I think you have hit the point That is not coming across in the instructions found in 921. That is the fact that the proper use of the scientific method is not to prove one’s hypothesis is correct, but to prove it is not correct. Too many times I see in the investigator’s report the investigator saying that the scientific method supports his findings. Instead, he should be saying something like using the scientific method and the known data that he was unable to prove his finding were incorrect. That you have used the available know science to test your hypothesis on the subject and this testing method was unable to prove your hypothesis was incorrect. There are times where due to the limitation of the data that this testing method will leave on with multiple hypotheses that are not disproved.

Let me ask you this, is the word “undetermined” the best word to be used at the point where there are multiple hypotheses remaining that were not disproved based on the data. My problem is the history of the word in the fire investigation profession. For decades, if not longer, that word has been directly associated with the classification of the incident. To stay away from a possible misrepresentation of a classification would it not be better to use a term such as unresolved or undecided. These words have not been associated with classifications in our profession.

I think your wording is better than mine. What I have been trying to say needed to be used in the situations where one has multiple hypotheses that with the known data has not been disproven. I think what I am using is the probabilistic analysis when I am saying there is a place for the use of probabilities in a conclusion based on multiple hypotheses.

When you ask how one determines a probability in a deterministic analysis it is important to understand that determining the probability is based on a probabilistic analysis. This is different from a deterministic analysis. A deterministic analysis is one which aims to demonstrate that a facility is tolerant to identified faults/hazards that are within the “design basis”, thereby defining the limits of safe operation. Probabilistic Analysis, which aims to provide a realistic estimate of the risk presented by the facts. Probabilistic risk is the chance of something adverse occurring. This method assesses the likelihood of an event(s) and it contains the idea of uncertainty because it incorporates the concept of randomness. A deterministic methodology is a method in which the chance of occurrence of the variable involved is ignored and the method or model used is considered to follow a definite law of certainty, and not probability.

Whether one uses a deterministic or probabilistic approach often depends on the type of question to be answered and disaster risk management decision to be made.
One would use a probabilistic approach to determine the likelihood of a number of different events. One might adopt a deterministic approach to test an evacuation plan or mitigation strategy against a selected event. However, even if we are interested in knowing a specific risk scenario for a specific event, we can obtain this from a probabilistic assessment. In fact, probabilistic approaches allow us to identify and model scenarios whilst also accounting for their return period. Measuring the likelihood of events means that decision-makers are more informed and better able to select appropriate strategies for different scenarios, e.g. risk reduction in the case of extensive risks and risk transfer in the case of more high-impact (but less likely) events.
Assessing risk probabilistically remains a challenge, particularly because of the number of factors to account for and because risk is not static and is increasingly influenced by a number of other drivers, including climate change. But probabilistic risk assessments are increasingly becoming the standard for risk assessment because they are the more comprehensive approach. These assessments provide us with a means of quantifying the impact and likelihood of events, while also accounting for the associated uncertainty.

The conclusion is that there are multiple hypotheses that were not disproved using the scientific method. When evaluating the multiple hypotheses, I apply the probabilistic risk analysis. This method assesses the risk of each of the underproved hypotheses to cause the event that took place. I use historic data in this evaluation. I do not say the one I conclude to have the cause the event is an absolute but say that based on historic data compared to the others is has caused the event a greater number of times. Then I say this does not eliminate the other hypotheses as being the cause. What I am doing is giving the judge or jury additional data to assist them in reaching a conclusion. Here I have a level of certainty that is uniquely consistent with the available know data.

Hope someone is enjoying reading this information.

Jim Mazerat
Forensic Investigations Group