Abstract: The employer operates a marine construction and repair facility. Two to three years prior to the accident, the employer fabricated two approximately 600 gallon diesel fuel tanks for an Alaska fishing boat. In the interim, the tanks had been used to off load diesel fuel from another boat. Once the tanks were emptied and steam cleaned, Employee #1 and a coworker installed them on the rear deck of the fishing boat and hooked the exhaust from the diesel welder to the fill pipe at the top of a tank. This was the normal procedure to inert the tank to prevent an explosion. While Employee #1 welded a doubler (a rectangular piece of metal) onto the tank, the coworker went to the shop to make a bracket. The coworker said that the welder had been running less than five minutes when he heard an explosion. Employee #1 lost an eye and suffered severe head injuries, a shattered arm, and a broken leg in the explosion. According to the employer, the normal procedure is to run the welder for 15 minutes to inert the tank prior to welding. No testing for the flammability of the vapors in the tank was done. Also, there was a baffle in the tank with the exhaust entering on one side and the work being done on the other side of the baffle. Diesel fuel, when heated, will give off flammable vapors which, when combined with a source of ignition and oxygen, can cause an explosion. The employer was cited for a serious violation of 5420(a)(2) for not testing for the flammability of vapors in the tank.