Pre-Conference Seminar: NFPA 921 Overview
|2008 WORLD SAFETY CONFERENCE & EXPOSITION PREVIEW
The new edition of NFPA 921, Guide for Fire and Explosion Investigations, will help fire investigators develop investigative hypotheses that use their own knowledge, training, and experience to the greatest advantage.
NFPA Journal®, May/June 2008
By Dennis W. Smith
The 2008 edition of NFPA 921, Guide for Fire and Explosion Investigations, is the sixth edition of the guide since 1992. Designed for use by fire investigators in the public sector and by private-sector investigators looking into fires for insurance or litigation purposes, the 2008 edition includes rewrites of Chapter 5, "Basic Fire Science;" Chapter 6, "Fire Patterns;" Chapter 17, "Origin Determination;" Chapter 25, "Motor Vehicle Fires;" and Chapter 27, "Management of Complex Investigations."
There is also a new Chapter 28, "Marine Fire Investigations," and new and revised text has been added to Chapter 4, "Basic Methodology;" Chapter 12, "Safety;" and Section 18.2, "Process of Elimination."
The discussion in Chapter 4 clarifies Section 4.3.4, Analyzing the Data; Section 4.3.5, Developing a Hypothesis—Inductive Reasoning; and Section 4.3.6, Testing the Hypothesis—Deductive Reasoning.
Section 4.3.6 advises investigators that they must depend on their "knowledge, training, experience, and expertise" to develop a hypothesis. But the guide also makes an important distinction: The criteria for developing hypotheses are insufficient for testing them deductively. Section 4.3.6 reminds the investigator to think critically so that his or her hypothesis can withstand "careful and serious challenge." The chapter also reminds investigators that they can test a hypothesis either by conducting experiments or relying on the research of others in similar circumstances. When relying on experiments or the research of others, the conditions should be sufficiently similar, and references to the research should be noted.
Chapter 5, "Basic Fire Science," will now include more detailed information, examples, tables, and charts on topics such as the fire tetrahedron, phase changes and thermal decomposition, products of combustion, fluid flows, and heat transfer. New detailed information about the thermal structure of a flame, smoldering ignition and initiation of solid fuel phase, flame spread, fire spread in a compartment, and compartment fire development has also been added.
Chapter 6 was revised and reorganized to include a discussion of how to recognize fire patterns and the fire effects that create those patterns. Some sections that involved techniques for analyzing fire patterns, such as measuring the depth of char and measuring calcination, were relocated to Chapter 17, "Origin Determination."
Changes to Chapter 17
The more noteworthy changes in the 2008 edition of NFPA 921 will be found in Chapter 17, "Origin Determination," which was revised to align the search for, and identification of, the fire origin with the scientific method described in Chapter 4. The investigator is advised to consider his or her origin determination a hypothesis and to test that hypothesis accordingly. Figure 17.2 even provides a hypothetical flow chart, using the steps discussed in applying the scientific method from Figure 4.3.
Chapter 17 still recommends an initial scene assessment, previously called a "preliminary assessment," to obtain an overall look at the fire scene to determine the scope of the investigation. However, it no longer specifically recommends that the search for the origin be conducted from the area of least damage to the area of greatest damage. Instead, it recommends that the investigator
establish an order of the examination so that all areas are assessed. In fact, the new text specifically warns the investigator not to "assume that the fire at the origin burned the longest and therefore fire patterns showing the greatest damage must be at the origin." The chapter explains that greater damage can result from "differences in fuel loading, the location of fuel packages in the compartment, [and] increased ventilation or firefighting tactics," as well as the fuel heat release rate, something investigators who rely strictly on the greatest damage often fail to consider.
The chapter also asks investigators to consider not only the fire patterns they observe, but also the sequence in which the patterns were created. As Section 17.2.3 states, "the key to determining the origin of a fire is to determine the sequence in which these patterns were produced." This discussion is more focused than the "fire spread scenario" discussion in previous editions.
Chapter 17 also coordinates the techniques investigators can use to help determine fire origin in Section 17.4.2, Heat and Flame Vector Analysis; Section 17.4.3, Depth of Char Analysis; Section 17.4.4, Depth of Calcination Survey; and the much-expanded information on the use of arc surveys or arc mapping in Section 17.4.5. The chapter concludes by reintroducing and applying the techniques and steps of the scientific method to determine fire origin.
Additional explanatory text added to Section 18.2, Process of Elimination, is intended to further explain the appropriate and inappropriate conditions and circumstances in which an ignition source can be inferred where no physical evidence of ignition source exists. New text in Section 18.2.1 delineates the conditions of a "clearly defined origin" as being "known conclusively, to the exclusion of all other potential origins."
Chapter 27, "Management of Complex Investigators," was also revised and updated. Important additions include Section 27.3.1, Notice to Interested Parties, and Section 27.4.5, Developing Protocols, which were absent from previous editions.
Finally, Chapter 28, "Marine Fire Investigations," has been added. Like Chapter 25, "Motor Vehicles," and Chapter 26, "Wildland Fires," this chapter has loss-specific definitions of terms used in the text and in the field.
Dennis W. Smith
is a senior fire expert with Kodiak Enterprises, Inc. of Ft. Wayne, Indiana. He is a member of the NFPA Technical Committee for Fire Investigations and of the NFPA Technical Committee for Fire Investigator Professional Qualifications.