Wildland Urban Interface Fires: Managing a Cascade of Risk


It was a normal summer across Colorado’s Front Range, where America’s prairie heartland gives way to the imposing Rocky Mountains. August 2010 saw slightly above normal temperatures and below normal rainfall. By September, a short-term drought stressed vegetation and raised the danger of a large fire event. Fuel moistures in the forests above the city of Boulder were marginally below normal, and abundant grasses and shrubs were seasonally dry.

Residents and response agencies in the historic mining communities, trendy subdivisions, and upscale homes in the mountains and steep canyons above Boulder took the ever-present risk of catastrophic wildland urban interface (WUI) fire seriously. Area resident Carrie Barker explained that when the fire danger is elevated in the summer and fall, “We don’t even burn tiki torches up here.”

As is common in late summer, diurnal downslope and down canyon winds (localized, time-of-day winds) daily clocked at 10 to 20 miles per hour (mph) with gusts frequently exceeding 40 mph. Barker’s worst fears were realized when a strong downslope gust fanned three-day-old embers in the backyard burn pit of a local volunteer firefighter.


On September 6, 2010, at 1002 hours, a 911 call reported a fire off Emerson Gulch Road near its intersection with Four Mile Canyon Drive. Within hours, the fire was spotting more than a half mile ahead of multiple crown fires blasting through treetops. In less than a day, the Four Mile Canyon Fire would destroy more homes than any wildfire in Colorado’s history and earned the dubious distinction of being the largest fire then burning in the United States.

The scope and complexity of the incident immediately blew past the resources of the new Boulder County Type III Incident Management Team (IMT). A much larger Type II regional team quickly assumed responsibility, which, in turn, was soon replaced by a national Type I management team under authority of the Colorado Department of Natural Resources and the Boulder County Office of Emergency Services.

“On September 9 at 1600 hours, management of the fire transitioned to our team during a Red Flag Warning, which is not very comfortable—especially given the fuel type, terrain, and weather conditions,” recalls Operations Section Chief Dan Buckley of the Great Basin Type I IMT that assumed management of the fire.

On the ridgetops and in the canyons, the fire assumed by the Great Basin team was still very much alive. A Red Flag Warning signaled weather conditions highly conducive to another round of extreme fire behavior. Predicted west winds threatened to push the fire down the foothills into Boulder, which would have necessitated the immediate evacuation of a medium-size city in a very short window of time.

“We developed a contingency plan and organization with the Boulder City Fire Department should the fire burn toward the city. We knew a westerly wind event would have really caused problems, including evacuations of thousands of citizens,” said Buckley.

Save for a 3.5-acre breach in the fireline, which was quickly extinguished, control lines held—even after peak gusts of 64 mph that night.

(1) Most residential structures were destroyed by ground fire or smoldering embers after the fire front passed.
(1) Most residential structures were destroyed by ground fire or smoldering embers after the fire front passed. A smaller number of homes were quickly consumed by the direct flames and intense radiant heat of crown fires—a percentage consistent with most interface fires. (Photos by author unless otherwise noted.)

When the last pockets of heat were finally cooled a week later, residents were allowed to return. Many found nothing but ash-covered foundations. The fire had charred 6,200 acres in the foothills, ridgetops, and canyons west of Boulder and consumed 169 structures, mostly homes. Insured losses alone totaled nearly a quarter-billion dollars. The acreage included a diverse mix of federal, state, and private land that blurred jurisdictional responsibilities—and ultimately who would pay millions in suppression costs.

Nearly 475 homes were in the fire perimeter or within 100 feet of the fire edge. Of the homes lost, 29 were ignited by the initial flame front; 139 were ignited by surface fire or ember wash.1

For all the Four Mile Fire’s devastation, it could have been much worse, including a high loss of life. The canyons, forests, and grasslands of Boulder County are historically fire prone. Residents, local and state land managers, emergency management professionals, and emergency responders not only recognized the extreme dangers long before the Four Mile Canyon Fire, but they took action by adopting programs to address complex, high-risk, multijurisdictional emergencies. Many area communities had implemented the National Fire Protection Association (NFPA) seminal Firewise Communities™ program.

