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As reported in the July issue, on Feb. 24, 2012, the Prince George’s County, MD, Fire/Emergency Medical Services Department (PGFD) responded to an arson fire in a single-family dwelling at which seven firefighters were injured. Given the severity of the injuries and the magnitude of the event, an investigative team was ordered by Fire Chief Marc S. Bashoor, in accordance with the department’s General Order 08-18: Safety Investigation Team (SIT). This series of columns provides an overview of the fire and the process used to determine what went wrong – and how those issues can be avoided in the future.
Additionally, the Prince George’s County Fire/EMS Office of the Fire Marshal conducted an investigation of the fire. Assisted by members of the Prince George’s County Police Department and special agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), the Fire Marshal’s Office determined the fire was incendiary in nature. The case remains as an open active criminal investigation.
Fire behavior prior to the fire department’s arrival:
The fire originated in the basement of the condemned structure. Prior to the arrival of the fire department, the fire had enough fuel (minimal contents), oxygen, heat and time to grow to a size sufficient to have smoke and flames exiting at least two windows in the basement on sides Bravo and Charlie.
Flames extending out of the windows and observations of smoke throughout the rest of the structure indicate that the fire had reached a ventilation-limited state. These two windows were in the Bravo quadrant of the basement and included a small window in the bathroom on side Bravo and a larger window in the kitchenette on side Charlie. These windows, aided by the wind, provided an inflow of air that supplied oxygen to the fire and supported rapid fire growth in the basement.
The exterior basement door initially was intact and closed. The status of the basement windows outside of the Bravo quadrant is not known. However, the scene examination indicated that they were intact and closed at the start of the fire. All of the windows and the door on the first floor were closed. Therefore, the two windows in the Bravo quadrant of the basement provided the only means of ventilation during the initial development of the fire. Based on the size and location of the windows, the wind and observations, it is likely that the majority of the inflow was provided by the larger window on side Charlie and the smaller window on side Bravo was mostly an outflow.
The interior door to the basement steps was open, which let the smoke and hot gases produced by the fire fill both the basement level and first floor. Smoke was initially observed pushing from the eaves on the first floor. At this point, the first floor was filled with smoke and was at a positive pressure (above neutral plane) due to the fire-induced, buoyancy-driven flows and the wind conditions. Even though the interior door to the basement steps was open, this lack of available oxygen and positive pressure prevented the spread of fire to the first floor and kept the fire’s flow path in the basement level. The flow path of the fire was effectively contained in the Bravo quadrant of the basement.
Fire behavior after the fire department’s arrival:
Approximately 6½ minutes after the initial 911 call, firefighters forced the door on the first floor, side Alpha. The term “ventilation” has been defined as the systematic removal of the products created by a fire (i.e., smoke, hot gases) and replacing them with cooler, fresh air to facilitate operations. Historically, forcing the front door of the structure to make entry may not have been thought of as “ventilation” by many firefighters. However, whenever an opening is created, ventilation has occurred.