Machine Design

Toys Aid Accident Investigation

A farmer seriously injured his foot, leg, and ankle when he was thrown from a hay rack. His father had been towing the rack behind a tractor and baler while his son stacked bales onto the hay rack.

When they finished, they pulled onto country roads to deliver the hay to a barn a few miles away. The father was still driving the tractor and the son was sitting on a bale in the middle of the rack.

At a four-way stop, the father slowed and made a sharp right-hand turn. Bales of hay bounced out of the rack on both sides, and the son was thrown from the vehicle to the right.

The injured man sued his father and his father’s insurance company for his injuries and damages. The court case hinged on whether the man had been doing something that caused his fall, independent of his father’s actions while driving.

Two witnesses said the hay rack’s right wheels hit one of Minnesota’s famous springtime potholes about 30 ft from the intersection. The right-hand wheels then ran onto a 25-ft-long, 6-in.-high curb that led to the intersection before bouncing off the curb with enough force to throw hay bales and the son from the hay rack.

The insurance company’s expert witness had a doctorate in physics and was a professor at a local university. His careful mathematical analysis indicated the son could not have been thrown off the hay rack by the same force that threw bales of hay in all directions. If he had been sitting as still as a bale of hay, the centrifugal force of the vehicle taking the turn would have thrown him off the left side of the hay wagon, not the right.

Therefore, the professor concluded, the man must have been doing something that caused him to fall off the right side of the rack, independent of the vehicle’s path.

I was an expert witness for the plaintiff. I often use models of machines when evaluating safety during hazard analyses and when presenting cases to juries in court. However, in this case, I used toys to prove to myself and the court how the accident happened.

All of the farm implements in the case were at least 30-years old. Using the Internet, I found a manufacturer that makes toy versions of each piece of equipment involved in this accident, including bales of hay, at 1:48 scale.

Thanks to the accuracy of the models and an understanding wife, I recreated the accident scene on my dining-room table. After playing with the scaled-down accident scene for a while, I was able to reproduce the accident as it was described by the witnesses.

Despite the fact that I was, in fact, using toys to prove my analysis of the accident, when I showed my findings to insurance-company representatives, the case settled quickly. This is just the latest example I’ve seen that pure mathematical analysis is no substitute for physically recreating an accident scenario.

Lanny Berke

Lanny Berke is a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at [email protected].

Edited by Jessica Shapiro

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