Abstract: At 2:00 p.m. on May 10, 2019, several employees were working for a firm that cleaned railroad tank cars. Typically, the tank cars had been used in unit trains that transported crude oil. Cleaning the cars involved de-gassing, hydroblasting, washing, and steaming. The cars would come in from major railroad carriers. The employees were inside a tank car with the number DPRX 259379. They were performing de-heeling operations inside the tank car. The de-heeling process involved the removal of hazardous chemical residues such as but not limited to residual natural gas condensate, crude oil and hydrocarbon sludge, and other petroleum-based materials from the interior walls and floor of the tank car's interior. De-heeling required steam cleaning, pressure washing, and scraping and squeegeeing. At the time of the incident, two employees were inside the railcar. For some reason, there was an ignition source, and a flash explosion occurred. The two employees were burned or asphyxiated. One employee was pronounced deceased onsite, and the other employee suffered third degree burns to a majority of his body. He died of his injuries three days later. The occupation of one employee was not given. The other employee worked as a laborer. There were other employees outside the tank car. One of these employees was hospitalized, and five of these employees were not hospitalized. There were two inspections associated with this investigation, 1400037 and 1401738.