Abstract: A three-person dive team arrived at a hydroelectric power generation plant to seal off leaks on valves that were thought to be giving excessive water flow. The team was told by plant operating personnel that the valves were in the closed position. After the first dive was conducted, the diver reported that he thought the valves were in the open position. This was verified by the plant operating personnel. The diver returned to the surface, and the winch was started to close the large gate valve. The 762-millimeter pad valve was manually cranked shut, with the operating personnel and the dive team taking turns on the crank handle. A dive team member was the last person on the crank, and the team questioned the operating personnel as to the status of the indicator, which was not indicating fully closed. The operating personnel stated that the indicator was never correct and directed the divers to close the valve until it the crank handle could not be turned any more. When the employees reached that point, the operating personnel informed the dive team supervisor that there was still a serious leak and that the diver should use caution. This was relayed to the diver. The supervisor told his diver to take his time and not take any chances, as they had plenty of time and could figure out a different approach if this was unsafe. The diver was proceeding down the stem of the pad valve when he screamed, "Ahhh, it's got me, it's got me." The supervisor tried to raise him on the intercom with no success. The tender started to pull the umbilical line with assistance of the supervisor, and the line broke loose. When they reeled in the lifeline, they found that the connection to the diver's harness was broken. The communications line and air hose were also broken away from their attach points to the helmet. The gates were cycled open while awaiting a rescue dive team. When the diver did not surface, a plan to search for him was implemented by the company with concurrence of the emergency people on site since they were the most experienced in the area. Two dives could not locate the missing diver, and the decision was made to close the valves and complete the sealing so that a lower chamber entrance hatch could be unbolted and entered by a rescue dive team. Following this procedure, the rescue dive team recovered the missing diver 12 hours after his lines were broken. He had drowned. There was no tearing of the wet suit or any physical damage to the helmet. However, there was abrasion on the brass weights and a bent valve on the helmet indicating the possibility that the diver was drawn into the pad valve area. The lifeline connector was still attached with a small amount of rope still entwined on the eyelet. It appeared that the lifeline did not have a thimble for the polypropylene rope connection to the main rope. There appeared to have been two wraps of the polypropylene rope around the 6-millimeter-diameter attachment ring, and the loose end was woven into the main rope. This is where the break had occurred. The diver had apparently been sucked into the fully open pad valve and down the tube.