On August 13, 2006, a 55-year-old male, career, Engineer (the victim) died and another fire fighter was injured after falling through the floor at a residential structure fire. The victim and fire fighter had arrived in their ambulance and assisted the first-due engine attach a 5-inch supply line at approximately 1227 hours. The engine company was conducting a fast attack on a suspected basement fire, while a ladder company conducted horizontal ventilation. The ambulance crew had advanced to the front of the structure when the Incident Commander requested them to conduct a primary search. The victim and injured fire fighter proceeded to conduct a left hand search at approximately 1234 hours. They took a couple of steps to the left just inside the front door to conduct a quick sweep. Visibility was near zero with minimal heat conditions. Because of the smoke conditions, they kneeled, sounded the ceramic tile floor, and took one crawling step while on their knees. They heard a large crack just before the floor gave way sending them into the basement. The basement area exploded into a fireball when the floor collapsed. The victim fell into the room of origin while the injured fire fighter fell on the other side of a basement door into a hallway. The injured fire fighter was able to eventually crawl out of a basement window. The victim was recovered the next day. The NIOSH investigators concluded that, to minimize the risk of similar occurrences, fire departments should: 1. Conduct pre-incident planning and inspections of buildings within their jurisdictions to facilitate development of safe fire ground strategies and tactics. 2. Use a thermal imaging camera (TIC) during the initial size-up and search phases of a fire. 3. Ensure fire fighters are trained to recognize the danger of operating above a fire and identify buildings constructed with trusses. Additionally, building code officials and local authorities having jurisdiction should consider modifying the current building codes to require that lightweight trusses be protected with a fire barrier on both the top and bottom.