A fire investigator can spend decades examining scenes, earn respected certifications, and testify numerous times—and still be unprepared to defend a particular opinion. Experience may establish familiarity with the work. It does not, by itself, establish that the work was done correctly. The question every insurance and law firm client should be willing to ask is, “Is the investigator I just retained truly qualified to testify as an expert witness?”
Consider what that question demands. Does this investigator have a thorough understanding of fire dynamics? Do they understand the fire effects observed? Do they recognize the evidence that mattered—and the evidence that might contradict initial thinking? Did they ask the right questions, test reasonable alternative hypotheses, and document the reasoning behind conclusions? If they missed something important, would they even know it?
It is often easier to identify deficiencies in another investigator’s work than to recognize them in our own. The purpose is not to undermine confidence. It is to ensure that confidence is earned through sound science, disciplined methodology, and work that can withstand scrutiny.
Preparation Starts Before the Scene
When does preparation for an expert opinion report or courtroom testimony begin? Not when an attorney requests a report, a deposition is scheduled, or a trial date is set. It begins before the investigator ever enters the scene.
Every assignment should be approached with the understanding that the investigator may eventually have to explain each significant observation, decision, and conclusion under oath. Credibility rests on what the investigator knew, recognized, collected, analyzed, and documented when the opportunity existed. Credibility rests upon training and education.
Consider a few questions. Is your investigator genuinely inquisitive about why fire effects occurred? How often do they pursue meaningful continuing education? Can they explain the professional qualification requirements addressed by NFPA 1033? Do they understand NFPA 921 well enough to explain which guidance they applied, and why? Can they use their documentation equipment effectively—and recognize its limitations?
There is a substantial difference between accumulating training certificates and demonstrating the knowledge those certificates are intended to represent. The real test comes when an investigator must apply that knowledge to a fire or explosion scene.
Familiarity with a standard or attendance at a seminar is only a starting point; competency must be demonstrated in the decisions made during the investigation.
Knowing the Standards Is Not the Same as Applying Them
Origin and cause vendor questionnaires commonly ask whether an investigator follows NFPA 1033, NFPA 921, and the scientific method, and whether they had ever been excluded from testifying. A few affirmative answers and a negative answer to the last question were generally sufficient.
But what do those answers establish? An investigator may say they follow NFPA 921 while lacking a meaningful understanding of fire dynamics, ventilation effects, arc mapping, or fire pattern interpretation. Claiming to apply the scientific method is not the same as applying it competently.
NFPA 1033 addresses professional qualifications, while NFPA 921 provides guidance for the scientific investigation of fire and explosion incidents. The question is not merely whether the investigator knows the documents exist, but whether their work reflects an informed understanding of them.
The scientific method is not a checklist that can overcome inadequate technical knowledge. Its effectiveness depends on recognizing and collecting relevant data, analyzing that data accurately, developing reasonable hypotheses, and testing those hypotheses against the evidence. If the investigator misunderstands ventilation-generated damage or overlooks electrical activity that warrants examination, the problem begins before any hypothesis is formulated.
That knowledge gap can shape an entire investigation. Consider witness interviews. An investigator unfamiliar with ventilation effects may not ask when a door or window opened, when glass failed, or how fire behavior changed after suppression crews arrived. Someone unfamiliar with a potential ignition source may fail to ask about the equipment’s condition before the fire. Questions not asked can mean information never obtained.
This matters because analysis is often limited by the questions asked and observations made early in the process. A witness may recall that a door was opened shortly before a sudden change in fire behavior, but that detail may never enter the investigative record unless the interviewer recognizes its potential importance. The same is true of pre-fire electrical conditions, appliance operation, building alterations, and suppression activities. Investigators cannot reliably analyze information they never sought to obtain.
Incomplete data collection compromises analysis. Flawed analysis undermines hypothesis testing; and inadequately tested hypotheses can produce unsupported opinions. What begins as a technical deficiency can become a serious credibility problem in deposition or trial.
Documentation of the Investigation Conducted
Each investigation should leave an accurate, transparent record of the work performed. That record begins with the assignment and its scope and continues through communications, scene examinations, interviews, photographs, evidence collection, notes, research, testing, and consultations.
Fire scenes change, are repaired, or disappear. Thorough documentation preserves the conditions and observations on which later opinions depend. Original notes are particularly important for this very reason, and investigators should also understand applicable preservation and disclosure obligations and should not assume that informal messages or preliminary opinions will remain outside discovery.
Documentation should distinguish what was personally observed from what was reported by others. When an opinion evolves because additional records, laboratory results, or research become available, the investigative record should make that progression understandable. The goal is not to produce a perfect-looking file; it is to preserve an accurate account of what was known when and how the reasoning developed.
Modern tools—including high-quality digital photography, three-dimensional imaging such as Matterport or iGUIDE, drones, and tablets—can substantially improve the investigative record and can, in a sense, help to preserve the scene and aid in potential future expert witness preparation and testimony. This technology can also be effectively utilized in any future expert witness testimony.
