NFPA 921, Guide for Fire and Explosion Investigations, outlines the scientific methods used to develop fact-based conclusions about the origin, cause, responsibility, and prevention of fires, as well as the potential for damage and injury. The Organization of Scientific Area Committees (OSAC)—a group of more than 600 forensic science experts—endorses NFPA 921 as the consensus standard for fire investigation practices.

The 2024 edition introduces expanded guidance on forming investigative opinions, addressing confirmation bias, and expressing levels of certainty. Notable updates include the relocation of content related to fire effects on electrical systems and components to Chapter 6. Additionally, it covers how suppression efforts can impact fire ventilation and flow paths in areas far from the point of origin.