Abstract: At 4:30 p.m. on November 5, 2021, an employee was participating in a training exercise while wearing an Edelhoff, full facepiece, type C, positive pressure, supplied-air respirator. The exercise simulated air supply issues employees may face when inside reactor vessels. The employee climbed into a mock reactor vessel to complete the training exercise. The employee climbed into the bottom of the reactor, completed a 5-step procedure, and climbed back out of the vessel. When the employee made it out of the vessel, he collapsed onto the vessel's platform. The employee's respirator was removed, and he was transported to the hospital. The employee was pronounced dead shortly after the arrival to the hospital. The medical examiner determined the manner of death was natural caused by hypertensive cardiovascular disease with coronary arterial arteriosclerosis contributed to by obesity.