Wildland fires present investigators with a very different challenge from structure fires. The "scene" may cover hundreds or thousands of acres, the ignition source may be a spent match or a small piece of metal, and fire behavior is driven by fuels, weather and topography rather than compartments and ventilation. Yet the same disciplined, scientific approach applies. At the 2022 Utah Chapter IAAI conference, attendees heard a session on an NWCG course and wildland fires. This article introduces the key concepts for structural investigators and first responders who may be called to wildland or wildland-urban interface scenes.
The National Framework: NWCG, PMS 412 and FI-210
The National Wildfire Coordinating Group (NWCG) publishes the Guide to Wildland Fire Origin and Cause Determination, known as PMS 412, which describes recommended procedures, practices and techniques for a systematic approach to wildland fire investigations. NWCG announced an updated version of the guide in 2025. The NWCG course FI-210, Wildland Fire Origin and Cause Determination, is the primary way the guide's principles are taught to wildland fire investigators, combining classroom instruction, pre-work and field exercises. NWCG notes that competent wildland investigators need knowledge from two backgrounds, fire behavior and law enforcement.
NFPA 921 also contains a wildfire chapter, which was revised in the 2024 edition. Structural investigators who respond to wildland fires should be familiar with both references. Our certification guide explains how wildland qualifications fit alongside other credentials.
How Wildland Fires Spread
Understanding fire spread is the foundation of origin determination. Investigators describe spread using three vectors:
- Advancing fire moves with the wind or upslope, is usually the most intense and produces the most pronounced indicators.
- Lateral fire moves at an angle to the main direction of spread, with intermediate intensity.
- Backing fire moves against the wind or downslope, slowly and with lower intensity.
As a fire grows from its origin, it typically transitions from low-intensity burning near the point of ignition to higher-intensity advancing fire. Tracing indicators backward from intense areas toward low-intensity areas leads the investigator toward the origin.
Reading Fire Pattern Indicators
Wildland fire indicators are physical changes in fuels and objects that show the direction the fire traveled. Common categories include:
- Protection: the unburned or less-burned side of an object that was shielded from the approaching flame.
- Angle of char and char height on trees, posts and brush.
- Grass stems: the way stems fall or the residual stubble is shaped relative to the fire's approach.
- Foliage freeze: leaves and needles set in the direction of heated winds.
- Cupping on the ends of burned twigs and small branches.
- Sooting and staining on rocks, cans and other noncombustible objects.
- Spalling of rock surfaces on the side exposed to heat.
- White ash from more complete combustion on the exposed side of fuels.
No single indicator is reliable on its own. Investigators look for consistent patterns across many indicators and often mark them in the field with color-coded flags representing advancing, lateral and backing indicators, as taught in NWCG training, so the pattern can be seen and photographed.
Narrowing the Origin
Investigators typically work from a broad area toward a small one. A general origin area is the broader area in which the fire started, identified from witness information, fire behavior and macro-scale indicators. Within it, the investigator identifies the specific origin area, a much smaller area where the ignition source is expected to be found. Systematic search techniques, such as grid or line searches, are used to examine the specific origin area closely, sometimes on hands and knees, with magnets or other tools to help locate small metallic evidence.
Protecting the Origin: A Job for First Responders
The earliest arriving firefighters and law enforcement officers have an enormous influence on the success of a wildland investigation. Helpful actions include:
- Noting where the fire was when they arrived, its size, direction and intensity.
- Recording vehicles, people and activities near the suspected origin.
- Keeping engines, dozers and foot traffic out of the suspected origin area whenever it can be done safely.
- Flagging and protecting the area until an investigator arrives.
These observations are the same kind of data NFPA 921 asks investigators to collect at any scene; see our article on interviews and canvassing.
Common Wildland Fire Causes
Wildland investigators consider a wide range of potential causes, including lightning, campfires, debris burning, smoking, equipment use, vehicles and exhaust systems, railroads, power lines, fireworks, target shooting, children playing with fire and deliberately set fires. Each hypothesis must be tested against weather records, the fire's spread, witness statements and physical evidence, just as in any origin and cause analysis described in NFPA 921 and the scientific method.
Wildland-Urban Interface Fires
Many Utah communities sit at the edge of rangeland, foothills and forest. Fires in the wildland-urban interface can begin in vegetation and spread to structures, or begin in a structure, vehicle or yard and spread into wildland fuels. These cases require investigators to combine structural and wildland methods, and often to coordinate with several agencies that have jurisdiction over different parts of the fire area, including land management agencies, fire departments and law enforcement. Agreeing early on who will lead the origin and cause investigation, and how evidence and information will be shared, avoids duplicated effort and gaps in documentation.
Evidence and Documentation
Wildland evidence can be very small: a match head, a cigarette filter, a metal fragment from a dragging chain, or a spent casing. Photograph evidence in place, record GPS coordinates and measurements, and package items appropriately. Weather data, such as information from nearby weather stations, aerial imagery and dispatch records help establish the timeline. General principles are covered in our guide to evidence collection and preservation.
Safety on Wildland Scenes
Burned areas contain smoldering fuels, burned-out stump holes, falling snags, unstable slopes and rolling debris. Weather can change quickly and re-ignite fires. Coordinate with fire personnel, wear appropriate PPE and always know your escape routes. More in our fire scene safety guide.
Keep Learning
Wildland fire investigation is a specialized discipline that rewards formal training such as FI-210 and field experience alongside experienced investigators. Check the Training page for upcoming Utah Chapter IAAI sessions and explore more investigator resources.