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The Case of the Tippy Hippie
Myron J. Boyajian, President, Engineering Consultants -- Design News, September 12, 2004
An attorney representing a do-it-yourself building materials store called and told me that a customer was injured in an accident at a home improvement center. The attorney said the plaintiff, a "reformed hippie," was renovating his "crib." A load of paneling had fallen onto him, and he was suing to recover medical and other expenses. I was retained to investigate the plaintiff's claims and reconstruct the accident.
The plaintiff and his dad had loaded up a flat-bottomed cart with paint and other materials. They then obtained another type of cart to transport paneling and furring strips. This cart had tubular frame members to make up side "pockets" for holding paneling and like materials on the edges of the far-left and far-right sides of the cart. The center pocket had cross bars about waist high for loading smaller, long pieces, such as furring strips or two by fours.
They had placed furring strips in the center pocket and all the panels with the long sides horizontal in one side pocket. The paneling was sufficient to fill the slot, and the plaintiff said he leaned the panels toward the outside rails. In leaning one panel against the other, the innermost panels were raised somewhat from the outermost panels with their bottom edges resting against the inside vertical members of the side pocket.
Investigations at the scene
At the store, I measured the paneling, the subject cart and the accident location at the front of the store. The store's corporate counsel sent cart weight, cart platform height, width and length, and caster wheel locations. I made a scale drawing of the cart and its load to determine the location of the combined center of gravity, and drew a plan view of the accident site that included exit door opening, side walk width, distance to the street surface, and slope.
With this information, I could mentally step into my "way-back" and reconstruct the plaintiff's movements leading to the accident. Using records, testimony, and measurements, I constructed the following scenario: The shoppers pushed the loaded carts to the cashier station, and the father paid for the goods. Telling his son to wait, he went to bring his pickup truck to the store-front loading area. Upon seeing his father heading toward the entrance, the plaintiff proceeded to push the cart with paneling out the door to meet him. The gentle slope of the sidewalk combined with a brisk push on the cart gave it a good forward velocity. The plaintiff walked along the side of the cart, grasping the paneling to accelerate and steer the cart.
Just then, another car left the loading area close to the exit, and the plaintiff's father quickly pulled up and stopped short in the spot. The plaintiff quickly swung the loaded cart in the direction of the truck, pulling on the rear portion of the paneling in the process. The cart began to turn, then tipped and turned over, knocking the plaintiff down and spilling the paneling out, where it came to rest on his legs. He suffered a severe knee injury that required a joint replacement.
High C.G. is the culprit
Using scale drawings and measurements of the cart, sidewalk, street, and pickup truck location, I estimated the turn radius needed to swing the cart tightly towards the pickup truck. I determined that even at walking speeds of one to two mph when turning, the lateral force at the raised C.G. location was sufficient to overturn the cart. Using the load identified in this matter, I modeled different radii and forward speeds while staying within the dimensional limits of the accident site. Within these limits, I determined that the cart would always overturn.
I alerted the attorney that this was a weak defense case. Even taking into account the plaintiff's seriously offset loading method, this appeared to me to be a reasonably foreseeable misuse of the cart. Without disclosing the terms, the attorney later told me that the store had settled the suit out of court. The company subsequently made a design change to the carts that accommodates panels only in the center slots.
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A hippie doesn't have a "crib." He has a...
Don Marti - 2008-29-9 05:32:43 EDT
