Authored by: Rimkus Forensic Marketing Team
Published 6/19/2026
An estimated 178,500 highway vehicle fires in 2024 caused 450 civilian fire fatalities and $2.2 billion in direct property damage, according to the National Fire Protection Association’s (NFPA) Fire Loss in the United States During 2024 report. When one of these fires becomes a claim or a lawsuit, multiple parties often need answers about how it started and who, if anyone, bears responsibility.
Vehicle fire investigation can address those questions through a systematic, evidence-based process. The conclusions may inform coverage evaluations, subrogation analysis, product investigations, and other technical decision-making.
Forensic investigators can use documented evidence and hypothesis testing to evaluate vehicle fire cause. Standards such as NFPA 921 (2024 edition) guide that methodology. Vehicle fires involving lithium-ion battery systems can introduce additional investigative challenges, including thermal runaway, stranded energy, and reignition.
Key Takeaways: How vehicle fire investigation works
When a vehicle fire becomes a claim or a lawsuit, the strength of the investigation often determines how well the findings hold up. Defensible opinions depend on documented evidence, systematic methodology, and well-tested cause hypotheses.
What may affect a credible investigation
- NFPA 921 (2024 edition) provides a widely recognized framework; applicability depends on jurisdiction and circumstances
- Origin analysis informs the evaluation of cause hypotheses
- Investigators present findings as opinions supported by data, not absolute conclusions
How investigations typically proceed
- Investigators document the scene, preserve evidence, and maintain chain of custody
- Investigators develop and test hypotheses using the scientific method
- Electric vehicle fires add complexity, including thermal runaway and reignition risk
Rimkus applies forensic expertise and recognized fire investigation methodology to vehicle fire origin and cause investigations. Contact us to discuss your matter.
What factors are commonly associated with vehicle fires?
Many vehicle fires are associated with a limited set of contributing factors. The United States Fire Administration (USFA) Topical Fire Report Series for 2014 to 2016 identifies mechanical failure or malfunction, electrical failure or malfunction, and misuse of material or product as factors that together played a role in 79% of highway vehicle fires. These categories explain why forensic investigators often focus on specific vehicle areas and systems.
How do electrical and mechanical failures contribute to vehicle fires?
The same USFA report attributes 45% of highway vehicle fires to mechanical failure or malfunction and 21% to electrical failure or malfunction, such as a short circuit. Insulation around electrical wiring was the most common item first ignited, at 29%.
How does fuel and fluid ignition contribute to vehicle fires?
Flammable liquids in the engine area were the second most common item first ignited, at 18%, and these incidents can carry outsized severity. NFPA research found that incidents where the item first ignited included a flammable liquid or gas were the deadliest, accounting for an estimated 50% of civilian deaths.
How do electric vehicle and lithium-ion battery fires differ?
Electric vehicle fires introduce challenges that conventional methodology may not fully account for. The central phenomenon is thermal runaway, which the National Transportation Safety Board (NTSB study) defines as an uncontrollable increase in temperature and pressure within a lithium-ion battery cell. The NFPA 921 (2024 edition) expanded its HEV and EV investigation guidance, reflecting the increasing complexity these vehicles present.
Triggers can include mechanical damage from crashes, overcharging, manufacturing defects, and thermal abuse. State of charge can influence severity. In laboratory testing, only gas vented below 50% state of charge; above 50%, tests detected vented gas and jet fire simultaneously.
Reignition is a distinct hazard. The Federal Emergency Management Agency and the USFA define stranded energy as energy remaining inside undamaged battery modules and cells; that energy can contribute to multiple reignitions after extinguishment of an electric vehicle fire.
For investigators, a central question in lithium-ion battery fires is whether the battery initiated the fire or became a victim of an external cause. Physical changes in EV battery remains can reflect the battery acting as fuel source, victim, or initiator of a fire, and distinguishing between these roles may affect product liability attribution. Data on EV battery fires remains fragmented as the technology continues to evolve.
How do investigators approach incendiary and external causes?
Investigators may classify a fire as accidental, natural, incendiary, or undetermined. The undetermined classification means investigators cannot establish one of the other three causes to an acceptable level of certainty.
Intentionally set fires account for approximately 5% of all vehicle fires, according to the U.S. Fire Administration (USFA), and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) reported 899 incendiary vehicle fire incidents in calendar year 2023. An incendiary classification generally requires affirmative evidence, including ignitable liquid identification through gas chromatography-mass spectrometry under ASTM International standard E1618, fire pattern analysis, or arc survey findings; investigators generally rule out external causes first, including wildland fire spread and exposure from adjacent vehicles.
The National Association of Fire Investigators notes that the Negative Corpus Methodology was rejected by NFPA 921 beginning with the 2011 edition. Investigators are expected to develop and test origin and cause hypotheses using affirmative evidence rather than eliminating all other possibilities..
What standards guide vehicle fire investigation?
Investigators often rely on NFPA 921 for investigation methodology. When fire investigation opinions are used in legal proceedings, courts may separately evaluate the reliability of the methodology under the applicable evidentiary framework.
How does NFPA 921 guide vehicle fire methodology?
NFPA 921, Guide for Fire and Explosion Investigations (2024 edition), is a widely recognized framework for systematic fire investigation. Its applicability depends on jurisdiction and circumstances. The National Institute of Standards and Technology (NIST) has stated that NFPA 921 is regarded as the standard of care in the fire and explosion investigation community and in the courts.
NFPA 921 addresses basic methodology, origin determination, fire cause determination, and motor vehicle fires. The 2024 edition added guidance on confirmation bias and expressions of certainty, reinforcing the field’s emphasis on objectivity. With few exceptions, the commonly referenced methodology is to first determine the origin, then the cause. NFPA 921 directs investigators to accomplish factual analysis and express opinions objectively, truthfully, and without expectation bias, preconception, or prejudice.
