Fire Investigations and the Scientific Method

September 2022 - Fire Investigations and the Scientific Method

Origin and Cause investigations are becoming more and more technical in nature and increasingly science-based as the body of knowledge of fire science expands and refines. As a result of the many advancements in fire science, the fire investigator is forced to adapt, educate themselves, and become more of a scientist than ever before. Those who fail or refuse to do so will find themselves trailing behind the pack, and worse yet, embarrassed in a court of law.

Long gone are the days of the ipse dixit investigator.[1] “Ipse Dixit” is a Latin phrase translated as “he said it himself.” The phrase, as defined by, is “an assertion without proof.”[2] No longer can the fire investigator simply offer an untested and unverified opinion and expect that to hold up in a court of law. The ipse dixit investigator will get thoroughly challenged – count on it. For example, years ago, I once was involved in a fire investigation where the opposing expert claimed that the fire was likely caused by a cat knocking over a lamp. There was zero evidence to support that assertion. I was baffled at the experienced investigator unabashedly making such a silly and unsupported claim, in writing to boot. Those instances are becoming less and less frequent, and that is a good thing.


The Scientific Method

The Fire Investigation Handbook issued by the U.S. Department of Commerce / National Bureau of Standards in 1980 is 187 pages long including the annexes. This treatise is the precursor to NFPA’s 921 - Guide for Fire and Explosion Investigation. It should be noted, the scientific method[3] is not described or mentioned in this document. The first edition of NFPA 921 arrived in 1992. The earliest edition I own is the 1998 edition, which is just 167 pages long, including the annexes and index. A detailed description of the scientific method is included in this edition.[4] By contrast, the current 2021 edition of 921 is 449 pages long including the annexes and index. That is a massive 2.7 times lengthier than the 1998 edition! This increase is not the result of loquacious technical writers. On the contrary, it is the result of an explosion of technical knowledge. We should all welcome it..

One tenant of any scientific investigation is the adherence to the scientific method. As fire investigators, we must learn how to be a scientist, and not just an investigator. I like to refer to this new and improved investigator as the “Scientist-Investigator.” As such, we must treat all investigations as a science venture. As scientist-investigators, the scientific method is the absolute standard of fire investigation.[5]  Learn it and love it. It is how truth is discovered empirically without bias. The method involves thoughtful observation and a healthy dose of skepticism throughout. 

The method is simple and allows the scientist to generate and test numerous hypotheses. Its use avoids problems of bias and confounding variables. NFPA’s 921 breaks the method down into 7 steps or processes which are outlined below:[6]

  1. Recognize the Need
  2. Define the Problem
  3. Collect Data
  4. Analyze the Data
  5. Develop Hypotheses
  6. Test the Hypotheses
  7. Select Final Hypothesis.

I’ll quickly explain these seven steps or processes:

