The answer is "no." You only classify the "fire cause" and you can only classify the cause if you have a conclusion with a "probable" level of certainty. You cannot classify a "cause" (or support any conclusion on any matter, such as the nature of burn patterns) if your hypothesis is only "possible" (or the conclusion is supported to a possibilty.) You can all the possibilities in the world, with varying degress of certainty, but until you have one hypothesis that is more likely than not, and thus, dominant to other hypotheses, the conclusion is not supported or supportable. When referring to the fire cause classification, the classification is "unkonwn." That is specifically what the sentence initially in the "undetermined" section of NFPA 921, and more recently in each of the cause classification sections is addressing when it refers to "an acceptable level of certainty." Without an acceptable level of certainty (e.g. probale) the fire cause can only be classified "undetermined."

According to NFPA 921, a fire cause has three elements that all must be identified in order for any "cause" to be classified as "accidental" "incendairy" or "natural", basically anything other than "undetermined." The heat (or ignition) source, the first fuel and the ignition sequence (the conditions or circumstances that allowed the heat source and the first fuel get together) are all elements of the "fire cause." (Many investigators still refer to the ignition source as "the cause. It's important for discussing the fire cause, as referred to in NFPA 921, that the distinction be known.) Ultimately, it is the identification of the ignition sequence that allow a fire cause to be classifed.

The terms "accidental" and "incendairy" are classifications of a "fire cause." A heat source cannot be "accidental." A fuel cannot be "accidental." (Bob, I might be misunderstanding you, but that seems like what you were asking or implying).

Now, there may be times when an investigator can identify some of the elements of the cause and still have the "cause" classified undetermined. You may be able identify the heat source, identify the first fuel but NOT know or be able to prove the igniton sequence. In such circumstances, the only apporpriate cause classification of "the cause" is "undetermined." For example, materials stored too close to a heating appliance or a grease fire on a stove might lend themselves to such circumstances. Take the grease fire on a stove.

The heat source is known (heating element), the first fuel is known (oil or grease) but the ignition source (the circumstances in which the grease was left to ignite) is unknown. If the physical evidence cannot establish whether the circumstances were deliberate or non-deliberate the "igntion sequence" is considered "unknown", and thus cannot be proven "to an acceptable level of certainty." Thus, according to NFPA 921, the cause can only be classified "undetermined."

Denny Smith