USA –– BASTROP COUNTY, Texas — The long-accepted maxim that homeowners should have a defensible space of at least 30 feet around a home to help protect it from wildfires should be greatly extended, according to the final report on the 2011 Bastrop County wildfire.
“Of 341 homes that we studied and were destroyed in the fire, 85 percent had defensible space of at least 30 feet,” said Karen Ridenour, the principal researcher and author of the study and fire researcher for the Texas Forest Service. “This tells me we have to stop telling people 30 feet. We need to push that number out a lot farther.”
In the newly released report, Ridenour stops short of recommending a larger vegetation-free radius around a home but points to California’s law that requires 100 feet of defensible space.
The defensible space concept that has been around for decades recommends the perimeter of a home be free of vegetation because plants, trees and shrubs compromise a home in a wildfire.
The observation was one of many in the recently completed Bastrop Complex Wildfire Case Study, a 165-page report designed to spell out the lessons learned from last September’s wildfire and how to prepare for the next one.
Several state and county agencies, as well as Texas State University, collaborated on the study. The report is available at the Bastrop Public Library and will be available on Bastrop County’s website later this week.
The report praises the quick reaction of firefighters, sheriff’s deputies and others who evacuated people out of the fire’s path. It also includes a Sept. 4 transcript between 911 dispatchers and emergency responders when the fire broke out.
The report concludes that no matter how much homeowners, firefighters and county officials prepare for such a natural disaster, a bad wildfire in so-called wildland urban interfaces — areas where people live in wildlands such as forests — will do major damage.
The Bastrop wildfire — the most destructive in Texas history — began on Labor Day weekend 2011, scorched 32,400 acres, destroyed 1,696 homes and claimed two lives.
A Texas Forest Service investigation concluded that the likely cause was trees that crashed into overhead power lines.
Wind gusts of more than 30 mph on Sept. 4 apparently knocked down trees that tumbled into the electrical lines at two locations, causing sparks that fell into the dry grass and tree litter below, according to the investigative report.
Many of the Bastrop homes were built from masonry and had roofs made of asphalt and metal — which are not typically considered combustible, Ridenour said.
Of the 341 destroyed homes studied in the report, 80 percent of them had masonry construction, 84 percent had asphalt roofing, and 83 percent had metal roofing.
“That tells me it wasn’t the roof but the accumulation of debris in the valleys and leaves in the gutters” that probably led to the homes’ destruction, Ridenour said.
Mike Fisher, Bastrop County’s emergency management coordinator and a co-author of the study, agreed.
“Part of the conclusion is that firewise construction and defensible space that we’ve talked about for years is not an insurance that your home won’t burn,” Fisher said. “Homes were destroyed because of the fire behavior, a behavior that was extraordinary and phenomenal. It had to do with the conditions of that day. It was a year’s worth of drought. It was dry and windy.”
Ridenour said it’s the “little things” that homeowners overlook that put them in jeopardy.
“It’s the bush that is too close to a window and compromises that window, (then) flames or heat break the window, and you will have embers going into the house. It’s debris in the gutters and the straw mat heated by embers that will catch a house on fire,” she said.
Researchers also looked at other factors that may have contributed to the destruction, such as the dates homes were built, topography and weather.
Of destroyed homes studied in the report, 34 were built in the 1970s, 116 in the 1980s, 103 in the 1990s, and 67 in the 2000s.