(2) The Four Mile Fire Protection District lost its station and apparatus in the Salina Community to the explosive September 2010 Four Mile Canyon Fire near Boulder, Colorado.
(2) The Four Mile Fire Protection District lost its station and apparatus in the Salina Community to the explosive September 2010 Four Mile Canyon Fire near Boulder, Colorado. The historic canyon community was almost completely destroyed by the fire.

Boulder County built on the experience gained from large fires in the area such as the Black Tiger Fire (1989), Olde Stage Fire (1990), Walker Ranch Fire (2001), and Overland Fire (2003). An interagency Type III IMT was organized in 2009 and accredited by the State of Colorado in spring of 2010—just months ahead of the Four Mile Canyon Fire.

The county has continually added infrastructure to support major emergency events through the Boulder Emergency Operations Center. Reverse 911 capabilities for evacuation notification were established in 2000. Local fire districts frequently conducted and rehearsed fire scenarios typical of the Four Mile Canyon Fire, going so far as to pre-produce detailed community maps for distribution to incoming mutual-aid units.

(3) A firestorm approaches the town of Secesh, Idaho, in the East Zone Complex Fire in September 2007.
(3) A firestorm approaches the town of Secesh, Idaho, in the East Zone Complex Fire in September 2007. Wildland urban interface fires are some of the most dangerous, costly fires in North America. Structural firefighters are challenged by the myriad variables of wildfire. Wildland firefighters face the complexities of structure fires. For both disciplines, it is a netherworld of extreme fire behavior, eclectic fuel loading, unrealistic public expectation, high media interest, and a fluid mix of multiagency responders of varying abilities. Situational awareness is obscured, and span of control is rapidly exceeded in a torrent of competing demands. (Photo by Anthony Rhead.)

Summer-based in Idaho Falls, Idaho, and completely unfamiliar with the water sources, roads, and residences of the Boulder area, I used this map extensively when my engine was dispatched to the Four Mile Canyon Fire by the Eastern Idaho Interagency Dispatch Center through the National Interagency Fire Center in Boise. We and dozens of other out-of-state fire units arrived on the fire less than 24 hours after the initial alarm. Our unit served for nearly two weeks in the region on the Four Mile Canyon Fire and a second large interface incident near neighboring Fort Collins, the Reservoir Road Fire that broke out only a week later. It could have rivaled Four Mile in size and damage, but it was quickly suppressed, as an army of aerial and ground resources were immediately transferred from Four Mile.

Despite the most thoughtful preparations, risk factors and environmental conditions in the WUI environment can never be completely anticipated. The Four Mile Canyon Fire stands as a harsh reality: WUI incidents across North America remain some of the most dynamic, dangerous, and costly fires in the world.

In 30 years of structural, wildland, and WUI firefighting—including service as an engine captain on the Four Mile Canyon Fire—I’ve learned that the WUI fire environment is, at its minimum, a minefield of risk. Structural firefighters are challenged by the myriad variables of wildfire. Wildland firefighters face the complexities of structure fires.

For both disciplines, it’s a netherworld of extreme fire behavior, eclectic fuel loading, unrealistic public expectation, high media interest, and a fluid mix of multiagency responders of varying abilities. Situational awareness is obscured, and span of control is rapidly exceeded in a torrent of competing demands.

Because of these dynamic challenges and imposing risks, interface fires require reasoned response and disciplined management.


In the United States, many responders equate WUI events with fall Santa Ana winds fanning firestorms in upscale canyon neighborhoods of southern California. Although many of this nation’s most devastating WUI fires are in California, the Southwest, or the Great Basin and Rocky Mountain regions, nearly every fire agency in the United States has some type of interface fire risk.

(4) The Bull Complex Fire, July 2006, near Mataqua, Utah. Providing
(4) The Bull Complex Fire, July 2006, near Mataqua, Utah. Providing “point protection” for structures with nearby critical fire activity is inherently dangerous. Unburned fuel between firefighters and the flame front requires proactive tactical planning and solid safety controls.

Texas was particularly hard hit in 2011. An ongoing drought left heavy fuel loads tinder dry. By mid-May, the Texas Forest Service (TFS) responded to 1,096 fire incidents involving more than 1.8 million acres. Property damage included the loss of nearly 600 structures. As is often the case, these staggering property losses were not without a human toll. One firefighter was killed and five others were injured while battling a wildfire west of Fort Worth. Another firefighter died and three others were injured on the Crawford Ranch Fire.

