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Photo of a car burning on Interstate I-90 near Winona, Minnesota.

No one was injured in this March vehicle fire on an interstate highway near Winona, Minnesota. Though attention is now focused on three Tesla incidents, fires in gasoline vehicles are surprisingly common, most of them due to electrical or mechanical failures.

Photograph by Joe Ahlquist, Winona Daily News/AP

Josie Garthwaite

for National Geographic

Published December 6, 2013

Tesla Motors' Model S sedan began 2013 with the distinction of becoming Motor Trend's Car of the Year—a first for an electric car. (See related, “Tesla Motors' Success Gives Electric Car Market a Charge.”)  Heading into 2014, the sleek poster child of a battery-powered future is now at the center of a U.S. government investigation into fires that began after Model S drivers struck road debris at highway speeds.

The core question in the probe is whether a safety defect in certain Model S vehicles caused the fires and must be fixed. While the investigation unfolds, here are some answers to basic questions about fires in vehiclesboth electric- and petroleum-powered. (See related, “Pictures: Cars That Fired Our Love-Hate Relationship With Fuel.”)

What do we know about the Model S fires?

Three Model S cars, including two in the United States, have been involved in fires since early October. One car caught fire in Mexico after its driver crashed the Model S into a concrete wall. Two others caught fire after metallic roadway debris struck the low-slung Model S undercarriage and damaged the battery pack, which is configured as a flat, heavy pancake on the car's belly. The fires did not spread to the passenger compartment and no one was seriously injured.

The U.S. National Highway Traffic Safety Administration (NHTSA) has opened a formal investigation into the two Model S incidents in the United States. The agency said that impact damage to the battery's enclosure triggered what's called thermal runaway, in which a battery’s temperature rises uncontrollably as its cells rapidly release stored energy and heat adjacent cells.(See related, “ Quiz: What You Don’t Know About Batteries“) According to the official investigation summary posted on NHTSA's website, "In each incident, the vehicle's battery monitoring system provided escalating visible and audible warnings, allowing the driver to execute a controlled stop and exit the vehicle before the battery emitted smoke and fire."

How has Tesla responded?

Tesla has now updated software for the Model S air suspension system to keep the car's underbelly raised higher above the roadway when it's traveling at highway speeds. (Related Quiz: What You Don't Know About Cars and Fuel) "To be clear, this is about reducing the chances of underbody impact damage, not improving safety," Tesla Chief Executive Elon Musk wrote in a November 18 post on the company blog. The company has also said it will expand its warranty to cover damage from fire, even if it's due to driver error. "Unless a Model S owner actively tries to destroy the car," Musk wrote, "they are covered." (See related, “Pictures: Eleven Electric Cars Charge Ahead, Amid Obstacles.”)

While the NHTSA investigation could go on for weeks (Tesla's full response to NHTSA's request for information is not due until January 14), German authorities have already concluded an inquiry into the safety of the Model S, according to a translation of a letter dated November 27 and posted this week on Tesla's website. Germany's Federal Motor Transport Authority, Kraftfahrt-Bundesamt, wrote that it had found "no manufacturer-related defects."

How common are car fires?

Car fires are not as common as Hollywood might lead us to believe, but not as rare as we might hope. Highway vehicle fires reported to local public fire departments in the United States numbered 172,500 in 2012—down more than 50 percent from the numbers reported in the 1980s despite a steady increase in the number of miles driven. That works out to about one vehicle fire every three minutes, mostly in passenger cars. Between 2006 and 2010, automobile fires killed an average of four people each week, according to data from the National Fire Protection Association (NPFA).

Photo of emergency workers responding to a fire on a Tesla Model S electric car in Smyrna, Tennessee.
Photograph courtesy Tennessee Highway Patrol, AP
The fire that destroyed this Tesla Model S in Smyrna, Tennessee in November followed two other fires, triggered a U.S. safety investigation.

