During the final stages of rigging-up operations, a offshore platform rig collapsed, resulting in 3 fatalities and 13 injuries. The rig, which consisted of an upper, intermediate, and lower substructure, was aligned transversely to the platform’s skidding beams and supported by shimming, support, and false capping beams. The supporting beams did not extend to the end of the lower and intermediate substructures. As the upper substructure was skidded to within a foot of its targeted position in preparation for the derrick positioning and raising, the underlying substructures tilted and slid to the side to which the skidding was directed. As a result of that movement, the upper substructure and other rig components fell into the water. Three employees died, and 13 employees were injured.