The massive scale of these incidents required the TFS to seek assistance from agencies across the United States. Responders included 33 states, federal resources, local fire departments, numerous state agencies, regional IMTs, and departments within the Texas Intrastate Fire Mutual Aid System.

The Federal Emergency Management Agency (FEMA) doctrine of all-risk response—developing local, state, and national resources in nontraditional emergency disciples—challenges agencies but adds critical layers to the nation’s post-9/11 emergency management veneer. The doctrine has produced curious results. I served on a massive wildfire in the rugged mountains of central Idaho managed by none other than the Fire Department of New York, as in New York City, which has embraced the doctrine of “all risk” and is actively seeking to build expertise in nontraditional disciplines.


WUI fires are notorious for clouding situational awareness and pulling responders into frequently fatal whirlpools of reaction. History sadly demonstrates that WUI fire doesn’t often forgive lack of experience, poor tactical plans, adrenaline-fueled myopia, and unbridled machismo.

I speak from experience. Two years ago, my engine crew only narrowly saved an inexperienced team that was brashly attacking an explosive, fast-moving WUI fire at its head. Its engine overturned in a small ravine in front of the flame front. Burnover was only seconds away. At great risk, my engine entered the fire behind a remote deck gun water curtain and knocked a hole in the flame front wide enough to save the engine and its crew. This is the second time we’ve saved an engine crew in a similar situation. This is not something I ever wish to do again.

As a task force leader, I frequently remind engine crews that no houses or trees are worth their lives and that all WUI fire suppression activities must focus on their primary mission:

1. life safety of responders,
2. life safety of impacted civilians,
3. property protection, and
4. resource protection.

It’s all too easy and common to invert these priorities when public, political, and media pressures mount.

Incident management and tactical response must include ongoing identification of WUI “Watch Out” situations and a cognitive effort to maintain situational awareness.

Response strategies and tactics are formulated considering a combination of factors:

1. Number, type, and experience level of response personnel and apparatus.
2. Evacuations, traffic, and other public considerations.
3. Fuel type, weather conditions, and terrain features that are or will contribute to problem or extreme fire behavior.
4. Size and availability of safety zones.
5. Number of structures, type of construction, defensible space, power lines, nearby vegetation, terrain challenges, vehicle access, and available water supply.
6. Current and expected fire behavior: how much time crews have to triage and prepare structures.

Synthesizing these factors into workable response and suppression plans is a complex balancing act. And at the end of the day, are we successful because of luck or competence?

Indirect Firefighting

Fire suppression in the interface is inherently dangerous because it often involves “indirect firefighting.” Naturally, the most efficient way to suppress fire is with direct attack—as we often say, “putting the wet stuff on the red stuff.” And having unburned fuel between firefighters and the fire is ignored at our peril.

(5) The Eagle Creek Fire, July 2002, Hamblin Valley, Utah.
(5) The Eagle Creek Fire, July 2002, Hamblin Valley, Utah. A P2V Neptune drops a load of fire retardant to protect ranch buildings from a wind-driven flame front. Although aircraft can slow the fire’s progress, ground forces, including engines and hand crews, remain the primary suppression tools. Sadly, a firefighting P2V Neptune crashed and killed its crew in June 2012—10 years to the month later—just miles from where this photo was taken.

Fireground and environmental conditions often preclude direct attack. Lack of safety zones, extreme fire behavior, weather factors, challenging terrain, shortage of personnel and equipment, and limited water supplies—among many other factors—prevent engaging the fire at its head. When we’re not able to perform direct attack, we can fall back to indirect fire control tactics that focus on removing fuel from the fire equation. This can include physically removing fuels, treating the fuels with water or retardants, or burning the fuel.

Indirect attack could be likened to structural firefighters’ attacking a room-and-contents fire in a home’s laundry room by setting a backfire in the kitchen to save the prize Steinway piano in the living room after throwing the sofa and love seat out the window and ripping up the carpet. In WUI firefighting, we call this fuels management.


“WUI fire suppression is really risk management. A firefighter losing his life to save a pet from a burning building or a tree falling on a responder when he shouldn’t even be there—these are the things that should change our way of thinking and entire direction,” says Rowdy Muir, National Type I interagency incident commander. The National Wildfire Coordinating Group (NWCG) Incident Response Pocket Guide outlines safe WUI response strategies and tactical guidelines.

