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Question on car safety

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Old Sep 16th, 2018, 13:41   #1
oragex
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Default Question on car safety

As well all know, the P2 cars have the main battery located inside the trunk, basically just behind the rear bumper. How safe is this if the car is rear ended in a more severe crash? Could the battery catch fire?
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Old Sep 16th, 2018, 14:11   #2
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That's an interesting point, and one that came immediately to mind when I first saw the P2 battery location. One would imagine some sort of failsafe strong zone around the battery box could be implemented, although not sure how effective it would be as it's so close to the rear crossmember & surely the crumple zone would be compromised in this case too?

Having said that, some of the salvage rebuild channels I watch on Youtube have shown a fair few nasty impacts where the battery has been crushed/broken on various cars & it hasn't resulted in a fire. I think when the battery gets smashed it tends to leak all it's electrolyte fairly quickly and the plates within become less capable of producing power/heat even if they're mushed together somewhat.

I think technically yes, an electrical fire *could* result from a rear impact to a P2 car but the chances probably are not significantly higher than a similar impact to any other car with different battery locations. Certainly interested to hear other's opinions and/or experiences around crushed batteries though.
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Old Sep 16th, 2018, 22:01   #3
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Originally Posted by ma70 View Post
That's an interesting point, and one that came immediately to mind when I first saw the P2 battery location. One would imagine some sort of failsafe strong zone around the battery box could be implemented, although not sure how effective it would be as it's so close to the rear crossmember & surely the crumple zone would be compromised in this case too?

Having said that, some of the salvage rebuild channels I watch on Youtube have shown a fair few nasty impacts where the battery has been crushed/broken on various cars & it hasn't resulted in a fire. I think when the battery gets smashed it tends to leak all it's electrolyte fairly quickly and the plates within become less capable of producing power/heat even if they're mushed together somewhat.

I think technically yes, an electrical fire *could* result from a rear impact to a P2 car but the chances probably are not significantly higher than a similar impact to any other car with different battery locations. Certainly interested to hear other's opinions and/or experiences around crushed batteries though.
Hmm, Interesting, but think you could be right....The battery in my 940 is right at the front near side corner of the car and I remember (I think) my dads 1988 740 had it's battery at the front offside corner.
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Old Sep 16th, 2018, 19:14   #4
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Originally Posted by oragex View Post
As well all know, the P2 cars have the main battery located inside the trunk, basically just behind the rear bumper. How safe is this if the car is rear ended in a more severe crash? Could the battery catch fire?
If it caught fire under the bonnet all the fuel lines are there.

I don’t believe it would catch fire
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Old Sep 16th, 2018, 20:59   #5
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If it caught fire under the bonnet all the fuel lines are there.

I don’t believe it would catch fire
Indeed, it's about as far as it could be put from anything significantly combustible.
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Old Sep 16th, 2018, 21:23   #6
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Great points, good to know acid batteries don't catch fire when crushed - I had the Tesla battery in mind but that's a different composition
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Old Sep 16th, 2018, 21:39   #7
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Great points, good to know acid batteries don't catch fire when crushed - I had the Tesla battery in mind but that's a different composition
I don’t know that they don’t catch fire but the Tesla type batteries are lithium polymer which are very unstable (obviously fine when used as supposed to). They also have horrific peak output.

Lead acid I think are less likely.
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Old Sep 16th, 2018, 21:51   #8
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The lead acid accumulators (to give them their dullest name) are pretty robust, but they do depend on the electrolyte to provide the potential difference. Yes, they could split in a rear end whack but if they do split, they leak a bit of acid and don’t do a lot more afterwards. Naturally, the plastic they’re encased in is flame proof etc. They could provide a spark, but not much else.

With reference to the LiIon batteries that Tesla and others use, they are self oxygenating so cannot be put out byconventional means. If one remembers the triangle of fire, under thermal runaway conditions, they have heat, fuel and oxygen, more or less whatever you do so burn they will.

In planning a LiIon test facility, I spend ages considering dousing with water, auto spuression systems and a whole lot of other kit, and in the end, I’m going to just place the batteries on a sled and basically jettison them if they go up and just let them burn.

Consider that a V70 battery contains sufficient energy to run a starter motor for 90 seconds or so. A Tesla battery can move 2.4 tons of metal whilst keeping it cool or hot for 270 miles; there is a considerable difference in stored energy.
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Old Sep 16th, 2018, 23:18   #9
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Originally Posted by oragex View Post
As well all know, the P2 cars have the main battery located inside the trunk, basically just behind the rear bumper. How safe is this if the car is rear ended in a more severe crash? Could the battery catch fire?
Remember volvos have been crash tested , It would take a massive smash to damage the battery , something like a train or truck hitting it .. most cars disintegrate when they go into the back of a volvo , leaving the volvo almost unmarked , ok slight exaggeration but not far off what happens in most crashes .
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Old Sep 17th, 2018, 22:36   #10
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My money's on there being essentially no chance of an FLA (Flooded Lead Acid) battery bursting into flames upon impact of any amount.

The shining star of battery fires is a hydrogen explosion. Remember the Hindenburg?
A spark at the right time in the right place can ignite lingering hydrogen and blow the top off a battery-voiding its warranty.

In the case of a smash there wouldn't be much, if any, hydrogen lingering about, in the first place. If sparked, it would go up in a small, uncontained little poof. We ignited small amounts of hydrogen in science class as I'm sure you did. That sample had to be collected in a test tube.

The polypropylene case, if smashed would allow the acid to drain out. Sulfuric acid isn't flammable. Buckled steel wouldn't contain any hydrogen produced were the engine and alternator to continue to run.

SOURCES: Fire Departments, Insurance Companies, Automotive Engineers, Chemists, Battery Manufacturers

SOURCES I CONTACTED: None of the above.
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