For Tesla, the fires reported this fall occurred in just three of the more than 13,000 Model S sedans sold in the 2013 model year. "They had three fires in a short time, which is kind of a lot," said fire protection engineer Peter Sunderland, an associate professor at the University of Maryland who is currently fire-testing lithium battery cells for Ford. (See related, “Pictures: A Rare Look Inside Carmakers' Drive for 55 MPG.”)

Musk views the data more favorably. "Based on the Model S track record so far, you have a zero percent chance of being hurt in an accident resulting in a battery fire," he wrote in a post on the company's blog this week. "It is literally impossible for another car to have a better safety track record, as it would have to possess mystical powers of healing."

What causes car fires?

Again, reality differs significantly from what we see in movies, where fire typically follows car chases gone awry. In fact, three-quarters of car fires are due to far less cinematic mechanical and electrical failures, such as leaks, breaks, backfires, and worn out or improperly installed parts, or short circuits.

Every vehicle fire has three basic ingredients: a heat source, something that burns, and oxygen. Common sources of heat in highway vehicle fires include powered equipment, electrical arcing, smoldering objects, and sparks resulting from friction. Although a tank full of gasoline or diesel might seem like the most obvious place for fire to begin, most fires begin in the area of the engine, running gear, or wheels. Only a small fraction of highway vehicle fires begin in the area of the tank or fuel line. These fires tend to be among the most deadly, however, because gasoline can burn so quickly, said Marty Ahrens, a fire data analyst for the NFPA.

The Model S fires are unusual in that they started after an impact rather than due to some internal malfunction. According to Ahrens' most recent analysis for the NFPA, collisions or overturns were factors in only 4 percent of all automobile fires between 2006 and 2010.

Also significant: Motorists survived more than 998 out of every 1,000 automobile fires reported from 2006 to 2010, according to NFPA.

When do car fires become deadly?

Although crashes are the least common trigger for car fires, they are the most deadly. Close to 60 percent of the 300-400 deaths in U.S. car fires each year follow a collision or overturn. In many cases, the crash itself may be survivable otherwise, but it leaves the driver unable to act before being overcome by smoke or flames. "Collisions or overturns are the scenarios that are most likely to be fatal, and because speed is such a factor,” said Ahrens. “Basically good driving can prevent an awful lot of those." Significantly, the least experienced drivers, older teens and young adults, are at the greatest risk of highway vehicle fire death.

A fire after a crash is somewhat different from a mechanical fire, but the basic ingredients are the same. "In a crash, everything gets moved around," Ahrens explained. "Maybe the fuel line breaks, or maybe something in the engine compartment breaks, so you have something that is very, very hot coming in contact with something that can burn pretty easily."

Fumes also present a hazard. Whereas older car interiors featured more cotton and natural materials, Sunderland said, today's designs rely heavily on polymers and plastics, which produce "more thick, black smoke and things like cyanide and carbon monoxide, and burn faster than the old stuff." These fast-burning materials are often the next thing to catch fire after gasoline, he said.

What's different about fires in electric cars?

The stuff that burns and the situations in which fire is likely to arise are quite different in EVs than in traditional gasoline-fueled vehicles. The rate at which technology is changing complicates matters even further. (See related, “Range Anxiety: Fact or Fiction?“)

"You need a lot of energy to propel a big, heavy car fast and far," said Sunderland. Lithium ion batteries used in today's electric cars store electrical energy as well as chemical energy, in the form of a flammable electrolyte (the medium through which ions are transported between electrodes). While automakers have designed sophisticated systems for protecting batteries from abuse and managing temperature, thermal runaway can result from excess heat, mechanical damage, charging problems, and poor design or defective manufacturing of cells. (See related, “How to Compare the Cost of Electric and Gas Cars.”)

If a fire does ignite, the fumes from batteries are different from those that come from gas. "When gasoline burns, you can breathe it—you don't want to, but you could," Sunderland said. "With lithium, the smoke is more toxic." And although gasoline and diesel fires are likely to occur when the car is being driven, "Battery fires in cars can also happen when it's charging or parked," he said. A plug-in hybrid Chevy Volt, for example, burst into flames two years ago while parked, weeks after its battery and cooling system were damaged in government testing.

