For those interested in this discussion who have not yet read the changes in the new 2014 edition of 921 regarding the “process of elimination” and the “scientific method,” here are the pertinent sections.

Changes were made to Sections 4.3.6, 4.3.6.1, and 19.6.5 particularly to alleviate misunderstandings about the “process of elimination” and the “scientific method” from previous editions. Please note that section 19.6.5 is the only paragraph in 921-2014 that even uses the phrase “process of elimination.”



NFPA 921-2014
4.3.6* Test the Hypothesis (Deductive Reasoning). The investigator
does not have a valid or reliable conclusion unless the
hypothesis can stand the test of careful and serious challenge.
Testing of the hypothesis is done by the principle of deductive
reasoning, in which the investigator compares the hypothesis
to all known facts as well as the body of scientific knowledge
associated with the phenomena relevant to the specific incident.
A hypothesis can be tested physically by conducting experiments,
analytically by applying accepted scientific principles,
or by referring to scientific research. When relying on
the research of others, the investigator or analyst must ensure
that the conditions, circumstances, and variables of the research
and those of the hypothesis are sufficiently similar.
Whenever the investigator relies on research as a means of
hypothesis testing, references to the research relied upon
should be acknowledged and cited. If the hypothesis is refuted
or not supported, it should be discarded and alternate hypotheses
should be developed and tested. This may require the
collection of new data or the reanalysis of existing data. The
testing process needs to be continued until all feasible hypotheses
have been tested and one is determined to be uniquely
consistent with the facts and with the principles of science. If
no hypothesis can withstand an examination by deductive reasoning,
the issue should be considered undetermined.

4.3.6.1* Any hypothesis that is incapable of being tested either
physically or analytically, is an invalid hypothesis. A hypothesis
developed based on the absence of data is an example of a
hypothesis that is incapable of being tested. The inability to
refute a hypothesis does not mean that the hypothesis is true.

19.6 Testing the Cause Hypothesis. Each of the alternate hypotheses
that were developed must then be tested using the
Scientific Method. If one remaining hypothesis is tested using
the “scientific method” and is determined to be probable,
then the cause of the fire is identified.

19.6.5* Appropriate Use. The process of elimination is an integral
part of the scientific method. Alternative hypotheses
should be considered and challenged against the facts. Elimination
of a testable hypothesis by disproving the hypothesis
with reliable evidence is a fundamental part of the scientific
method. However, the process of elimination can be used inappropriately.
The process of determining the ignition source
for a fire, by eliminating all ignition sources found, known, or
believed to have been present in the area of origin, and then
claiming such methodology is proof of an ignition source for
which there is no supporting evidence of its existence, is referred
to by some investigators as negative corpus. Negative corpus
has typically been used in classifying fires as incendiary,
although the process has also been used to characterize fires
classified as accidental. This process is not consistent with the
scientific method, is inappropriate, and should not be used
because it generates untestable hypotheses, and may result in
incorrect determinations of the ignition source and first fuel
ignited. Any hypotheses formulated for the causal factors
(e.g., first fuel, ignition source, and ignition sequence), must
be based on the analysis of facts. Those facts are derived from
evidence, observations, calculations, experiments, and the
laws of science. Speculative information cannot be included in
the analysis.

Pat Kennedy, CFEI, CFPS, MIFireE
Fire and Explosion Analyst
Sarasota, Florida
[www.kennedy-fire.com]