An employee was inspecting trays inside an amine tower vessel to determine what needed to be replaced. The employee climbed down through the 20 percolator trays, going through 18" x 22" openings in the trays, until he reached the third or fourth tray from the bottom. The employee then slipped and fell approximately 20 feet to a metal surface below. The employee sustained injuries to their back, left elbow, and ankles and was hospitalized.