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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Members and Friends
As you all are aware, we at CCAI want you to be informed. Therefore, I will relate to you an incident that happened in Irvine, CA.
A young school teacher was living in an upscale three story apartment complex on the second floor. The apartment had one bathroom, one bedroom, a living room, and a kitchen area off the living room. The ceiling above the kitchen was at 7 feet while the rest of the apartment was standard height of 8 feet. The apartment has fire sprinklers and one sprinkler is located above the kitchen counter and would reflect water onto the range and counter top if activated.
For some reason the school teacher was burning a Citronella candle on the counter top adjacent to the sink. The candle she purchased was in a small metal bucket with a hoop handle; the candle was not confined in glass. The teacher was washing dishes in the sink when her cat jumped onto the counter top and knocked over the bucket containing the candle. She reacted and reached for the toppled candle with both hands. In one hand she had a glass that she was washing, which contained an amount of water. Some of the water went into the bucket with the candle. A flame came out of the bucket and caused the sprinkler to activate. The water from the sprinkler also got into the bucket and there was an explosion. This entire event happened in a matter of seconds.
The thought of a candle exploding was a mystery to me and investigator partner, Harry Hatch. We checked several stores trying to purchase the same type of candle the school teacher had described, but no luck. We wanted to see just what the candle would do and also prove or disprove the event.
After looking up Citronella candle fires on the net, we were very surprised to learn that yes, if you add water to a burning Citronella candle it will flare up and sometimes cause an explosion. We all learn something all the time. Be informed and go to yahoo, type in Citronella candle fires and have a look at the videos; you may be as surprised as we were.
Do not be afraid to write us with your hints or new investigation experiences. CCAI is in the business to keep you up to date and informed.
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