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You can't just "shut down" electric pathways. Not exactly. There is a manual cut that first responders need to make to sever the high voltage circuit before the

by abalone 13y ago

You can't just "shut down" electric pathways. Not exactly. There is a manual cut that first responders need to make to sever the high voltage circuit before they can work on the car. However there's still capacitors, converters and the battery itself that remain dangerous especially if they've been compromised. As for "fast draining" the battery, where would the power drain to? That's exactly the problem.. NOT giving the power a path to go when you're working on the car. This is not much of an issue with most cars because the electrical systems are low voltage (12V car battery). With Tesla it's enough to cause major injury or death with one touch if you complete the circuit. Watch the video, it explains all this. http://www.youtube.com/watch?v=ntK3rvVl2Qw http://www.youtube.com/watch?v=ntK3rvVl2Qw

agumonkey 13y ago
And I guess it's unrealistic to think of a special draining device to be brought on crash sites to exhaust the car battery. All in all, are electric vehicles more 'instable' energy wise when crashed, compared to petroleum based one ? or is it different flavours of similarly sh*tty situations ?
- abalone 13y ago
  That's a very big question and probably only time will tell. Without getting into it too much, a very basic difference is.. Gas can explode like a bomb but (a) it needs an ignition source and (b) there can be visible signs when the fuel is leaking to let you know to take extra precautions (like spray fire retardant). You can actually get fuel on you and you'll be fine. High voltage systems don't (usually) explode, but they have lethal amounts of energy stored that can find its way into your body if you complete a circuit. Furthermore in a mangled wreck there aren't necessarily visible signs when a component is electrified. You find out the hard way. Basically Tesla deserves props for making an extremely strong car. That's what was tested here. But the spin is they're claiming "safest car" while completely side-stepping the high voltage safety issue.
  - masklinn 13y ago
    > Gas can explode like a bomb but (a) it needs an ignition source and (b) there can be visible signs when the fuel is leaking to let you know to take extra precautions (like spray fire retardant). And (c) if it's a diesel car (very common in europe), good luck getting it to explode.
    - Casseres 13y ago
      Want to scare your friends? Put out a lit match or cigarette using Diesel fuel. Diesel fuel requires a lot of heat to combust. Diesel engines don't contain spark plugs, they heat the fuel by compressing the air that the fuel is atomized in.
  - TWAndrews 13y ago
    Technically they only claimed "ACHIEVES BEST SAFETY RATING OF ANY CAR EVER TESTED" which is completely true. The "unaware of any Model S or Roadster occupant fatalities in any car ever" is also a pretty strong argument for actually being the "safest car" too.
  - icelancer 13y ago
    >Basically Tesla deserves props for making an extremely strong car. That's what was tested here. But the spin is they're claiming "safest car" while completely side-stepping the high voltage safety issue. That's not a side-step. IIHS doesn't test for this, and Tesla is not beholden to do so.
- kec 13y ago
  There isn't really a good way to quickly and safely dump all the energy from a battery the size of the Tesela's. Think about it: to drain in an hour, the battery would have to source 65kW continuously, converting all that energy into either heat or light somehow.
- jlgreco 13y ago
  85KWh is a lot of energy. Back of the envelope calculations puts that at enough to boil around one metric ton of water from 25C.[1] If you wanted to rapidly drain a Tesla you would have to dump that energy somewhere. That might actually be plausible for firefighters to do[2], but I doubt the battery itself would withstand being drained anywhere near fast enough for an emergency situation. It would probably find some interesting way to fail if you forced it to discharge that fast (bypassing all the safeguards). [1] 3.06e8 J / (4.181(J/(g * k)) * 75K) = 976,000g ...I probably got that wrong, it's been a long time. [2] I mean, their main job is getting rid of large concentrations of heat, right? ;)
  - abalone 13y ago
    Also remember we're talking about an accident scenario. There's no way emergency responders would intentionally run a high voltage circuit like that where there's a risk of short circuit in a physically compromised vehicle. They're going to be focused on containing the energy not draining it. It is fun to do back of the envelope calcs though.. You could run 50 space heaters for an hour off that sucker. Insane.
    - lutusp 13y ago
      > They're going to be focused on containing the energy not draining it. In an emergency that involves extracting passengers from an electric car, the most likely outcome is that the battery will get shorted to the car's chassis, at which point the emergency links in the battery will open up, isolating the battery from the rest of the car and its passengers.
      - abalone 13y ago
        As the video explains, even when the battery has been isolated there are other components that remain electrically hazardous such as capacitors and the converter. Also there is the possibility that the battery itself may be physically compromised in an accident, e.g. it could protrude into the cabin (it sits right under it). Not much you can do to isolate it then.

