The session addresses the significant changes that have occurred in the 2021 NFPA 921 Guide for Fire and Explosion Investigations. Major changes associated with the use of the scientific method and negative corpus will also be discussed. The class will address best practices and application of the guide to actual scene investigations. Changes to NFPA 1033, the Standard for Professional Qualifications for Fire Investigator, will also be addressed, plus an explanation of the job performance requirements and requisite knowledge as they relate to the professional qualifications of fire investigators.