Abstract: At 1:30 p.m. on March 11, 2020, two employees were responding to a heater-temperature alarm transmitted to the control room from a heater tube thermocouple. Initially, just prior to activating a shutdown response, multiple operators reported a more than usual smoke volume emitting from the smokestack for this heater. It was reported that an even greater smoke volume emitted. Then, there was a sudden deflagration. The two employees, who at this time were responding to the heater-temperature alarm in the field and positioned right next to the heater peering into the heater's port holes, were thrown by the blast pressure, sustaining serious burn injuries from the fire. The direct equipment cause of this fire was due to the failure of a specific heater tube located in the convection section of the heater, the same tube, tube #66, that had failed in the past. The heater tube ruptured, spewing flammable distillates into the open space within the active, flaming heater box that ignited, erupting into an uncontained fire, eventually contained, and then extinguished by DCRC's fire brigade. One employee had serious burns to the face, neck, back and one hand; the other employee had serious burns to the face and neck. Both employees were hospitalized.