Bulk Sampling Methodology, Handling, and Chain of Custody
Sampling is where an inspection either holds up or falls apart. The governing principles are representativeness, adequate quantity, avoidance of cross-contamination, and documentation.
First, define homogeneous areas: materials that are uniform in appearance, texture, and application, applied at the same time, and likely the same formulation. Sample within each homogeneous area at the density appropriate to the material category and program. Surfacing materials typically require a density-based number of samples (roughly three for small areas, rising with area); TSI is sampled by system and component; miscellaneous materials are sampled per homogeneous area. Random or distributed sampling across the area is preferred over grabbing a single convenient piece.
Use wet methods and proper tools to minimize fiber release. Sample the full cross-section where layers may differ (e.g., pipe insulation with a jacket, lagging, and core). Place each sample in a sealed, labeled container; label with project, homogeneous area, sample number, location, date, and sampler. Complete the chain-of-custody form at the time of collection, note the analysis requested (PLM with point count, or TEM as needed), and ship or deliver with tamper-evident sealing. Keep a field log and photographs.
Traps: taking one sample and calling it representative of a large area; sampling only the surface layer; failing to sample mastic under tile; inadequate sample mass for the requested method; and chain-of-custody gaps that make results challengeable. Also watch for sampling a material that is not actually homogeneous with a neighbor.
Rule of thumb: sample the material, not the location. Each sample must be mass-adequate, layer-complete, individually labeled, and traceable from wall to laboratory.