NFPA Journal - May/June 2020 - 73

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Investigators at the site of a home fire in
Somerville, Massachusetts, in 2017.

"undetermined" because the investigator could not determine the intent of
the homeowner.
This confusion, along with concern
on the part of people who were completing NFIRS reports that someone could
use NFPA 921 to challenge their classifications, caused a disproportionate
number of fire incidents to be classified
as "undetermined," reducing the overall
accuracy of fire statistics. This concern
was brought to the attention of the
committee by various fire marshals'
organizations prior to the issuance
of the 2017 edition. A task group was
appointed to look at the problem, and a
new section was added to Chapter 1 to
indicate that the completion of NFIRS
reports was not covered by this guide-
those reports should be considered
incident reports rather than investigative reports. With this change in the
2017 edition, a public input was made
for the 2021 edition to delete the fire
cause classification chapter, since classification relates to NFIRS reports and is
thus outside the scope of this guide.
This proposal was supported by the
observation that the classifications

listed in NFPA 921 and those listed
in NFIRS were different. It was also
pointed out that attempting to apply
the scientific method to fire cause
classification was problematic. As
part of an ongoing effort to move the
document to a more scientifically
sound footing, the committee made
the decision to delete the fire cause
classification chapter. The committee
also added a short paragraph to the
end of the fire cause chapter to direct
investigators in need of guidance on
the classification of fire cause to the
appropriate standards.
Fire patterns
Another significant change was the
reorganizing and editing of the chapter on fire patterns. For example, the
topic of arc mapping was moved into
the fire patterns chapter from the
origin determination chapter. Arc
mapping is a process by which a fire
investigator evaluates the electrical
circuits within a fire-damaged location. The investigator then examines
the circuits looking for locations of
electrical activity (arcing). These

locations are then mapped to identify
clusters. The concept is that there will
be indications of electrical activity
where the fire first breaches the wiring
insulation of energized conductors,
likely providing information for determining the fire origin area. As the fire
progresses, electrical activity will not
be visible due to the circuit protection
device (breaker or fuse) activating and
de-energizing the electrical circuit.
The relationship between arc mapping
and origin determination meant that
arc mapping was originally placed in
the origin chapter.
There were numerous public inputs
and comments relating to this subject,
however. The task group working on
the patterns chapter ultimately recommended that the full discussion
concerning arc mapping be moved to
the patterns chapter, because the electrical activity was an effect of the fire
that created a pattern of arcing. The
committee decided to keep all of the
arc mapping discussion together in the
fire patterns chapter.
-Randy Watson, chair,
NFPA 921 committee
N F PA . O R G / J O U R N A L * NFPA JOURNAL

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NFPA Journal - May/June 2020

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