NFPA 921 Guide For Fire and Explosion Investigations, 2001 Edition
By A. Elwood Willey, CFI
Engineers, investigators, and other professionals who have been using the 1998 edition of
NFPA 921 Guide for Fire and Explosion Investigations will need to check out the new
2001 edition which has been extensively revised. If you are involved in fire
reconstruction activities, it is strongly recommended that you become familiar with the
latest edition. Be assured that NFPA 921 will be used in the cross-examination of
The membership of the National Fire Protection Association (NFPA) approved the
current 2001 edition of NFPA 921 Guide for Fire and Explosion Investigations at the
November 2000 Fall Conference. This is the fourth edition of the document developed
by the Technical Committee on Fire Investigations over the past decade. The evolution
of NFPA 921 has brought the application of fire science to the field of fire investigation
and analysis, and it has provided national consensus guidelines for fire investigators in
the public and private sectors. It contains important new chapters and key revisions to
existing sections published in the 1998 edition. The following discussion presents an
overview of the 2001 edition, including highlights of principal changes.
The 2001 document was expanded to 229 pages from the 197-page 1998 edition, and it
now has 25 chapters, compared to 20 chapters in the previous edition. The 2001 edition
has been reorganized into three general areas. Basic information such as methodology,
fire science or fire pattern recognition appear in Chapters 1 through 11; the details of
conducting an investigation are arranged in Chapters12 through 16; and specialized
topics such as explosion analysis or incendiary fires are found in Chapters 17 through 25.
A cross-reference of chapters is included at the end of this paper.
What is NFPA 921?
NFPA 921 is a guide for the methodology of conducting fire and explosion
investigations; it does not contain mandatory requirements which must be followed by
investigators. Under the Regulations Governing Committee Projects, the NFPA defines a
Guide as: “A document that is advisory or informative in nature and that contains only
nonmandatory provisions. A Guide may contain mandatory statements such as when a
guide can be used, but the document as a whole is not suitable for adoption into law.”
In Section 1.2, NFPA 921 states that, “The purpose of this document is to establish
guidelines and recommendations for the safe and systematic investigation or analysis of
fire and explosion incidents.... This document has been developed as a model for the
advancement and practice of fire and explosion investigation, fire science, technology,
and methodology.” NFPA 921 further states, “As every fire and explosion is in some
way different and unique from any other, this document is not designed to encompass all
of the necessary components of a complete investigation or analysis of any one case. Not
every portion of this document may be applicable to every fire or explosion incident. It
is up to investigators (depending on their responsibility, as well as the purpose and scope
of their investigation) to apply the appropriate recommended procedures in this guide to a
particular incident.” The document is applicable to both fire and explosion incidents. It
is also applicable to fire scene examinations and the fire analysis phase of investigations
after the fire scene is no longer available.
As with any document developed through a consensus process by a technical committee,
NFPA 921 is not perfect. For example, the 1998 edition contained errors in certain
electrical and fire-growth-related formulas, and errata were published by the NFPA.
Also some technical issues are hotly debated and may be subject to close ballot votes and
negative comments. Some topics contained in NFPA 921 may not be universally
accepted by all investigators and may be subject to technical challenge. However, the
document has become an important reference and tool among other fire engineering and
investigative literature and practices to support the reliable determination of fire origin
and cause for fire investigators and fire analysts.
The Scientific Method. In revised sections of Chapter 2, Basic Methodology, the
Committee has reaffirmed that the scientific method is applicable to the field of fire
investigation as a systematic approach in developing and proving origin and cause
hypotheses. Chapter 2 provides guidance on the step-by-step process of the scientific
method from defining the problem through the testing and selection of a hypothesis. An
investigator does not need to be a fire scientist; however, NFPA 921 does provide a
recommended, systematic method for selecting, testing and accepting, or discarding
possible fire origin and cause determinations. Further, when testing a hypothesis, an
investigator does not necessarily need to utilize scientific tests to arrive at a conclusion.
A hypothesis may be supported by reason based on experience. Specifically, Section
2.3.6 states that in the testing of a hypothesis by deductive reasoning, “The testing of the
hypothesis may be either cognitive or experimental.”
Process of (Fire Cause) Elimination. Related new text in Section 16.2.5, Process of
Elimination, recognizes that in a certain fire scene with a well-defined area of origin
(after determining the area of origin first), it may be possible to make a fire cause
determination without having physical evidence of that cause. An example could be the
selection of an open flame as the heat of ignition even if the evidence of an open flame
device is not found. However, for the conclusion to be credible, the analysis should
follow the scientific method steps covered in Chapter 2 to eliminate other causes.
Section 16.2.5 also states that the elimination of all accidental causes to arrive at a
conclusion that a fire was incendiary may be justified in limited situations where there is
a defined area of origin and other possible ignition sources can be examined and
eliminated. Such a determination becomes more difficult if there has been heavy fire
damage to the area or room of interest.
