Abstract: On the morning of May 6, 1990, Employees #1, #2, and #3 were working at the Mallard Workover and Drilling, Inc., yard in the port of Iberia near New Iberia, LA. They had been instructed to check for conditions inside a rectangular tank on the lower portion of rig barge #24. The employees entered the tank, which measured approximately 10 ft by 5 ft, through a circular manhole opening. Mud lines passed through the tank, which was used to hold additional water for drilling operations. Without taking any gas or air quality readings, Employee #1 climbed down a ladder into the tank where he was overcome due to insufficient oxygen. He fell face down into accumulated water and died. Employees #2 and #3 also entered the tank and passed out. They were hospitalized and stayed at least one night in the Intensive Care Unit. There was insufficient oxygen in the tank and the employees were not wearing respirators.