Thomas Cocchiola, PE, CSP ::::
Case Synopsis: A woman was injured while inflating a tire on a four-wheel utility wagon. Her husband used an air compressor to inflate two tires before she volunteered to inflate the other two. Unfortunately, the rim failed catastrophically when she placed the air chuck onto the valve and began to inflate the tire. A piece of the rim struck and injured her.
Engineering Analysis: The split rim assembly included two relatively thin gage metal halves secured with five hex head bolts and nuts. As a tire is inflated, air pressure exerts forces on the interior surfaces of the two split rims. The forces are transmitted to the five bolted connections, which should hold the two pieces of the rim together. Engineering analysis and testing determined that the catastrophic rim failed because of a design deficiency; the bolted connections lacked flat washers to provide necessary load bearing surface. Testing demonstrated the failure mode for the existing split rim design and confirmed flat washers will prevent failure under anticipated conditions of service. During the analysis, it was discovered that the manufacturer of a similar cart with virtually identical rims implemented a safety recall and changed the design to include flat washers.
Result: This federal court case was resolved before trial.