Originally published April 1989 in Courier: News Magazine of the National Park Service, reprinted to commemorate the 25th anniversary of the 1988 Yellowstone Fires.
Fire Is Fire—Or Is It?
One area of special fire management concern is the “urban/wildfire interface” — the places where wildfires encroach on
man-made structures. The National Park Service has management
responsibility for many wildland areas and numerous structures
located within or adjacent to them. The purposes, materials and
contents of these structures vary. Even concession-operated
buildings range from modern steel and concrete designs all the
way to very old, all-wood buildings on the National Historic
Register (Old Faithful Inn, for example). Visitor centers and
museums contain 25.6 million artifacts, many of which are
irreplaceable. The remainder of the approximately 16,000 structures
in parks include residences, warehouses, garages, and
administrative and historic buildings. NPS cities-in-the-wild also
house the usual support activities, such as gas stations and fuel storage areas. So what happens when fire rages up to the perimeters of these occupied areas?
To better understand fire-control problems associated with wildlands and structures, it's perhaps best to begin by looking at how the two differ. Fire fuels, behavior, and suppression tactics change, depending on which kind of fire is being fought. Let's look at wildfire first.
The word “wildland” might conjure up grasslands, brushfields or forests of pines and oaks. But fuel type isn't the only wildfire determinant. Vegetation varies widely in form, age, condition and moisture levels. Thousands of species of plants, each with its own size, shape, flammability and response to fire, comprise wildlands.
External factors also influence the behavior of fires burning across wildlands. The shape of the land also affects direction and rate of spread; in the absence of wind, for example, fires will run uphill. Prevailing temperature and relative humidity influence fire in opposite ways, with higher temperatures and lower relative humidity favoring burns.
Wildfires also follow a pattern of occurrence. Though they seem to pick the worst locations and the hottest days, in reality they follow a sequence of regional fire seasons, dictated by climatic and vegetative factors. Different tactics have evolved to meet these conditions. They generally aim at cutting off the spread of the fire, working from the origin around to its head, and burning out between the fireline and the fire. Taking advantage of changes in vegetation to locate the fireline in the easiest and most effective location is one option. Most of these lines are built with handtools such as shovels and pulaskis in the west and flappers and rakes in the southeast.
In almost every respect, fire behavior and suppression techniques
vary markedly for structural firefighting. Although the
availability of fuel, heat, and oxygen (the standard fire triangle)
govern structural fires also, the rate of fire growth and spread in
building is greatly influenced by the configuration of fuels into roofs, walls, floors, and doors. Structural fires have no season;
they generally burn from the inside out and in any weather. The
character and condition of the building and contents likewise differ.
Building design can aid or obstruct the ability of firefighters to attack and control fires.
Structural fires usually begin within a building, so the environment of the room or building determines fire spread. Typically they start slowly, then flare up rapidly. They flash over and catch walls, ceiling and contents. Windows or roofs are soon involved, and, with a fresh supply of inflowing oxygen, the free-burning fire rapidly intensifies. All this can take place in a matter of minutes.
The design and construction of communities and developed park areas include fire provisions that, at older and smaller park stations, may be marginal at best. Since rescue of occupants is the primary concern, response time is of major importance, and is affected by the distance between fire stations. Unlike wildfire responses, which are measured in hours, structural fire response times must be measured in minutes.
Because of this urgency, warning and rapid suppression systems are a major concern. Modern electronic fire or smoke detectors announce beginning fires, and some transmit alarms directly to a firehouse. In some buildings, sprinkler systems both suppress fires at an early stage and trigger alarms. When arriving on-scene, engine crews locate and attack the fire and protect adjacent buildings or vehicles from fire exposure. Heat, smoke and toxic fumes require firefighters to use heavy, waterproof insulated coats, gloves, helmets, boots with steel in the soles, and a tank-type breathing apparatus.
These descriptions characterize pure wildland and pure urban fire conditions and tactics. Fires that occur on the interface between these two types are harder to define. There is no single solution to the complex problems such a fire often presents.
Some generalizations can be made about these fires, however. As a rule, an “interface fire”: involves a mixture of buildings and wildland fuels; is beyond the reach of water mains and hydrants; may be hard to reach, since access may be along narrow drives from the main roads; are in areas where structures are few, which means a low tax base for private lands; involve wildland fuels that terminate at a building's foundation, thus creating an attractive but hazardous situation; receive fire protection limited to a volunteer brigade with large response areas and an extended response time; usually involve multiple jurisdictions; and affect buildings constructed of highly flammable materials.
Because of hazards created by these factors, only a concerted effort by all fire protection authorities affords proper protection to structures. The Incident Command System (ICS) developed by the National Wildfire Coordinating Group (NWGG) is a field approach aimed at the problem. Fire training on ICS aids the effective merger of several fire departments when fires do develop.
Once a problem almost exclusive to Southern California, the volatile mixture of structures in forests and other wild areas now exists nationwide. Because wildland fuels form the matrix that surrounds structures, wildland fire danger causes critical structural fire incidents to develop. A national conference entitled “Wildfire Strikes Home” focused attention on the causes and possible solutions to these problems in late 1986. Strong support from the National Fire Protection Association and the NWCG has helped to spread word on the problem, but the main focus has been on local solutions by departments in the field.
That brings us back to the parks and their neighbors. A fire
specialist soon will be added to the NPS payroll in order to address
the “interface problem” in parks, to determine its scope
and nature, and then define a course of action for the Service.
While it's true that “fire is fire,” wildfire and structural fire
now have to be understood at the point where they come together if losses of life and property are to be avoided. The Service realized this in a particularly dramatic way at Yellowstone last summer. It will be focusing more attention on it in the months ahead.
David Butts is Chief, Fire Management, at Boise, Idaho. By the time this article appear[ed] he... [had] joined the Ranger Activities staff in Washington.