Traditional Fire Organizations and WUI Firefighting

Without infrastructure, WUI doesn’t exist


WUI firefighting and prevention must become a core service for traditional fire departments with current or future existing WUI in their jurisdictions. (Photo by Steve White.)

By Alex Rivera, FireRescue Magazine Issue 6 | Volume 1

In my short 17-year fire career, I have had the experience of operating on many wildland/urban interface (WUI) incidents that have tested the most seasoned of firefighter and taxed personnel and resources to their breaking points. These experiences have brought out the best in me and many firefighters and have proven our ability to be resilient, adaptive, and steadfast even when all seems lost or impossible.

The vast majority of firefighters across the country work in traditional fire departments that do not spend a whole lot of time, money, and resources on WUI firefighting and prevention efforts. Most of their focus is on a common set of core services predominantly in the areas of structural firefighting, emergency medical services, technical rescue, and hazardous materials response. Traditionally, the United States Forest Service, the Bureau of Land Management, and other federal and state fire agencies have been responsible for managing fire suppression and prevention activities in wildland areas; but, as more people have congregated and settled in and around forests, grasslands, and other natural areas, the actualization of WUI incidents becoming commonplace is now a reality and one that traditional fire organizations must face head on, realizing their roles and responsibilities in WUI fire efforts.

WUI Firefighting and Prevention

With more than 30 percent of the United States’ population living in WUI areas and rapidly growing,1 WUI firefighting and prevention must become a core service for traditional fire departments with current or future existing WUI in their jurisdictions. First, attempt to understand WUI. Next, create a comprehensive analysis that surveys, identifies, and describes the WUI areas in your jurisdiction and the risks and threats to life, property, and environment associated with each WUI. Once this process is completed, complete a strengths, weaknesses, opportunities, and threats (SWOT) or similar capabilities and needs analysis that focuses on the department’s capabilities to combat the identified threat-in this instance, WUI. The combination of the two analyses will now allow the organization to establish a preplan that establishes strategy, direction, and guidance.

The intent of this article is to define WUI in the context that traditional fire departments must understand to effectively plan for a WUI fire incident and outline several basic yet foundational factors that should be identified and answered in your WUI risk and capabilities analysis prior to establishing the organization’s strategic and tactical objectives for WUI prevention and mitigation.

Defining and Understanding WUI

There are several definitions that describe WUI, differing slightly in verbiage, but all more similar than not. Simply put, WUI has commonly been defined as an area where urban infrastructure and wild natural areas converge. Fire departments have to identify these areas within their jurisdiction and must understand the threats and risk factors associated with WUI.

The greatest threat WUI poses is damage to infrastructure. Without infrastructure, WUI doesn’t exist; it’s just open grass, brush, or forest land. So as a traditional fire department, the priority must be to protect the infrastructure from the threat that the wildland vegetation poses. To do this effectively, fire departments must understand why wildland vegetation is a threat.

Vegetation Threats

There are two major factors that make the vegetation in the WUI a threat: lightning strikes and human activity. Lava flow is another, less frequent, cause.2 Most wildland fires are caused by human activities. From 2001 through 2011, on average 85 percent of wildland fires in the United States were caused by human activity. This accounted for 717,527 human-caused fires compared to 121,849 fires caused by lightning in that same time span. (1)

In WUI areas, human activity is everywhere. These human-caused fires are a result of several negligent actions that include unattended campfires, improperly discarded cigarettes, and arson. Other human, nonnegligent causes include down power lines, ruptured gas lines, and vehicle fires. Lightning strikes are not constant and may not occur very often in every jurisdiction’s WUI areas; however, if they do, all lightning strikes have the potential to start a fire. In 2008, my department responded to two major lightning-caused WUI incidents simultaneously. In June 2008, we responded to both the Klamath Theatre Incident in Siskiyou County (CA) and to the Basin Complex (CA), which was in our own backyard. Both incidents became two of the largest fires in state history and in all destroyed 58 structures and took two lives. Unlike human activity, lightning cannot be tamed and is a major threat to start fires.

