Article No: 92

2006-05-02 07:29:19
Protecting homes from wildfires
By: Larry Storer


Naturally occurring wildfire can help sustain and maintain healthy forests. To residents, however, the results are often devastating. In 2002, Colorado, Arizona and Oregon reported their largest forest fires in the last century. Fueled by extreme drought conditions that existed throughout most of the United States, wildfires claimed more than 7 million acres and more than 2,300 structures in that year alone. Early estimates from 2003's October/ November Southern California wildfires have resulted in more than 800,000 acres burned, 3,400 homes destroyed and 22 lives lost.

The United States' history of annual wildfires has fueled a growing scrutiny of the urban-wildland interface — those areas where structures and other human development meet or intermingle with wildland or vegetative fuels. With the increasing trend of building in forested areas, the size of this urban-wildland interface continues to grow, and with it grows the risk to homes and property from wildfires.

The Aspen, Ariz. fire started on June 17, 2003, in the Santa Catalina mountains, a popular retreat from Tucson's scorching heat. During the course of 30 days, the fire consumed more than 100 square miles, destroying 335 residences and 10 commercial properties.

Overwhelmingly, residents have vowed to rebuild. This time, however, the county wants to ensure the community builds in some protection from future fire damage. As a direct result of the devastating Aspen fire, Pima County, Ariz. enacted emergency legislation last summer to adopt the International Urban-Wildland Interface Code (IUWIC) published by the International Code Council. According to Chuck Huckleberry, Pima County administrator, "We're intent on basically trying to assist people in rebuilding sensibly. We really need to address safety. It's not as if it's an imaginary threat or a potential problem. We don't want to pay for repetitive disasters."

The International Urban-Wildland Interface Code provides a comprehensive approach to protecting structures from wildfires and preventing a fire within a building from spreading into a full-blown wildfire.
Adopting jurisdictions, such as Pima County, must first define the local fire hazard. Levels of fire hazard (moderate, high or extreme) are assigned geographically, depending on: local climate; topographical features such as elevation changes and location of roads, bridges and railroads; and on geographic features such as earthquake fault lines, hazardous material routes and vulnerability of the infrastructure to damage. The code includes requirements for exterior building materials, as well as mitigating the fuel load of the immediate surrounding landscape (see page 22 for more information).

Concrete masonry provides a distinct advantage to structures in the urban-wildland interface, as it is inherently noncombustible. The IUWIC requires exterior walls of buildings subject to high or extreme fire hazard to be constructed of one-hour fire resistive construction or be built of approved noncombustible material. In fact, most concrete masonry walls easily exceed a one-hour rating, as shown in Table 1 (see page 22 for information describing how to determine the fire resistance rating of concrete masonry walls).

Other building materials may not provide the same level of protection. Although wood siding can be treated with UL-approved fire-retardant chemicals, the Federal Emergency Management Agency's checklist for homeowners to avoid wildfire damage warns that this treatment and the resulting protection are not permanent. According to Jim Paxon, a former wildfire fighter and forest ranger now retired from the U.S. Forest Service, "The one-hour rating is a good code supplement. It allows the firefighter to get in there and take action to save the home."

Traditionally, building and fire safety codes have addressed what firefighters describe as urban fires — fires that start within a building. Firefighters try to extinguish the fire before it can spread to other portions of the building or to other buildings. Codes such as the IUWIC reflect the unique conditions and risks of wildfires. Fighting a wildland fire is intrinsically different from battling an urban building fire. Firefighters trying to tame the Aspen fire were instructed to target only homes that could be saved in 10 to 15 minutes. This can be a difficult order for urban firefighters, who are accustomed to saving every home. However, with wildfires it's a necessary approach.

A wildland fire is much different than in urban areas. In the wildland, there are many structures, so you have to save the ones you can and leave the rest — it's a triage situation. The one-hour rated exterior versus 20 minutes gives the firefighters a chance to save it. Otherwise, they need to pass over it and go on to the next one," Paxon said.

This isn't just good theory, it works

Mark Kluver, regional codes manager for the Portland Cement Association, surveyed damage from three of the largest fire areas in southern California last fall and found that despite the large number of homes lost, almost all of the recently built dwellings located on more than 40 miles of the most explosive fire perimeter were still standing. Kluver found that these homes typically included the one-hour rated noncombustible exterior walls and Class A fire-retardant roofs mandated by the IUWIC.

All-in-all," Kluver said, "I found strong evidence that local jurisdictions and homeowners took major corrective action following the fire storms that raced through southern California 10 years ago. I believe that if fires of the magnitude that hit this year had occurred back then, several times more dwellings may have been lost."

Paxon said he believes the IUWIC provisions must be combined with public education to more effectively increase safety. Paxon attended the public meetings in Pima County when the IUWIC was adopted and commented: "The reaction from people who lost homes there was shocking — very few supported it. People are naïve. They don't know how to protect themselves when living in the wildland. We need to change people's perspective."

As the nation's wildland areas continue to be developed, growing numbers of homeowners will face the potential devastation of wildfires. Building with concrete masonry provides them proven fire protection and security for the life of their home.

Concrete masonry

Fire resistance ratings of concrete masonry walls are based either on testing (ASTM E 119, Standard Test Methods for Fire Tests of Building Construction and Materials) or, more commonly, using the equivalent thickness method on the aggregate type(s) used to manufacture the unit and its equivalent thickness.

Equivalent thickness is essentially the solid thickness that would be obtained if the same amount of concrete contained in a hollow unit were recast without core holes. It is calculated by multiplying the actual unit thickness by its percent solid. Walls that contain more concrete will have a higher equivalent thickness and will tend to have a higher fire rating.

Aggregate types used to manufacture concrete masonry units affect fire ratings because aggregates have an effect on the heat transfer properties of concrete. In general, lightweight aggregates slow the passage of heat through the unit, and consequently produce higher fire resistance ratings. CH

This article is courtesy of the National Concrete Masonry Association, and is reprinted with permission from Concrete Masonry Design magazine.