It's important to remember, however, that electric car technology does not present an inherently greater fire hazard than the old internal combustion engine, Sunderland said. "Gasoline and diesel are also dangerous," he said, but people have become used to this hazard and accept the risk because of 100 years of experience. He suggests considering how we’d react today if "someone said, 'Let's use gasoline, keep it in a one-eighth-inch thick sheet metal tank.' We'd say 'Are you crazy? Gas pools everywhere. It ignites and everyone dies.' It would never get approved."

Understanding the real fire risks associated with electric cars will take time—first, because the number of battery electric vehicles on roads today is still so limited; second, because most of these cars are only a few years old; and third, because the new technology does not fit neatly into old data-collection schemes. The national system for vehicle fire reports does not have a category for the type of fire that was sparked in the Teslas. "Running over an object in the road—our coding system doesn't have a good way to capture that," Ahrens said.

"As with any new technology," she added, "It's going to be interesting to watch how it ages and how it functions when people don't do exactly what they're supposed to do, taking it in for all the regularly scheduled maintenance." (See related, “Driving the Limit: Wealthy Nations Maxed Out on Travel?")

What should I do if my car catches fire?

NFPA advises drivers to follow three steps:

Stop. Pull over, if possible. Turn off the car in order to cut the flow of gasoline and electric current. "Keep the hood closed because more oxygen can make the fire larger," NFPA warns.

Get Out. Move at least 100 feet away from the vehicle, looking out for traffic and keeping your passengers together.

Call for help at 911 or the emergency number for the local fire department. Do not try to fight the fire yourself. "Vehicle fires can be tricky," NFPA says, "even for firefighters."

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

21 comments
Allen Schaeffer
Allen Schaeffer

Vehicle fires are never a good thing no matter what the fuel source or type of fuel.  

This story lumps gasoline and diesel fuel together and they are different from a safety perspective.  This is in part why the majority of school buses are powered by diesel fuel instead of gasoline.  

The flashpoint is a good indicator of how likely something is to catch fire if there is an ignition source nearby. Flashpoint is where material will have just enough vapor available to support a flame; the lower the flash point the more of a fire danger.  Gasoline flashpoints are -45 degrees F; Diesel fuel is about 125 degrees F.



m s
m s

At this point I have to wonder if there's something else going on here, oil companies would do anything to make anything other than oil cars look bad in the press and this seems like the perfect op for them. Seriously, it's just stupid if people actually believe that batteries are more combustible than gasoline.

Ozee Flee
Ozee Flee

NHTSA please take note: there's a difference between a "probe" and "probing someone over". You are probing Tesla over.

Ozee Flee
Ozee Flee

There seem to be a lot of Ozee's in the electric car world. I don't own an electric car dealership. I dont have a website. Im not on TV. I dont work for Tesla. I worked my butt off to get a higher education and a good living. Im just a doode that got called Ozee in college. That's the point. All of us, regardless of what we do, have a responsibilty to uphold what America is about. Election time is just a gesture of belief for things to come. Like that person that organized 100,000 people to go to the white house and petition for Tesla right to a "fair shake", like those guys that go around defending whales, like recycling, the right to innovate and be part of the market is a common good that Americans have a civil duty to uphold. The middle class is what makes America great! Civil duty is what makes the middle class and America! Every immigrant to this country becomes American through civil duty. Things like Tesla are way more than just a company, they are our stance on our right, as a group, to be in this country, have great ideas, and change the world for the better - and make the US, and ourselves, rich through sheer brilliance and market competition, create new jobs, attract the best minds, raise the standard our middle class above all. What is happening to Tesla now, and what the citizens of this country watch while it happens, sets the tone for future innovations to come. Tesla is a textbook example because they have the created the new highest rated vehicle in history. You shouldn't even have to do that in order for the government to defend your chance to fair competition. It's a question of whether you are going to allow the US to increase the polarization of its classes, look at the middle class die, and end up like the countries that Americans left in the first place - because of their polarization of classes. My income level is in the top 5% of the US population, but I've been at the bottom 10%... Elon Musk had a similar story (except with much greater success)... that ability to be American is getting crushed, for the long run, when innovations like Tesla are cheated by the system that is supposed to propell them forward. Hopefully, the NHTSA and certain bankers will remember that at the end of the day, they are American.

