Abstract: On December 21, 2021, APS hired a cleaning contractor to pump out residual fuel and to clean the fuel tank of a boat (8MSC1606). It had a 250-gallon capacity (gasoline). The cleaning contractor cleaned the tank by accessing an approximate two inch hole in the tank. The contractor used acetone (a flammable substance) soaked rags attached to a wire to clean the tank. Due to the metal baffles that separated the interior of the tank into nine compartments, the majority of the surfaces on the interior of the tank were not cleaned. The tank was removed by APS the same day and placed on wooden saw horses. APS conducted an initial pressure test on the fuel tank and discovered that there was a pin-hole leak in the vent connection of the tank. Employee #1 was notified that his services were needed to make the repair on the fuel tank on December 27, 2021. At 9:50 a.m. on December 28, 2021, Employee #1 set up his welding operation and area and commenced to weld (TIG). Shortly upon beginning to weld, the tank exploded. The blast caused the tank to forcefully strike Employee #1. The blast caused the 1/4-inch aluminum lid to separate from the rest of the tank and land on the roof of an adjacent business. Employee #1 sustained major head trauma as a result of the explosion. Employee #1 was transported to a hospital, where he was pronounced dead. There are several factors that contributed to the accident. APS permitted hot work to be done on the fuel tank without the tank being adequately purged and without any testing for the flammability of gasoline vapors. APS did not designate an area free from fire hazards for the hot work and did not post an effective Fire Watch. The employer was issued a Willful-Serious-Accident related citation [CCR T8 8355(g)] for not having the tank tested and certified by a Marine Chemist.