Model S Battery Fires: A different view

Model S Battery Fires: A different view

Here's a new perspective on the battery fires:

=>The world did NOT see videos of the battery pack on fire.

Instead, we saw sensational images of the FRUNK on fire (and of course no one mentions that the passenger compartment remained completely undamaged). The frunk fires probably grew in intensity long after the battery pack stopped venting. Thus if Tesla could make the frunk fire resistant, Fox News will need to look elsewhere for ratings-inspiring videos as the hapless caltop-damaged Tesla on the side of the road will just vent white smoke for a while.

=> What if Tesla were to use flame resistant material as upholstery to line the frunk? In this case, the venting battery pack flames,(or maybe it was just super-heated gas and not actually flames) would after a short period of time, subside without resulting in a CAR fire.

One such material might be Nomex, commonly used in fabricating flame-proof safety suits:

Still, it's my personal belief that the fires are not a safety issue due to Telsa's isolation (fireproofing) of the passenger compartment, and so they don't really need to change anything.

logicalthinker | December 5, 2013

That's so weird I'm not even going to comment on this post.Oops, I did.

I will say I agree with your last sentence. Enough said.

Docrob | December 5, 2013

I don't follow, you actually don't believe the battery was the source of the combustible material fueling the fire and the materials making up the frunk were? Or you know it was the battery but are advocating lying to the public about it anyway?

puppybite | December 5, 2013


But of course the battery started the fire due to its vented heat causing the frunk to burn: It was certainly the ignition source.

The battery pack's vented heat may have been actual battery flames or superheated gas exiting the battery. It doesn't matter.

I'm proposing that if the frunk's upholstery material were flame resistant, then it's possible that there would not have been an escalating car fire to the extent shown in the videos, but instead a thermal event limited to just the battery pack (and just the damaged SECTION of the pack: I think there are 16 sections isolated from each other).

Big T | December 5, 2013

That video didn't run only on Fox News. It also ran on ABC, CBS, NBC, CNN, HLN, CNBC and MSNBC. The 24 hour cable news networks such as Fox News do run the same video more often due to their repeating format. The same stories run over and over since viewers tune in and out during the 24 hour cycle. More people will see the video on Fox News because their viewership is about the same as the other three 24 hour cable news networks combined. Perhaps the network is a little more sensational with everything being a "Fox News Alert." Maybe that accounts for their ratings.

mauer | December 5, 2013

Tesla has demonstrated, that they can swap the battery pack. So my idea was to drop the battery pack in emergency (fire) case ?

chrisdl | December 6, 2013

And then the Tesla behind you runs over it and catches fire. But no problem, because that Tesla will also drop its battery. But then the Tesla behind that Tesla will run over it and catch fire. Which then is hit by the Tesla driving behind the Tesla which was behind the second Tesla, causing said Tesla to catch fire and drop its battery. OMG, the whole road will be full of burning batteries in no time! Inferno! Aarghl!

chrisdl | December 6, 2013

Unfortunately, Li-ion battery thermal runaways burn even without a (theoretically) flammable frunk:

The Model S has several security systems in place to minimize the risk (firewalls, paste which expands when heated to isolate the cells, active cooling, etc), but the individual cells can still burn and explode something fierce.

DallasTXModelS | December 6, 2013


DonS | December 6, 2013

I think there is consensus that the fires start in the battery, but where is most of the fuel for those flashy videos?

Since the battery pack has 16 sections, a fire releasing all the energy of that section is 85kWh/16 = 5.3kWH = 18,127 btu. Plastics making up the frunk liner and carpeting are easily several times this energy. A single pound of polyethylene contains 19,900 btu and a pound of polypropylene contains 19,850 btu. These are higher energy densities per pound than gasoline. By the time fire consumes the frunk, the tires and front facia are involved too. The total weight all the plastic is a guess, but estimating about 50 lbs, roughly 50 lbs x 19,850 btu/lb = 992,500 btu.

