What can be used as evidence of fire effects?

The identification of visible or measurable changes as evidence of fire effects is critical in fire investigations. These changes directly relate to the physical and chemical transformations that occur during a fire event, providing tangible indicators of its intensity, duration, and behavior. For example, the charring of wood, discoloration of surfaces, or the melting of certain materials can reveal important information about the fire's heat flux and exposure levels.

When investigators analyze these changes, they can draw conclusions about the fire’s progression, the location of the origin, and how the fire spread throughout the structure. This evidence is essential not only for understanding the incident but also for determining the cause and evaluating possible fire hazards. Understanding these fire effects is a fundamental component of the fire investigation process as outlined in NFPA 921 guidelines.

The other options, while relevant in certain contexts, do not directly correlate to the evidence of fire effects in the same way. Structure size may be a factor in understanding the overall scene, firefighter actions may indicate response strategies rather than fire dynamics, and building materials can affect fire behavior but are not, in themselves, evidence of fire effects. Visible or measurable changes provide the most direct and interpretable evidence of the impact that fire has had on a structure or environment.