An employee was in an aerial lift installing sheeting on top of the roof and sidewall of a building. An excavator working below the lift struck the aerial lift boom causing the boom to bounce up and down and side to side. The employee was ejected from the aerial lift basket and landed on the roof of the building. He then slid down into a roof gutter. The total height of the fall was 12 feet. The employee was hospitalized for broken ribs and a ruptured spleen.