Pictures of the fire and its aftermath are 2% battery damage and 98% plastics damage. puppybite's idea seems to have merit for at least some shielding near battery vents.

jbunn | December 6, 2013

I must be the only one that understands what the OP is saying. I said the same thing to my cousin when he showed me the fire.

Under the hood, there is a plastic frunk liner. Probably about 20 pounds of plastic like ABS. Then carpet in the frunk. Rubber gaskets for the hood, boots for the stearing rack, plastic hoses and other parts for the aircon, and braking systems. All together probably about 40 or 50 pounds of plastics under the hood. Then we have the tires.

If you've ever burned plastic, or seen it burn, it kicks off a huge amount of black smoke and flame.

When I looked at the Washington car, my first thought was "looks like plastic burning".

So if I'm reading the OP correctly, he's not suggesting the battery is not burning. He's suggesting the visible smoke that makes it so dramatic is as a result of all the burning plastic under the hood.

jbunn | December 6, 2013

Looks like Don and I were writing the same analysis at the same time.

Bighorn | December 6, 2013

I think you were copying off his paper.

Doug H | December 6, 2013

puppybite - I was thinking the same thing. With a firewall between the battery and the frunk material, the fire would stop when the punctured battery cell burned out.

2-Star | December 6, 2013

Except for the fact the battery pack is cooled by flammable ethylene glycol, and there was a big puddle of it burning under the front of the car. Apparently each cell is not independently isolated for the coolant, so one puncture will cause a fairly big puddle from the leak. If the overheating causes the fluid to ignite, that will cause at least some problem.

puppybite | December 6, 2013

DonS and Jbunn,

BINGO!!!, you have added validation to my intuitive theory with data regarding the combustion energy in the frunk's lining materials. Maybe you should start a new post reiterating your data in case it's being missed in this reply section to my post.

So, in summary:
The fuel SOURCE sustaining the dramatic fires is not the battery pack.
The battery pack merely STARTS the fires as an ignition source, but after that, the fires burn because of the large amount of combustible
energy-dense materials the frunk.

I've witnessed Li-ion battery fires with R-C battery packs. They flame-out intensely, but only for a brief time, a "flash-in-the-pan" effect. I don't know if the same effect is true for the Tesla packs though, but I doubt the battery pack has enough fuel to burn for more than a few minutes after the onset of its cells flaming-out.

If the frunk materials were not combustible, then there probably wouldn't be a steady 30 minute fire event that consumes the entire front section of the car, resultant from the impacted battery pack burning out its damaged section, venting super heated gasses/flames towards the tires and frunk.
Tires will always be combustible though, but perhaps this could be addressed by a thermal shield that prevents vented gas/flames from direct exposure to the tires.

THIS DISTINCTION IS CRITICAL: The public's perception is that the steady flames on the videos are actually the battery pack continuing to burn, which then leads to the proclamation (by some) that the battery pack is unsafe.

Still, even with the fires as shown on the two viral videos, it's nevertheless the case that there was not a passenger safety issue:

1. The fires started slowly after the impact event with the road debris. There was ample time to stop and exit the vehicle before the flames were visible.

2. The flames were isolated from the passenger cabin and confined only to the front section of the vehicle, where by design, the battery pack is vented.

3. After the fire events, the passenger cabin still remained undamaged. This is due to a firewall that protects the passenger cabin.

In fact, it could be argued that the battery SAVES occupants by covering the entire bottom of the passenger compartment. Do a Google image search on "3 prong tow hitch" and you'll see an object that could have pierced the floorboards in a standard vehicle. Imagine what could have happened to an occupant with that tow hitch breaching the cabin at 70 MPH....

Pungoteague_Dave | December 7, 2013

@puppy. While the frunk liner may have contributed in a small way to the fire, the primary source of fuel for the fires is 27 quarts of ethylene glycol that seves as coolant and heating catalyst. It is extremely flammable and in certain situations, explosive. If you look closely at the pictures and videos, you can see flaming liquid pouring out, and pooling on the ground, fueling the fire. It is an intense burn.

