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Comment by dreamcompiler | Hacker News Reader

Firefighter/EMT here. Our department has trained on hybrids (don't cut the big orange cable!)[0] but not electric per se. Doesn't matter. Unless there's someone in the car, we're going to stand back, let it burn, and keep it from spreading.

Cars contain bigger hazards than batteries: Airbags are basically bombs, and gas lifters (the things that make the hatchback open smoothly) can become missles in a fire. And that bit about cyanide? Ha! When your sofa catches on fire it releases cyanide. That's why we wear positive pressure SCBAs.

[0] We typically cut battery cables on conventional cars to lessen the danger of an airbag exploding in our face during a rescue.

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> Our department has trained on hybrids (don't cut the big orange cable!)

Keep training up to date. Hybrid HV wiring has a conductive sheath around the actual wiring, separated by non conductive layers. The purpose of this is that when your tool cuts such wiring, it shorts the sheath first and trips a breaker, so that you should be able to cut.

There's a group near here (WA state) that does demos including "throwing" (dropping) battery packs into wading pools while still supplying power, and cutting HV cables on running hybrids to demonstrate this.

But then again, there's near zero reason to do so. Stabilize the vehicle, kill the 12V. Our general go-to? Put the hazard lights on. If you stop the hazards, the vehicle is "generally electrically safe".

Biggest risk that isn't often talked about? HID headlights. Picture being up against the frame of the car. Regular headlights, bulb broken, possibly? Pretty low risk. Broken headlight, and behind it is a high voltage arc? That's a very real electrocution hazard.

Holy crap! I learned a lot from this; gonna research and take it to the crew. Thanks and stay safe!

You too. For sure, I remember when I got an 07 Prius, and we started talking about this stuff, and there was a lot of urban legends and myths.

That being said, while electricity obeys the laws of physics, MVA/MVCs throws a wild card into the equation. I err on the side of caution... "Why am I cutting this cable if the vehicle is powered down and stabilized?"

Yup. It's easy to pull out the trusty center punch and shatter the side glass when you're amped up on adrenaline trying to get to the patient, but as my Chief says: "First try the door handle." That usually works.

Makes me think of Terminator 2, when JC teaches T to flip the sunshade for keys instead of mashing the ignition key hole.

That in turn makes me think about that - was it common during those days to do that, store the keys there? Perhaps for shared service vehicles?

This is a Hollywood thing where writers in Hollywood don't know how the normal world works: storing the keys under the sunvisor is a thing that is done with studio vehicles in studio lots because the car changes hands a lot and so keeping the keys in it just makes sense.

It might've been common in a few American cities Hollywood-adjacent post-WW2 as well, but the accepted explanation is essentially that it's Hollywood being Hollywood - probably that it's a rite of passage as a junior team member to be unable to find the keys and then have someone show you they're in the "obvious" place.

Though I suspect at this point it's a writing shortcut more then anything else: we all know it's a movie, in movie's this happens, and in the plot in that moment you don't want to deal with "can these characters start this car".

> and in the plot in that moment you don't want to deal with "can these characters start this car".

yet that's always the most implausible part of the story. Even as a kid, I remember asking "are we the only people who take the key out of the car when we leave? everyone we see on TV seems to leave their keys in the car". If character A just took their damn keys with them... movie would have been over 20 minutes earlier!

And... in murder mysteries... or TV sitcoms... if someone just had a working cell phone, the "communication problem" (misunderstanding or missing) that's at the heart of 90% of plots would be removed and the show would be over. Would definitely make the writers have to work harder.

>Pretty low risk. Broken headlight, and behind it is a high voltage arc? That's a very real electrocution hazard.

There's not enough amps available there to do anything serious.

80-90V to keep it running are above the "low voltage" guidelines and their ~500mA is enough to kill.

Presumably the driver circuit would notice that no current is flowing from a ruined bulb, try the sparker a few times to restart the arc, then give up and turn off the 90V drive. But it might be cheaper to build…

Unscheduled airbag deployment is a terrifying concept if you're trying to lean in to access a person.

Why do military aircraft have RESCUE --> levers that disarm all the pyros but we can't make that a thing on cars? It wouldn't have to be a big red sign but it could be a standard.

