What happens when you can't give your client an answer?

60-year-old San Francisco high-rise; a mysterious fire in its 10th floor penthouse; and no answers. Our forensic engineering firm recently tried to solve this mystery, after the main parties concerned with liability assessment asked us to determine the cause and origin of the fire.

Both the building's boiler/machinery insurance company and fire insurance company received claims. Of course, each hoped the other would have complete liability. More optimistically, each hoped it could pass financial loss onto the elevator manufacturer, elevator maintenance contractor, building management company, or possibly the roofer.

Our job was to help them make a decision, but there was one big problem: The findings were inconclusive. Could we still help the clients and bill for our services with a clear conscience?

The details. A private fire investigation company made the initial inspection. As often happens with electrical equipment, this firm called us to help determine the cause and origin of the accident. Upon inspection, we found a dated relay controller, which served the motor, generator, indicators, and controls for one elevator of a bank of three interconnected elevators, destroyed.

Before beginning our analysis, we tried to get a feel for the scope of the needed repair work as well as assess the financial "exposure" of the insurance companies. The management company needed all three elevators running. However, a new replacement relay rack wasn't available, and a used one would be difficult, if not impossible, to find. A new rack of updated design would be difficult to integrate into the old system. More importantly, it might trigger a municipal requirement to update the entire elevator system to current fire and safety codes.

One alternative was to update and replace all three racks. However, this solution would be difficult, considering we would have to maintain at least two of the elevators. Otherwise, we thought the building tenants might insist on reimbursement for lost time while using the stairs during the lengthy repair and retrofit.

Next, we began a detailed visual inspection of the burned relays and wires. As always, we asked ourselves: What had changed? Then, we questioned: Was there anything unexpected or unusual? Could a capacitor have exploded, a coil or resistor overheated, or a wire become overloaded to the point of ignition of its insulation?

Existing site conditions. The building and its equipment penthouse were made of reinforced concrete with a recently repaired flat tar and membrane roof. A large multi-paned skylight with cracked wired glass and a deteriorated galvanized steel frame rested over the three relay racks. Beginning at an edge of the skylight and above the burned rack, a rust colored water track meandered across the rough gray concrete, ending at a stalactite deposit. Water had obviously been dripping here.

The old rack had scores of open frame relays on one side and hundreds of feet of interconnecting wires on the other, all fastened to horizontal insulating bases. Distributed through an array of fuses (fed from a common bus) was the rack's 240V control power. The fuse and wire sizes varied because some fed only relays or indicator lights while others fed large contactors for the elevator motors. Impregnated woven fabric insulation covered the old wire.

Within the last 10 years, someone added a sizable array of LED status indicator lights. Their tiny, thermoplastic-insulated wires reached throughout the old intertwined harness. These newer wires weren't separately fused, perhaps because they only carried the minuscule LED current. If they were protected at all, it was by the 15A to 30A fuses previously mentioned.

As we conducted our on-site investigation, we heard staccato clacking that accompanied the incessant relay operation of the two unburned racks. These relays occasionally spit sparks of molten metal to the machine room floor as they operated.

The burn patterns indicated the fire was limited to the relay rack, which appeared completely burned from bottom to top. The burning within the rack was fairly uniform. No single component appeared to have failed, although many had severe fire damage.

Questions and more questions. We eventually realized we would have to leave the site with various possible theories but no definitive solution. We had many questions: Did a component failure within the rack cause the fire, or did external causes burn the rack? Did the sparks from the relays ignite oily rags on the floor? Was the roof leak involved in the fire? Could water cause the fire? Used to extinguish fires and limited to only 212 degrees F, how could water start a fire? What about the small retrofit wires? Was the water leak from a poorly repaired roof membrane or the broken skylight? Could leakage current through deteriorated backboard insulation start the fire? Finally, could one of the over-fused red LED wires have ignited from excessive leakage current induced by contaminated water that had saturated the rack?

Our conclusion: no conclusion. At the fire insurance carrier and boiler/machinery carrier meeting, we stated we could not determine the cause of this fire. To do so, we'd have to disassemble and microscopically inspect the rack components and hundreds of feet of wire, hoping to find an arc or discoloration. But, the probability of a positive result would be very low for such an expensive procedure.

Since the cause was unknown, there was also no point in quibbling over who might be responsible for the leak. Likewise, oily rags and an unkempt environment weren't enough to implicate the building owner or manager. Also, we weren't able to identify who designed and installed the LED indicators with their small wires. Based on this, the fire seemed solely to be the liability of the fire and boiler/machinery insurance carriers.

The agreement. An elevator repair company supplied a fixed bid for complete Code-compliant repairs. Both insurers had some exposure. Rather than increase their losses by fighting each other, they agreed to a 50-50 split over a handshake. In this case, forensic engineering contributed to the peaceful settlement of a complicated claim.