Building Systems, HVAC, and Homogeneous Area Assessment
An inspector who does not understand building systems will miss ACM and misjudge homogeneous areas. Think in systems: structural (beams, decks, fireproofing), envelope (roofing, siding, sealants), mechanical (HVAC, plumbing, boilers), electrical, and interior finishes.
HVAC deserves special attention. Air-handling units, ductwork, duct insulation, vibration isolators, gaskets, and fire dampers may contain asbestos. Interior duct insulation and sprayed fireproofing on structural members are classic friable surfacing/TSI materials. HVAC also matters because air movement can distribute fibers from a disturbed source; that is why return-air plenums and duct interiors are inspected and why O&M programs emphasize keeping friable material sealed and undisturbed. Remember that HVAC systems change over time: added chillers, rerouted ducts, and patched insulation create mixed vintages.
Homogeneous area assessment is the bridge between building systems and sampling. A homogeneous area is a group of materials that are alike in appearance, texture, and application and were likely installed at the same time with the same product. System boundaries help you draw them: all the pipe insulation of one type on one system installed in one era is usually one homogeneous area; a patched section of different insulation is a separate one. Traps: treating an entire building's pipe insulation as one area when vintages differ; missing concealed materials inside chases, above ceilings, and in mechanical rooms; and forgetting that fireproofing on beams and decking is a surfacing material with its own sampling density.
Rule of thumb: walk the building by system and by era. Every material you can see or reasonably infer gets classified, and every change in appearance or vintage starts a new homogeneous area.