1. What the specialist does on site
A proper visit is an investigation, not a swab-and-go. Expect the specialist to: take the exposure history (which fire, when, how far, wind direction); walk the smoke pathways — windows, doors, attic vents, crawlspace openings, and the HVAC system EPA identifies as a primary entry route[1]; inspect the places residue concentrates (windowsills, attic insulation, duct interiors, filter media); and then build a sampling plan around a hypothesis — for example, "smoke entered through the fresh-air intake and distributed through supply ducts."
The visit typically runs 60–90 minutes for a home. You should see the specialist photograph sample locations, label every sample, and record it all on a chain-of-custody form — the paper trail that makes results defensible to an insurance carrier.
2. The sample types, in plain language
Every plan should also include comparison samples — an unaffected room, an outdoor surface, a neighboring area. NIOSH guidance stresses that standardized, comparable sampling is what makes results interpretable.[3] A single sample with nothing to compare against is the mark of a weak investigation.
3. What the lab reports — and what the words mean
The laboratory examines samples by microscopy (and GC-MS for air samples) and reports what it found: soot (fine carbon from incomplete combustion), char (burned material fragments), ash (mineral residue), often graded as trace / moderate / heavy or as a percentage. Three translation notes:
- "Consistent with" is the honest phrasing. Labs identify particle character; connecting it to a specific fire is the investigator's job, using event history, distribution patterns, and comparisons. Reports claiming a lab "proved" a specific fire caused everything are overreaching.
- "Non-detect" means below the reporting threshold for that method, on that sample — not a certificate that the building is clean. Location and method matter.
- Dark dust isn't automatically soot. Candle residue, cooking aerosol, rubber particles, and ordinary urban dust can look similar; good labs distinguish them (ASTM D6602-based microscopy exists for exactly this[4]), and good reports discuss the alternatives.
4. Rigorous investigation vs. sales visit
The standards frame matters too: ANSI/IICRC S700 describes assessing the presence, intensity, and boundaries of fire residues affecting buildings, systems, and contents.[5] Boundaries are the point — a good investigation tells you what's affected and what isn't, which is what keeps remediation scoped honestly.
5. Costs, timing, and what happens next
Lab turnaround is typically 3–10 business days depending on analyses. Timing favors early sampling — residues are undisturbed, the event is fresh, and results are easier to attribute. If you've already cleaned, testing can still work; the porous and hidden reservoirs (carpet backing, attic insulation, duct interiors) hold evidence long after visible surfaces are wiped — just tell the specialist exactly what was cleaned and when.
If results confirm contamination, a licensed industrial hygienist writes the remediation protocol, the claim proceeds with laboratory evidence attached (see the insurance guide for that path), remediation follows the protocol, and clearance testing verifies the work actually removed what it was supposed to. If results come back at background: you're done, with documentation in hand — useful at resale and for peace of mind.
Sources
- U.S. EPA. Wildfires and Indoor Air Quality (IAQ). Entry routes including HVAC intakes and infiltration.
- U.S. EPA. Compendium Methods TO-15A / TO-17 — VOC air sampling and analysis.
- NIOSH. Surface Sampling Guidance, Considerations, and Methods in Occupational Hygiene.
- ASTM International. ASTM D6602 — distinguishing carbon black and combustion soot from other particulate.
- IICRC. ANSI/IICRC S700-2025 Standard for Professional Fire and Smoke Damage Restoration.