On November 23, 2006, a 33-year-old male career fire fighter (the victim) was seriously injured during a fire in a single story abandoned duplex house. The victim was working the interior of the structure fire with other crew members for less than a minute when they were ordered to evacuate the structure because of extreme conditions. At about the same time a flashover or flameover occurred; the victim became disoriented and was unable to exit the burning structure. The victim was rescued approximately 4 minutes later and transported via ambulance to a metropolitan trauma center where he remained in critical condition for several days in the burn unit before succumbing to his injuries on November 29, 2006. Key contributing factors identified in this investigation include an initial size-up not being conducted, a failure to recognize the signs of an impending flashover/flameover as fire fighters entered the structure, inadequate communication on the fire ground and the possibility that ventilation induced the rapid fire progression. NIOSH investigators concluded that, to minimize the risk of similar occurrences, fire departments should: 1. Ensure that an initial size-up of the incident scene is conducted before beginning interior fire fighting operations. 2. Ensure that the first arriving company officer does not become involved in firefighting efforts when assuming the role of incident commander. 3. Ensure that a Rapid Intervention Team (RIT) is established and in position with a backup hoseline prior to initiating an interior attack. 4. Ensure that ventilation is closely coordinated with interior fire suppression operations. 5. Ensure that crew integrity and accountability are maintained during fire suppression operations. 6. Ensure that all fire fighters are equipped with a radio and trained on how to initiate emergency traffic. 7. Train fire fighters to recognize the conditions that forewarn of a flashover/flameover and communicate fire conditions to the incident commander as soon as possible. 8. Train fire fighters on actions to take if they become trapped or disoriented inside a burning structure. 9. Ensure that fire fighters serving as acting officers are adequately trained. Additionally, fire departments, municipalities, and standard setting bodies such as the National Fire Protection Association (NFPA) should consider developing and implementing a system to identify and mark unoccupied, vacant or abandoned structures to improve fire fighter safety.