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Fire Behavior

If and when a WUI fire starts, it’s important for the fire department to identify the factors that will contribute to the fire’s ignition, growth, and spread. Fire behavior factors the rate of a fire’s spread and its intensity (flame lengths and heat generation). Once a fire ignites in vegetation, its behavior depends on the three factors that drastically affect the fire behavior triangle: weather conditions, the amount and arrangement of vegetation, and the topography. The fire behavior triangle is not to be confused with the fire triangle. The fire triangle represents the three elements necessary to have a fire whereas the fire behavior triangle describes the three elements that will determine a fire’s behavior.3

Weather: Weather influences vegetation in many ways. Weather determines vegetation moisture content and determines the time frame in which the vegetation dries out, making it more susceptible to ignition. Some parts of the country, such as the Southeast, have higher humidity levels, which saturate the atmosphere with high-moisture content. The more moisture, the less likely it is for vegetation to ignite and burn. Low humidity levels, which are common in the western, desert regions of the United States, leave vegetation dry and vulnerable to fire. Extensive periods of drought and high winds consume vegetation moisture quickly, leaving the vegetation dry.

Wind has a major impact on fire behavior. Wind plays a major role in fire spread, pushing embers and convected heat to unburned areas, causing new fires. Wind direction, speed, and pattern are not always predictable and are greatly impacted by topographical features such as canyons, saddles, and ridges.

Understanding high- and low-pressure systems is important as well. High-pressure systems bring warm, dry conditions with little to no precipitation, and low-pressure is associated with cloudy, rainy, and overcast weather conditions.4 Constant high-pressure weather patterns create the conditions for vegetation to burn. The fire department should become familiar with area weather patterns, particularly wind shifts and the times of day this usually occurs. In some places, a declaration is made at the local and state levels announcing the start of wildland season; be informed on this declaration and the factors used to determine the start of the season.

Vegetation Types (Fuel): Knowing the types of vegetation in the WUI will help in projecting how a particular fuel type will react when exposed to heat. Certain fuels, based on their size, moisture, and chemical content, will have a lower ignition temperature and burn hotter, faster, and with more intensity. Determine the fuel types in your WUI. Identifying whether these fuels are predominantly surface or crown fuels or a combination of both will help in predicting fire behavior. Surface vegetation consists of your grasses, shrubs, and bushes, while crown or aerial vegetation consists of the canopies of leaves and branches that sit atop trees. Overgrown grass, taller shrubs, and low-hanging branches are categorized as ladder vegetation because of their ability to spread the fire from the ground surface into the aerial vegetation. The amount of fuel and the arrangement will also give a good indication of fire spread. The fire department should be aware of vegetation in WUI areas that has not burned for several decades, since these areas are the most vulnerable to burn.

Topography: Areas with a large, high-sloping topography, to include mountainous and hill terrain, will tend to influence faster upslope spread (from bottom to top) than downslope spread (top to bottom). Slope has an affect that increases heat transfer between the flame and fuel ahead of it.5 The addition of wind greatly increases the transfer of heat on an upslope into the vegetation above the fire, creating perfect conditions for fast-moving fire spread. This concept is greatly increased when fire is located in a box canyon or intersecting drainages.

Fires in a box canyon can have an upward draft like a fire in a fireplace. This dangerous condition occurs when unstable air conditions at the surface cause a convection current through the canyon; air is drawn in at the base of the canyon to support the convection currents, and fuels are available to support a rapid burnout in the head of the canyon. Fires burning at the bottom of narrow canyons can also have a fireplace-like or chimney effect. This is because of the fire burning or smoldering, creating superheated air that is being carried by convection upward in the canyon, drying out vegetation at the top. Flying embers from the fire below carry into the dry vegetation and create a fire. This is especially dangerous to firefighters working above the fire and for infrastructure at the top of the hill or mountain.

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Topography can determine the extent in which weather affects vegetation. Vegetation in higher elevations tends to carry more moisture because of higher levels of precipitation than vegetation in lower elevations, which more commonly have higher temperatures and drought conditions.

