Abstract: At 10:30 p.m. on May 29, 2020, an employee working as a production supervisor for an aluminum foundry was moving a container of parts. The employee was working with Coworker #1, Coworker #2 and Coworker #3 in the mill room. Coworker #4, a maintenance employee, heard an air leak in a 3000-gallon compressed air tank and proceeded to the area to investigate. Coworker #4 was called to another job and left the area. About that time, the tank failed at one end and blew off causing an explosion-like event. An investigation revealed that the area of the tank wall that failed was significantly thinner than the original tank thickness. The investigation could not determine what caused this defect. The tank was equipped with a safety relief valve. Coworker #1, Coworker #2, and Coworker #3 sustained unspecified injuries and received medical treatment without hospitalization. The employee was hospitalized with a head laceration and brain bleed.