The ethylene glycol circulates throughout the battery. When it leaks out it is no longer available to help regulate battery temperatures. This is why there is typically a 5 minute delay before the affected battery cells begin to spontaneously combust. Hence the safety margin compared to typical vehicle fires. Changing the frunk formulation will have little or no effect on the size or duration of a Tesla battery fire.

Bighorn | December 7, 2013

I've seen you mention 27 quarts a few times now while before it was units of which you were unsure. Have you received confirmation on this point or is this the start of an urban legend?

chrisdl | December 8, 2013

DonS (and by extension, jbunn and puppybite ;-)

In your calculation, you base the battery btu solely on the energy storage capacity of the battery. However, the battery has other highly flammable parts which you have not taken into account (pressurized electrolyte, coolant liquid, ...) The total amount of energy when it catches fire will be a lot more than only the energy in the cells.

Other than that, it sounds like a good idea to add a firewall between the battery and the frunk. So I agree with you guys, nevertheless :-)

bonaire | December 8, 2013

A small venting battery can ignite ethylene glycol just as much as jf an accident with an ICE had a puddle of gasoline nearby a sparking battery cable or other ignition source. EG has a flash point of 271F which is about the same temp as a thermal runaway in a Li Ion cell. Why is Tesla using such a liquid in a battery system where such a breach could cause not only a battery vent with flame plus leak of EG which then can burn? The chiller is mounted in the center of the undercarridge in front of the battery pack and is probably something that was hit by fire events which also pierced the battery chamber. If the coolant leaking is seen as a fuel source in a battery system breach then it is a danger in a multi vehicle accident.

I think the NHTSA will need to recommend a non flammable coolant, if one is available.

chrisdl | December 8, 2013

Problem with the non-flammable coolants is that they're usually poisonous. So yeah... which one is worse? But you make a good point, though.

Pungoteague_Dave | December 8, 2013

@bighorn, I asked at the last service visit, and the "units" are, in fact, quarts. The battery coolant system has 27 quarts of ethylene glycol circulating through it and the radiator.

Bighorn | December 8, 2013

Thanks for clarifying, PD. Good to know!

Miggy | December 8, 2013

A Lamborghini Aventador, Gallardo and Gallardo Superleggera burnt to the ground after an accident.
A montage of photos showing a Lamborghini Aventador, Gallardo and Gallardo Superleggera burning to the ground after an accident.

Three Lamborghinis burnt to the ground on Friday when a charity drive turned disastrous.

Supercar owners were reportedly driving from Singapore to Kuala Lumpur when a motorist swerved toward their exotic car convoy on a Malaysian highway.

The incident triggered a collision between a Lamborghini Aventador, Gallardo and Gallardo Superleggera, all of which caught fire after coming to a stop.

Authorities said no-one was hurt during the incident, though all three cars were destroyed.

The trio of cars are believed to be worth around $2 million thanks to high taxes that make the Aventador cost more than $1 million in Singapore.

The owners may have difficulty replacing their cars, as Lamborghini has finished building the Gallardo and is gearing up for a replacement.

The new car, believed to be called the Cabrera, is expected to have a V10 engine mounted to a new twin-clutch transmission and all wheel drive.

The charity drive disaster came less than a week after The Fast and The Furious star Paul Walker and his friend Roger Rodas died when their Porsche Carrera GT crashed and exploded into flames in California.

Car fires have made headlines throughout 2013 thanks to a spate of incidents affecting the battery-powered Tesla Model S, while Ferrari’s 458 Italia was the subject of unwanted publicity when several of its cars burnt in 2012.

-Fairfax News Australia
9th Dec 2013

Miggy | December 8, 2013

Video of 3 Lambo's burning:

mauer | December 8, 2013

chrisdl: Clearly drop the battery in safe conditions (not at full speed), like car is on the emergency lane, out of lane and does not move.

chrisdl | December 9, 2013

Currently physically impossible because the front of the pack is so high that you wouldn't be able to drive over it. The top of the battery pack is not flat. Plenty of other issues with that idea as well, but this ia a showstopper.

Brian H | December 9, 2013

Another issue: it's dumb. Wrong solution to wrong problem.

chrisdl | December 10, 2013