Abstract: Employees of Employee/Employer #1 rented a gasoline-powered pump and took it into a tank two decks below the weather deck to pump out some water. The tank was the aft peak tank aboard the vessel Gem State. After 1 1/2 to 2 hours of operation, Employee #2 became dizzy as he climbed the ladder out of the tank and passed out just outside the manhole. He was discovered by Employee #3, who went for help. Employee #3 returned with Employees #4 through #9 after calling 911. Employee #3 sent another employee down to shut off the pump. Fire fighters #10 through #27 arrived on the scene and gave oxygen to Employee #2 and evacuated him. They then began three rescue attempts of Employee #1. Some fire fighters were not wearing any respiratory equipment. No ventilation was provided in the tank and no testing for carbon monoxide was conducted.