NFPA 921: Guide for Fire and Explosion Investigations provides a scientifically grounded framework for conducting fire and explosion investigations. Investigators use this guide to develop fact-based conclusions about fire origin, cause, responsibility, prevention, and resulting damage or injuries. The Organization of Scientific Area Committees (OSAC) recognizes NFPA 921 as the forensic science consensus guide for fire investigations. More than 600 forensic science professionals contributed their expertise to this standard.

The 2024 edition introduces updated guidance to address emerging investigative challenges and modern best practices. It expands discussion on confirmation bias, investigative opinions, and expressions of certainty. The edition also explains how suppression activities affect ventilation and fire flow paths away from the area of origin.

Additional updates include the reorganization of electrical system fire effects into Chapter 6 and the introduction of four general fire cause classifications for investigators and authorities having jurisdiction (AHJs). NFPA 921 strengthens guidance on investigator safety, health, and wellness. It also expands coverage of fires involving hybrid and electric vehicles. A fully revised chapter on wildfire investigations adds new terminology and identifies unique fire indicators.