Probably budget, and ejection seats are a bit more dramatic than airbags.

> "Why do military aircraft have RESCUE --> levers that disarm all the pyros but we can't make that a thing on cars?"

Not sure if it's standard on all EVs, but cutting the first responder loop on a Tesla will disarm the airbags & SRS, in addition to disconnecting the high voltage system.

Source: Tesla first responder guide: https://www.nfpa.org/-/media/Files/Training/AFV/Emergency-Re...

> first responder guide

This is exactly what I'm complaining about. Every car is different. Volunteers have so many trainings to take, it's unreasonable to ask them to take a whole training for EVERY MODEL CAR on the road. There should be a simple, standard, HV and pyro cutoff control, standard on ALL cars, that can be actuated without a hydraulic shear. Put it in the wheel well or behind a gascap-like door.

Imagine you are a civilian or first responder and want to help people out of a car and you don't have a hydraulic shear or hundreds of hours of model-specific training? This is an everyday usecase.

Training on fire suppression and extrication techniques for cars doesn't take THAT much training. Most techniques would be standard across the board, with a few exceptions for electric vehicles.

Additionally, never underestimate the hours of training that most firefighters go through anyway and get this, they live for that stuff.

Hmm, so it's not like the movies? You don't dial back in to a central command center where they call the guy who tells you to cut the red wire or not? Makes sense, I guess. Just interesting. It seems like there's value in centralization. Can't be two Teslas on fire at the same time in SF.

Business opportunity?

You know, perhaps it is.

I imagine the best placement is probably just about the middle of the dashboard, between where any airbags should go off. It would be something that could be jabbed by a blunt pole of any kind (the butt of a fireaxe pole for example) which would dislodge a connection between two points. That shouldn't be the main bus, but rather supply the power MOSFETs with the go bias current.

This sounds great in theory, and would work well until your 8 year old jabs a pen in there while you're going 70 on the freeway. There are two completely different scenarios you have to optimize for, and their optimizations really compete with eachother; ease of access is a benefit in one, and a danger in the other.

I find it hard to believe electronically controlled airbags would just pop out of nowhere. Don't they need a specific message to fire?

They contain explosives, which often don't need more than a bit of heat to go off.

There are several preconditions. It's not a computer message; think 1970s tech. There's a accelerometer to say you need a head-on crash and a seat mass sensor to say there's a large enough human in the seat. There are cases where the passenger bag did not deploy, for example a stuck-closed accelerometer, and then a responder knelt on that seat getting to the driver, satisfying the last condition, and causing a deployment with obvious injury.

But those conditions are met by computer / logic chip. Again find it hard to believe it accelerometer keeps broadcasting for more than 100ms after crash or so.

I've seen one in a pillar fire off during training while the vehicle had no battery and the same pillar was being cut through with hydraulic cutters.

A few people have pointed out that explosives can explode regardless of the message; I'd like to question, if it needs a specific message to fire them, how fragile is the system that delivers the message?

Yes, in an accident the airbag generally fires so quickly that it happens before physical damage occurs to the device firing it, but needing a specific message (over CAN bus perhaps?) makes the system much more fragile. What if there's a fender bender the week or month before, and causes light damage to the system? One bit is more robust by an order of magnitude than two, and so on.

How could you have an external lever that would disarm airbags without someone randomly pulling it when you leave your car in the shopping centre for example? I would expect military aircraft are always guarded so wouldn't have this problem.

It could also be a wire you need to cut, or a glass you have to smash first. The problem wouldn't be much different from someone breaking your car window to get your purse while your in the shopping center.

On the off chance you get in a crash later? The car could just give an alert if it's started with the emergency lever engaged.

It probably would disable the ignition anyway.

Former firefighter here also. We also used to have to worry about the compressed gas cylinders on bumpers.

Wait what?

Do you cut the cables twice?

I read the electric vehicle procedure and they say to cut the battery cutoff cable twice.

I thought that was interesting - I guess it makes sense you don't want to release that cable so the two ends fall back together and create a welding rig.

Be more worried about the carbon fiber. In many ways it is like dealing with flamable aspestos.

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