What’s the science behind EV battery fires?

[Packard]

It seems that every manufacturer of pure electric powered vehicles (EV) has experienced battery fires.

Tesla has been plagued with many.

Ford just shut down the production line for the F150 Lightning EV.
https://www.foxbusiness.com/lifestyle/ford-battery-fire-caused-lightning-production-stoppage

If these fires keep happening, why are the manufacturers caught by surprise?

What burns in these fires?  A fire official (I don’t remember where) said that the manufactures of these EVs should publish fire fighting instructions.  (Apparently, a fire raged on while the department was using an incorrect fire fighting method.)

Fires in cars can trigger strange responses by the drivers.  When I was 20 years old (54 years ago), I stepped out of a retail store on Route 27A in Wantaugh to see a car with flames shooting out from under the hood of the vehicle.  The flames were 15 to 20 feet high. 

A large crowd had formed on the sidewalk.  No one approached the car.  I ran to the car to see if the driver was OK.  When I got there, I saw that there was an infant in the front seat.  I ran around to the other side of the car and grabbed the baby and handed it off to one of the women standing on the sidewalk.

I ran back to the car to get the mother out. Despite the flames (or because of them) she had a death-grip on the steering wheel. I tried yanking her out of the car, but she held on too tight. 

I managed to peel one finger at a time of the left hand from the steering wheel, at which time I was able to pull her free.

At the time I was bench pressing 365 pounds and could easily do more than 25 pull-ups.  I was fairly astonished by the strength of her grip on the steering wheel.

By the time the fire department arrived the entire front seat was engulfed in flames.

A woman said, after I got both of them out, “That was so stupid.  The car could have exploded and you could have been killed.

I was disappointed to see that out of all the adults standing on the sidewalk, it took a college kid to do the right thing.  Very disappointing. 

That was kind of not the response I was expecting. 

In any event, fires in cars can trigger panic responses that are quite contrary to survival responses. 

So to get back to my question:  Why to EVs burn?  What is the science behind the fires? And, finally, why are the car manufacturers surprised by the fires?

 

[six-point socket II]

It's a chemical reaction.

->https://pdf.sciencedirectassets.com...e05535e0759595b5353&rr=79a979006ec63662&cc=de

That is why, at least over here in Germany, the fire department will bring a large container, fill it, and dump the car in it if possible.

->https://www.emicontrols.com/en/fire/solutions-for-electromobility/

You can extinguish the flames, but not the actual chemical reaction - you need to cool it to slow it down & control it.

It's the same for example with Acetylene gas bottles. Once they get over a certain temperature threshold, all you can do is cooling, cooling and more cooling.

That's to the best of my, layman, knowledge.

Kind regards,
Oliver

 

[zapdafish]

I think Tesla being plagued by many is a myth.
https://www.crsautomotive.com/how-prone-are-electric-cars-to-catching-fire/#:~:text=Tesla%20claims%20that%20fuel%2Dpowered,40%20fires%20have%20been%20reported.

 

[luvmytoolz]

Not EV related but car fire related, when I was a teenager my Monaro would keep blowing fuses, and I couldn't work out why not knowing too much about cars in the early days.

So I temporarily replaced the fuse with a metal curtain hook, and it was while we were in the drive thru at Macca's that we started seeing smoke coming from the dash, there was a cop car in the line a few cars behind and a Monaro coupe was already prone to being pulled over, so we were really worried. While my future wife furiously fanned the smoke to help disperse it, we got home fast and while we didn't see any flames, the entire wiring loom behind the dash had melted and was this huge mass of burnt crap!

I learnt that day the importance of correctly sizing fuses! ;-)

 

[eschumac]

Why to EVs burn? 

Lots of stored energy. Physics.

What is the science behind the fires?

Different chemistry and different designs have various different ways to manage safety. Some battery types are safer because by design they are self extinguishing. Think layers melt as heat increases. Those layers then block the chemical reactions used to release energy.

Some battery packs require active cooling and liquid cooling to maintain safe temps. When the cooling system fails the battery temps can rise to unsafe levels. For some battery types this can be catastrophic.

why are the car manufacturers surprised by the fires?

They aren't. They would just prefer they happen a small percentage of sold volume and without the optics similar to the F150 incident.

 

[woodferret]

Shorts.  Heat.  Polymer substrate burn.
https://www.ckaero.net/blogs/articles/lipo-battery-anatomy-fire-behavior-and-safe-practices

Lithium batteries typically are made with relatively lightweight casing in comparison to say lead-acids (which are made to resist substantial swelling).  Manufacturing defects in removing moisture when building that lithium polymer sometimes causes very localized hot spots and swelling.  Sometimes that punctures the casing.  Once open to ambient air, the combination of heat and humidity that can burn quite a while.  Normally, the batteries are designed to resist spontaneous combustion when just exposed through an external puncture.  Heat is the key to get it above the ignition temperature of the plastic polymers.

There's also manufacturing issues with welds and such externally that can also cause runaway charging and shorts.  Again, usually taking advantage of some residual moisture to swell and break the cell.

 

[simnick]

Did you ever do pure sodium in water in science classes in high school? Smokes and runs around the water, maybe catches on fire or explodes? Well, Lithium is even more reactive that sodium. Which is great for battery energy, and bad for fires.

 

[Packard]

Ah!  And since water ignites it, it would be futile to spray water on the fire in hopes putting it out.

But why are the manufacturers continually being blindsided by the fires? Clearly they are.  The recalls and stopped production lines are going to be prohibitively expensive.

 

[squall_line]

As far as 'Why do the manufacturers seem surprised or caught off-guard by fire issues', the skeptic in me says that it's called "plausible deniability".

Until or unless there's an internal document and a whistleblower, any major issue like this is "a complete surprise" until it isn't.

See also: Takata airbags.

 

[rmhinden]

What burns in these fires?  A fire official (I don’t remember where) said that the manufactures of these EVs should publish fire fighting instructions.  (Apparently, a fire raged on while the department was using an incorrect fire fighting method.)

EV manufacturers do publish fire fighting instructions.  For example, for the Tesla Model 3

INFORMATION FOR FIRST AND SECOND RESPONDERS EMERGENCY RESPONSE GUIDE

First responder information for all Tesla products be found here:

Tesla First Responders Information

It includes EV Safety and Training information.

I assume there is similar info for other manufacturers.

Bob

 

[woodferret]

For note, lithium metal is different than the lithium polymer.  EVs are a class B fire, not class D.

Lithium metal has a direct exothermic reaction with water and room temperature.  The lithium polymer fires are actually the burning of off-gassing and plastics.  The cathode starts to degrade at about 65C.  The gas that it emits is flammable.  The cell and separator material is usually designed to 500C, but charging issues can easily create localized hotspots that run up to that temperature you get bursting and potential subsequent fire as the jet of flammable gases is mixed with air (and it already has heat).

 

[Packard]

Interesting.  Very different from fossils fuel car fires.

Of note, a fireman explained to me that burning gasoline fueled cars will only explode if there is an impact to the vehicle.  Only on TV and in movies will car fires spontaneously explode.

Basically, a second vehicle has to crash into the burning car for an explosion to occur.