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Modern Origin and Cause Investigation

By David M. Smith, C.F.I.
Speaking of Fire, Volume 2 – Number 1, (Spring, 1995)

Until recent times, investigating a fire to determine the location of its initiation and then the reason for the initiation was accomplished by individuals who received their training from more experienced investigators.

Traditionally, an investigator’s knowledge base was the result of on-the-job training (working directly with a more experienced investigator) and classroom study through seminars taught by more experienced investigators. The experienced investigator was taught in the same manner. Therefore, if a piece of inaccurate information was ‘taught,’ it was passed from one generation to the next, each believing it to be true and a solid indicator.

While field investigators were basing conclusions and opinions on the age-old, tried-and-true fire cause indicators, the scientific community was conducting fire testing through entities such as The National Institute of Standards and Technology (formerly the United States Bureau of Standards) and similar organizations in other countries. Through actual fire testing, the scientific community found that many of the very indicators used by the field investigators were inaccurate and misleading. The results of these tests were published in government documents and scientific journals. The tests results were not known or as easily accessible to the field investigator as was traditional training. No real effort was made by either group to assist each other. Many members of the scientific community did not believe that a field investigator without an advanced degree was capable of understanding fire dynamics. Investigators were suspicious of the scientists who were conducting tests ‘in a laboratory removed from the real world.’ However, the chasm between these two areas has slowly diminished through direct communication as well as through trust and mutual respect. It is now known that many scientists are competent field investigators and that many field investigators are knowledgeable in thermal dynamics.

Through this alliance, investigators now receive training based on science rather than on tradition, resulting in a more accurate assessment of the origin and cause of a fire loss. This results in better identification of criminal activity as well as in the identification of any unsafe products and practices.


Annealing of mattress, couch and chair springs has formerly been used to indicate that a fire began in a piece of furniture as a result of a low heat source, such as a smoldering cigarette, or that the fire began on the exterior of the furniture as a result of an accelerant such as gasoline. In reality, it is now known that the collapse of furniture springs is a function of temperature over time (low temperature over a long time or high temperature over a short time) and the prefire condition of the furniture. As an example of the latter, in an auto fire, the driver-side seat is often more collapsed than is the passenger side; quite simply, the driver-side seat is used more and prestressed more often than is the opposite side.

Glass conditions, including the size of the broken pieces and the color and characteristics of the finish, were long used as indicators of fire intensity. These conditions were also used as indicators to determine what material first ignited. Clear and crazed glass or glass with a black soot was often cited as an indicator of an accelerated fire. Likewise, glass broken in large pieces with an amber finish was proclaimed as proof positive of a fire smoldering in the incipient stage. Modern information indicates that glass crazing may be interpreted more appropriately as a function of cooling. Staining of glass may be indicative of a material combusting in proximity to the glass at the time of failure and not at the time of the fire initiation.

Likewise, previously held indicators of an accelerated fire, such as spalling of concrete, holes burned through floors, pronounced alligatoring, and excessive temperatures at floor level, have all been proven incorrect or of little value in the overall origin and cause determination process.


The National Fire Protection Association Technical Committee on Fire Investigations was formed for the purpose of having ‘primary responsibility for documents relating to techniques to be used in investigating fire, and equipment and facilities designed to assist or to be used in developing or verifying data needed by fire investigators in the determination of the origin and development of hostile fires.’ Pursuant to that assignment, the committee developed the NFPA 921, Guide for Fire and Explosion Investigations (1992 edition). The document was reviewed by the NFPA membership, as well as by investigators throughout the world, with public comments resulting in several changes before the final document was released. Recently, the 1992 version has been revised, and five new chapters have been added. The new document has passed through review and will be available in February 1995. It is particularly ironic that the major criticism of NFPA 921 is that it ‘dispels too many misconceptions about fire and explosion investigation.’

The International Fire Service Training Association (IFSTA) will publish the second edition of the Fire Cause Determination manual in the near future. This document is the result of a committee action during which earlier misconceptions had been eliminated.

Many sources of valid information are present. Modern fire investigators wishing to pursue their career using both the practical and technical worlds find that information is now within easy reach. Using modern techniques will allow fire investigation to become a science rather than to remain an art.

David M. Smith is the President of the Associated Fire Consultants, Tucson, Arizona, and is a certified fire investigator with twenty-three years of experience in both the public and private sectors. He is a member of the IFSTA Fire Cause Determination committee. David is a current member of the NFPA Technical Committee on Fire Investigations and is a past president of the International Association of Arson Investigators.