Abstract: On April 17, 2009, Employee #1, a carpenter, and a coworker were removing a circular work platform from the inside of a large concrete tank. The approximately 4 ft wide platform was approximately 35 ft above the floor and completely circled the tank wall. They removed all but the last section, each approximately 4 ft wide by 7 ft long. A single scaffold that was 4 frames tall plus approximately 30-in. of extensions had been erected directly below the last section of the work platform. The scaffold was not secured to the wall but was angled against the wall by extending the back adjustable legs. They could no longer use their ladder as this scaffold was in the way. They accessed the platform with an 8 ft extension ladder that was set on top of the scaffold to enable them to reach and complete the removal of the work platform. The coworker, who had been working on the platform, was using personal fall protection tied off up through the roof opening approximately 10 to 12 ft. Employee #1, who had been working from the ladder, climbed onto the guard rail scaffold to assist. The coworker made several trips up and down the ladder and was again climbing up when he felt something shift. He saw the scaffold moving away from the wall and the ladder sliding and falling out from under him. He observed Employee #1 fall over the front, unguarded edge of the scaffold about the time the scaffold struck an inner tank wall that was approximately 15 ft from the outside wall of the tank. This was a large tank, 195 ft diameter, with a smaller tank inside of it. Employee #1 fell head first to the second frame above the floor where he struck the inside x brace with his torso. He then lowered himself to the floor where he fell to a prone position. Employee #1 was hospitalized with an injured abdomen.