A 23-year-old mechanic (the victim) was struck and fatally injured after the sudden release of a side ring from a multi-piece (split) rim. The victim was installing a multi-piece rim wheel that had been serviced by a co-worker the day before the incident. The wheel was remount pressurized, checked, and stored overnight inside a safety cage. The victim retrieved the wheel from the safety cage and began to install it on a dump truck. After the victim hand-tightened all six lug nuts on the spokes, he placed an impact wrench on one of the lug nuts. A co-worker walked over to the victim's location and was standing behind and to the victim's side. As the lug nut was tightened, the side ring of the rim released and struck the victim. Based on the findings of the investigation, to prevent similar occurrences, employers should: 1. Establish an inspection program for all (used and new) multi-piece rims to ensure proper matching of parts and serviceability; 2. Ensure workers have been trained on proper servicing of multi-piece rims, including demounting, inspection, and mounting procedures; 3. Ensure demounting/mounting procedures and rim matching charts are posted in the immediate service area per CFR 1910.177; 4. Ensure a competent person inspects all multi-piece rim parts, used and new, before placing in-service, permanently removes all parts deemed unfit for use, and inspects final rim wheel assembly before installation. In addition, Employers, distributors, and manufacturers should consider placing highly visible labels on all rim parts to prompt inspection and matching of identification stamping prior to use.