Borderline PLM Results in a 1970 School
A consultant samples four homogeneous areas in a 1970 school: 12-inch floor tile with black mastic, 2x4 ceiling tile, pipe insulation, and plaster. He collects two tile and mastic samples, three ceiling tile samples, three pipe insulation samples, and one plaster sample because the plaster was visually identical throughout. The laboratory uses PLM and reports: floor tile 2% chrysotile; mastic 1% chrysotile; ceiling tile none detected; pipe insulation 15% amosite; plaster none detected. The plaster sample came from a patched area. The school plans to remove only ceiling tile and plaster during summer break. The abatement contractor asks whether the floor tile and mastic and the pipe insulation are ACM and whether the plaster sampling is adequate. The project designer plans to use the report as-is and not resample. The mastic result is exactly 1%, and the lab did not perform point counting.
1. Which materials are ACM under the regulatory definition, and how should the 1% mastic result be handled?
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Under the NESHAP and OSHA definition, ACM contains more than 1% asbestos by weight. Floor tile at 2% chrysotile is ACM. Pipe insulation at 15% amosite is ACM. Mastic at exactly 1% is not ACM by that definition, but the result is at the PLM reporting limit and should not be treated as a clean bill of health. Because PLM has poor precision near 1%, the mastic should be point-counted by PLM or analyzed by a more sensitive method, or the project should treat it as ACM conservatively. If the mastic is disturbed, the conservative assumption protects workers and avoids a failed clearance. Ceiling tile with no asbestos detected in three samples is likely non-ACM, but the report should state the analytical method and detection limit.
2. Evaluate the sampling adequacy and the homogeneous area assumptions.
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Two samples from the floor tile and mastic homogeneous area do not meet the usual minimum of three samples per homogeneous area. The mastic and tile may be separate homogeneous areas and should be sampled separately. Three ceiling tile and three pipe insulation samples are adequate for those areas if collected properly. One plaster sample is not adequate; plaster often varies between patched and original areas, and the sample came from a patch. The patched area should be a separate homogeneous area, or the plaster should be assumed ACM until three representative samples per area are analyzed. A single visual judgment is not enough.
3. What should be done before bidding and removal, and how should the report be corrected?
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Before bidding and removal, resample the mastic and plaster with an accredited laboratory, use point counting where results are near 1%, and document chain of custody and sample locations. Update the inspection report and project design. If the plaster is not sampled, treat it as ACM and include it in the notification and work plan. Even if only ceiling tile and plaster are removed, the project must protect adjacent ACM floor tile and pipe insulation from damage. The designer should not use the report as-is; the contractor should bid on confirmed quantities and waste volume.