Capabilities Analysis

When the risks and threats associated with WUI areas in your jurisdiction have been identified and understood, a capabilities and needs assessment of the department’s ability to prevent and combat WUI fires should be conducted.

Labor and Incident Command System (ICS) Capabilities: WUI fires are very often extremely labor intensive, requiring an exceptional amount of staffing to effectively mitigate the incident, particularly when faced with extreme weather patterns, rugged topography and terrains, overgrown and dry fuels, and urban interface that threatens large numbers of people and infrastructure. The labor intensity and staffing effort are based on the strategies and tactics employed. For example, staffing needs and labor efforts will be more greatly expanded for firefighters attempting to access a fire on a 20-degree slope through thick brush and rugged terrain than they would be flanking a grass fire on flat terrain.

Traditional fire organizations must identify their staffing needs for every possible WUI fire scenario that can threaten their jurisdiction. Daily firefighter staffing, which includes operations and command staff level personnel, must be identified and the numbers compared against possible WUI scenarios. Travel distance and time, district backfill coverage, duty recall (paid and/or volunteer), and mutual/auto aid must be factored when realistically determining staffing capabilities. Not all departments will have a large command staff contingency to establish early incident command and disseminate responsibilities through proper span of control measures. WUI incidents will likely involve several operational periods and go beyond local-level jurisdiction capabilities.

Operational periods can range from 12-hour periods to 24-hour periods in length, but this mostly pertains to operational personnel. Command personnel can remain in place for several days at a time. This must be understood preincident, and a contingency must be in place with state-level incident management system teams to respond immediately on request. This capability is essential to ensure that, as the incident grows, the incident commander is able to focus on macro level objectives while using division/sector and group supervisors to oversee the completion of the tactical-level objectives.

For the incident commander, a good rule of thumb for span of control is three to seven divisions/sectors or groups under his control, with five being optimum. This same rule applies to the division/sector and group supervisors for company assignments. This is paramount to the success of a WUI fire being mitigated as safely and effectively as possible. For departments that do not have an adequate number of command-level officers, ensure mutual/auto-aid agreements are in place to supplement and properly prepare your company officers through mentorship and training to be prepared to operate in this capacity.

Tools and Equipment: WUI fires require firefighters to be properly equipped with appropriate tools and equipment to perform a variety of functions from cutting line to progressing hose; falling trees, limbs, and brush; mopping up hot spots; and prepping, extinguishing, and overhauling structures. Tools should include both hand and power tools. Chainsaws with enough power and the right blades and bar lengths should be readily available. (Remember: This is WUI; a wildland saw blade is not always the best choice on the roof of a house.) Hand tools come in all shapes, sizes, and purposes. Choose hand tools that will positively affect your operations. For wildland duties, there are always safe choices, and there is an assortment of tools available on the market that can meet your expectations.

Proper wildland personal protective equipment (PPE), to include wildland-rated boots, should be issued to each individual firefighter. There are many organizations that outfit an apparatus with wildland PPE of differing sizes instead of personally issuing equipment to each individual. While I understand that budgetary constraints may be the reason, avoid this practice if at all possible. This is not a practice for structural PPE and should not be practiced with wildland PPE for the same reasons. At a minimum, PPE should include a jacket, pants, gloves, a helmet, boots, eye protection, and a fire shield. Structural gear is too heavy and thick, holding in heat and causing extensive amounts of perfusion. This works in a structural setting where your amount of activity is in shorter durations, but it is not conducive to an outdoor, WUI setting where you are working for longer durations and moving longer distances while being exposed to nature’s elements. Wildland PPE is lightweight, which allows it to breath, keeping personnel cooler and more comfortable.

