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 Interviewing, Report Writing and Fundamentals
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The Central Valley Arson Investigators association continued the tradition of providing outstanding training at their annual Advanced Explosive Recognition class. The training was held once again at the Tulare International Agri-Center grounds. This year’s topic was the history of the American criminal bombings. Guest speaker Ed Nordskog, LA Sheriff’s Department, lead the class through the history of American bombings, from the earliest bombings in America right up to the most current-day events.
While in the classroom, we were given a taste of what was to come in the afternoon on the range, a few large booms came from the range-site, and this, of course, sparked the interest of the attendees filling the room with anticipation for the afternoon’s activities. I’m not really sure if that was part of the scheduled shots, or if Frank just couldn’t wait to try out his handy work.
Thanks to Geary Baxter and his crew, everyone was treated to a hot dog lunch with all the fixings, chips, chili, and drinks. Shade covered bleachers were provided to keep the sun off the students during the demonstrations. The range was arranged with several props from mail boxes (fairly close to the bleachers), to two transit buses and an ambulance several hundred feet down range. And, of course, there was a pressure cooker, which was placed down range, so that we could see the effects of a device similar to the one used in Boston.
The students were given the count down, so they could get their cameras ready to capture the moment, “Fire in the hole, three, two, one”! Our very own Scotty Baker, the voice of the AER range, would call out when each prop was ready to be set off. This year had more than its fair share of silence when the charge was supposed to go off. After making our first run down range to get a closer look (and see the handy work of the Sheriff’s bomb team), it was clear what had happened, the fragmentation from the first explosions took out the six-pair lead-in wire. By the way, the trip down range was in a people mover provided by CVAI; these guys think of everything.
The class was attended by nearly one hundred and fifty students from police, fire, and evidence people from all over the state. There was even a fellow from New York City in the class (and I thought it was a long drive from San Diego). There was great representation from the CCAI elected officials; President Scotty Baker, First Vice-president Tom Peirce, Second Vice-president Eric Emmanuele, Director Dale Feb, and myself Director Troy Morrison.
Thanks to all the folks at Central Valley Arson Investigators for all their hard work!! Another great training class. We are all looking forward for what is in store for next year when the theme for the AER class will be “First Responders”.
Troy Morrison, PIO CCAI
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