Why Cars Catch Fire in an Accident

Cars typically catch fire in a crash when fuel, battery energy, or flammable materials are suddenly exposed to heat, sparks, or damaged electrical systems; the impact can rupture tanks or lines, short wires, or compromise a lithium-ion battery, allowing ignition. In most collisions, modern safety designs prevent this outcome, but high-speed impacts, rollovers, poor maintenance, or aftermarket modifications can overwhelm protections and create the conditions for fire.

What Actually Ignites in a Crash

Vehicle fires are usually a chain reaction: a flammable source is released or heated, an ignition trigger appears, and oxygen feeds the flame. Understanding the common fuels helps explain why some crashes escalate into fires.

• Gasoline or diesel: liquid fuel and vapor from tanks, lines, injectors, or rails can ignite quickly if sprayed onto hot surfaces or sparks.
• Motor oil, transmission and power-steering fluid, brake fluid, and coolant with glycol: these petroleum-based or glycol fluids can burn when atomized and heated.
• Lithium-ion battery cells (EVs and hybrids): damaged cells can enter thermal runaway, generating intense heat and flammable gases.
• Interior materials: seat foam, plastics, carpeting, and insulation can sustain and spread flames once ignited.
• Wiring insulation and underhood plastics: melt or burn when exposed to arcs or hot exhaust components.

In most crashes, these materials remain contained or cool enough to avoid ignition; fire incidents typically involve both a fuel release and a credible ignition source.

How a Crash Triggers Ignition

Impact forces and deformation can rapidly create ignition sources. The mechanisms vary with vehicle type and the dynamics of the crash.

• Fuel system breaches plus heat: a ruptured tank, broken fuel rail, or severed line sprays fuel that can hit hot exhaust manifolds or catalytic converters.
• Electrical short circuits: crushed wiring harnesses arc against metal, generating sparks that ignite vapors or plastics.
• Battery thermal runaway (EVs/hybrids/12V): punctured or crushed cells, internal shorts, or damaged busbars can trigger runaway and off-gassing, which can ignite.
• Overheated components: locked brakes, seizing bearings, or friction in a crash can superheat metal, igniting nearby materials.
• Post-impact leaks: coolant or oil dripping onto red-hot parts after the vehicle comes to rest can ignite minutes after the crash.

The common thread is energy meeting fuel: if the crash compromises containment and delivers heat or sparks at the same moment, the risk of a fire rises sharply.

Why Modern Cars Are Less Likely—But Not Immune

Regulations and design have significantly reduced fire risk compared with older vehicles. Still, severe collisions can defeat protections.

• Fuel system protections: reinforced tanks, safer tank placement, anti-siphon valves, and crash-triggered fuel-pump cutoffs reduce liquid fuel release.
• Firewalls and heat shielding: barriers slow flame spread from the engine bay to the cabin.
• Electrical safeguards: fuses, relays, and smart battery disconnects limit arcing during a short.
• EV-specific features: high-voltage contactors open in a crash; pyrotechnic “pyrofuses” can instantaneously isolate battery packs; thermal management slows runaway.
• Material choices: more flame-retardant interior components than in past decades.

These measures make post-crash fires relatively uncommon, but they cannot prevent ignition when impacts are extreme, components are modified, or maintenance lapses exist.

What the Data Shows

U.S. fire and highway safety data consistently indicate that post-crash fires are a small fraction of total crashes. Internal-combustion vehicles account for the vast majority of highway vehicle fires because they dominate the fleet and carry liquid fuels. On a per-vehicle basis, multiple national studies and insurer datasets in recent years have found fully electric vehicles ignite less frequently than gasoline vehicles, though EV battery fires, when they occur, can be longer-lasting and require specialized firefighting tactics.

Situations That Raise the Odds

Certain crash scenarios and vehicle conditions make ignition more likely by increasing both fuel exposure and heat or sparks.

• High-speed impacts and rollovers that tear open tanks, rails, or battery packs.
• Side or underbody strikes that puncture fuel lines or battery enclosures with road debris or guardrails.
• Aging hoses, brittle plastics, corroded fuel lines, or prior leak history that fail under impact.
• Aftermarket wiring or performance mods that bypass fuses, route lines poorly, or remove heat shielding.
• Cargo hazards: spare fuel cans, propane cylinders, aerosol cans, lithium tool batteries, or oxygen tanks in the cabin/trunk.
• Overheated brakes or driveline parts just before impact, providing immediate ignition sources.
• Flood or saltwater damage (past or present) that compromises wiring and battery integrity.

When multiple risk factors stack—like a high-speed rollover in a modified, poorly maintained vehicle carrying flammables—the probability of a fire increases markedly.

What To Do If a Vehicle Catches Fire After a Crash

Quick, calm action can save lives. Prioritize evacuation, distance, and professional help over fighting the fire yourself.

1. Stop and shut off the vehicle if you can do so safely; place the car in park and set the parking brake.
2. Exit immediately and help others out; leave belongings behind. Move at least 100 feet (30 meters) upwind and uphill if possible.
3. Call emergency services and report any hazards (fuel smell, smoke, battery-electric or hybrid vehicle, people trapped, cargo like propane).
4. Do not open the hood or trunk—introducing oxygen can flash the fire.
5. If the fire is very small and just starting, use a Class B/C (or ABC) extinguisher from a safe position, aiming at the base; stop if it grows or smoke thickens.
6. For EVs/hybrids, stay well clear of the underbody and avoid any orange high-voltage cables; bystanders should not apply water.
7. Warn others away; secondary events like airbag inflators or struts can explode in heat.
8. When responders arrive, tell them the vehicle type (gas, diesel, hybrid, EV) and what you observed; follow instructions.

If flames subside, do not reapproach—reignition is possible, especially with damaged batteries that can smolder internally.

Prevention and Risk Reduction

While accidents are unpredictable, maintenance and preparation can lower the chance that a collision becomes a fire.

• Address recalls promptly, especially those involving fuel systems, electrical harnesses, or battery packs.
• Fix fluid leaks and replace cracked hoses or corroded lines; keep heat shields intact.
• Use proper fuses and avoid DIY wiring shortcuts; have accessories installed professionally.
• Secure the 12V battery; a loose battery can short against metal in a crash.
• Keep the cabin/trunk free of spare fuel, unprotected lithium battery packs, and aerosol cans.
• Choose quality replacement parts; poor aftermarket tanks, lines, or connectors can fail under stress.
• After any significant curb, debris, or underbody strike—especially in EVs—get an inspection to check for hidden damage.
• Carry a small ABC extinguisher and first-aid kit, and know how to use them.

Good upkeep doesn’t eliminate risk, but it reduces the number of failure points that can turn a crash into a fire.

Aftermath, Towing, and Insurance Considerations

If a vehicle has smoked or burned, do not attempt to restart it. Photograph the scene (if safe), notify your insurer, and arrange professional towing. Many manufacturers and fire agencies advise storing damaged EVs outdoors, away from buildings and other vehicles, because battery packs can reignite hours or days later; some guidance specifies isolating the vehicle by at least 50 feet and monitoring for heat. Salvage facilities increasingly follow these protocols, and insurers may require them before transport or storage.

Summary

Cars catch fire in accidents when crash forces release fuel or damage electrical/battery systems and an ignition source is present. Modern engineering makes such fires uncommon, but high-energy impacts, compromised maintenance, risky cargo, and modifications raise the odds. If fire occurs, evacuate, keep your distance, call for help, and avoid opening compartments or touching high-voltage components. Regular maintenance, recall compliance, and cautious post-crash handling—especially for EVs—are the best defenses against a rare but dangerous outcome.