Strategy and tactics applied to large area fires in urban areas.
NFPA Journal®, November/December 2008
Conflagrations occur less frequently now than in the past, but they remain a possibility in many jurisdictions. Fire departments should recognize the extraordinary challenge conflagrations present and identify potential risks in their response areas.
Generally, NFPA uses the term “conflagration” to describe a fire with major building-to-building flame spread over some distance. A number of common factors greatly increase the chance of a conflagration in an urban setting, including:
closely built structures;
the use of untreated wood shingles as exterior covering for roofs or walls;
poor water supplies, weaknesses in automatic or manual fire suppression systems;
dilapidated structures, especially abandoned buildings in large numbers;
large-scale combustible construction or demolition projects;
wildland/urban interfaces; and
built-up areas near high-hazard locations, where a transportation or industrial fire or explosion could quickly involve large numbers of buildings.
Most urban conflagrations have two or more of the factors listed above. If your response area contains one or more of these conditions, an increased possibility of a conflagration exists. That risk becomes even greater during dry, windy weather.
Understanding the methods of heat transfer is the first step in developing a conflagration strategy. One method of heat transfer is via burning materials, or flying brands, that move upward on convection currents and are then carried by the wind. The 2002 Santana Row fire in San Jose, California, in which flying brands ignited wood-shingled roofs a half a mile (806 meters) away, serves as an excellent example of the dangers associated with flying brands and wood shingled roofs.
Flying brands pose a difficult tactical challenge to incident commanders. The hazard is best addressed by deploying brand patrols into areas downwind that contain combustible structures.
However, the primary method of heat transfer to an exposed building is radiant heat. The large flame front creates extremely high radiant heat. The bigger the flame front and the closer the exposed buildings, the more likely the fire is to ignite nearby buildings. Radiant heat is the primary means of fire extension from building to building and from groups of buildings to other groups of buildings. When the fire is spreading along a wide, radiant flame front, the primary tactics are protecting exposures by narrowing the flame front and setting up primary and secondary lines of defense. When setting up lines of defense, consideration should be given to natural firebreaks, such as wide streets.
Figure 1 shows three lines of defense that the Houston, Texas, Fire Department developed during a 1979 conflagration at an apartment complex. Firefighters had to abandon the first two lines of defense before a successful stop was made at the third. When setting up primary and secondary lines of defense at a conflagration, apparatus should be positioned so they can be rapidly redeployed if the line of defense must be abandoned.
It is imperative to allow enough time and provide adequate resources when setting up a line of defense. Having a fully staffed planning section is of great value when commanding a fire that is spread over a wide geographic area.
Halting a conflagration can seriously challenge any water supply system. Realizing the importance of water conservation, the incident commander must set and communicate priorities for the use of water with individual units.
In most cases, water being discharged into a flame front is of little value. The top priorities are maintaining the firebreak at the lines of defense and protecting exposures. Once the decision has been made to write off an area, water should not be wasted trying to save what will surely be lost. Many large cities have multiple water service areas. Auxiliary sources of water should be identified. When water mains were destroyed in the Marina District fire area during the 1989 San Francisco earthquake, for instance, the San Francisco Bay became an auxiliary water source as fireboats relayed water to the shore.
As always, life safety is the top priority, followed by extinguishment. With conflagrations, being proactive and evacuating people in the fire’s path long before they are actually threatened is the key to success. The evacuation area must be beyond the secondary line of defense.
A large-area fire presents a substantial challenge in terms of command, control, and logistics. The emergency action plan for such fires should include evacuating people in the endangered area beyond the secondary line of defense, establishing a primary line of defense in an area with natural or artificial firebreaks, narrowing the flame front, providing flying brand patrols, and setting up a secondary line of defense.
This column is adapted from the authors’ book Structural Fire Fighting, available at www.nfpa.org or (800) 344-3555.