Here is the language we use in all of our reports to make it clear to the reader how we reached our opinions and established our level of confidence/certainty.


NFPA 921 provides that the basic methodology that a fire investigation should rely upon is the use of a systematic approach and attention to all relevant details. The systematic approach recommended is that set forth in the “scientific method”, which is used in the physical sciences. This methodology provides for the organizational and analytical process so desirable and necessary in a successful fire investigation. The scientific method is a principal of inquiry that forms a basis for legitimate scientific and engineering processes, including fire investigation. The scientific method is applied using the following six steps:
a) Recognize the Need. First, one must determine that a problem exists. In this case, a fire or explosion has occurred and the cause must be determined and listed so that future, similar incidents can be prevented.
b) Define the Problem. Having determined that a problem exists, the investigator or analyst must define in what manner the problem can be solved. In this case, a proper origin and cause investigation must be conducted. This is done by an examination of the scene and by a combination of other data collection methods, such as the review of previously conducted investigations of the incident, the interviewing of witnesses or other knowledgeable persons, and the results of scientific testing.
c) Collect Data. Facts about the fire incident are now collected. This is done by observation, experiment or other direct data gathering means. This is called empirical data because it is based on observation or experience and is capable of being verified.
d) Analyze the Data (Inductive Reasoning). All of the collected and observed information is analyzed by inductive reasoning. This is process in which the total body of empirical data collected is carefully examined in the light of the investigator’s knowledge, training and experience. Subjective or speculative information cannot be included in the analysis, only facts that can be clearly proven by observation or experiment.
e) Develop a Hypothesis. Based upon that data analysis, the investigator must now produce a hypothesis or group of hypothesis to explain the origin and cause of the fire or explosion incident. This hypothesis must be based solely on the empirical data that the investigator has collected.
f) Test the Hypothesis (Deductive Reasoning). All other reasonable origins and causes must be eliminated. The investigator does not have a truly provable hypothesis unless it can stand the test of careful and serious challenge. This is done by the principle of deductive reasoning, in which the investigator compares his or her hypothesis to all known facts. This testing may be either cognitive or experimental. If the hypothesis cannot withstand an examination by deductive reasoning, either it must be discarded as not provable and a new more adequate hypothesis tested or the fire cause must be listed as “unknown”.
NFPA 921 recommends that the investigator/analyst also establish a “level of confidence” for any hypothesis or opinion, which is formulated. There are four levels of confidence that can be regularly applied to hypotheses.
a) Conclusive. At this level of confidence, the hypotheses has been tested and withstood all appropriate challenges while all reasonable alternatives to the hypotheses have been considered and eliminated due to their failure to withstand a valid challenge, leaving only that hypothesis under consideration as true.
b) Probable. This level of confidence corresponds to being more likely true than not. At this level of confidence, the chance of the hypothesis being true is more than 50 percent.
c) Possible. At this level of confidence, the hypothesis can be demonstrated to be feasible but cannot be declared probable.
d) Suspected. This level of confidence corresponds to a perception that the hypothesis may be true, but there are insufficient data to draw a conclusion to the exclusion of any other reasonable conclusion.
If the level of confidence is only “possible” or “suspected” then the cause should be listed as unknown, undetermined or under investigation.
In the 1998 edition of NFPA 921, a reference to Daubert v. Merrel Dow Pharmaceuticals, Inc. 509 U.S. 579, 113 S. Ct. 2786 (1993) was added. Recently the application of this case law to fire investigation was broadened by Kumho Tire Company, Ltd v. Patrick Carmichael 119 S.Ct. 1167 in which the court decided that the gate keeping function of the courts under Daubert applies to all types of evidence, not merely traditional science. This case law is consistent with the provisions of NFPA 921 recognizing the use and application of the scientific method.

James G. Munger, PhD, FIFireE, CFPS
www.qdotengineering.com
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