Significant Changes to NFPA 921 Guide Future Fire and Explosion Investigations

Root Cause Analysis: Electrical Fires & Explosions​ [EECS]

September 1, 2020

Updates to the industry standard document reflect the complex interactions between a fire & the damage it leaves behind

The new 2021 edition of NFPA 921, the Guide for Fire and Explosion Investigations, was released to the public on August 21, 2020. NFPA 921 is the industry standard reference guide, renewed by consensus approximately every four years. The most recent edition contains some significant edits and updates related to fire patterns, arc mapping, and fire classification.

Chapter 6, Fire Effects and Fire Patterns, was completely rewritten. The concept of fire effects was elevated and defined as "observable or measurable changes" to materials. There are four identified fire effect categories — discoloration, deformation, deposition, and mass loss — and each fire effect within them includes a description of related limitations. For example, one of the limitations for mass loss is that the investigator should correctly identify what mass existed before the fire while analyzing the fire damage.

Arc mapping is now categorized as a fire pattern, and there have been a number of changes to the text to reflect that change. Arc mapping has been removed as one of the four sources of information available for origin determination and absorbed into the fire patterns category. There have also been additions to the text on the probabilistic nature of arcing, added emphasis on the importance of a complete arc map, and renewed cautions that arc sites are not necessarily located at the area of origin.

The chapter on fire classification has been removed from the document. Previously, this chapter provided guidance on classifying a fire as natural, accidental, incendiary, or undetermined. Classification of a fire is different than determining origin and cause. The scope of NFPA 921 specifically excludes the National Fire Incident Reporting System (NFIRS), and reportedly, the removal of classification was intended to reflect that exclusion. Suggestions for alternative classification systems, if needed, are discussed in Chapter 19, Origin Determination.

How Exponent Can Help

Exponent engineers are well versed in the scientific investigation techniques used in fire and explosion investigations. The changes to NFPA 921 reflect the industry's evolving understanding of the relationships between observable fire damage, ventilation, and fire origin. Exponent's engineers excel in applying the fundamentals of fire science, fire dynamics, and electrical system evaluation to scientifically analyze and determine a fire's origin and cause. Exponent's multidisciplinary teams are well positioned to help clients understand the complex interactions between a fire and the damage it leaves behind.