Spoliation of Evidence. Another debated topic in the investigative and forensic
community has been a concern for spoliation of evidence at the scene or later during
activities such as equipment examinations. The 2001 edition of NFPA 921 defines
spoliation in Section 9.3.6 as, “Spoliation of evidence refers to the loss, destruction or
material alteration of an object or document, that is evidence or potential evidence in a
legal proceeding by one who has the responsibility for its preservation.” It also states
that spoliation of evidence may occur when movement of evidence or alteration of the
scene significantly impairs the ability of other interested parties to obtain evidentiary
value of evidence compared to the initial investigator.
NFPA 921 provides guidance for investigators to help understand the issues and avoid
• Investigations should be conducted in ways that minimize the loss or
destruction of evidence.
• Before a scene is altered, the scene should be photographed and documented
and relevant evidence preserved.
• The responsibility to notify other parties may vary among public and private
• The photographing and documentation of key evidence relevant to an
investigator’s opinion and evidence of alternative hypotheses that are
considered and ruled out as well.
• Given the nature of fire scene examination work, which requires the
movement of evidence or alteration of the scene, such scene examination
activity should not be considered spoliation.
• It also may be necessary to remove items of evidence from the scene to
protect it from further damage. Such activity to protect evidence should not
be considered spoliation.
Section 9.3.6 also references several relevant ASTM forensic standards addressing the
collection, preservation, and examination of evidence. Chapter 14, Physical Evidence
provides specific guidance on methods of evidence collection, identification,
transportation and testing of evidence.
Chapter 6, Electricity and Fire has a few useful revisions, particularly section 18.104.22.168,
Melting by Fire and Section 6.11.1, Melting Caused by Electrical Arcing. New
companion photographs are included illustrating arcing through charred insulation and
damage resulting from fire melting of conductors.
There are five new chapters in the 2001 edition of NFPA 921. The following is a
summary of some of the highlights:
Chapter 5, Building Systems provides a primer on building construction and
related terminology and how building design and construction have positive and negative
impact on fire development and spread. It also covers special types of construction such
as manufactured housing.
Chapter 8, Fire-related Human Behavior. This chapter describes how and why
individuals and groups respond to fire cues and take actions such as fire fighting, giving
the alarm or escaping. This material is based on the work of researchers such as Dr. John
L. Bryan of the University of Maryland. A section also includes material on actions of
people related to the cause of accidental fires such as improper maintenance,
housekeeping or failure to follow warning labels or safety instructions. A section on child
fire play and juvenile fire setting is also included.
Chapter 17, Failure Analysis and Analytical Tools. Chapter 17 includes a
variety of analysis tools which can assist an investigator in developing and testing fire
origin and cause conclusions. Event time lines are described, which can help to organize
incident information and events into chronological order to support the analysis using
actual (“hard time”) or estimated time (“soft time”). Systems analysis techniques using
fault trees and other methods are covered. General information on the application of
mathematical fire models and the various types of models is included and the limitations
of fire models as well.
Chapter 20, Fire and Explosion Deaths and Injuries. This new chapter
addresses fire scene documentation considerations when fire deaths and injuries are
involved; pathological and toxicological examination of victims; and the mechanisms of
death, such as carbon monoxide inhalation, hypothermia (exposure to heat), or hypoxia
(exposure to oxygen deficient environments). A section is included which discusses fire
and explosion injuries including degrees of burn, body area distribution, the mechanism
of burn injury by hot gases or flames, and the mechanism of inhalation injuries.
Chapter 22, Motor Vehicle Fires was extensively re-written. It includes more
comprehensive text on fuel, mechanical and electrical systems; and covers the
examination of fire patterns in modern vehicles.
Chapter 23, Wildfire Investigations is a new chapter which covers the fire
development and spread factors in wild land fires and origin and fire cause aspects
unique to wildfire investigations.
The Next Revision Cycle
Engineers who have ideas for changes to NFPA 921 are encouraged to participate in the
revision process. The next NFPA 921 revision cycle will begin in 2002 culminating in a
revised document in 2004.
1. Freestone, A., Tools of the Trade, the New NFPA 921, NFPA Journal, July/August
2. Hewitt, T-D, On the Hot Seat, NFPA Journal, January/February 2000.
2. NFPA 921 Chapter Renumbering chart, PDF format, Fire Findings,
4. Pavlisin, M and Horan, S, Are Origin-and -Cause Investigators “Fire Scientists,” Fire
Engineering, June 1999.
5. Regulations Governing Committee Projects, NFPA Directory, 2001.
NFPA 921 Chapter Reorganization
Chapter 2001 Edition 1998 Edition
Administration 1 1
Basic Methodology 2 2
Basic Fire Science 3 3
Fire Patterns 4 4
Building Systems * 5 --
Electricity and Fire 6 14
Building Fuel Gas Systems 7 19
Fire-Related Human Behavior * 8 --
Legal Considerations 9 5
Safety 10 10
Sources of Information 11 7
Planning the Investigation 12 6
Recording the Scene 13 8
Physical Evidence 14 9
Origin Determination 15 11
Cause Determination 16 12
Failure Analysis & Analytical Tools * 17 --
Explosions 18 13
Incendiary Fires 19 17
Fire and Explosion Deaths & Injuries * 20 --
Appliances 21 18
Motor Vehicle Fires 22 15
Wildfire Investigations * 23 --
Management of Major Investigations 24 16
Referenced Publications 25 20
Key: * New Chapter