Abstract: At approximately 4:50 p.m., on June 4, 1998, Employee #1 and a coworker were working on the United Airlines B777 jet aircraft Number 2072 in Oakland, CA. They were preparing for the inspection of an internal potable water tank. Employee #1 started to release the snap ring on the tank cap, when the end cap blew out and hit him in the face. Employee #1 was taken to the Alameda Hospital for treatment. He was hospitalized. Apparently, the pressure in the tank had not been released prior to removal of the snap ring holding the cap in place. Employee #1 and coworker during the inspection of the water tank had to follow a set of elaborate instructions, given in a job card, Potable Water Tank Inspection (1660-40-11-00). It appears that steps A and B in the instructions were not completed prior to the removal of the snap ring from the tank. The tanks hold approximately 200 - 300 gallons of water. The cap on the tank is approximately 8.125 in. in diameter and 1 in. in depth.