Clearance Sample Count on a Small Bathroom Abatement
A contractor has completed removal of friable ceiling texture from a 6 ft × 8 ft bathroom in an occupied apartment building. The containment is a single small room with one entry. The project manager wants to release the unit to the building owner the same afternoon. He has collected two air samples inside the containment and one outdoor sample, and all are below the clearance threshold on the laboratory report. He argues that because the room is small, two samples are plenty and the outdoor sample "covers" the rest. The building owner is asking whether the unit is safe to reoccupy. A tenant with asthma lives next door.
1. Evaluate the sampling plan. What is wrong with relying on two interior samples and one outdoor sample for clearance in this situation?
Read the worked answer
The plan has several weaknesses that make it unreliable as a clearance decision:
- Sample count and placement: clearance sampling should be sufficient in number and positioned to represent the work area, including areas where dust may have settled and been disturbed. Two samples in a small room may be defensible only if the sampling scheme and the applicable standard/contract specify that number; the count must follow the governing protocol, not convenience.
- Outdoor sample: an outdoor (or background) sample is useful for comparison and for documenting that the work did not affect the exterior, but it does not substitute for interior clearance samples. It cannot demonstrate that the interior is clean.
- Aggressive sampling: clearance should generally follow the specified method (e.g., aggressive disturbance of settled dust before sampling) so that the sample represents reoccupancy conditions, not a settled, undisturbed room.
- Timing: releasing the same afternoon assumes results are final and the method was correct; the PM should confirm the lab's analysis and the sampling method before release.
The decision to reoccupy should rest on a complete, methodologically sound clearance scheme, not on a shortcut justified by room size.
2. The tenant next door has asthma. How should that affect the release decision and communication?
Read the worked answer
Sensitive occupants raise the stakes but do not change the technical standard; they change the risk-management posture. The contractor should:
- Not release the unit until clearance is properly documented per the governing protocol.
- Ensure the containment was maintained and that no dust migrated to the adjacent unit (visual inspection, and samples if warranted).
- Communicate results and the basis for the release decision to the owner in writing, including what was sampled and the method used.
- Advise the owner that the adjacent tenant should not be exposed to dust during any remaining work, and that any residual debris should be cleaned before reoccupancy.
Judgment: a sensitive occupant is a reason to be more rigorous and more transparent, not a reason to accept a thin sampling plan.