Safety Zones

Company officers must carefully formulate and evaluate initial response tactics and structural protection on WUI fires. The overriding consideration should be to identify adequate safety zones in the operational area. Crews should never commit to stay and protect a structure unless a safety zone for them and their equipment has been identified during size-up and triage. An effective safety zone allows crews to safely ride out extreme fire behavior without extraordinary efforts.

Effective safety zones include the following:

  • clean burns;
  • natural features such as rocks, waterways, and meadows; and
  • constructed sites including clear-cuts, roads, and helispots.

These areas must be well scouted for adequate size and hazards:

  • Is the safety zone upslope from the fire? There will be a greater heat impact; thus, a larger area will be necessary.
  • Is the safety zone downwind from the fire? Greater heat impact necessitates a larger area.
  • Is there room for all resources?

The bottom line on the adequacy of a safety zone is, Can a crew survive the flame front passage without deploying a fire shelter?

Structural Size-Up: Fire Behavior

What is the fire doing now? How will it behave three or six hours from now? If the fire is running at 10:30 in the morning, it could be a challenging day when prime burning conditions are reached in the afternoon.

The NWCG Standard Fire Orders instruct that all strategic plans and tactical actions be based on current and expected fire behavior. How much time is available before the fire arrives? Always consider the worst case and unexpected when planning and responding.

Structural Size-Up: Site Considerations

  • Is there a dedicated lookout whose only job is to keep eyes on the fire and the location of crews? Is this person equipped with adequate communications? Is he experienced enough to recognize changes in weather and understand fire behavior risks?
  • Is there adequate defensible space around the structure based on surrounding vegetation? Consider radiant heat impact on the structure from surrounding combustibles, ember wash, and direct flame contact. How long will the fire reside around the structure?
  • Narrow canyons, mid-slope homes with fire below, and narrow ridges near chimneys and saddles can increase fire behavior.
  • Hazardous materials risks such as petroleum products, chemicals, and illegal labs increase fire loads.

Tactical Challenges and Hazards

  • Narrow roads, limited bridge capacities, and septic tank locations frequently limit access of suppression equipment to structures.
  • Combustible debris next to structures creates ember traps. Ornamental plants in close proximity to structures can produce intense radiant heat and direct flame contact.
  • Wooden siding and wooden roof materials provide little protection for structures and lead to rapid rates of spread.
  • Open vents, eaves, and decks are ember traps. As the Four Mile Canyon Fire demonstrated, most structures destroyed in WUI fires are ignited by smoldering material several hours after the initial flame front passes.
  • Fuel tanks and hazardous materials.
  • Power lines frequently limit apparatus access because of height restrictions. Treated wood utility poles burn rapidly and can trap equipment on roads and driveways behind live downed power lines.
  • When it comes to water, we often have to do more with less. Water sources and supplies are frequently limited, requiring careful water usage and the discipline to “know when to hold ’em and when to fold ’em.”
  • Most states do not allow the physical removal of civilians from their residences during “mandatory” evacuation orders. This can be problematic, especially when citizens ignore evacuation orders and try to escape at the last minute with RVs, horse trailers, and vehicles piled with personal effects when fire resources are responding to the incident on inadequate neighborhood access roads and winding, narrow rural highways.
(6) Class A fuels adjacent to a wood-sided structure can trap embers.
(6) Class A fuels adjacent to a wood-sided structure can trap embers. This structure triage Class One building would require pretreatment by reducing the Class A fuel fire load or, at a minimum, an extensive mop-up after the flame front passes. A nearby safety zone made it a good candidate for mitigation by our structural protection task force.


To better emphasize life safety tactical considerations, the NWCG has revised WUI structural triage criteria from three categories to four:

1. Defensible—Prep and Hold.

Determining factor: SAFETY ZONE PRESENT.

Size-up: Structure has some tactical challenges.

Tactics: Firefighters needed on site to implement structure protection tactics during fire front contact.

2. Defensible—Stand Alone.

Determining factor: SAFETY ZONE PRESENT.

Size-up: Structure has very few tactical challenges.

Tactics: Firefighters may not need to be directly assigned to protect structure—not likely to ignite during initial fire front contact.

Patrol following the passage of the fire front will be needed.

