Sherlock Challenge: Was It Faulty Design or Improper Repairs?

Poor hose locations cause leaks of flammable fluids, resulting in devastating fire at a local mill.

By Myron J. Boyajian, Contributing Writer

At a paper recycling mill, cardboard and other waste paper was shredded and turned into a mulch to be mixed with water, de-inked, bleached, and turned into cardboard and other types of paper. A skid-steer loader moved the piles of incoming waste to shredding machines. The loader’s four-wheel drive and nearly zero turn radius let it get into tight corners to scoop up waste paper. The loader ran with fast, short, choppy movements needed to maintain the throughput at this busy recycling plant where trucks dropped off waste along two open sides of the building.

One winter night, as a worker ran past the open-sided building, the sight of flames coming from the loader stopped him in his tracks. He frantically waved the loader to a halt. The driver stopped, saw the flames, and baled out.

Soon, the waste paper all around the loader began burning, its flames spreading to the building itself. The local fire department responded quickly, but there was still significant damage to the building, with heat great enough to warp steel beams and trusses.

Initial opinions from the fire marshal pointed to paper accumulations on the hot engine of the loader or on its exhaust components. An attorney for the insurance company that covered the fire loss retained me to inspect the loader to see if, indeed, the cause was accumulated paper, or if there were other causes. The loader was now at the shop of the dealer that sold and serviced it.

Each squad of consultants involved in the investigation took turns digging into the remains. Sheet metal parts on the loader were warped and light alloy components melted, looking like bizarre metal lava flows and metallic icicles. The coolers above the engine compartment were damaged, with the plastic cooling fan now just a charred hub, while the light alloy hydraulic fan motor was another metallic icicle.

Because the loader used a number of hoses to convey pressurized fluids, I began to look at what was left of the hoses. Starting at the frame sides and working inward, I examined each hose and its connection point and support clamp. The cab/ROPS had been raised and safely blocked up, so I donned my HAZMAT suit and proceeded to climb into the loader.

I was able to get close to the remains, but as I did, drops of engine lube oil hit me on the side of my face and my right hand. I looked around and traced the source to hoses going into a cabin heater unit at the top left side of the cab. The fire consumed the hoses leading to it, so I tried to determine the way the hoses were laid in by the clamp locations. It seemed to me that these hoses were not located as shown in the shop manual.

After being initially puzzled by the presence of lube oil in the cabin heater, I remembered this model loader circulated lube oil in the engine cooling jacket to avoid coolant freeze-up. The fittings on the engine block that were to feed the burned away heater hoses should have pointed to the side of the engine compartment to route the heater hoses away from engine components. Instead, the two fittings were angled straight up resulting in the hoses being routed across the engine to the heater. Hoses so routed would be exposed to high temperatures from the engine’s turbocharger. Any drip or leak would result in a fire, as the turbo hot side can be as hot as 1,000F, well above the 446F flash point of lube oil. I thought this might be the cause, but I still was not certain.

Later, I pored over service records and found that several hoses, including the heater hoses, had been replaced due to abrasions and leaks. My opinion report cited the likelihood that leaking lube or hydraulic oil was ignited by the hot turbocharger, and that the cooling air pathway made it unlikely that paper accumulated near places hot enough for ignition. However, I was unable to learn if the loader’s hose locations were placed in early production and then relocated to more protected areas in later production units, as shown in the manual.

Myron J. Boyajian, P.E., ([email protected]) is president of Engineering Consultants, a consulting service for forensic and design activities. Cases presented here are from his actual files.