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Wildland Fire Research: Mitigating the Effects of Ember Storm Conditions

Return to the March 15, 2012 issue of On Scene

IAFC On Scene: March 15, 2012



Want to learn more? Dr. Stephen Quarles will present a Thursday session at WUI 2012 about advancements in wildland fire research at the IBHS research center. To learn more about this session and conference registration, visit the WUI Conference webpage.

fThe Insurance Institute for Business & Home Safety (IBHS) Research Center has the unique distinction of being the only facility capable of subjecting full-scale buildings to ember storm conditions like those experienced in an actual wildland fire. The facility is also capable of simulating exposure from near-building flames using a large radiant panel. This has enabled researchers to further investigate building vulnerabilities in wildland-fire conditions and to develop and evaluate mitigation options.

These options find their way into best practices that property owners can use to reduce fire-related property damage. It’s a major step toward creating more fire-adaptive communities.

IBHS’s general research objective is to scientifically identify actions that strengthen homes and businesses against natural disasters, including wildland fire. IBHS scientists recently worked with the U.S. Forest Service and other researchers to master the ability to simulate an ember attack in a controlled laboratory setting.

This involved the use of five combustion chambers located below floor level. The chambers were filled with a mixture of bark mulch and wooden dowels. Gas burners at the bottom of each chamber ignited the mixture and a fan pushed the burning embers up through vertical ducts and into the wind stream generated by 105 individually controlled fans inside the test chamber.

A test house is subjected to an ember storm inside the IBHS Research Center in South Carolina.IBHS researchers subjected a test building built with various types of roof coverings, gutters and siding materials to ember-storm conditions. The test house was rotated on a 55-foot diameter turntable to expose the different materials and design features to wind-blown embers. Vegetation and mulch were also placed around the house during testing. This investigation demonstrated the vulnerabilities of these materials, as well as building components, to ember entry.

While ember exposure is a major risk to properties, direct flame contact is also a threat during a wildland fire. The importance of protecting your home from direct flame contact exposure can’t be overstated. An effective vegetation management plan to create defensible space around your home and property will reduce the chance of direct flame contact from the wildland fire itself. Creating a noncombustible zone within five feet of your home, removing vegetative debris from your gutters and roof and avoiding storage of combustible materials under your deck or next to your home will minimize the chance for ignition and subsequent flame contact exposure from wind-blown embers.

IBHS researchers constructed a radiant panel to evaluate material performance to radiant heat exposures. This panel consists of 50 infrared natural-gas burner heads arranged in five rows of 10 burners each. The radiant-heat exposure level is adjusted by moving the target material or assembly closer to or further away from the radiant panel. Most testing has been conducted at the 35 kW/m2 exposure level; this is sufficient to ignite combustible materials and break annealed glass after several minutes of exposure.

The goal of IBHS research is to develop real-world solutions that will minimize property damage from wildland fires. Here are some examples of lessons learned in recent testing:

  • The cotton curtain shown in this photograph ignited more than a minute after the upper section of the window fell out. The stand behind the curtain holds heat flux sensors. During the test, these sensors are positioned directly behind the upper and lower window sections.Mulch and surrounding areas – Testing has demonstrated the ease with which embers can ignite vegetative debris and mulch. If the ignited mulch or debris is adjacent to a wall, under a deck or in a gutter, these areas will be exposed to direct contact with flames and can ignite if combustible components or construction materials have been used.
  • Window screens – IBHS studies have shown that a window screen will prevent larger embers from entering; however, the type of screening used makes a difference. A fiberglass window screen will fail when directly exposed to flames, thereby allowing embers and flames inside. This reinforces the importance of careful selection and maintenance of vegetation adjacent to a building.
  • Curtains – Tests were conducted using the radiant panel and a vinyl frame, dual-pane annealed-glass window and cotton curtains. The purpose of these tests was to demonstrate whether curtains would ignite before the window failed. The curtain did ultimately ignite, but ignition didn’t occur until after the glass in the upper section of the window fell out.

The results from this research IBHS is conducting will contribute to the development of real-world solutions to minimize property damage from wildland fires.

Stephen L. Quarles, PhD, is a senior scientist with IBHS.


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