Special Issues in Wildland Urban Interface Fires
WUI fires are complex because they are both wildland and structural fires that, traditionally, have been treated differently by firefighting organizations.
Fire behavior in WUI fires is unusual because it is a combination of the patterns of burning in man-made structures with the burning of vegetation. Fire behavior in structures differs from fire behavior in wildlands. Heat release from a burning structure is significantly higher than an equivalent area of vegetative fuels, but, unlike a wildland fire that spreads, a structural fire generally is confined to buildings. Structures can influence the spread of a wildfire by functioning as ignition sources for other houses or vegetation by producing high levels of radiant heat and firebrands (Cohen 1995). The primary fuels for wildland fires are living and dead plants, whose structure, arrangement, and size influence fire behavior. Fine fuels such as grass, pine needles and small leaves have high surface area to volume ratios; when dry, they burn rapidly and fire spreads through them quickly. When vegetation is continuous, with no vertical or horizontal separation between plants, the rate of fire spread is much quicker than if the vegetation is in patches. Dry fuels, high winds and steep slopes can increase fire intensity and rate of spread dramatically. Large timbers – like those used in construction – require significantly more heat to ignite but burn for a longer time. Compared to wildland fires, the materials used to construct structures are heavier, with lower fuel moisture content, so the residence time of flames is longer (Pyne and others 1996).
Temperatures are usually much higher in structural fires than in wildland fires, and structural firefighters require heavier equipment to protect them from the heat (Long and others in press). Wildland firefighters use a wildland helmet, protective “Nomex” (aramid fabric type II, fire-resistant) clothing, gloves, eye and ear protection, leather boots, radio, and canteen. All wildland firefighters also must carry a fire shelter to be used as a last resort in a life-threatening situation. It is estimated that since 1977 the fire shelter has saved more than 300 lives in the United States.
WUI fires require a different approach from firefighters. Traditionally, wildland firefighters handled burning vegetation while structural firefighters dealt with burning buildings. But the duties of the two types of firefighters are merging. Structural firefighters, for instance, are often deployed for initial attack on brush fires. And wildland firefighters frequently have to defend people and their property during ‘wildfires’. In a WUI fire, both structural and wildland firefighters are called upon to work side by side to protect lives, structures, and forests. Traditional fire suppression and prevention activities are being modified to match the traits of WUI fires and to train crew for working on both types of fires.
The increase in WUI fires makes it increasingly important to train fire crews to combat both wildland and structural fires. WUI firefighters must be trained to work under a unique set of constraints that include the following dangers:
- fire-induced hysteria on the part of homeowners, which may lead to rash acts and subsequent injuries
- toxic or highly combustible fertilizers, pesticides, or herbicides contained in garages and outbuildings
- explosives
- flammable liquids in above ground gasoline and diesel tanks, small gas cans for lawn and garden equipment, and propane gas
- equipment traps such as septic tanks, bridge limits, and road grades too small to allow large equipment
- electrical wires
Triage is a method used to set the priorities for firefighting in situations where there are insufficient resources to protect all structures at risk during a WUI fire (Governor’s Wildfire Response and Mitigation Review Committee 1998). Triage can help firefighting organizations determine where to focus firefighting efforts and how to allocate resources to protect the structures or land that can potentially be saved while not endangering the lives of firefighters and homeowners. Triage was used during the 1998 fire season in Florida to categorize each fire incident as:
- Area will burn regardless of action,
- Area will not burn regardless of action, and
- Area will burn unless action is taken.
If the fire was categorized as #1 or #2, then the solution was also to take no action. And if the fire was determined to be #3, then the solution was to take action.
The Florida Division of Forestry’s Wildland Firefighter’s Guide Training Manual, suggests triage decisions be based on the following five factors:
- Susceptibility of the structure to burning (roof construction material, size of windows and structure, siding material)
- Fuel load around the structure (size, arrangement, and moisture content of vegetation, defensible space)
- Current fire behavior (rate of spread and direction, topographical influences, weather predictions, spot fires)
- Available resources (personnel and equipment, on-site or potentially available)
- Firefighter safety (routes of egress and ingress, grade and surface of the road, presence of hazardous materials)
The logistics of WUI fires can be difficult and require a merging of structural firefighting tactics with wildland firefighting strategies. One problem with the logistics of WUI fires is that narrow, windy roads can make it difficult to access remote homes and buildings that are threatened by wildfires. Another problem is there is sometimes a lack of available water to douse the flames. To attack wildland fires, firefighters create control lines around the burning area with specialized (e.g., tractors and handtools) and douse the flames with foam and water (Schlobohm 1995). Structural fires are principally controlled with water from a nearby fire hydrant. But, water sources may be insufficient or unavailable for large WUI fires. Structural fire engines have larger capacity tanks and higher volume pumping capacities compared to wildfire truck tanks. Wildland fire fighting engines are capable of off-road operation and can typically carry 300 gallons of water with a hose 50 feet in length and 3/4 inch diameter. Structural fire engines carry water tanks with 500 to 1,000 gallon capacities and multiple hoses 100 to 250 feet in length and 1 to 1.5 inch in diameter.
Interagency collaboration is essential to combat WUI fires. A WUI fire requires cooperation, communication, training, and command structure to ensure that local, state, and federal firefighting agencies from multiple jurisdictions work effectively together. In Florida, the state Division of Forestry has statutory responsibility for all wildfires within the state. Local fire agencies have responsibility for fire protection within their jurisdictional boundaries, while federal agencies have responsibility on federal land. Other states have similar ways of delegating responsibility. A WUI fire may involve several of these different agencies, which requires that they have cooperative agreements in place for them to work together and that they are all familiar with the Incident Command System (ICS).
Encyclopedia ID: p826
