1. The anatomy of the report
Whatever the lab, a competent fire-residue or VOC report contains the same skeleton. Learn to find these seven parts:
| section | what to check |
|---|---|
| Sample inventory | Every sample ID matched to a real location description — "S-03, kitchen windowsill, north wall, pre-cleaning" — and to the chain-of-custody form. IDs that say only "Sample 3" weaken everything downstream. |
| Method statement | PLM / reflected-light / SEM-EDS for particles (often ASTM D6602-based); TO-15A / TO-17 GC-MS for VOCs; TO-11A HPLC for carbonyls. The method defines what the result can and cannot say. |
| Analytes / targets | What was actually looked for: soot, char, ash, black carbon; or the specific VOC list. Compounds not on the panel were not tested — a non-detect says nothing about them. |
| Results table | Per-sample findings with the reporting format defined (see §2). Watch for footnote flags — dilutions, matrix interference, holding-time exceedances. |
| Reporting limits | The threshold below which the lab won't report. "ND" always means "not detected above this number" — the number matters. |
| QA/QC block | Blanks, duplicates, calibration checks, accreditation ID. Its absence is a red flag for any contested claim. |
| Limitations | Strong reports state them plainly. A report that claims to answer everything answers to nothing. |
2. Result formats and their traps
Qualitative ("detected / not detected," "consistent with fire residue") is common in particle screening. It is legitimate — and vulnerable when the descriptors are undefined. Ask the lab for its category definitions in writing. Semi-quantitative ("trace / few / common / abundant," percent of field area) supports the comparison that matters: affected room vs. background. Quantitative (µg per sample, particles/cm², ppbv for VOCs) looks strongest but inherits every weakness of the sampling: a precise number from a bad sample is precisely wrong.
And the classic: "ND" ≠ zero ≠ clean. Non-detect means below the reporting limit, for that analyte, in that sample, by that method, on that day. It does not rule out compounds off the panel, residue in unsampled rooms, particles in the ducts, or VOC reservoirs that re-emit when temperature rises.
3. The background comparison is the report
Every occupied building contains combustion particles at some level — candles, cooking, fireplaces, vehicle exhaust. NIOSH surface-sampling guidance is built around comparability: standardized collection across locations, times, and investigators is what makes results mean something. So the decisive rows in the results table are the comparisons: complaint rooms vs. unaffected rooms, indoors vs. outdoors, supply registers vs. return grilles, pre- vs. post-remediation. A report with no comparison samples asks the reader to take "elevated" on faith — which an opposing expert will decline to do.
The same logic governs source attribution. Soot in a kitchen means little; soot at concentrations 10× background, heaviest at the windows facing the fire, present in attic insulation and the HVAC filter, absent in the interior bathroom — that pattern, plus the documented event, supports "consistent with the reported exposure." Character (what the particles are), quantity (vs. background), and distribution (where they are) — interpretation stands on all three legs or not at all.
4. What the lab states vs. what the investigation concludes
The right-column statements require the exposure history, building inspection, HVAC documentation, and comparison logic — assembled by a qualified consultant or industrial hygienist (AIHA's framework for fire investigations expects exactly this pairing of data and professional judgment). When a claim file quotes the lab for right-column conclusions, that's the overreach carriers attack. When a denial quotes one ND for the same purpose, that's the same error in reverse — and you can say so.
5. A worked example
Reading it: the gradient from fire-facing windowsill (abundant) through the HVAC register and attic (common) down to the interior control (rare/ND) is a spatial pattern consistent with outdoor-origin smoke entering and distributing — the outdoor reference confirms heavy exterior fallout. The interior control near background is what makes the elevated rooms meaningful. A defensible conclusion cites that pattern plus the documented event; it does not claim the lab "proved" the fire did it, and it does not extrapolate beyond the sampled rooms without saying so.
6. Ten questions to ask of any report
- Is every sample tied to a photographed, described location and a chain-of-custody record?
- Is the analytical method named, and is it appropriate to the question?
- What exactly was on the analyte panel — and what wasn't?
- What are the reporting limits, and are NDs being read as "clean"?
- Are there background/comparison samples? Indoors and out?
- Do the results show a spatial pattern, or isolated points?
- Are alternative sources (candles, cooking, fireplace, traffic) addressed?
- Was the building's cleaning history documented before sampling?
- Is there a QA/QC section and laboratory accreditation?
- Does the written conclusion stay within what the data supports?