Ozee Flee
Ozee Flee

Germany can conclude an inbestigation in several weeks. The NHTSA seems used to seeing regular gasoline engine cars crash, catch on fire, and kill people without conducting a "probe"... just because they come from traditional car brands?! The bailout boys? Tesla demonstrated that you can crash against thisngs like a three prong two hitch (hardly just road "debris") and make it out unharmed. Please, NHTSA, show us how you do that with a gasoline car, and walk away unharmed. Maybe its just gonna take a while for the NHTSA to get "used to" the greater safety of Tesla's cars... aka curruption. In the meantime, watch the rest of the world pass the US economy by.

Ozee Flee
Ozee Flee

The chevy volt is not an electric car!!! it is a hybrid - basically a gasoline powered electric generator!! you cannot, in a million years, compare it to an all electric car!

Ozee Flee
Ozee Flee

Even by your own statistics, there are 6,800 car fires per year, or 18 per day, due solely to collisions by cars other than Tesla. Where is the NHTSA's "prove" then? Tesla is as American as any of the other companies... even though they didn't get bailed out, even though US banks don't look like fools when it comes to Tesla, even though Tesla actually deserves everything they have, even though they are good for the world's automotive industry in so many ways, even though (thanks to the US goold old boys reluctance to change) the US auto industry will really be left behind without Tesla... and then even a bailout wont work.

Ozee Flee
Ozee Flee

At this point, it is the NHTSA that needs to be investigated!

Ozee Flee
Ozee Flee

Tesla got a perfect 5/5 safety testing score, the highest score EVER achieved, period! The rest is a bunch of... The NHTSA needs to address the fact that, with their perfect score being EARNED by Tesla, it must be incredibly difficult for there to be a safety issue. Otherwise, NHTSA, call your self selectively incompetent.

Bottom line is, a number of dimestic US manufacturers produce cars, which require gasoline or are hybrids, which have gotten in all sorts of gasoline fires as a result of crashes, and (unlike Tesla) whose technical specs have caused them to be a fire risk. They have been dealt with like disabled children who need our sympathy. After all, we are used to domestic brands offering cheap reliability, cheaper financing, and ads with women in skimpy dresses looking for you to forget about it all. Tesla, for the first time in a long time, is an American car that has achieved the highest overall score, plus a consumer report recommendation, plus the highest safety score... period.

Ozee Flee
Ozee Flee

Maybe the NHTSA would be happier, maybe US legislators and bankers would like it better, if the Chinese were the ones to flood the world with A Tesla-like car. That is what they are doing by causing every possible speed bump to Tesla's absolutely-earned success. Maybe weve been used to having the Japanese talking down at the US car industry for making mediocre cars. Ask any of the three recent, most notorious, Tesla drivers, what they think about their cars. They all love the performance, the safety, the range... they all hoped onto another one as quickly as possible.

Ozee Flee
Ozee Flee

Ok, so if the NHTSA is anything but massively currupt, it needs to investigate every single manfacturer that has two fires within several weeks despite them being at 80 mph against large chunks of metal like three pron hitches... where's the outcry about those gasoline car fires NHTSA? If you are leeping us "safe", why is there a car fire, from traditional gasoline companies, every five minutes. The car fire in Mexico is not jurisdiction of the NHTSA... what a joke!

Benjamin Cooley
Benjamin Cooley

Also, Tesla is the only car company to ever make a car that has Zero deaths/serious injuries in one of it's vehicles.  aka...the model s is the safest car ever made.

