Wildland Urban Interface: Ensuring the “Defensibility” of Defensible Space


Defensible space, the area around a structure in which fuels have been modified to increase the likelihood that the structure will survive a wildland fire front, has evolved through many definition revisions. This concept evolution is based on continual research by members of the fire science community and the personal experience of all-risk firefighters charged with suppressing fires in the wildland urban interface (WUI). This definition evolution can also be attributed to the numerous resource conservation groups and Fire Safe and Fire Wise councils that provide property owners with information and education for preparing their homes for the inevitable wildland fire season.

When property owners modify the surrounding and adjoining vegetation, they assist fire personnel in making decisions during the structure triage phase of operations in the WUI. Defensible space around a structure can come in many forms and differs in relation to fuels and building construction features. If you were to travel through the multitude of communities in the wildfire-prone areas of our nation, you would see the broad spectrum of personal property preparation, which ranges from excessive clearance and fire resistive construction to nonexistent defensible space, problematic construction materials, and poor topographic placement.


A critical component of defensible space is how that space is positioned in the greater landscape; unfortunately, this is a factor that is often overlooked when the space is being assessed during triage decisions. This lapse in complete defensible space evaluation is understandable when considering the often chaotic nature of the initial attack on rapidly growing fires or a distant fire that catches personnel off guard because of a change in conditions. Add to this the massive mobilization of resources from out of the area and unfamiliarity with local factors—not to mention challenging access issues—and the stage is set for personnel to miss the defensible space “big picture.”

(1) Photo by author; other photos from the formal investigations of the wildfires.

Failing to evaluate the “big picture” of a structure’s defensible space placement in the landscape when making triage decisions about that structure can be dangerous. Regardless of how modified the fuels may be or even if fuels are absent, there will be no safe place for responders to stay if the landscape concentrates, channels, or delivers the approaching fire’s intensity directly on the structure’s location. Because of this fact, I urge all fire suppression personnel tasked with structure protection to remember this statement: “Defensible space must be properly placed.”

In this day and age, the amount of information available to homeowners on the topic of defensible space is astounding. It is available in the forms of publications and brochures, at trade shows and conferences, and on the Internet. Direct access to this information benefits all in our communities. If homeowners use the information properly, it may increase firefighter safety in the traditionally dangerous WUI.

As a firefighter asked to serve our community when threatened by wildfire and appreciative of the information available to property owners regarding defensible space, I must interject my observations and concerns of the near-miss and, unfortunately, fatal fires in recent large WUI incidents. In particular, I would like to draw attention to the incidents that reinforce my observations, research, and subsequent suggestions for future firefighting operations: the Cedar, the Esperanza, and the Jesusita Fires.


Let me first make the humble and sincere statement that I am in no way trying to point to blame, deficiencies, lack of skills, deficient training, limited experience, poor situational awareness, or even inferior equipment with regard to the agencies and personnel involved in the mentioned tragedies or accidents. I am merely citing these incidents as examples of how even with defensible space created around structures, terrain and local factors can channel fire on a specific location with disastrous results. I was not present at any of these incidents and am not trying to second-guess the decisions made by those involved. I am deeply appreciative of the sacrifice made by all involved, especially the firefighters, some of whom gave their lives. For the greater good and improvement of the fire service, it is our obligation and duty to use these incidents as learning opportunities so we can better prepare for our job and ensure that our fellow firefighters did not die in vain.

(2) Most of the energy of a large fire run is focused in the drainages. Locate these pathways, and avoid them during extreme fire behavior.

The above statement, “Defensible space must be properly placed,” appears to be a stating of the obvious and perhaps is information we encountered while training or reflecting on the basic safety concepts of operations in the WUI. However, it is crucial for our safety that we explore its subtle implications. On further reflection, it becomes obvious that numerous issues with safety implications for firefighters are imbedded within it. The many principles of accurate situational awareness, the dynamic nature of the interrelated relationships of fuels, weather and topography, the constant revision of tactical and strategic priorities—all are required to be constantly processed during the high-pressure atmosphere of WUI operations, and it is almost overwhelming.

