An employee was standing on the landing of a set of portable stairs washing out filter cake build-up from the raised bed of a dump truck. A clump of the filter cake broke free and slid down the bed of the truck onto the concrete floor. The force of the filter cake struck the base of the stairs, causing the base to move and the stairs to topple over. The employee fell 10 to 12 feet from the stair landing to the ground, sustaining an open fracture to his elbow and multiple rib fractures.