Benjamin Cooley
Benjamin Cooley

Please note that this article is sponsored by shell...

David Cutter
David Cutter

Josie Garthwaite's article is impossibly misleading. The writer posts statistics related to gas-powered car fires and then mixes it up with the absolutely separate matter of investigating the 3 recent Tesla S electric car fires. Although she reports the pertinent statistics of both types of car fires, the reader is shown fire damage to a Tesla S -- but the verbiage and description preceding the photograph pertains to gas-powered cars and not EVs. This kind of irresponsible reporting does nothing but bring unwarranted safety concerns about EVs to otherwise interested buyers and it reminds me of the sort of ''hit piece' one might expect from a shill representing the big oil companies, who after all, still have trillions of dollars worth of oil products yet to sell to their cornered market customers. The oil peddlers wouldn't want to see their profits diminished anytime soon because of the growing success of Tesla Motors. It's irresponsible journalism at best to mislead your readers. It's positively shameful that it appears to have been done knowingly so. How much do they pay you?

David Cutter
David Cutter

Josie Garthwaite's article is impossibly misleading. The writer posts statistics related to gas-powered car fires and then mixes it up with the absolutely separate matter of investigating the 3 recent Tesla S electric car fires. Although she reports the pertinent statistics of both types of car fires, the reader is shown fire damage to a Tesla S -- but the verbiage and description preceding the photograph pertains to gas-powered cars and not EVs. This kind of irresponsible reporting does nothing but bring unwarranted safety concerns about EVs to otherwise interested buyers and it reminds me of the sort of ''hit piece' one might expect from a shill representing the big oil companies, who after all, still have trillions of dollars worth of oil products yet to sell to their cornered market customers. The oil peddlers wouldn't want to see their profits diminished anytime soon because of the growing success of Tesla Motors. It's irresponsible journalism at best to mislead your readers. It's positively shameful that it appears to be done knowingly so.

David Cutter
David Cutter

Josie Garthwaite's article is impossibly misleading. The writer posts statistics related to gas-powered car fires and then mixes it up with the absolutely separate matter of investigating the 3 recent Tesla S electric car fires. Although she reports the pertinent statistics of both types of cars, the reader is shown fire damage to a Tesla S -- but the verbiage and description preceding the photograph only pertains to gas-powered cars. This kind of irresponsible reporting does nothing but bring unwarranted safety concerns about EVs to otherwise interested buyers, and reminds me of the sort of ''hit piece' one might expect from a shill representing the big oil companies who after all, still have trillions of dollars of oil products yet to sell. They especially wouldn't want to see their profits diminished anytime soon because of the growing success of Tesla Motors. It's shabby journalism at best to mislead your readers. It's shameful that it appears to be knowingly so.      

Ivor O'Connor
Ivor O'Connor

Nice factual article without bias. Tesla represents a new paradigm and new data-collection schemes are needed. The NHTSA needs to understand the vehicle thoroughly before they can adequately prepare the new categories. 

Cynthia Carlson
Cynthia Carlson

@David Cutter My first thought when I read this article. I still intend on purchasing an EV - a Tesla as a matter of fact.

Daniel Mercado
Daniel Mercado

@Ivor O'Connor I agree with you. For very powerful reasons, I am a big fan of electric vehicles and would also like to see the use of fossil fuels greatly diminish. With that said, I sold my Tesla stocks about a year ago after the illogical design of the Model X made me wonder what else Tesla got wrong. However, because I hope that the EV becomes the car of the present soon and Tesla is leading that charge, I really hope that Tesla do more to correct these mishaps and produce an excellent redesigned Model X. 

Ivor O'Connor
Ivor O'Connor

@Daniel Mercado @Ivor O'Connor

I too think EVs are the future and the Tesla Model S is the first wave of many fantastic Tesla vehicles. And as long as the NHTSA is impartial it is possible they can help usher in EVs at an even faster rate. 


I can hardly wait for future EVs that are four wheel drive with 500 mile ranges. They are coming...

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