Codes, Standards, and the Scientific Method (NFPA 921 / NFPA 1033)
The scientific method and standards
NFPA 921, Guide for Fire and Explosion Investigations, is a guide describing the scientific method: identify the problem, collect data, analyze the data, develop hypotheses, test the hypotheses against the data, and select the final hypothesis. NFPA 1033 sets professional qualifications for fire investigators, including education, training, and continuing education. Both are foundational, but the investigator must demonstrate a reliable methodology rather than merely citing a document number. Hypotheses must be tested; eliminating alternatives is part of testing, but a conclusion cannot rest solely on eliminating accidents (the negative corpus).
Application and review
Peer review, documentation, and reproducibility matter. NFPA 921 expects the investigator to be able to explain the reasoning behind every conclusion. Testimony frequently uses the "reasonable degree of professional certainty" formulation. The guide covers origin, cause, fire patterns, explosions, electricity, and building systems; know the subject matter of the chapters, not page numbers.
TRAP: Treating NFPA 921 as a legally binding standard, or assuming NFPA 1033 dictates investigative conclusions rather than qualifications.
RULE OF THUMB: If your report says "incendiary because everything else was ruled out," it conflicts with NFPA 921. If you can list the data, the hypotheses, and the tests applied, you are on solid ground.