3. Non-Defensible—Prep and Leave.

Determining factor: NO SAFETY ZONE PRESENT.

Size-up: Structure has SOME tactical challenges.

Tactics: Firefighters not able to commit to stay and protect the structure.

  • If time allows, rapid mitigation measures may be performed.
  • Set trigger points for safe retreat.
  • Patrol following the passage of the fire front will be needed.
4. Non-Defensible—Rescue Drive-By.

Determining Factor: NO SAFETY ZONE PRESENT.

Size-up: Structure has SIGNIFICANT tactical challenges.

Tactics: Firefighters not able to commit to stay and protect the structure.

  • If time allows, ENSURE PEOPLE ARE NOT PRESENT, especially children, elderly, and invalids or the handicapped. Set trigger points for safe retreat.
  • Patrol following the passage of the fire front will be needed.


All triage evaluations must be based on these objective criteria. Simply put, can it be saved or not? Neither emotion nor prejudice has a place in this process. A small, poorly maintained house could be the residence of a senior citizen on a fixed income and may not be covered by insurance. Its loss would be devastating. A high-end, attractive structure may simply be a well-insured weekend retreat for a wealthy owner.


Structure protection teams can minimize fire danger around even challenging Type III structures by doing the following:

  • Removing small combustibles next to the structure.
  • Closing windows and doors, including in the garage. Always witness and document any entry into private structures.
  • Clear the area around fuel tanks and shut-off valves.
  • Charge garden hoses.
  • Apply compressed-air Class A foam, nozzle-aspirated Class A foam, or gel retardants if available.


There is a temptation to “tie in” and prepare for a protracted battle by hooking up to hydrants or extending extensive hoselays off engines. Resist the enticement, and stay mobile.

  • Charge hoselines.
  • Long hoselays are not recommended.
  • Keep 100 gallons of water in reserve.
  • Identify backup water sources.
  • Identify power lines for aerial resources.
  • Never rely on water for your safety.

Don’t expend valuable suppression resources on lost causes. Trying to suppress a well-involved structure could mean losing the entire neighborhood.


As previously discussed, most structures do not burn until after the fire front has passed. Reentering the fire zone when it’s safe to do so can save many structures in the fire-impacted area:

  • If you are not able to safely shelter at the structure, move to the closest safety zone, and let the fire front go through.
  • Return as soon as conditions allow safe access to structures.
  • Secondary ignition is caused by residual heat, spot fires, and creeping ground fire.
  • Take suppression actions within your capability.
  • Call for assistance as needed.2


The following questions will help you determine your course of action for a WUI incident:

  • Are there life safety issues?
  • Can the structure be saved? How?
  • How much time do you have before the arrival of the fire front?
  • How many structures need protection, and what resources are available to you?
  • Can you safely perform direct attack on the fire?
  • Are you tactically limited to indirect attack?
  • Do you have the resources and time to perform both direct and indirect attack by suppressing the fire while mitigating threatened structures?

Accept that whatever decision you make, someone will not be happy with it and will find a way to publicly express displeasure.

(7) Despite near complete destruction during a fire storm, the pressure relief features on this 500-gallon residential propane tank performed as designed, and the vessel remained intact.
(7) Despite near complete destruction during a fire storm, the pressure relief features on this 500-gallon residential propane tank performed as designed, and the vessel remained intact. However, burning Class A fuels near the tank would have compromised its integrity and caused a burning-liquid/expanding-vapor explosion.

For example, A WUI fire near Wenatchee, Washington, saw the owner of a large, attractive rural home refuse to leave during a state Level Three mandatory evacuation. After the day’s dramatic fire behavior and the incident’s reaching national prominence, media poured in from across the country. This homeowner parked himself in front of a TV camera and publicly branded my engine task force “cowards” on national TV news; we had pulled back to our safety zone during the fire storm in his canyon.

The initial flame front destroyed a neighboring home we had already triaged as Non-Defensible—Rescue Drive-By, but our team saved many other homes when we reengaged and performed mop-up when it was safe to return. Although we saved many more homes than we lost and my team safely and successfully completed its assignment, to this citizen, we were deserters.

