Guide · Working with experts
How to read an origin-and-cause report
A battery-fire expert report can look authoritative and still be vulnerable. Whether you retained the expert or you're cross-examining one, the same handful of questions separate a defensible report from one that will not hold up. Here is what to look for.
Origin and cause are two different findings
Every fire investigation is really answering two questions. Origin is where the fire started — narrowed down to an area, a device, and ideally a specific cell. Cause is how and why it started — the sequence and the factors that produced it. A report that asserts a cause without first firmly establishing origin has skipped a step, and that gap is often where the opinion falls apart.
What a strong report contains
A well-built report makes its own reasoning transparent. Look for:
- A stated methodology. The investigation should follow the systematic approach of NFPA 921 — forming hypotheses and testing them against the evidence — and say so.
- A documented chain of custody. Where the evidence came from, who handled it, and how it was preserved.
- The evidence actually examined. The device, battery, charger, and scene — not just photographs of someone else's work.
- Alternative hypotheses considered and eliminated. A credible investigator explains what else could have caused the fire and why the evidence rules those out.
- A clear basis for each opinion. Every conclusion should be traceable to specific evidence, not stated as a conclusion on its own.
- Stated limitations. What could not be determined, and why. Honesty about limits is a sign of rigor, not weakness.
The test: could a qualified investigator, handed the same evidence, follow the report's reasoning and reach the same conclusion? If the path from evidence to opinion isn't visible, the opinion is an assertion — and assertions do not survive cross-examination.
Red flags in a weak report
- A cause opinion with no clearly established origin.
- No chain of custody, or evidence examined after others had altered it.
- Alternative causes never addressed or eliminated.
- The charger and other components ignored in favor of blaming the cell by default.
- Opinions that reach beyond what the evidence can support.
- No methodology stated at all.
Questions worth asking in deposition
Whether testing your own expert's work or challenging the other side's, these questions expose how solid the foundation really is:
- How was the area and point of origin determined?
- What alternative causes did you consider, and how did you eliminate each?
- What evidence did you personally examine, and in what condition?
- Was the charger evaluated, and what role did it play?
- What is the specific basis for the opinion on cause?
- What could you not determine from the available evidence?