Abstract: At approximately 3:00 p.m. on July 6th, 2009, Employee #1, a refinery worker, was working inside a demineralizer vessel, Number 2331. Inside the 40 ft high and 25 ft diameter vessel were four metal grated platforms. She was climbing a metal chain ladder, a Jacob ladder, from a grated metal platform inside the vessel, attempting to exit from the top of the vessel. Employee #1 climbed the Jacob ladder through the first metal grate in order to reach the top egress hole. The Jacob ladder's set up required workers to begin the climb from a slight overhanging position. Upon reaching the top metal grate, and going through a hole in the grate, the Jacob ladder turns into a slight inward pitch to the top of the vessel. Before climbing the Jacob ladder, Employee #1 attached a wire retrieval line to her harness. She made two attempts to climb the Jacob ladder, both were aborted due to equipment falling off her. On the third attempt, she began climbing on the wrong side of the Jacob ladder. She was approximately 10 to 12 ft above the second grate and could not get through the upper grate. She unhooked the retrieval line from the fall protection harness and attempted to swing from one side of the Jacob ladder to the other but fell off the ladder. Employee #1 suffered a severe head concussion, resulting in prolonged memory loss.