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Comment by VladRussian2 | Hacker News Reader

>What exactly do you think should happen when a jagged metal object collides with your car with enough energy to rip through critical components? Do you think susceptibility to telephone poles and meteorites is also a defect that auto makers need to fix?

>Short of encasing the car's primary energy store with 6 inches of plated steel, what are you looking for, exactly?

that is a bunch of 6in fallacies. Car fuel tanks are made of something like 1-2mm steel. As far as i understand Tesla doesn't have a 1mm steel sheet below the battery. That is the defect made obvious by these 2 accidents.

Btw, modern cars are much better at hitting telephone poles and does tend to explode less when being hit by "meteorites" (say bullets) than they were say 40 years ago. So, yes bad crash results ("susceptibility to telephone poles") for example would be a defect.

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You're right, Tesla doesn't have a 1mm steel sheet beneath the battery - it has a 5mm thick sheet [1]: "Musk explained that damage to the armor plating on the bottom of the vehicle was inflicted by contact with debris of a specific shape that resulted in a lever action, puncturing the bottom of the Model S. He noted that 25 tons of force would be required to make the three-inch-deep puncture in the quarter-inch-thick armor plating."

[1]http://www.eetimes.com/document.asp?doc_id=1319728

Does it need 25 tons of force or 3 inch hole to get the battery to catch fire?

If the battery container is blend out of shape a bit, would it potentially cause small short in part of the battery somehow? Would that start a fire for the rest of the battery.

If this is the case, wouldn't the probability of car catch fire might be higher?

An easy test might be take a few batteries and start shoot them with nail gun and see it get shorted/heatup/catch fire?

If it does catch fire, put a 5 mm sheet there and see how many nails and how big nails can get it to heat up / catch fire?

If any of the above tests can get the battery catch fire, I would be very concern if I am an Tesla owner.

at this thickness it would be something like aluminum, not steel. Good as a frame material, while softness make it not that good for point penetration resistance (it would be somewhere like 1mm steel equivalent, so seems i was wrong above). 5mm Al cover for 10ftx6ft battery would weight 80kg - doesn't look like there is much room for increasing.

So it doesn't sound like they did a screwy job - that's good to hear (as i said i'm a fanboy of Tesla and think nothing can stop them but their own hubris - when/if it appears), yet it also may mean that there is no easy, "low hanging fruit", way out.

That's a 3in fallacy. The battery in the Tesla S is significantly more resistant to damage than any passenger car fuel tank I've ever seen.

Do you honestly think that Tesla left that pack hanging underneath the car totally unprotected? Beyond that, you completely and utterly missed BHSPitMonkey's point.

> Car fuel tanks are made of something like 1-2mm steel.

Many, many car fuel tanks are made of plastic.

It's the position of the tank in the car rather than the material involved that's important.

This is a hard problem for Tesla to solve because their batteries are bigger by volume, really heavy, don't get lighter as they discharge, and don't shape as easily as a liquid, so the bottom of the car is the only really good place for one.

That's why Tesla used the "heavy armor" approach and actually -do- have several mm of metal located beneath the battery, but no armor is perfect.

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