Abstract: Approximately 2 1/2 hours before sunset, Employee #1, a fully trained tree trimmer, and two coworkers were in a suburban area trimming tree limbs near power distribution lines. Employee #1, the crew foreman, was working from a Holan aerial articulating work basket that was mounted on a truck. He had supervised and assisted in positioning the trimmer truck so that the outriggers on the right side were set on bare macadam and the ones on the left side were set on a grassy shoulder. The left outriggers were on a wooden block that was only 2 1/2 in. larger on all sides than the outrigger plate. After about 10 minutes, the outrigger pad slipped off the wooden block and the outrigger sank into the soft earth. The truck overturned onto its aerial boom, breaking the overhead power lines and pinning Employee #1 to the ground beneath the work bucket. He sustained injuries that required hospitalization. The employer provides all personal protective equipment required for its work assignments.