Abstract: At 10:00 a.m. on December 5, 2020, several employees were working for a firm that provided oil spill site remediation, vessel decontamination, and tank cleaning services. The employees were at a tank yard, removing sediment from tank number 142. The tank was leased and had been drained of product three weeks earlier, but condensate, sludge, paraffins, "bottoms," and petroleum-based sludge were still inside the tank. The employer had rented a Triton portable high performance diesel-powered vacuum to remove the sediment. The employer provided hoses, which connected the vacuum to a box provided by the owner of the tank yard. Lines ran from the box to the tank to collect product. The boxes, contracted by the tank yard's owner, had arrived five days earlier. The employer visually inspected the boxes for damage and to evaluate their chains and gaskets. A supervisor from the employer was onsite to ensure that equipment was staged as required. The employer provided all tools and equipment for the procedure. When each box had been filled, it was changed out. For this step, the hose had to be removed from the box. In this incident, an employee was using a DeWalt cordless drill or impact wrench and a Pittsburgh 33-mm socket to change out the hose. The vacuum system was not adequately grounded. An ignition source in the form of a spark occurred, and the contents of first one tank and then a second one ignited and exploded. The initial explosion occurred at 9:56 a.m. and the second at 10:00 a.m. Seven employees were injured and taken to a local hospital. Five were then sent to a burn unit in a larger hospital. On January 21, 2021, one of the employees died. Neither the cordless tool nor the socket was intrinsically safe. Before placing the vacuum system into operation, the employer did not verify and record that the system was adequately grounded in accordance with Article 250 of the National Electric Code. The supervisor did not conduct a resistance test on the vacuum or boxes.