The Scientific Method

Step 1: Recognize the need

  • Realize there is a problem that needs to be solved


Step 2: Define the problem

  • May include determining the origin and cause of the fire, responsibility of the incident, whether an appliance contributed to a fire cause, or determining the circumstances surrounding the death of a victim.

  • Includes defining the manner in which the problem will be solved, such as the steps to be taken and tasks to be performed


Step 3: Collect the Data

  • Systematic evaluation of the scene

  • Physical evidence (fire patterns, fuel loads, ventilation, building construction

  • Collecting materials such as debris samples for laboratory analysis

  • Witness statements, security cameras

  • Documenting the scene through photographs, sketches, and notes

  • Official reports (such as Police and Fire reports)

  • Results of prior scene investigations

  • Weather reports, property records, and pre-fire photos


Step 4: Analyze the Data

  • Examine evidence objectively to evaluate meaning

  • Based on the expertise, knowledge, experience, and training

  • Use only data that is known to be true (empirical data)


Step 5: Develop Hypotheses

  • Inductive reasoning

  • Based on empirical data

  • Develop hypotheses to explain the events of the incident

  • Represents potential solutions to the problem identified in Step 2

  • Develop all hypotheses that might be supported by the data

  • If the hypothesis does not have factual data support, it should not remain in consideration (may need to gather additional data)


Step 6: Test the hypotheses

  • Deductive reasoning

  • Using knowledge, skills, and the facts of the case to analytically challenge the hypothesis

  • Cognitive testing

  • Through deductive reasoning, hypotheses are either supported, unsupported, or refuted by the complete body of evidence

  • If a hypothesis is incapable of being tested, it is an invalid hypothesis (such as a hypothesis that is developed based on the absence of data)




  • The inability to prove the hypothesis false does not mean that it is true

  • What other hypotheses could be supported by the same set of facts? (Key question to ask oneself when testing)

  • May need to seek further data if: (1) A valid hypothesis cannot be developed; (2) one or more hypotheses have been developed but are not supported withing an acceptable level of certainty; (3) multiple possible hypotheses remain that have not been falsified

  • A hypothesis that is “possible” is one that has not been falsified

  • Recommended that only hypotheses that are “probable” be expressed as expert opinions with the certainty of the legal system

  • Fire investigator is not required to eliminate all possible doubt before expressing an expert opinion

  • Probable: More likely true than not true (more than 50% likely to be true)

  • Possible: Feasible (often used when two hypotheses have the same level of certainty). At times, evidence and data may support two hypotheses, but neither can be ruled out without additional information or testing.

  • Suspected: Term not normally used in reports or conclusions. Used when then opinion does not qualify as an expert opinion.

  • Expectation bias: making premature conclusions without having examined or considered all the relevant data.

  • Confirmation bias: Relying only on the data that supports a preferred hypotheses and ignoring data that are not supportive or contrary. (Consider all theories supported by the data and attempt to disprove the hypotheses by comparing it to the evidence in an effort to show that it is not true)

  • Data should stand on their own and be tested in relation the fire or explosion scene

  • If a hypothesis cannot withstand a reasonable challenge or test, it cannot stand

  • If no hypotheses are supported, may need to return to previous steps in the scientific method (gather more data, further analysis, etc.)


Step 7: Select the Final Hypothesis

  • Occurs only after all the previous steps have been performed fully and carefully. \

  • Must be reliably and fully tested

  • Must be independently supported by the facts and evidence

  • Review the entire process to confirm all data are accounted for, and all feasible hypotheses have been ruled out

  • Negative Corpus: Identification of an ignition source that is not supported by data, based on the supposed elimination of all of the other ignition sources that were found, known, or suspected in the area of origin

  • All hypotheses must be supported by facts and data, and the logical inferences that come from them; observations; calculations; experiments; and the laws of sciences