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I am going to include hose in this section because it is a tool but more significantly because proper hose selection is important during a WUI incident. One and a half-inch hose is a great all-purpose hose that can be used for both direct attack on burning vegetation and for structure protection and extinguishment. Some may question 1½-inch hose for structural applications, especially if one is not familiar with WUI tactics. When dealing with structures during a WUI incident, it is most common that several structures will be threatened or on fire at one time, and it is very likely that a single resource will be responsible for a cluster of structures singlehandedly. With this all-too-common scenario, the single resource must assume a defensive posture and treat the situation as a triage operation. This will require the ability to move the single resource quickly from structure to structure with handlines deployed, ready to defend. One and a half-inch hose is lightweight and easy to pack up to move as needed while at the same time providing enough water to attempt a defensive exterior fire attack.

Apparatus: Review your apparatus types and capabilities. Determine each of your apparatus’s pump capabilities and tank sizes. Ascertain whether your apparatus have off-road capabilities, pump-and-roll capabilities, and an auxiliary pump. A good reference is the National Wildfire Coordinating Group’s (NWCG) “Incident Response Pocket Guide,” which categorizes apparatus by type, operational capabilities, and equipment inventory.

For example, structure engines are identified as either type 1 or type 2 apparatus. Some factors that determine their type include tank capacity, minimum pump flow, rated pump pressure, maximum gross vehicle weight, and staffing. Generally, type 1 and 2 apparatus are assigned to structure protection duties because of their pump capacities, water tank size, and equipment. Wildland apparatus are typed from 3 through 7, with the type 3 apparatus providing the most capabilities to your type 7s, which provide the least amount of capability. These apparatus are assigned to direct or indirect wildland attack or may be assigned to support a progressive hoselay. Conduct road tests on steep up-slope roads to ensure that your apparatus have the power to make it to the top with little effort, and then test the brakes on steep down-slope roads. Review how each apparatus is equipped. Is each equipped similarly, or are they all different? This may seem like a tedious and taxing endeavor, but it is a necessary one that ensures operational readiness.

Training: Fire departments must ensure that all of their personnel are trained in both wildland and WUI operations. A thorough inspection of all department personnel’s training records should be completed to gauge familiarity with wildland and WUI operations. More importantly, a review of the department’s wildland and WUI experience should be performed by reaching out to your personnel through the best means of communication for your organization. For large organizations, this may be a survey or questionnaire; for smaller departments, face-to-face communication with each shift may work. Whatever the means for gathering this information, understand that it is important and gives you a good starting point for establishing or improving your training program.

ICS training along with operations-level training must set the foundation. The NWCG provides a list of courses that are position- and level-specific and are an excellent source for training information and certification coursework. When possible, incorporate mutual/auto-aid partners into the training plan. Schedule weekly and monthly training drills and classes centered on wildland and WUI operations, ICS, and communications at agreed-on locations. A combination of classroom and practical application for each session is a good way to disseminate and practice all pertinent information.

All parties involved have to speak the same fire language and operate in a similar fashion. This can only be accomplished through consistent practice and interaction. WUI incidents are labor intensive and require lots of bodies. Whether you know it yet or not, WUI incidents will require aid. Get everyone on board preincident and get on the same page. There is nothing more dangerous than firefighters in the same fight playing from a different playbook.

WUI Foundation

The information provided in this article explains some of the basic foundational factors that must be included in determining your department’s WUI capabilities. Although basic, they are important in jump starting a comprehensive analysis that is a necessary part in preparing your department for WUI.


1. United States Department of Agriculture, “Wildfire, Wildlands, and People: Understanding and Preparing for Wildfire in the Wildland-Urban Interface,” January 2013, General Technical Report RMRS-GTR-299. Retrieved from

2. National Park Service, “Wildfire causes.” Retrieved from

3. National Park Service, “The science of fire.” Retrieved from

4. ABC Science, “How do high and low weather systems work?” Retrieved from


Alex Rivera is a 17-year veteran of the fire service and a captain with the Fort Jackson (SC) Fire Department.


Without infrastructure, WUI doesn’t exist   By Alex Rivera, FireRescue Magazine Issue 6 | Volume 1 In my short 17-year fire career, I have had the experience of operating on many wildland/urban interface (WUI) incidents that have tested the most seasoned of firefighter and taxed personnel and resources to their breaking points. These experiences have […]

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