scope:

Description of Driving Event:

An onsite maintenance and operations contractor was tasked to erect scaffolding inside of a wind tunnel test section so that a heavy gas door seal could be replaced. The test section floor is level until it opens into the tunnel where the floor slopes downward. The portion of tunnel that slopes down from the test section is called the contraction wall. One end of the scaffold had to be placed on the down slope. In order to secure the scaffold, three pads were welded onto the test section floor which had a pivoting vertical tube attached to it. The vertical scaffold legs were slid into the tubes. Safety straps were attached to the test section floor because an outrigger section, which extended out over the contraction wall, was installed on the main scaffold.

After the completion of work, the onsite maintenance and operations contractor began to take down the scaffold. Four workers were tasked to disassemble the scaffold. Due to the uniqueness of the scaffolding arrangement, the workers were told to wait for their supervisor to coordinate the effort. The workers took it upon themselves to disassemble the scaffold. During the disassembly, with the outrigger section still in place, the safety straps were removed. Two employees were on the scaffold when the straps were removed. As they continued to disassemble the scaffolding, the center of gravity shifted over the outrigger. This caused the scaffolding to topple over since the straps had been removed. Both employees rode the scaffolding to the bottom of the contraction wall. One employee sustained no injuries. The second employee told his co-workers to call 911. He was taken to a local hospital and released with minor injuries.

All employees involved had received training on the assembling and disassembling of scaffolding. The crew lead was one of the employees working on the scaffolding. Under normal conditions, the crew lead would supervise the work, but the crew supervisor told the crew lead to not begin disassembly until he was present to supervise the work. The crew lead ignored this request and began disassembly. Because the crew lead was actively involved in the take down, he did not see his error in removing the straps. He only saw the straps as being in his way of removing scaffolding pieces.