How are fire investigation methodologies evaluated when expert opinions are offered in legal proceedings?
When fire investigation opinions are presented in legal proceedings, courts generally evaluate whether the opinions are based on sufficient facts, reliable methods, and reliable application of those methods to the facts of the case.
Published methodology, accepted fire investigation practices, and recognized professional standards remain important foundations for fire investigation opinions. Applicable evidentiary requirements vary by jurisdiction.
How are vehicle fires investigated?
Investigators use a structured sequence that moves from documentation and preservation to origin analysis and cause determination. That structure connects physical evidence to opinions in a way that insurers, attorneys, courts, and other stakeholders can evaluate.
Documentation
Investigators document the scene before disturbing it. NFPA 921 motor vehicle guidance identifies the exterior, engine compartment, passenger compartment or interior, cargo compartment, and the underbody or underchassis as the five major areas for motor vehicle examination. Investigators commonly use photography, videography, sketching, and scene measurements.
Investigators typically collect fire debris evidence in airtight containers such as heat-sealed nylon bags, unused metal paint cans, or glass jars with airtight lids. Investigators generally do not air-dry evidence before analysis; chain of custody begins when an item is collected and remains unbroken through final disposition.
Evidence preservation also affects later disputes. ASTM E860 defines spoliation as the loss, destruction, or material alteration of evidence by one responsible for its preservation; spoliation rulings are fact-specific and typically turn on demonstrated prejudice.
Area of origin
Origin analysis identifies the area where investigators reasonably believe the fire began. The area of origin is the structure, part of a structure, or general geographic location in which investigators reasonably believe the point of origin is located.
Investigators commonly evaluate fire patterns and proximate first fuels, then compare possible ignition sources, fuels, and oxidants in the area of origin. Together, these steps can build the evidentiary basis for an origin hypothesis.
Burn pattern analysis can inform origin, but it has recognized limitations. NIST cautions that burn patterns may be confusing because the origin may not necessarily be located where observable damage is most severe.
Arc mapping can help identify the area of fire origin or spread, but generally cannot alone establish whether electrical arcing preceded or resulted from fire spread; that determination typically requires correlation with fire patterns and may require laboratory or metallurgical analysis.
Hypothesis testing
NFPA 921 directs investigators to use a systematic approach and all relevant details. The process does not stop at identifying a plausible ignition source; investigators also typically test alternate hypotheses against the available facts.
The USFA case-preparation curriculum requires investigators to develop and test alternate hypotheses using the scientific method. NFPA 1033 requires data, facts, records, reports, documents, scientific references, and evidence to support an opinion concerning origin, cause, or responsibility. Findings remain professional opinions to a reasonable degree of certainty rather than absolute conclusions.
What role does expert testimony play in vehicle fire investigations?
Expert testimony may translate technical findings into evidence a court may weigh. NFPA 1033 requires that a fire investigator remain current in 16 required knowledge topics that the standard identifies. On testimony, NFPA 1033 directs the investigator to clearly identify opinions and conclusions and present the reasoning behind each one.
Courts apply a probability standard. The Texas Supreme Court rejected testimony where the expert stated that a battery or its cable could possibly have ignited the fire, holding that possibility is not evidence of probability. Testimony within the bounds of reliable methodology may support admissibility under amended Rule 702.
These forensic findings may inform coverage and subrogation recovery analyses, along with product liability claims. National Highway Traffic Safety Administration recalls may also document known vehicle fire hazards relevant to those claims.
Why methodology may affect the strength of a vehicle fire opinion
A defensible vehicle fire opinion depends on evidence handling, origin analysis, and tested cause hypotheses. NFPA 921 (2024 edition) and Daubert set expectations that may help those opinions withstand challenge. Electric vehicle fires often call for particular care in separating a battery that caused a fire from one consumed by it.
For claims managers and attorneys, rigor in the underlying methodology may determine whether a final opinion holds up under scrutiny. Evidence handling, hypothesis testing, and careful standards application each contribute to that outcome.
Rimkus applies forensic expertise and established methodology to vehicle fire origin and cause investigations. To discuss the specific facts of a matter, Contact us.
Frequently asked questions about vehicle fire investigation
How do investigators use event data recorders and onboard electronics in vehicle fire investigations?
Investigators treat onboard electronics as timestamped records that can test fire-origin hypotheses and may help distinguish pre-fire faults from fire-caused failures. Relevant data sources include engine control modules, airbag modules, ABS systems, telematics units, and battery management systems in electric vehicles; acquisition follows forensically sound procedures and investigators correlate fault sequences with burn patterns, witness accounts, and physical evidence.
What role do witness statements play in vehicle fire investigations?
Witness statements and driver interviews may provide timeline context and observational details that physical evidence alone may not reconstruct, including pre-fire symptoms such as unusual smells, warning lights, or smoke from specific locations. Investigators use these accounts to corroborate or challenge driver narratives and evaluate credibility through consistency over time, sensory detail, and alignment with physical findings and electronic data.
How do investigators account for environmental factors such as wind or weather when analyzing burn patterns?
Investigators integrate wind direction, weather conditions, fuel moisture, and terrain analysis into burn pattern interpretation, comparing physical evidence against weather station data, witness accounts, and fire behavior principles. The goal is to distinguish potential origin indicators from patterns shaped by flame tilt, ember transport, humidity, slope, or uphill spread.
This article is intended to provide general information and insights into prevailing industry practices. It is not intended to constitute, and should not be relied upon as, legal, technical, or professional advice. The content does not replace consultation with a qualified expert or professional regarding the specific facts and circumstances of any particular matter.