Jim,

The statement, that the investigator did not need to "eliminate all possible causes", to support his conclusion is correct.

The level of certainty (or confidence) whereas a conclusion is "probable", means that the conclusion is more likely true than not, and is dominat to any other hypotheses (thus the >50%). But such a level of certainty does not exclude other potential hypotheses as being "possible" or "suspected" (i.e otherwise supported, even remotely, by the data). There cannot be two hypotheses with a level of confidence of "probable", yet there can be many that are "possible." A "conclusive" level of certainty is one in which there is only one potential conclusion that is suported by all the facts to the exclusion of all other hypotheses.

Occassionally, the term "possible" is used where the term "potential" is appropriate, because "possible" is a quantifiable or qualifiable term when used as a level of certainty. If the level of certainty is deemed "conclusive" then "all other possible (or potential) causes" automatically eliminated, by virtue of the term "conclusive."

The "conclusive" and "probable" language (I believe) appeared in sec 16.8.2 until the 1995 or 1998 edition of NFPA 921. However, the "probale" wording was reinstated (I beleive) in the 2001 ed.

However, the "elimination of all possible causes" (sic) is not a conclusion that provides any affirmative evidence or support of any other "cause" although this statement is used frequently and erroneously as a pseudo-scientific measure of support by those relying on a negative corpus methodology. The only "evidence" the statement "I eliminated all other causes" provides is that the potential "fire causes" (more specifically, ignition sources) that were considered and examined, were eliminated and thus, they are not the "fire cause." (Furthermore, any ignition sources which were not considered, known or examined cannot be eliminated.)

Denny Smith