  • First, “Recognize the Need” gives reference to the fact that a problem exists, namely, a fire has occurred, and that there is a need to figure out how that fire started. The need to know why and how the fire started is based in the desire to prevent that event from happening again and potentially save lives. This charge to figure out how the fire started is typically given to fire investigators through interested parties (insurance adjusters, attorneys, etc.).
  • Second, “Define the Problem” involves the scientist-investigator initiating an investigation into the matter. In other words, how can this problem, the fire at hand, be solved? The answer is almost always reached through conducting a thorough scientific investigation.
  • Next, “Collect Data” involves the gathering of information. This is often completed through observation, experimentation, or other empirical methods. The collected data is empirical in nature and can be verified through many means including independent testing or through photographic evidence.
  • “Analyze the Data” involves a thorough review of all the collected data. This step is key and benefits from a well-educated, trained, and experienced scientist-investigator. Simply put, the analysis is only as good as the scientist doing the analysis. If an investigator lacks understanding or expertise in an area, a significant piece of evidence may go unnoticed. This may, and often does, result in an erroneous final opinion.
  • “Develop Hypotheses” involves generating not just one, but often several potential scenarios as to the origin and cause of a fire. In fact, I encourage generating a number of plausible scenarios, as I have found this helps prevent “pet” hypotheses that we coddle and protect from careful examination. Under most circumstances there are often a number of plausible origins and causes that a scientist-investigator must either rule out or investigate further. 
  • “Test the Hypotheses” involves rigorous examination, either through physical testing or “thought experiments.” Often, critically thinking through a scenario can quickly rule out or in a hypothesis. Nine-twenty-one says it best, “The investigator does not have a valid or reliable conclusion unless the hypothesis can stand the test of careful and serious challenge.”[7]  Does it make sense? Does it follow the laws of physics? What else could explain this? Is it even possible, if not probable? These are the types of questions we must ask ourselves during this process.
  • Re-collect, Re-analyze, Re-develop Hypotheses. Here, the scientist-investigator may need to revisit some of the above steps if a hypothesis fails to stand the test of scrutiny. The scientist-investigator may need to collect additional data, or analyze the collected data further, or differently. The scientist may need to develop a completely new hypothesis to include newly discovered facts. This process can be repeated as many times and as often as needed until a valid hypothesis can be found. Sometimes, the wise scientist-investigator may need to seek additional expertise.
  • “Select the Final Hypothesis” is the final step. It requires a robust understanding of the facts of the case. This step cannot be attempted until the scientist knows everything there is to know about the fire and the often convoluted facts surrounding it. The scientist-investigator’s final hypothesis is the basis for the formulation of his or her final expert opinion(s). Note, there may be times when other hypotheses seem to fit the facts equally as well as the scenario the scientist-investigator has selected. If that is the case, the wise scientist-investigator must admit that fact and be willing and able to scientifically support his or her selected hypothesis and expert opinion(s) as the most probable scenario. The scientist-investigator must be able to support and defend a “more likely than not” scenario. This is where education, training and experience play an immense role.

Final Note

If your investigator has not followed the scientific method in their investigation into the fire they are tasked with, they must be able to support their chosen methodology and why they preferred to follow it instead – not an easy task. At Ponderosa Associates, we’ve found that the safest and most robust methodology is to follow what Sir Francis Bacon established over 400 years ago – the Scientific Method.  At Ponderosa Associates, we couple our skills, knowledge, experience, and training with the scientific method to produce a solid product for our clients. This proven method of trial and error has allowed scientists, physicists, and engineers to put a man on the moon, develop cures for maladies that a hundred years ago would prove fatal, develop computers that process data at lightning speed, and provide cellular telephones that allow communication to anywhere in the world in a matter of seconds. This method can also provide answers to why and how a fire started with a level of confidence otherwise unseen in history. 

Happy investigating to all!
-J. Cord Guthrie, MFS, CFEI, CVFI   

Meet Cord

Cord is a licensed Private Investigator in the state of Arkansas, and New Mexico.  He is a member of the National Association of Fire Investigators (NAFI), a member of the National Fire Protection Association (NFPA), and the International Association of Arson Investigators (IAAI). Give Cord a call to discuss more about fire investigations where gas-fired appliances may have been involved!

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[1]  “Ipse dixit is a Latin phrase that translates to “he said it himself.” Ipse dixit means a person’s own assertion without relying on any authority or proof. It usually implies an assertion of authority, as in a statement is true based on the speaker’s authority and nothing else. In legal context the term is usually used to criticize arguments based solely upon authority and not backed by any proof.
For an example of usage, “An expert's simple ipse dixit is insufficient to establish a matter; rather, the expert must explain the basis of his statement to link his conclusions to the facts.” Earle v. Ratliff, 998 S.W.2d 882, 890 (Tex. 1999).” 


[3] NFPA 921, 2021 ed., §4.2.

[4] NFPA 921, 1998 ed., §2-2

[5] For an excellent discussion on the scientific method see Icove & Haynes, Kirk’s Fire Investigation, 8th ed., §1.5.

[6] NFPA 921, 2021 edition, Figure 4.3.

[7]  NFPA 921, 2021 edition, §4.3.6.

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