At a paper recycling plant, waste paper was cooked to a watery oatmeal consistency and processed with pressure and heat to produce paper products. One product, paperboard, was wound onto large 4,000 lb rolls. Forklifts with hydraulic clamp arms attached to a hydraulic rotator moved the rolls. Rolls picked up from the horizontal spindles of the paper mill could be turned 90 degrees and set on end for storage.
Scene of the Crime
On this day, a worker was putting a shipping label on a roll of paperboard as another forklift brought over another roll. Without warning, the roll — fresh from the mill with its axis still horizontal — slipped from the clamp attachment and rolled forward toward the dockworker. He never saw the roll that fatally crushed him.
The Investigation An attorney representing the deceased’s family described this tragic turn of events and retained me to determine the cause. At the mill, the subject forklift was sequestered in the mill’s maintenance shop. Due to a planned move to new facilities, the mill was quiet. It appeared to be a fairly run-down place with piles of debris about, and with a fleet of some of the most decrepit forklifts I had ever seen. Witness statements and depositions indicated this mill had a reputation for poor maintenance and repair, and a history of continuing labor/plant disputes. A hired, local technician assisted with mechanical work needed for clamp tests.
With some difficulty, our mechanic got the balky forklift going. I drove the ragged-looking machine and operated all the hydraulic controls. The clamp appeared to open, close and rotate correctly. I suspected insufficient clamp force may have caused the roll to drop, and requested connecting a gauge to pressure taps on the attachment.
There was no paper roll to test the clamp, but the mechanic blocked the arms to let us pressurize the clamp cylinders. I observed pressure readings while the mechanic operated the attachment, turned the rotator and operated the lift and tilt functions. Clamp cylinder pressure remained solidly at manufacturer’s specs. Other than the forklift driver, a longtime careful operator, mistakenly releasing the roll, what could have caused the paper roll to release
Guided by the manufacturer’s parts and repair manuals, I continued with an inspection of the clamp and its component parts. There appeared to be a misalignment of the pivoted clamp pads. These two pads, located at the edge of one clamp arm, permitted grasping paper rolls of various sizes. Pairs of ears welded on the back of each pad straddled a single ear welded to the inside of the clamp arm, with each group of ears held by a retaining pin in double shear.
I also found that both pads had been misaligned axially so each pivot pin was no longer in double shear, but stressed with an overhung load. On one pad, one bent pin remained and one was missing. The other pad had both pins missing with the pad retained by a leaf spring tensioner. Without both pads fully working, it became obvious how the weakened clamp force could let the paper roll drop. While not present at the inspection, the clamp manufacturer’s attorney refused us permission to remove the remaining pin for metallurgical analysis. I completed the inspection and departed.
The Smoking Gun
While awaiting results of further discovery and perhaps an OK to remove the remaining bent pin for tests, I began calculations to determine the loss of clamp force given the paper roll size, and attachment linkage dimensions and pressure. More depositions revealed some eye-opening information. Maintenance workers said when pivot pins wore or broke, they were quickly replaced with shop-brewed pins made of low carbon steel rather than wait for relatively expensive alloy-steel pins from the clamp manufacturer. They simply “popped in the pins,” without attention to correct pad alignment. Had they used the proper alloy pin, its correct length would likely have signaled improper pad alignment. The fatal failure in this case now appeared to be a combination of improper component material and dimensions, and improper installation, all by careless maintenance workers. I asked my client to alert the plant management to check all clamp-equipped lift trucks, and to remove any misaligned soft pins and replace them with proper alloy pins. He told me this was now a moot issue as the plant had gone into bankruptcy and all equipment had been scrapped or sold.