Determining the origin and cause of a fire requires adherence to the scientific process as well as the painstaking collection and analysis of evidence. Details that point to the possibility of arson introduce a criminal and emotional element to the investigation that may seem daunting, but keeping a cool head and following the scientific method allows you to draw an unbiased, evidence-based conclusion.

Remember that confirmation bias can derail an investigation. Just because you may suspect that the fire was deliberately or maliciously set, it's important to engage a certified, experienced fire investigator to complete an inspection and determine the cause of the fire. The National Fire Protection Association (NFPA) 921 provides guidance for the methodology used to conduct an unbiased investigation. This document requires the seven steps of the scientific method to be used to determine the origin and cause of all fires.

• Recognize the need: A fire has occurred and the origin is unknown.
• Define the problem: Determine the origin of the fire or explosion.
• Collect the data: Gather the basic site data; determine the pre-fire and post-fire conditions; evacuate, examine and reconstruct the scene; collect witness statements; obtain fire department information, alarm, detector and security data.
• Analyze the data: Complete a fire pattern analysis, identify ventilation-generated patterns, conduct a flame and vector analysis, finish an origin matrix analysis, complete depth of char and calcination surveys, finalize arc mapping, complete event sequencing, consider fire dynamics, and study building construction and occupancy.
• Develop hypotheses: Formulate an initial origin hypothesis, determine a working origin hypothesis and consider alternative hypotheses.
• Test the hypotheses: Determine whether there is a competent ignition source in the area of origin, whether the origin explains the data collected, whether all contradictions are resolved and whether an alternative origin explains the data equally well.
• Select final hypothesis: Determine the area of origin and the point of origin, or that there is insufficient information to determine the origin.

The NFPA defines arson as an incendiary fire "intentionally ignited in an area under circumstances where and when there should not be a fire." Because arson is a crime, adherence to the scientific process is of the utmost importance to your investigation. Make sure you engage a reputable and fully licensed fire investigator to ensure that your investigation is completed professionally and conclusively.