When working around businesses and residences, document your decisions and actions with photos and detailed notes. Our fire department, as have many, created a Structural Assessment Form that includes address and location, type of construction, risk factors, and mitigation actions. This form is one component of our structural response officers’ kit that includes the following:

  • NWCG Fireline Handbook.
  • NWCG Incident Response Pocket Guide.
  • Initial attack fire behavior and risk assessment Tactical Worksheet. We use a simple, effective form created by the U.S. Forest Service and U.S. Bureau of Land Management at the Eastern Idaho Interagency Fire Center.
  • Structure Assessment form.
  • Card stock paper for numbering triaged structures, displaying their rating and any special warnings or life safety issues. This also documents the evaluation team and date. The sign is stapled at the mailbox or end of the driveway so it can be seen by other teams, incident officers, and law enforcement.
  • Digital camera.
  • Permanent felt markers.
  • Heavy-duty stapler.
  • Plastic surveyor flagging in a variety of colors.


The Department of Homeland Security (DHS)-U.S. Fire Administration-National Fire Academy, in cooperation with the NWCG, has produced several excellent WUI training programs for structural response agencies, including the following:

  • Wildland Urban Interface Firefighting for the Structural Company Officer, F-610. This program identifies many of the operational activities and safety concerns when a company officer is assigned to a WUI fire.
  • Command and Control of Wildland Urban Interface Fire Operations for the Structural Chief Officer, F-612. This course provides chief and command officers with the necessary tools and skills to operate safely in a wildland/urban interface incident including those involving fire behavior, safety, and operational considerations.

As required by the DHS, every new and existing DHS training course includes the National Incident Management System (NIMS) and the National Response Framework (NFR).

At the heart of NIMS is the venerable Incident Command System (ICS), used by federal land management agencies since the 1980s. NIMS takes ICS further by integrating four components into its traditional framework:

  • national compliance,
  • uniform training,
  • response and technology standards, and
  • mutual-aid and resource management.

The NWCG publishes several invaluable WUI field resources. In January 2010, it published a major revision of the seminal Incident Response Pocket Guide (IRPG) (PMS 461, NFES 1077, January 2010). The handbook’s expanded section on WUI fires reflects decades of input from both state and federal agencies.

Specifically, the guidelines address structural triage and demonstrate an increased emphasis on life safety. The Guide is only a tactical field guide, however. More in-depth resource material is available in Chapter Six of the federal Fireline Handbook (PMS 410-1, NFES 0065).

Additionally, the NWCG’s Fire Operations in the Wildland Urban Interface (S-215) is a valuable training program for those responding in the interface environment who have a basic understanding of wildland firefighting. IRPGs, Fireline Handbooks, and S-215 training material are available from U.S. Bureau of Land Management—Great Basin Fire Cache in Boise, Idaho.

For communities and homeowners, the International Association of Fire Chiefs (IAFC) released the new Ready, Set, Go! (RSG) WUI risk management program. RSG has its origins in the Leave Early, or Stay and Defend homeowner policies historically used in Australia. RSG stresses personal responsibility on the part of homeowners while focusing on prevention, preparation, and evacuation and is available at the IAFC Web site (www.iafc.org).

The NFPA’s Firewise Communities™ program is a successful multiagency effort that coordinates homeowners, community leaders, planners, and developers. Its mission is to protect people, property, and natural resources from the risk of a wildland fire. It is directed and sponsored by state and federal wildland fire agencies in the United States. Go to www.firewise.org.

Like the residents and emergency responders of Four Mile Canyon, Colorado, when all the tumblers of the environmental lock line up and Nature’s door opens to a devastating fire storm, departments can never fully predict the time and place of a WUI.

After countless structural and wildland responses, I have experienced some of the most dangerous fire environments, difficult professional failures, and valuable lessons on the WUI fireground. It is these lessons learned and those of countless others that must guide our strategic and tactical WUI planning and response—or we will continue paying a high price of blood and treasure.


1. Four Mile Canyon Fire Preliminary Findings, U.S. Department of Agriculture Forest Service, Rocky Mountain Research Station, Revised October 12, 2011).

2. National Wildfire Coordinating Group WUI Response Guidelines from: Incident Response Pocket Guide, PMS 461, NFES 1077, January 2010.

EDWARD A. WRIGHT is a fire science instructor at Bates College, Tacoma, Washington, and a senior officer, task force leader, and incident commander IV in the Poulsbo (WA) Fire Department.

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