ARC MAPPING - FINDING THE FORENSIC NEEDLE IN A HAYSTACK

A few weeks ago I was called in to investigate a fire that broke out in a barn. I arrived on site in the early hours of the morning. The fire department had arrived a few hours earlier still, but the area was still smoldering and the smell of burning hung heavy in the air. With no witnesses to interview and no time to waste, I immediately began scanning the area for fire patterns.

FIRE PATTERNS 

Fires leave patterns on walls, ceilings, and on contents, like furniture. Analyzing those patterns can help narrow down the origin, and therefore the cause, of a fire. For example, patterns that indicate the greatest amount of burning may indicate where the fire burned the longest, and therefore where it started.

The fire department had reached their own conclusion as to the origin and cause of the fire – a riding lawnmower in the middle of the fire damaged area. Judging by the patterns, which indicated intense burning, I agreed that the riding lawnmower was a possible origin. But fire patterns are only one aspect of fire investigation. We also have to take into account fire dynamics.

In a nutshell, fire dynamics is the physics and chemistry of fire initiation and growth and the interaction between the fire and the building’s systems. We have to consider factors like ventilation: Open doors and windows let oxygen in, which assists in the combustion of the fire, causing it to burn more intensely. In this case, combustibles on the lawnmower, including the seat, fuel, and oils likely fed the fire, resulting in more severe damage in that area.

Proceeding under the assumption that those fire patterns were the result of fuel load, and not the origin, I had to develop a new hypothesis. I noticed another area that showed distinct burn patterns. It was in a different location than the lawnmower, and at first glance it was difficult to explain. However, an exposed electrical cable in the ceiling showed evidence of arcing.

ARC MAPPING 

When a fire attacks energized wiring, it causes the insulation protecting that wiring to burn and char. The charred insulation forms a semi-conductive path, which allows current to flow through the charred insulation between the conductors in that cable. This heats up the conductors and the charred insulation until sufficient current flows, eventually resulting in arcing. When arcing occurs, it can be seen as a flash of light and sparks coming from the conductors. As investigators we don’t typically see arcing as it happens, we see the after effects: Small divots and beads of copper on the wires. Sometimes the wires sever from the arcing.

I began my investigation at the electrical panel, which confirmed what I had suspected – a circuit breaker had tripped (arcing eventually results in a short circuit fault that trips the circuit protection). Tracing that circuit, I found only one area that displayed physical evidence of arcing. Below the arced cable was an electrical receptacle on the wall behind a fuel tank, where fire patterns indicated fire had spread from. Closer examination of the receptacle showed that the cable not only powered the receptacle on the wall, but also continued outside to an irrigation pump.

Arcing can only happen when a cable is energized. Once a circuit protector trips, arcing ceases. As the fire spreads, it consumes more wiring insulation, but there won’t be any other evidence of arcing left anywhere else on those wires. This is critical in assisting in the determination of the origin of the fire. It means that arcing will typically take place close to where the fire had first attacked those wires, indicating the origin, or the direction of fire spread when arcing on several circuits is documented.

Upon re-examining the fire damage in context with the arcing, I developed a new hypothesis (which was later validated): The fire started at the receptacle, due to a poor connection, before spreading above to the ceiling where the arcing took place. As the fire grew and spread, hot gasses from the fire radiated down, igniting the combustibles on the rider lawnmower, which served as further fuel. Based on the arc mapping, the fire patterns and fire dynamics, I was able to conclude that the cause of the fire was an electrical failure at that receptacle due to an improperly made electrical connection to the irrigation pump outside.

THE SCIENTIFIC METHOD 

In the past 25 years, fire investigation has evolved from an art-based field into a science-based discipline. We rely on our knowledge and experience, technology, and methodology to determine the origin and the cause of a fire.

Every fire involves the same four components: Fuel, oxidizing agent (oxygen), heat, and an uninhibited chemical chain reaction. But apart from that commonality, every fire investigation is different, and at every scene, the potential causes of a fire are numerous. It can be very easy to make a mistake, and declare the wrong cause if the origin of the fire isn’t first correctly identified – or if it isn’t defined well enough. This can result in missed opportunities for subrogation, or it could lead to insurers pursuing the wrong party altogether. In either case, time is wasted and money is lost. We scrutinize every detail, and use every tool at our disposal to make sure we get it right. 

While investigating a fire and trying to determine the point of origin, we’re constantly developing and testing hypotheses. Sometimes, like in the barn, something doesn’t quite fit, and you have to go back and reconsider how all the information fits together. Fortunately, even when the damage is extensive, by utilizing all four sources of information for origin determination – witness information, fire patterns, fire dynamics, and arc mapping – we can still arrive at the correct point of origin and determine the cause of a fire.

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About the Author:

Vladimir Chlistovsky, B.A.Sc., CFEI, CVFI, P. Eng.

With more than 25 years of professional experience, Vladimir’s career has encompassed a number of industries and roles: Insurance appraiser of commercial and industrial machinery, equipment and buildings; quality, production and design engineer; and forensic engineer. Vladimir has completed over 600 forensic cases, investigating fires and explosions, product failures, and other types of losses. Vladimir graduated with an Industrial Engineering degree from the University of Toronto. He is an Internationally Certified Fire and Explosions Investigator, and serves as a board member and National President of the Canadian Association of Fire Investigators (CAFI).  Vladimir also assists the Standard Council of Canada (SCC) as a designated expert in their Certifying Body (CB) and Laboratory Accreditation programs.