An employee was lying on a floor dolly on his back underneath a newly fabricated bin weighing approximately 1,000 lbs. The bin was supported on all four corners by 6-foot-long metal saw horses. The employee was painting the underside of the bin using a spray gun. When he attempted to scoot the dolly along the floor, his foot pushed against one of the saw horses, causing it to move. The saw horse pivoted out from under the bin, which then tipped and fell on the employee, breaking his arm.