Abstract: At approximately 3:10 p.m. on June 17, 2011, Employee #1, an Electrical Transit Mechanic and Assistant Supervisor with the San Francisco Municipal Transportation Authority, was at the Presidio Maintenance Shop repairing a door's tie rod end assembly unit. The tie rod end assembly unit was 8.25 in. long and had a 3-in.-long bolt welded on its end. He used a pneumatic sander (Ingersoll Rand, Model Number 317, rated speed 18,000 rpm, rated pressure 90 psi) equipped with a Type 1, 6 in. abrasive wheel (rated speed 11,000 rpm) to cut the welded bolt as he held it in his hand. When the abrasive wheel fractured, a large piece lodged in Employee #1's left forearm. He was hospitalized for three days and underwent surgery. The causes of the accident were lack of a guard on the machine and the rated speed of the sander exceeding that of the abrasive wheel. A contributing factor was failure to secure the rod to a work bench.