Arc Mapping: All Too Often Overlooked and Undervalued

Arc Mapping: All Too Often Overlooked and Undervalued

Article by: Jason D’Ornellas, P.Eng.

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If you’re an insurance claims professional or lawyer representing an insurance company in a matter involving a fire loss, you’d want your fire investigation expert’s opinion to be as bullet proof as possible, right? Assuming that you yourself are not a fire investigation expert, how do you know how strong your expert’s opinion is? Often, you don’t. You trust that they have completed a thorough investigation and have collected as much data as possible and accurately analyzed this data to ensure their opinion is as strong as it could be. It’s not until an opposing expert completes a review of your expert’s report that you start to see the holes in your expert’s investigation.

NFPA 921 Guide for Fire and Explosion Investigations is widely recognized as the standard to which fire investigations are judged. The guidance it provides is based on accepted scientific principles and research. Chapter 18 of the current edition of NFPA 921 deals with Origin Determination. It states that the determination of the origin of a fire involves the consideration of information derived from Witness Information, Fire Patterns, Arc Mapping, and Fire Dynamics.

As a forensic engineer, specializing in fire and explosion investigations, clients often ask me to review reports prepared by other experts or government agencies. In discussing what led to their determination of area of origin of fires, these reports most often limit their discussions to eyewitness observations, if available, and will typically involve a description and analysis of the observed fire patterns, as recommended in Chapter 18 of NFPA 921. What these reports all too often exclude is arc mapping.

Eyewitness observations can be extremely valuable, but an investigator should always be somewhat skeptical of the information provided as eyewitnesses may have motive to mislead an investigator. They may feel that if it is found that their negligence caused a fire (careless smoking, candles left unattended, stove left on) the insurance company may not cover the loss. They may also be embarrassed or feel guilty if they know they did something careless to cause a fire. To avoid this embarrassment, they may provide less than honest accounts of what they observed to lead an investigator in the wrong direction. It is also very common for a fire to develop unnoticed, with no eyewitness observations of it during its incipient stages.

Fire patterns are the physical marks left on materials or objects caused by heat, deposition, and consumption. Fire dynamics involves the physics and chemistry of fire as they relate to fire initiation, growth, and spread. You will often read or hear about ‘V’ burn patterns, lowest level of burning, or heaviest charring when an investigator is describing the origin of a fire; however, it is common for opposing experts to disagree with the other’s interpretation and analysis of fire patterns as they relate to the origin of a fire.

This is where arc mapping comes into play. Arc mapping involves the identification of arc sites (on conductors, conduit, and grounded surfaces) within a room, appliance, vehicle, or any other compartment, detailed documentation of these arc sites; and an assessment and understanding of the electrical circuits within the area being surveyed. Figures 1a and 1b depict electrical arcing damage (from NFPA 921). The presence and absence of arcs can provide valuable information. The spatial relationship of the arc sites requires careful analysis and can help to create an objective understanding of how the fire spread to affect the various electrical circuits. Figure 2 depicts a bedroom within which a fire originated. The purple arrows show the approximate locations of various arc sites, both in the ceiling along building electrical cables, and along an appliance power cord at floor level.

Figure 1a. Electrical arcing along flexible cord
Figure 1b. Electrical arcing along solid copper wiring
Figure 2. Arc mapping of bedroom fire – purple arrows depict arc sites

If I’m reviewing another expert’s opinion and I’m not convinced that the expert’s analysis of the fire patterns is accurate, or if the eyewitness observations don’t seem reliable, I will always ask about arc mapping. In fact, even if eyewitness observations and fire patterns seem to point to a specific area of origin, I will still inquire about arc mapping. Why? When you have as much information as possible, your analysis will be as complete as possible, and your opinion will withstand scrutiny and any serious challenge.

As I previously stated, arc mapping is too often ignored by fire investigators. Why wouldn’t every fire investigator utilize this valuable tool? Well, maybe it’s that they don’t understand or appreciate the value. Maybe they aren’t confident in completing arc mapping due to a lack of understanding of electricity and electrical circuits. Maybe they can’t be bothered because it is often a tedious and time consuming task – it requires the expert to meticulously inspect every inch of every section of wiring, conduit and susceptible grounded surfaces.

If you’re an insurance or legal professional that is responsible for retaining or reviewing reports completed by a fire investigation engineer or expert, I recommend that you proactively ask your expert about the arc mapping they completed and what it says about the origin of the fire. If reviewing an expert report, confirm that it includes a section or discussion detailing the arc mapping they completed, and what this arc mapping says about the origin of the fire. If the report is without an arc mapping section or discussion, or if they tell you that arc mapping wasn’t completed or necessary, I suggest you consider using another expert.

The fire investigation experts at Roar Engineering have completed thousands of fire investigations. We know how difficult it can be to determine the cause of a fire due to its destructive nature. That is why we spend the time and make the effort to ensure we’ve collected as much information as we can, which always includes data we’ve obtained through arc mapping. The more evidence we have to support our opinions, the stronger our opinions are.

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