by abalone 13y ago

agumonkey 13y ago

And I guess it's unrealistic to think of a special draining device to be brought on crash sites to exhaust the car battery. All in all, are electric vehicles more 'instable' energy wise when crashed, compared to petroleum based one ? or is it different flavours of similarly sh*tty situations ?

abalone 13y ago
That's a very big question and probably only time will tell. Without getting into it too much, a very basic difference is.. Gas can explode like a bomb but (a) it needs an ignition source and (b) there can be visible signs when the fuel is leaking to let you know to take extra precautions (like spray fire retardant). You can actually get fuel on you and you'll be fine. High voltage systems don't (usually) explode, but they have lethal amounts of energy stored that can find its way into your body if you complete a circuit. Furthermore in a mangled wreck there aren't necessarily visible signs when a component is electrified. You find out the hard way. Basically Tesla deserves props for making an extremely strong car. That's what was tested here. But the spin is they're claiming "safest car" while completely side-stepping the high voltage safety issue.
- masklinn 13y ago
  > Gas can explode like a bomb but (a) it needs an ignition source and (b) there can be visible signs when the fuel is leaking to let you know to take extra precautions (like spray fire retardant). And (c) if it's a diesel car (very common in europe), good luck getting it to explode.
  - Casseres 13y ago
    Want to scare your friends? Put out a lit match or cigarette using Diesel fuel. Diesel fuel requires a lot of heat to combust. Diesel engines don't contain spark plugs, they heat the fuel by compressing the air that the fuel is atomized in.
- TWAndrews 13y ago
  Technically they only claimed "ACHIEVES BEST SAFETY RATING OF ANY CAR EVER TESTED" which is completely true. The "unaware of any Model S or Roadster occupant fatalities in any car ever" is also a pretty strong argument for actually being the "safest car" too.
- icelancer 13y ago
  >Basically Tesla deserves props for making an extremely strong car. That's what was tested here. But the spin is they're claiming "safest car" while completely side-stepping the high voltage safety issue. That's not a side-step. IIHS doesn't test for this, and Tesla is not beholden to do so.
kec 13y ago
There isn't really a good way to quickly and safely dump all the energy from a battery the size of the Tesela's. Think about it: to drain in an hour, the battery would have to source 65kW continuously, converting all that energy into either heat or light somehow.
jlgreco 13y ago
85KWh is a lot of energy. Back of the envelope calculations puts that at enough to boil around one metric ton of water from 25C.[1] If you wanted to rapidly drain a Tesla you would have to dump that energy somewhere. That might actually be plausible for firefighters to do[2], but I doubt the battery itself would withstand being drained anywhere near fast enough for an emergency situation. It would probably find some interesting way to fail if you forced it to discharge that fast (bypassing all the safeguards). [1] 3.06e8 J / (4.181(J/(g * k)) * 75K) = 976,000g ...I probably got that wrong, it's been a long time. [2] I mean, their main job is getting rid of large concentrations of heat, right? ;)
- abalone 13y ago
  Also remember we're talking about an accident scenario. There's no way emergency responders would intentionally run a high voltage circuit like that where there's a risk of short circuit in a physically compromised vehicle. They're going to be focused on containing the energy not draining it. It is fun to do back of the envelope calcs though.. You could run 50 space heaters for an hour off that sucker. Insane.
  - lutusp 13y ago
    > They're going to be focused on containing the energy not draining it. In an emergency that involves extracting passengers from an electric car, the most likely outcome is that the battery will get shorted to the car's chassis, at which point the emergency links in the battery will open up, isolating the battery from the rest of the car and its passengers.
    - abalone 13y ago
      As the video explains, even when the battery has been isolated there are other components that remain electrically hazardous such as capacitors and the converter. Also there is the possibility that the battery itself may be physically compromised in an accident, e.g. it could protrude into the cabin (it sits right under it). Not much you can do to isolate it then.