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Comment by justin66 | Hacker News Reader

> I hope very much the industry can improve electrical safety over time.

With regard to the electrical aspects, isn't the safety record on these cars perfect or close to perfect up until this date? That means it's only going to get worse. That does not mean electrical cars are unsafe, it just means there isn't much of a record yet.

My expectation is that there will over time be a small number of electricity-related accidents involving first responders and passengers and that they will be enough to fuel concern trolls until the end of time. That the electrical problems will be so enormous that they dwarf the massive safety gains from better passenger protection of the sort NHTSA is interested in (and frankly, anyone who is about to get hit by an oncoming SUV is interested in) seems awfully counterintuitive.

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Aren't those the same concerns people had when gasoline cars were introduced? It was considered to be too dangerous to use.

Fast forward to today, cars are not exploding. Battery safety issues will be dealt with.

Considering the fact that Tesla batteries are made for lots of really tiny cells, I can't imagine it is impossible to disconnect them from each other in the case of a crash.

I don't know about individually disconnecting each cell, but there is a loop that emergency responders are supposed to manually cut to disconnect the battery. However there are still components that retain power and remain hazardous such as the converter and capacitors. Firefighters need to take great care to cut around them. Plus there's the possibility of the battery compartment being compromised in an accident as well. Tesla's training video covers all this.

Nobody's arguing that Teslas are unsafe, just that the "safest car" claim sidesteps the electrical safety issue. You can't really argue that everything's fine because nothing bad has happened yet, because there are so few Teslas on the road. And it should be noted, a lot of people were hurt along the path to making gasoline cars as safe as they are today. Look at Ralph Nader's work on automobile safety for example.

I actually believe progress demands that we work through electrical car safety. But what irks me is it's just a little premature to be trumpeting "SAFEST CAR EVAR" when you've got a novel set of serious safety issues that the test suite doesn't even try to target.

Wish I had your crystal ball.

With improvement, I was referring to the complexity of cutting someone out of a Tesla and all the no-cut zones that could electrocute passengers, emergency responders, even guys towing wrecks. You're right, there is no real safety record yet.

> With improvement, I was referring to the complexity of cutting someone out of a Tesla and all the no-cut zones that could electrocute passengers, emergency responders, even guys towing wrecks.

As an electrical engineer with spacecraft experience, I can say that a car like the Model S isn't likely to electrocute anyone. While extracting someone from a wreck, emergency workers use tools like the "jaws of life", strong metal pliers meant to quickly snip a car's body apart.

When a tool like this cuts into an electric car, if it should slice through a power cable, in most cases the tool would short the cable to the car's chassis, thus grounding it and tripping the safety links that are integral to the battery pack. This means the car will become inoperative, but it doesn't mean anyone will get electrocuted.

I think the above will be the outcome in the vast majority of cases. Compare this to the plight of someone sitting in a wrecked gasoline-fueled car.

Hi there. Go ahead and watch this video from Tesla about how to cut someone out of a Tesla. The very first step is to cut the circuit like you say, but there are a few things you overlooked.

Much of the video is concerned with instructing responders how to cut around components that may remain electrified such as the converter and capacitors which, in Tesla's own words, present a "serious hazard of shock" because "they can release up to 400 volts in just an instant."

http://www.youtube.com/watch?v=ntK3rvVl2Qw

Nitpicking, I know, but releasing 400 volts means nothing. Current kills, tension does not. It all hinges on the internal resistance of the power source.

Voltage means A LOT. A regular 12V car battery is a perfect proof: it has enough current to kill you, but at only 12V it doesn't overcome your body's resistance much under most circumstances.

400V can overcome your body's resistance no problem. And obviously an EV has a crap ton of amperage as well.

That and time. You could get hit with high volts and current, but still be fine if the exposure is short. I have had a few 240v mains shocks on high current fuses, but they were all pretty quick and I had nothing but very slight burns and sore muscles for about ten minutes.

However, there is definitely a risk here, albeit what appears to be a manageable one. Perhaps there could be some use in building volt meters that glow into gloves for emergency responders to help mitigate some of the risk.

Perhaps it would be even better to say, "power transmission kills."

Well, also the resistance of the load.

Do other car manufactures provide such videos?

I know a paramedic in rural Australia. They get taken to local car dealers to get safety training with electric cars.

As I understand it it's done on a per-model basis, but that wont really work as an increasing number of electric car models end up on the roads. I'm not sure if this is done all over the state/country, or if it's the one local dealer being friendly with the local emergency services.

Would an independent accelorometer in the battery assembly shut of the power when the car is involved in a collision?

It wouldn't make sense for it to be dependent on a link from the airbag sensors, it would have to be local to the power plant.

Would the tools used not be developed?

I would've assumed the production of specialised tools for electric cars would be a priority once they become popular.

Presumably, avoiding electrocution of the passenger being extracted is also a goal.

I don't understand your response, is this not what the specialised tools would be primarily designed for?

What sort of tools are you envisioning?

maybe insulated ones

Insulating the tools isn't really the issue. There's already a fair amount of insulation between me (the tool operator) and the business end of the tool.

The problem is, we're cutting through and crushing various bits of the car that weren't really designed to be indiscriminately cut into (which is why training is so important).

Both rescuers and victims have been seriously injured and killed when extrication activities turned potential energy stored in the car into kinetic energy. Air bag deployment systems, seat belt pretensioners, even the little hydraulic tubes that hold your trunk open and be extremely dangerous if their energy is released in an uncontrolled way.

So you can understand why we're a little leery of 85 kWh of potential energy sitting under the car...

Here's an example of airbags being deployed when the SRS controller was crushed with a hydraulic spreading tool.

https://www.youtube.com/watch?v=yDSksTztHJk

Two firefighters were injured in that incident (one of them seriously).

85 kWh of potential energy sitting under the car...

A 40 litre petrol tank holds about 380 kWh though.

Yeah, but we've had almost a century of experience dealing with that...

The issues involved are also very different. A tank of gas is actually a very stable thing. Barring a puncture, there's not much you can do to a gas tank to make it do bad things.

Cutting a gas line is no major concern. Shorting a high voltage/high current power line to the frame of the vehicle is putting a lot of trust in the batteries failsafes (that trust is almost certainly justified, but with a track record measured in years, not decades, you'll forgive us for being a little paranoid...).

As far as I can tell, unless people have done something stupid, your worst worry is not the shock from the batteries. The batteries are a variety of potential difference spread over a large area and will go on fire rather then discharge everything at once, which is an issue, but they will not explode with their total chemical potential, not even close. It is any big fat capacitors that you have to worry about. Now they are not storing anywhere near the capacity of the battery, but they can let it out with very low internal resistance and after heavy braking are likely to be fully charged. So it is a current that can be easily discharged, but you have to know it is there.

edit - I said it earlier somewhere else, but EMT gloves with built in glowy multimeters might be a really good plan.

double edit - if you think this is a good plan, feel free to nick it.

A 40 liter petrol tank can't discharge 85kWh of potential energy in seconds without ideal conditions (good vaporization or atomization combined with sufficient oxygen)

Neither can a battery. The internal resistance is too high. They can cook and go on fire a bit, but much less than a gasoline fire, but they cannot shock you with their entire capacity in a few seconds.

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