Inspection Detail

Inspection: 508219.015 - Harrison Hoist, Inc.

Inspection Information - Office: Dallas Area Office

Investigation Summary

At 3:20 p.m. on July 7, 2012, Employees #1 and #2 were standing in the proximity of the top tower section and awaiting on the Terex Peiner, (Model SK 415) Tower Crane to hoist the rigging needed to lower the top section to the ground. The mast stood eleven tower sections high or approximately 220 feet high with the top section connected to a climbing adapter section. Each tower section was approximately 196- in length and weighed 9,300 lbs. Each tower section consisted of four corners and each corner consisted of two connecting points. One connecting point was located on the outside of the flange and the second one was located on the inside of the flange. Eight connecting elements (mast bolts) connected two tower sections at their connecting points such that the bottom tower section (tower section one) was anchored to the foundation by eight mast bolts and the bottom of tower section two was anchored to the top of tower section one by eight mast bolts. The sequence continued on all tower sections and climbing adapter section. Prior to the accident the jib, counterweights, and turning table/cab assembly had been removed. Prior to dismantling of the mast the employer removed mast bolts from every other tower section and placed these in their respective carriers. Some of the remaining bolts were also de-torqued. Five bolts were removed from the bottom of tower section two and placed in their respective carriers. Two bolts were removed from the NE corner and two bolts were removed from the SE corner leaving the east section of the mast at the bottom of tower section two unsupported. Prior to the accident a weather system began to move into the area. Immediately prior to the accident wind gusts of approximately 36 mph came into contact with the mast, At 3:20 p.m., wind gusts of approximately 36 mph came into contact with the mast causing the mast to hinge west between tower sections one and two. As the mast continued to lean west its center of gravity shifting beyond its tipping point causing the upper eleven sections of the mast to fall and collapse. The top section of tower section three collapsed on a concrete wall. The upper tower sections continued their descending trajectory collapsing on a steel structure anchored to the roof; killing both employees. The adapter unit collapsed on a concrete wall to the west of the steel structure. Both employees sustained blunt force injuries and were killed.

Keywords: Collapse, Crane, Crane Counterweight, Hoist, Rigging, Structural Collapse, Tower