For fire investigators, wildland fires are more than just natural disasters. They’re sprawling crime scenes, ecological puzzles, and legal minefields all rolled into one. The origin is often buried under miles of ash, and it's up to you to find the cause.
This guide walks through the process of wildfire investigation, from start to finish. Whether you’re working under IAAI guidelines, NFPA 921 standards, or your agency’s field protocols, the fundamentals remain the same: trace, verify, document.
Secure the Scene and Define Objectives
Before any investigative work begins, you need to lock down the scene physically and procedurally. That means establishing a secure perimeter as early as possible, ideally while suppression crews are still active.
Coordinate with the Incident Commander, law enforcement, and public land managers to restrict access and prevent evidence contamination. This is especially critical in the wildland-urban interface, where foot traffic, heavy equipment, or curious onlookers can easily destroy ignition clues.
Once the scene is secure, clarify your investigative mandate. Are you there for cause and origin determination only? Will you be collecting evidence for potential criminal prosecution? Is there a regulatory, insurance, or litigation component expected? This helps prioritize tasks, assign responsibilities, and reduce overlap with other agencies.
At a minimum, your core objectives should be:
- Identify and document the point of origin
- Establish the most probable cause of ignition
- Preserve and collect physical evidence under chain-of-custody standards
- Create a comprehensive, defensible investigative record
Use Systematic Scene Examination Methods
Wildland fire scenes are often vast, fragmented, and deceptively chaotic. A systematic approach is your best tool for cutting through the noise.
Walk the Fire Scene Backward
Always start from the most intensely burned area and work your way backward. This allows you to track fire indicators like char patterns, grass lays, spalling, and directional burn clues, toward their convergence.
Use a grid, transects, or spiral method depending on terrain and fire complexity. Document as you go. Don't trust memory. It fades faster than smoke.
Identify the Area of Origin
You're not looking for the exact matchstick yet. First, isolate the general area of origin, a zone where multiple fire indicators converge. This is often upslope or upwind of the deepest burn, but must be verified through indicators, not guesswork.
Clues include:
- V-shaped burn patterns pointing uphill or inward
- Protected areas beneath rocks or logs
- Halos of lighter charring
- Directional indicators, like curling grass and ash deposits
Determine the Exact Point of Origin
Once you’ve narrowed the area of origin to a manageable size, ideally a few square feet, begin a fingertip search. This is where fire investigation becomes a slow, methodical art.
You’re looking for the first fuel ignited. That could be dry pine needles, grass tufts, duff, or a manufactured item. The point of origin often sits in a small depression or pocket where wind dropped embers, or where heat accumulated undisturbed.
Use gentle hand tools and flag any items that could be foreign, suspicious, or out of place. Photograph before moving. Sketch the layout. Precision is everything here.
Evaluate Possible Ignition Sources
Now the forensics begin. What could have plausibly ignited the fire at that specific point? Here are a few categories of potential ignition sources.
| Source Type |
Examples |
| Natural |
Lightning, volcanic activity |
| Accidental |
Campfires, cigarettes, equipment, debris burns |
| Electrical |
Powerlines, transformers, conductors |
| Mechanical |
Vehicle exhaust, dragging chains, ATVs |
| Intentional |
Arson, incendiary devices, repeat fire setter behavior |
Every possibility must be examined, then methodically eliminated or supported. Don’t lean into bias. An “obvious” cause can blind you to the real one.
Collect and Preserve Physical Evidence
Evidence at a wildland fire scene is often fragile, degraded, or partially consumed, but it’s still critical. Any item suspected of causing ignition must be collected with care, precision, and strict chain-of-custody protocols. The scene may be hundreds of acres, but the ignition source could be no bigger than a coin.
Common evidence types include:
- Partially burned matches, lighters, or cigarette butts
- Fireworks casings, wires, fuses, or homemade devices
- Metal fragments, melted beads, or slag from vehicle or machinery contact
- Downed powerline components, conductors, or insulators
- Batteries, electronics, accelerant containers, or chemical residues
- Glass shards or lenses potentially linked to heat magnification
Use nitrile gloves to prevent contamination and sterile metal or plastic tools to extract items. Store evidence in breathable paper containers, never plastic, for anything with potential accelerant traces, to avoid off-gassing or mold growth. Label each item clearly with date, time, location, and your initials. Chain of custody is what makes your evidence admissible.
