Abstract: At 4:46 p.m. on August 11, 2021, the employee, a fire captain, and his fire crew were dispatched to a house that was reported to be on fire. Once the crew arrived on scene they found a large, two-story, single-family home that was on fire. The employee and his crew pulled a hose line to the home and began to flow water from the exterior of the structure. The employee then left the crew and began to conduct a 360 degree size-up of the structure. The employee met the department's assistant chief on the side of the structure where he had pulled a hose line from the engine and was flowing water from the exterior. The employee the entered the IDLH environment from the den exterior door and proceeded to a bay window from inside the structure. The employee and the assistant chief began to communicate about fire conditions. The assistant chief left the employee inside the structure and when he returned the employee was no longer visible. A "Mayday" was transmitted over the radio. The employee had fallen through the floor and was trapped in the basement. All fire department personnel on scene focused their efforts on rescuing the employee. The employee was found unconscious in the basement was removed from the structure in full cardiac arrest. The employee was flown by helicopter to a hospital center and pronounced dead by medical staff due to smoke inhalation.