Recognizing Wildfire Risk

Recognizing Wildfire Risk

How do you know if you’re at risk from wildfire? A home on the edge of a woodlot or in a field of overgrown grass is easy to identify. But homes within the Wildland-Urban Interface (WUI) are also at significant risk. The WUI can be anywhere along the suburban fringe. Many densely developed suburban neighborhoods, such as Ken-Caryl, with four-lane streets and stoplights are at significant risk from wildfire. It’s hard to say exactly where the risk ends, but having undeveloped woodlands and fields in and around a neighborhood means that residents should know how to prepare their homes for wildfire.

Two types of wildfire – surface and crown fires – can affect homes. Surface fires burn materials laying on or immediately above the ground, including pine needles, leaves, grass, downed logs, stumps, tree limbs and low shrubs. This type of wildfire can surround a home and slowly find vulnerable spots to ignite. Crown fires move through the canopy of a forest stand, burning from one treetop to the next. They can have extremely high flame lengths, which often start spot fires far ahead of the fire front. Surface fires throw embers as well, although typically not as far as crown fires.

Crown fires can catapult embers onto your property, including your roof and gutters. Crown fires are the most destructive of all wildfires, able to kill mature trees and shrubs, and can move over large areas in short periods of time. Some surface fires, especially grass or marsh fires, can move very fast in the high winds, which occur frequently across the Front Range and cause great injury or even death when they are underestimated. Surface fires can become crown fires in stands where there are “ladder fuels” (i.e. branches that extend to the ground and allow a fire to climb up a tree to its crown).

The Home Ignition Zone: Homeowners in the WUI should be paying the most attention to producing a safety zone immediately surrounding the home. Wildfire researchers have created the term Home Ignition Zone (HIZ) to describe the area around a home. Characteristics of the HIZ determine a home’s potential for being ignited by a wildfire. A well-managed HIZ will cause a crown fire that is approaching the property to decline in intensity due to reduced fuels. As the fire continues to get closer to a home, it will move from the crowns of the trees to the ground and slowly diminish due to a lack of flammable materials. The fire might continue to burn around the HIZ, but the home can remain intact with minimal damage. It is unlikely that we can prevent wildfires from occurring. The goal of a firewise approach is to improve a home’s chance of surviving a wildfire with little or no damage.

Foundation to Immediate Landscaped Area: Experts recommend keeping the first 3-to-5 feet around the base of the house and any outbuildings completely free of any fuel for a fire. It’s easy to understand why tall grasses or evergreen shrubs near the house are risky – when ignited, they could put hot flames directly against the siding and eaves. However, other materials can ignite when dry and should also be kept away from buildings. These include things such as leaves, pine needles, straw bales and organic landscaping mulch. These materials can host a smoldering fire long after the main fire has completely passed. In fact, a high percentage of homes lost to wildfire ignite well after the most intense portions of the wildfire have passed.

Moving farther away from the house, landscape trees, shrubs and plants should be managed to ensure that any fire in this area remains on the ground and burns quickly (i.e. no smoldering) and with low intensity. That means keeping the lawn clean of fallen pine needles and leaves. All vegetation should be well manicured, green and healthy.

Topography and Slope: Wildfires are typically most intense on sloped ground, particularly at the top edge of a hill, because fire burning uphill heats and dries the fuel in its path, causing those fuels to burn more rapidly and intensely. Because of this, the tops of slopes are dangerous places to build a house. Even small changes in topography can have significant impacts on fire behavior. If your house is built on, next to, or closer than 30 feet to the edge of a slope, the HIZ will need to be wider and extend farther downhill, away from your home. This will create a larger, reduced fuel area that the fire will have to move through as it burns uphill toward your house. The longer and steeper the slope around your house, the more the landscaped safety zone should be expanded.

Different weather such as wind and humidity, topography and fuel conditions lead to the final outcome on every fire. And sometimes homes that appear relatively prepared for wildfire burn, while those that look ready to burn are spared. A large part of this risk reduction has to do with creating defensible space—the area around a home where natural and manmade fuels are treated, cleared or reduced to slow the spread of wildfire.

There is no magic bullet to protect a home from wildfire, but if you take the necessary steps, the odds increase that firefighters will be able to successfully defend it. Although firefighters aren’t always able to protect every threatened home, addressing defensible space also will make structures better prepared to survive a wildfire on their own.

The Ken-Caryl Firewise Committee urges you to talk with your family about wildfire, prepare and practice an evacuation plan, and create defensible space around your home.

This article originally appeared in the March 22, 2017 Life at Ken-Caryl newspaper.


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