If you suspect arson, flag the scene and bring in law enforcement or a certified fire debris analyst before disturbing any potentially criminal materials. Accelerant residues, timers, and incendiary devices must be documented thoroughly in situ with high-resolution photos, GPS coordinates, and descriptive notes.
Analyze Fire Behavior and Environmental Conditions
Fire doesn’t spread in a vacuum. You must factor in weather, topography, and fuel moisture at the time of ignition.
Check:
- Wind direction and speed at time of start
- Temperature and relative humidity
- Fuel moisture (live and dead)
- Slope angle and aspect
- Historical weather patterns in the 72 hours prior
Use data from RAWS (Remote Automated Weather Stations), nearby fire towers, or satellite sources like NOAA or GOES imagery. Cross-reference this with observed fire spread to verify or challenge your origin theory.
Establish Cause Through Elimination
Determining the cause of a wildland fire requires methodical elimination. As emphasized in NFPA 921, the scientific method must guide your process. That means developing hypotheses based on observed facts, then testing those hypotheses by ruling out all but one credible explanation. If you can’t rule out other viable causes, you don’t have a conclusion.
Here’s what you must be able to answer before declaring a probable cause:
- Was the ignition source present? You need physical proof, credible witness accounts, or documented indicators showing that the source was actually at the point of origin.
- Was it competent? That means it had the energy, temperature, or chemical profile required to ignite the available fuel under existing conditions.
- Was the first fuel ignitable at the time? Consider environmental factors like fuel moisture, wind, shade, and slope. If the fuel couldn’t have caught fire at that moment, the cause doesn’t hold.
- Can all other potential causes be reasonably ruled out? This includes both natural and human-related sources. "Possible” isn’t good enough. You must show why other causes don’t meet the criteria.
When your wildfire investigation leads you to a cause that’s merely plausible, pause. Courts, insurance carriers, and oversight agencies require a probable cause, one that is more likely than any alternative based on observable, documented evidence. If you haven’t eliminated the rest, you haven’t proven the one.
Conduct Interviews and Cross-reference Data
The fire scene can tell you what happened. But people often tell you when, how, and why. Witness statements, when gathered skillfully, can either corroborate your findings or expose inconsistencies that shift the entire direction of your investigation.
Start with first-on-scene responders. These are often wildland firefighters, law enforcement, or local volunteers. Ask them what they saw upon arrival, such as smoke columns, visible flame direction, wind conditions, unusual vehicles, or anyone leaving the scene. They may have photos, radio logs, or firsthand observations before the fire took off.
Next, talk to local residents, ranchers, utility crews, or landowners. These individuals often have deep knowledge of the area and may notice patterns or disturbances, like unauthorized campers, trespassers, illegal burns, or recurring fire activity.
Include recreational users like hikers, ATV riders, hunters, or anglers who were nearby. Ask open-ended questions first, then narrow in. Did they hear fireworks? See lightning? Smell fuel? Capture anything unusual on their phones?
Cross-reference everything they tell you with:
- Fire behavior modeling
- Weather logs and RAWS data
- Physical evidence from the scene
- Dispatch logs, cell tower pings, or trail cam footage
Document Findings With Precision
The wildfire investigation doesn’t end when you leave the scene. You still need to write the report, review it, and make sure it’s defensible in court.
Your final documentation should include:
- A detailed origin and cause narrative
- All evidence logs with photos
- Maps, sketches, and diagrams
- Witness statements
- Weather and fuel condition data
- References to applicable NFPA or agency standards
Know What to Look For in a Wildfire Investigation
Investigating a wildland fire is a layered process that demands discipline, precision, and situational awareness. From securing the scene and reading burn patterns to isolating ignition sources and writing a defensible report, every step matters. You’re reconstructing how it started, why it spread, and who or what made it possible.
The goal is to uncover patterns, strengthen prevention strategies, and help land managers, utility companies, and legislators make better decisions. Your work feeds into broader systems, like policy, accountability, and wildfire modeling.
If you don’t already have one, consider building a recurring post-incident checklist or investigation debrief template. The stronger your documentation habits now, the more bulletproof your findings will be when they’re tested later.