An investigator’s report, the narrative, photographs, and supporting materials often reveal what they focused on—and what may have received insufficient attention, to be later picked apart by an opposing expert or counsel. A report need not be lengthy to be effective. It must simply allow the reader to understand the evidence, methodology, analysis, and basis for the conclusions.
Written conclusions should not be more certain than the supporting photographs, notes, or analysis appear to justify. A well-supported report identifies the relevant observations, explains their significance, addresses reasonable alternatives, and marks where the evidence places limits on the conclusion. A reader should not have to guess at the steps connecting data to opinion.
An Expert Must Also Be a Storyteller
A good origin and cause investigator must be an effective storyteller, not embellishing facts or advocating for an outcome. Rather, they must be able to take a complicated investigation and explain it in a clear, logical, understandable way.
An investigation has a sequence: assignment, observations, data collection, analysis, hypothesis development and testing, and conclusions. The written report should guide the reader through that sequence in a clear manner, explaining what was observed, and why it mattered. The report should flow in a chronological common-sense progression that should culminate in a conclusion that makes sense to any reader.
Photographs are especially useful when placed near the discussion they support. If the report describes a fire pattern, structural feature, or relevant component, let the reader see it at that point. As the saying goes, a photograph can be worth a thousand words, and the selection and arrangement of photographs are part of the story being told. Captions and references should also help establish the relationship between the photographs and the narrative.
The same principle applies to language. Fire investigation necessarily involves technical terms, but it is not always imperative for the report to involve technical terms. Many attorneys, insurance professionals, judges, and jurors will not be familiar with these terms. Using precise terminology when needed is fine, but being able to explain it in plain English is better. Every scientific assertion and technical term in the report is something an investigator may later be asked to explain in testimony; hopefully clearly and effectively; possibly not.
From the Report to the Witness Stand
An expert opinion report establishes much of the foundation for testimony. By the time an investigator sits for a deposition or takes the witness stand, the reasoning behind the opinions should be familiar—not something encountered for the first time while reviewing the file.
Preparation means examining the complete investigative record, reconsidering assumptions, anticipating legitimate challenges, and inviting critical review by another qualified expert when appropriate. What evidence supports each opinion? Which alternative hypotheses were evaluated, and how? What information appears inconsistent with the conclusion? Where does the evidence leave genuine uncertainty?
Critical review at every level is essential. Identify the assumptions on which the conclusion depends. Look for evidence that might conflict with the preferred hypothesis. Ask whether another reasonable explanation remains viable, and whether any claimed elimination of an alternative is supported by actual data. Where uncertainty remains, recognize it rather than trying to explain it away. That discipline strengthens both the investigation and the testimony that may follow. A good investigator should always try to disprove their own final hypothesis.
This is not an exercise in preparing rehearsed answers or defending an indefensible position. It is a disciplined, open-minded assessment of the strengths and limitations of the work. A credible expert knows the difference between what the evidence supports, what remains uncertain, and what cannot reasonably be determined, and that expert should communicate every bit of that to you, as the client.
Opposing counsel may challenge assumptions, methods, interpretations, and inconsistencies. It is their job to poke and to prod, to test an investigator’s “investigative literacy.” No investigator should let this type of questioning dictate their demeanor. A professional, qualified investigator will listen carefully, answer directly and accurately, and avoid unnecessary elaboration and confrontation. If a question misstates a finding, the investigator should clarify it respectfully. If the evidence does not support a definitive answer, they should acknowledge that limitation.
Preparation for testimony should include making sure the investigation can be explained in a common-sense, non-technical manner, utilizing a sound scientific methodology. A question about a ventilation-related pattern, for example, calls for a clear and understandable explanation of why the effects of ventilation matter in the investigation at hand. If a question exposes a genuine limitation, acknowledging it is more credible than arguing beyond the evidence. The objective is to assist the fact-finder in understanding the investigation, not to prevail in every exchange.
An investigator can be humble and authoritative at the same time, without appearing arrogant. Confidence should come from preparation, competence, and objectivity—not from the need to win an argument.
The Real Test of Readiness
Writing an expert opinion report and testifying are not isolated events at the end of an investigation. They are extensions of everything that came before: curiosity, education, scientific understanding, scene examination, interviewing, documentation, analysis, and hypothesis testing.
Credentials, experience, and confidence matter, but none can substitute for scientific understanding, sound methodology, or intellectual honesty. The investigator who can explain why an opinion is supported and candidly acknowledge what remains uncertain is better prepared than one who merely insists the conclusion is correct. The greatest vulnerability may not be what we do not know. It may be what we have never thought to question.
Before retaining a fire investigator, clients should ask themselves a fundamental question: Am I selecting an investigator whose qualifications, knowledge, and experience are appropriate for this assignment, or am I simply hiring a company that will assign the next available investigator?
Not every investigation results in litigation. Some may never progress beyond the initial report, while others may be scrutinized in depositions and courtrooms years later. The investigator's decisions, observations, and documentation made today may ultimately determine whether an opinion can be credibly defended on your behalf tomorrow.
About the author:
Mike Vergon is the principal at Vergon+Associates Fire Investigation. mike@vergonfire.com