Impacts -- Forklift

AB was a small, 35-year-old woman who had immigrated from Southeast Asia about twenty years earlier. For the last ten years, she had been doing maintenance work for a large metropolitan utility company.

AB had little experience in operating a forklift. On a few occasions she had driven a forklift up a ramp, but never down. On this particular day, according to AB, she was cajoled by her supervisor to drive the forklift down a ramp. The forklift carried a load of about 1600 pounds. Her supervisor had AB turn the forklift so that she would back down the ramp. According to AB, while backing down ramp, the speed of the forklift increased. She repeatedly hit the brake pedal, but could not slow down. She yelled to her supervisor, "Where's the brake? Where's the brake?" The forklift veered towards the wall and collided with it at least once. When the forklift came to a stop at the bottom of the ramp, AB was pinned between the wall and forklift.

AB was in intensive care for two months. Following her second operation, she went into a coma. When she awoke, her right arm had been amputated below the elbow, several fingers of her left hand had been lost, and most of her right foot had been removed.

A subsequent investigation found that the brakes were mechanically sound. It was proposed that AB could not locate the brake pedal, panicked, and jumped from the forklift while it was moving. AB denied this version of events. She claimed that her foot was on the brake pedal but the brake did not work, and that she was thrown from the vehicle when it hit the wall.

HF Issues: What criteria were adopted by the manufacturer with regard to the physical characteristics (e.g., body dimensions and strength characteristics) of the population of intended forklift operators?


If this profile existed, did AB fit it? If AB did not fit the profile, what was done to reduce the likelihood that such individuals would operate the forklift? How did AB end up between the forklift and the wall?

HF Investigation and Analysis: Photographs and measurements were taken of AB, of the forklift, and of AB in the seat of the forklift. A 3D computer model representing AB was generated and compared to figures constructed on the basis of anthropometric survey data (above). Literature on braking ability was reviewed with the purpose of establishing what would have been reasonable criteria for maximum brake force at the time that the forklift was designed.

A 3D computer model of the forklift on the ramp was created. Particular attention was given to the relationship between the brake pedal and the operator's foot location.

AB's ability to reach and fully depress the forklift's brake pedal while backing down the ramp was of primary significance.


In order to account for AB's rest position between the wall and forklift, I first conducted several simulations of the forklift going backwards down the slope.
The purpose of these simulations, which were created using Knowledge Revolution's Working Model, was two fold: First, to establish a range for the likely speed that the forklift was traveling when it struck the wall.

Second, to investigate changes in posture of a seated operator as the forklift moved from sloped to level pavement. (Estimates of the mass for each of the body segments of the figure representing the plaintiff were obtained using HumanCad by Biomechanics Corporation of America.)
Next, simulations of the forklift striking a wall were generated for a range of speeds and angles of impact.

In my opinion, the simulations were consistent with AB's assertion that she did not jump from the moving forklift but was "ejected" when it struck the wall. Further, it was my opinion that while the manufacturer was not obligated to design a forklift that would accommodate someone of AB's size and strength, it was necessary, if safety was a genuine concern, to alert smaller users that they were at risk of losing control of the forklift, especially when going down ramps.
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