Vytenis Babrauskas, Ph.D
Arc mapping was first introduced in the 2001 edition of NFPA 921 and was subsequently expanded so that in the recent editions it constitutes one of the four main methods for determining the origin of a fire. Careful consideration of engineering principles and large-scale experimental studies on the subject indicates that the relevance and prominence of arc mapping as a leading indicator of fire origin is greatly overstated. The technique is valid and applicable only in some very limited scenarios. Yet it has seen very extensive use in recent years by investigators preparing fire reports. In many cases, such attempted use of arc mapping is based on incorrect and invalid hypotheses, which are often implicitly assumed to be true instead of being explicitly stated. The following are myths: (i) An abundance of arc beads at a given locale means that fire originated in that area, while a paucity of arc beads indicates that it did not. (ii) When multiple arcs are present on a circuit, the direction of arcing will necessarily proceed upstream towards the power source. (iii) If an appliance is the victim of a fire, internal arcing will be primarily near the exterior of the unit, while arcing deep inside indicates a fire origin at that place. NFPA is urged to revise NFPA 921 to eliminate arc mapping as one of the four main methods for establishing fire origin, and to subsume it under the more general category of “fire patterns.” In addition, it is important that NFPA 921 reduce the implied general utility of the method and provide more explicit information on its interpretation and its limitations and on the circumstances under which it may be a valid method for assisting in the determination of the fire origin.
Vytenis Babrauskas, Ph.D.
Short circuits to building wiring can happen due to electrical mishaps, or as a result of fire impinging on the wiring. In either case, this may cause arcing. It is sometimes erroneously assumed that this must produce signs of ‘electrical activity,’ which is a term often used by fire investigators to mean discernable arc marks or arc beads. While such artifacts may indeed be produced, it is shown that it does not necessarily happen in every case. Shorting and arcing (whether due to fire or due to an accident) may occur without leaving physical evidence that is discernable as an arc bead. Ejecta also may, but do not have to be produced. Some variables have been identified which can influence the size of arc beads, when arc beads are produced. But stochastic aspects dominate, and no predictive correlations can be expected. It is also shown that there are no prediction methods available to establish if an arc locale will result in severing or welding together of conductors.
From Out of the Abyss...
This week’s article from the past is titled Incendiary Fires Can Be Spotted and was written by Benjamin Horton, CPCU, who was President of the National Adjuster Traing School in Louisville, Kentucky.. It is taken from the Decembe 1968 Vol. XVI No.5 issue.
Incendiary Fires Can Be Spotted
In the new issue of NFPA Journal®, President Jim Shannon said the Association will focus on the leading causes of home fires, including cooking. "We also need to continue to push hard for home fire sprinklers. That's still a large priority for NFPA, and we plan to work very aggressively in 2014 on our residential sprinkler initiative," he said.
From: The Desk of Scotty Baker
To: The CCAI Training Committee
Over the last several training seminars, even as an old hand, I have learned new information concerning fires and how they do what they do.
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The focus will be on Report Writing, Arc Mapping and Ignition Sources, Social Media as an Investigative tool, Fundamentals and more.
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When testifying in court as to the manner in which we conducted an interview, defense counsel will often ask us whether we just wanted his client to "confess." We answer that we do not seek confessions but rather truth. After all, no good cop is interested in false information, only truthful information. That is why our motto at Third Degree Communications is "Nothing but the Truth."
One little tidbit we impart on our students to help convey this concept is by reminding them that if obtaining the truth is their ultimate goal, then they should be doing nothing that might prevent them from obtaining the truth. For example, getting angry with a subject who is lying would most likely sever rapport and interfere with accomplishing the goal of obtaining the truth. Raising my voice, insulting him, or speaking to him in a condescending manner are all most likely going to be rapport killers that will stymie my ability to get to a successful and truthful outcome with the subject. If we want to get people to provide us with truthful information, we should avoid doing anything that will interfere with accomplishing this goal.
This actually applies to many areas of our lives if we think about it. Let's say I've made a new year's resolution to avoid gossiping about other people. There are several steps I can and should consider that will help me accomplish this goal, including but not limited to:
In the same manner, if my goal is to obtain truthful information, I must only engage in behavior that's more likely to help me accomplish this goal and to avoid behavior that will interfere:
Getting people to tell the truth means creating an environment that is conducive to helping them cooperate. Obtaining our goal means everything that I say and do is oriented toward achieving that goal. It's a remarkably simple concept, but a critical one to remember throughout the interview.
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