The Case of the Sinful Sole

DN Staff

June 23, 2008

4 Min Read
The Case of the Sinful Sole

Sometimes an accident or equipment breakdown appears to have been caused by some combination of equipment design and improper usage, but when seen from a different perspective, a totally different cause is found.

The Scene of the Crime

The forklift manufacturer I worked for brought to market a second generation of a popular 2,000 lb-capacity electric forklift. It had an efficient, smooth control, using silicon transistors to replace the prior system with its sensitive germanium devices. Reports of erratic operation of the new model filtered in and I was assigned to help find the cause. Users said the truck would operate erratically or shut down, but more critically, sometimes accelerate at full speed.

The Investigation

Engineering and our service reps isolated the problem to intermittent connections as one cause and moisture getting into multipin connectors as another. About this time, I was transferred from test engineering to the design engineering department and continued to help out. After some digging, I found a source of secure, moisture-proof connectors, put them into redesigned wire harnesses and then into production.

With the new connectors in place the problems seemed to fade away until I was assigned to assist a defense attorney in a case where a product defect was alleged to have caused a forklift/pedestrian accident. At a beer canning plant, a forklift driver dropped off a load of empty cans and as he backed out, he hit a pedestrian with such force that the shape of the pedestrian's body was pressed into a pallet load of empty cans leaving a bizarre, reversed Pompeii-like image. The pedestrian filed suit against my employer alleging negligent design and manufacturing.

Our department assisted by answering interrogatories regarding design and manufacturing details and our chief design engineer testified in a deposition, as well. Before the trial was called, I inspected the forklift. I expected to find the forklift was built prior to the connector and wire harness change and that ever-present moisture in the canning plant triggered the brief runaway.

Not so, as this machine was built to the latest specs and functioned faultlessly. I concluded the driver may have over-estimated the distance to the pedestrian, may have backed up without looking at all or hit the accelerator instead of the brake. In any event, OSHA rules for safe driving prohibit driving toward a pedestrian standing in front of a fixed object. Convinced of correct forklift functioning, improper driving behavior became the focus of our defense effort.

The Smoking Gun

I attended the trial sitting at the defense attorney's table. The plaintiff's attorney called each of his witnesses, but I had to take a deep breath when the forklift driver appeared to testify about his role in the accident. As this fellow stood to walk to the witness's chair, he didn't stop growing upward! Expecting to be released to go back to work after giving testimony, he was neatly dressed in a clean work uniform and safety shoes. Safety shoes! The nickname for large shoes, "gunboats," must have come from his clogs. Seeing this big guy and his giant shoes gave me an insight to the accident's cause that none of us had considered at all.

At day's end at the lawyer's office, I told him of my suspicion that the accident was initiated by the driver getting his right foot trapped between the brake pedal and the accelerator because of the truck's compact design. The driver, I thought, just seemed too big for the operator's compartment. With my new perspective, I called our engineering staff to ask if they had used Humanform standards when they laid down the truck design. They answered in the affirmative, but I had the sense that the driver's sheer physical size exceeded the standards used by our designers. The attorney considered all these factors and reached a settlement with the plaintiff.

Back at our plant, I could see the closeness of the brake and accelerator almost formed a trap for the thick and wide soles of the driver's extra-large safety shoes. I never experienced any problem operating the brake, but then my shoes are not so large. I suggested we move the brake pedal to the driver's left to open up a larger gap between the brake and accelerator. This change was made effective on all forklifts in production and in the field. This model continued to be an excellent seller through its long history with no reports of brake/accelerator problems.

Author Information

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.

Sign up for the Design News Daily newsletter.

You May Also Like