consider notifying the appropriate program authority. The 0.012 sample is a real result, not a negotiating position.