Abstract: Some electric utility employees were assigned to repair a level switch mechanism inside a 1136-kiloliter make-up water tank (condensate tank #11). The project required entry by a diver using a self-contained underwater breathing apparatus into the tank. Employee #2, the diver, obtained a diving permit and was evaluating means of entry as a predive drill to determine whether he could enter the manhole with his tanks and scuba or if they would have to be passed down to him after entry. He was wearing a lifeline when he went down the fixed ladder and into the tank. After he descended 203 millimeters, he was overcome and fell into the water. The diver tenders (Employee #1 and another employee) were holding the lifeline but could not see Employee #2 in the tank. Employee #1 entered the tank in an apparent rescue operation. He was not wearing a lifeline, nor was he using related emergency rescue equipment. The second diver tender, who was still holding the lifeline attached to Employee #2, yelled for assistance and, with the help of three coworkers, was able to raise Employee #2 to the bottom of the manhole opening. Since the line was around his lower chest, Employee #2's body was in a horizontal position, and the other employees had to reposition his body at an angle. The employees successfully completed the rescue and revived Employee #2 by administering cardio-pulmonary resuscitation. However, they could not see Employee #1 at this time. They summoned a professional diver, who found Employee #1 at the bottom of the tank. He had been asphyxiated. Employee #2 was hospitalized for his injuries. The dive team was not aware that a nitrogen blanket was in the space above the water. The team had not tested the atmosphere for oxygen. Employees were trained in confined space entry, but were not following entry procedures. In addition, the team had not obtained a confined-space permit, which would have required air monitoring from the Fire and Safety Department.