What happens when a seemingly closed case comes to life again after more than a year, but the main evidence turns up missing?

When it comes to forensic engineering, sometimes it's not enough to have sophisticated knowledge of fire and electricity. Today, forensic engineers must not only know their discipline inside and out, but should also become careful custodians of the evidence involved in their cases. Why? Critical evidence disappears more often than you think. And many times, such "spoliation," or the loss or damage of evidence, can cost you a case. In this case, it did!

After a fire caused considerable damage to a rental house and its contents, the argument began. Which of the two insurance firms involved in this "Cause and Origin Determination" case would pay for repairs: the owner's or the tenant's?

With a knee-jerk declaration, two fire investigators (one private, the other a municipal employee) determined the cause of the fire was extensive electrical arcing inside the front comer of the attached garage at the electrical service panel and adjacent subpanel.

As indicated by the burn patterns, the investigators placed the fire's origin at the opposite side wall, beneath a kitchen subpanel about 20 ft away. As a result, they held the landlord (owner) responsible for the damages. In response, the landlord's insurance company hired an independent forensic engineering company, who retained this author to determine if the building's electrical system could have caused the fire.

Once at the site, I found the scene still slushy from the water used to extinguish the fire several days before. Since the fire destroyed most of the structure's wooden shingles, sunlight streamed through the partial skeleton of the sagging roof frame that remained, providing adequate light for investigation. But to accurately interpret and record the scene, I brought a powerful search light, camera kit with flash and lenses, micro recorder, and note pad.

After some observation, I noticed the debris in the charred garage contained mechanics tools, oil cans, extension cords, furniture, clothing, washing machines, a hot water heater, coiled strings of lights used for seasonal holidays, and a stepdown transformer for low-voltage landscape lighting. Eliminating the obvious, I determined neither the Christmas tree inside the house nor the temporary lights strung under the outside eaves were factors.

I continued to dismiss possible causes and planned to find the root cause by process of elimination. In making my electrical analysis of the property, I carefully separated items belonging to the tenant (extension cords, appliances) and those belonging to the owner (panels, conduit, romex, fixtures). I "drew the line" at the interface where the plugs meet the outlets. During this process, I logged all discoveries, making sure not to damage any objects or disturb them for other investigators.

Keeping my senses open to anything unusual, I noticed two identical flex conduits over the hottest part of the fire: but only one was burned through. Closer inspection revealed the aluminum flex conduit had melted, but the steel one hadn't. No cause here; just another dead end.

Near the service entrance, the evidence indicated an air conditioning contractor had installed a 4-circuit subpanel without benefit of permit and inspection. Bonded only through a flex conduit, the subpanel's unprotected No. 6 feeders tapped into the service panel ahead of the main fuses. One of these conductors within the subpanel had briefly arced to the side of the box. The resulting short-circuit current overheated the flex, which melted the wire's insulation. This initiated a chain of arcing events that spread through the service panel, ending at the service drop that eventually arced through and fell off.

This report should have been easy. You can imagine the typical headline: "Improper Electrical Installation Fails and Causes Fire." But as an electrical contractor and engineer, I've never believed electrical systems were that fickle. I had a problem accepting the arc beads here were able to start the fire across the room instead of beneath these panels, (as would be expected with this massive amount of unbridled arcing).

I eliminated the extension cords, coiled light strings, and appliances as possible culprits because they were either not plugged in, or there was no arcing or signs of overcurrent. However, I found arcing on the wires at the low-voltage landscape lighting transformer. Since it had been in a fire, this was not unusual.

The question was: "Did the arcing cause the fire, or did the fire cause the arcing?" Since I deemed the low-voltage transformer to be the tenant's plug-in appliance, I collected it as a possible exhibit, storing it in the evidence locker of the engineering company that hired me.

I continued to inspect every inch of the building's electrical system. I climbed on counters and poked my head into torn Sheetrock looking at all aspects of the wiring; photographing everything as I went. Where conductor insulation was missing or burned, I checked the full length of the wire for indications of overcurrent. If absent, I looked for ways that electricity could have entered and exited in mid run. If no electrical cause surfaced, I stated in my notes that the burned wire was a result of the blaze, rather than the source of it.

After including the status of the circuit breakers and fuses, I determined each arc in the system had been caused by the one before-mindful that the one farthest from the source should occur first. I easily identified the initial arc in the A/C subpanel (clearly caused when high external heat from the fire across the room had melted the wire's insulation). Therefore, I reported the building's wiring system was not the cause of the fire. This implied the tenant was responsible for the damage. Though I was unable to determine the cause, I could confidently eliminate the building's wiring system. My investigation was finished...so I thought.

About a year later, the landlord's insurance company contacted me to refute the report of another expert, who stated the building's electrical system was responsible for the fire. I was not surprised, since it's a popular belief that electric arcing always causes fires.

I smugly objected to the other expert's opinion, referring to the low-voltage transformer's condition, and offered to do an "Auger" (pronounced Oh Zhay) analysis on all the arcs to determine if they occurred before or after the fire.

I immediately turned to the evidence for proof. But much to my dismay, the evidence (both the transformer and the arced conductors that were part of the A/C subpanel feeder) was gone. Although I had given "my" evidence to the forensic engineering company (my client) for safe keeping, they had contacted the insurance company for authorization to discard it and received permission. But no one bothered to consult me.

By carelessly discarding this evidence, the landlord's insurance company ended up paying for the house repairs and replacement of the tenant's contents. This is a perfect example of how an avoidable situation undermined a good defense.

To protect yourself from legal action resulting from spoliation and other oversights, it's a good idea for experts to obtain Errors and Omissions Insurance. Remember: No matter how strong your case, without the evidence it's impossible to support a finding.