The presence of civilians and structures in the wildland/urban interface (WUI) increases the complexity of any WUI or wildland incident. In addition to typical firefighting challenges, firefighters face unique problems, including the evacuation of civilians and animals; hazardous conditions, such as propane tanks, power lines and hazardous materials; and protecting high-value assets at risk, including homes and businesses. Because of these situations, firefighters must rapidly assess a structure to determine whether or not it can be safely and successfully defended. This evaluation process is called structure triage.
Structure Triage: A Review
Structure triage is the process of inspecting and classifying structures according to their defensibility or non-defensibility, based on fire behavior, location, construction and adjacent fuels.
The decision to engage in structure defense operations should always be based on the determination that the structure is, in fact, defensible and that any risks to firefighters can be safely mitigated. Therefore, structure triage decisions must be based on current and forecasted fire behavior. Any change in fire behavior can quickly change the defensibility status of a structure.
When making a decision to defend a structure, firefighters must continually assess the fire environment as well as the physical features of the structure and its surroundings, and make a reasonable forecast of what will happen when fire impacts the location. Firefighters have been injured or killed during structure defense operations in which firefighters underestimated fire behavior.
S-FACTS Defined
When making decisions about tactics and resources, and setting priorities during the structure triage process, it may be difficult to remember all the factors that must be considered. One helpful tool developed by the CAL-Fire WUI Working Group: the Survival Facts, or S-FACTS, memory aide.
S–Survival
When considering the potential for and risks to survival at a WUI incident, the most basic question to ask is, can I survive here? If the answer is no, leave immediately. Other questions to ask:
- Is there a safety zone nearby? If not, can one be constructed near the structure?
- Is there a viable escape route? If not, can egress be improved to create one?
- Is there a temporary refuge area (TRA) on site?
- At what point will you leave? (This decision is based on fire behavior and rate of spread.)
- Is the prep-and-go tactic an option?
- Do you have communications with your supervisor and adjoining forces?
- Can safety issues be mitigated? If any safety aspect cannot be mitigated and resources cannot safely defend the structure, firefighters should leave the structure and move on to another assignment.
F–Fire Environment
Triage includes onsite observations of current fire behavior and predictions of what the fire may do in the near future. Evaluate the fuel, weather and topographical features around the structure and estimate the intensity of the expected fire behavior.
Again, one of the most basic questions you must ask yourself when on scene is, can I survive based on current and expected fire behavior? If the answer is no, leave immediately. If the answer is yes, begin your evaluation of the area and/or structure by considering the “look up, look down” indicators: fuel (characteristics, moisture, temperature), wind, terrain, atmospheric stability and fire behavior.
Fuel
Evaluate the fuel around the structure, its relationship to the current weather and topography, and what measures firefighters can take to reduce the fuel load. Specifically, consider the following:
- Fuel type: What fuel type is carrying the fire front and contributing the greatest heat and ember production? Will fuel reduction efforts be easy or difficult (i.e., a grass model versus a brush model)?
- Fuel loading: How much fuel is present and how will that fuel load impact structure preparation timetables? Is there so much fuel that reduction efforts are impractical?
- Should fuel reduction efforts focus on smaller areas around the structure, concentrating on the fire impact zone where at least some fuel may be removed?
- When vegetation is cut, can it be stacked or spread without creating large piles that contribute to fire intensity?
- Fuel continuity: Assess vertical and horizontal continuity and how it will impact structure preparation efforts. Evaluate vertical fuel ladders that will allow the fire to spread from the ground into the crowns of trees and large brush.
Other Indicators
- Wind: What is the current speed and direction? Are changing winds expected?
- Terrain: What is your position relative to topography? Are you in a chute, chimney or saddle? If so, leave immediately. Are you mid-slope or on top of a ridge? Is wind in alignment with topography?
- Atmosphere: Is the atmosphere stable or unstable? Unstable atmospheres can lead to rapid fire growth. Are thunderstorms forecasted?
- Fire behavior: Is the fire spotting, crowning or sheeting? What is the rate of spread? What is the current and forecasted flame length and height?
- Other weather considerations: What is the current relative humidity? Is there an expected change?
A–Access
Of course, access to the structure must be safe in order for firefighters to enter and exit the area. It must also allow enough time and distance to serve as an escape route to a safety zone or TRA. To determine the degree of accessibility, firefighters should scout ahead before committing larger apparatus to specific locations and consider the following:
- Is access compatible with time and distance factors necessary to utilize as an escape route to a safety zone?
- Is the road surface adequate for the necessary speed?
- Does the road offer an adequate width for apparatus, and are there places that apparatus can turn around? Are there turnouts?
- Are there bridges and if so, can their weight limits accommodate apparatus?
- Are there other challenges, such as drainage ditches/culverts/steep grades?
- Is there a safe place to spot apparatus?
C–Construction/Clearance
Evaluate the structure to determine how it was constructed and what materials were used. Determine whether the structure has adequate defensible space, based on topography, fuels, and current and expected fire behavior. If defensible space is minimal or non-existent, determine whether problems can be mitigated quickly. Questions to ask:
- Will building materials and yard clutter compromise safety?
- Is the construction wood siding or shake shingle roof?
- Are there vent openings, open eaves, large glass windows facing the fire front, or decks with vegetation below?
- Will ember intrusion through attic or foundation vents be a problem?
- What are the contents in the garage and outbuildings?
- Are there hazardous materials or equipment present, such as propane tanks, fuel tanks or power lines?
- Is there an adequate water supply nearby?
- Are additional resources needed?
- Should you consider the “prep and go” or “prep and defend” tactic?
T–Time Constraints
The final triage variable to consider is time. Firefighters must determine how much time they have before the fire front impacts the structure, and whether they have enough time (and resources) to:
- Perform an adequate size-up and mitigate any safety concerns?
- Properly prepare and defend the structure before the fire front arrives?
- Retreat to a safety zone, if necessary, if fire conditions change? If the answer is no, again, leave immediately.
S–Stay or Go?
After considering all of the aforementioned elements, categorize each structure as not threatened, threatened defensible or threatened non-defensible (see sidebar). This will help you determine tactical decisions. For example, if you determine that it’s safe to stay, you may prep and defend the structure. If it’s not safe, use the “prep and go” tactic or the “fire front following” tactic. Note: For more information on WUI tactical terminology, visit http://tinyurl.com/wui-tactical1 or http://tinyurl.com/wui-tactical2.
Conclusion
Structure triage will help determine whether firefighting resources can safely stay at a structure or if they will be forced to leave. As with many tactical decisions, time is a critical factor during triage, as are fuel levels and the weather. At first glance, a structure may appear to be defensible with little or no intervention, but firefighters must always remember that as fire behavior changes, the classification of a previously triaged structure may change as well, leaving them no choice but to retreat to a safety zone or TRA.
Sidebar 1: Structure Triage Categories
Not-Threatened
- Safety zone nearby and TRA present at structure
- Construction features/defensible space make the structure unlikely to ignite
- Residents may/may not have evacuated
Threatened Defensible
- Safety zone nearby and TRA present at structure
- Construction features/defensible space require structure defense tactics during fire front impact
- Residents may/may not have evacuated
Threatened non-Defensible
- Lack of adequate safety zone nearby
- Structure cannot be safely defended
- Residents must be evacuated
Sidebar 2: S-FACTS Breakdown
S: Survival
F: Fire environment
A: Access
C: Construction/clearance
T: Time
S: Stay or go
Sidebar 3: LSI 3: Risk Management