The number of interconnected wildland fire suppression training concepts contained within the statement mandates that it be thoroughly analyzed. All firefighters should fully consider this basic statement and use it as part of their risk/benefit analysis, structural triage, and daily suppression responses. If you take the time to understand and process the entire situation presented to you, then you have completed the first vital steps in answering the most important question: Where can I safely engage the fire given the environmental variables on today’s shift?

The incidents listed above prove that if the entire concept of defensible space is not fully evaluated, especially the placement of the residence in the topography or the structure’s susceptibility to the influence of topographical fire behavior impacts, you are exposing yourself to excessive risk. The definition of defensible space needs more scrutiny; it should do more than merely note the horizontal distance of vegetation from a house. Although we train to the concept that there is a three-dimensional aspect to the fire environment, this concept often is not in the forefront of firefighters’ minds during suppression operations. The fire is moving quickly, other homes are burning, and suppression resources are stretched thin; all this distracts personnel operating in the WUI and directs them to more immediate concerns.


The answer is to identify the significant priority of analyzing your location in the landscape before you are tactically engaged and committed.

Begin in your initial attack area, and expand the initiative to include all of the areas to which you may have to respond—including assisting the adjoining agency and supporting statewide mutual aid. Although it is impossible to have specific knowledge of the entire state in which you live, you can develop a systematic approach to decision making that can be applied anywhere, under any incident-specific variables.

Start this process by gathering as much information as possible about the local factors influencing fuels, weather, and topography. This information is readily available from a variety of sources including the Internet, local residents, local jurisdiction emergency personnel, topographic maps, and satellite imagery. With the prevalence of computers in our apparatus and the growing numbers of smartphones with access to the Internet, the information is literally at your fingertips. Never before in the history of wildland firefighting has site-specific information been as accessible as it now is.

Within minutes, you can look up the fire most likely to be necessitating resources, find incident action plans and maps, obtain weather and fire behavior forecasts, and even remotely observe local roads and building construction by viewing pictures posted on popular mapping sites. In addition, you can use free applications that enable you to rotate the landscape to see terrain in three dimensions. If you do not have access to any of the information available remotely, you can still apply the basic skills of observation while traveling across the landscape to help in identifying locations that will pose safety concerns because of topographical influences.

Although the electronic information is valuable, technology can fail, batteries can run out, the Internet can collapse, and you can lose a signal. There is no replacement for the basic skills of map reading and understanding how fire moves across the landscape. Recognize features and elements that produce problematic and dangerous fire behavior, like chimneys and continuous fuels. Use the skills of observation to interpret the situation; look past the area directly surrounding the structure you are assigned and determine what influences in the larger area are at work to potentially deliver dangerous fire behavior to your area of deceptively adequate defensible space. Just as one of the common denominators of tragic fires, fires burning in deceptively light fuels, can lead to a tragic outcome, so can the presence of defensible space lure a responder into a false sense of security and to a tragic result.

(3) Overview from the accident site looking north to Cabazon.

Look at photo 3 from the Esperanza Accident Report. This photo simply and graphically illustrates the concepts I am discussing. The sobering clarity provided by this perspective, after the accident occurred, should serve as a reminder to all personnel assigned to structure protection the potency of topographic influences on fire behavior. Note the topography below the site and how wind in alignment with the drainage combined with the focusing of the fire’s convective heat and ember shower; the amount of defensible space around the home couldn’t possibly provide safety to the personnel given the incident variables of that day.

Training to protect homes during WUI fires should begin with refining the skills of rapidly assessing site-specific variables to determine a safe location from which to operate and tactical priorities. Keep in mind that if the topography will draw fire behavior to your location, the outcome will be dangerous and inevitable, despite the fuel modifications, construction features, and improved defensible space factors. When assigned to structure protection, always ask if the defensible space is properly placed.

TODD McNEAL is a captain in the Sonora (CA) Fire Department and has a diverse background in wildland and structural fire management and suppression. He has been serving as the wildland training officer, as well as a Division/Group supervisor, on a federal Type II Incident Management Team for the past five years. His career began with the National Park Service and U.S. Fire Service, working between California and Montana. McNeal has been actively instructing in the fire service for the past decade and has numerous ICS qualifications in wildland operations. Additionally, he is a registered instructor with California State Fire Training and a California fire officer. He has a bachelor’s degree in natural resource management.

More Fire Engineering Issue Articles
Fire Engineering Archives

No posts to display