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Comment by raldi | Hacker News Reader

Rather than admonishing everyone for wondering the obvious question, why not just explain your reasoning?

Current flowing through your body is what kills you. But it doesn't flow through you just because it is a high-current supply (think car battery for example). It flows through you because the source voltage divided by your impedance is what controls how much current flows through you. Impedance is the general concept for resistance and basically indicates how current and voltage are related. The higher the impedance, the less current flows. Wearing rubber gloves would increase your impedance from hand to hand significantly.

So while high current does kill you, what causes it is high voltage. What is considered high? Depends on your impedance (ex. are your hands sweaty or dry?).

When dealing with high-current systems, there are safety procedures and concerns, but they are generally different than high-voltage. The systems I have dealt with are more about burns than electrocution. For example accidentally shorting out a fork lift battery can be spectacular in a bad way.

There's no particular safety concerned when you're playing with hundreds of kilovolts in a typical school. You need it when the thing you're messing with has the capability of delivering a lot of amps.

415 volts on a 30A breaker, like you might find in an undergraduate electrical engineering lab, is very lethal. I'd hazard a guess that's what the OP is talking about.

415 volts on a 5A breaker is equally lethal, and not high-current.

1,000 Amps and 5 volts is dangerous (sort of), but not in an electrocution sense.

What you care about is how much charge is at that high voltage potential because current is charge/sec. Charge due to stray capacitance can be quite dangerous because if you don't know what you are doing, the amount of stray capacitance can be higher than you expect. I would be very careful doing anything with kilo-volts using a circuit, as opposed to a static charge device, such as Van de Graaff generator.

When you get shocked by a Van de Graaff generator, you do get high voltage, as well as high currents. The missing ingredient is time. The shock takes a very small time, so the energy delivered by the shock is very small. Skin-effect also helps.

Relevantly in the case of microwave oven transformers, your impedance depends on the voltage because a high enough voltage can and will arc right through your skin into your soft, low-impedance innards. You can do this safely with a commonplace Tesla-coil-driven consumer plasma globe by putting just enough aluminum foil on top of it to arc through your skin, leaving cute little black charred spots, but in short enough bursts that it won't stop your heart.

You haven't explained anything unsaid in this thread, including by me, but merely completely ignored my argument that there are far more hazards with electronics than merely fatal electrocution.

An analogy: while technically what kills you due to a fall is called “gravity”, that’s not the whole picture. In actuality, it’s the height you fall from, which allows gravity to build up enough velocity to kill you when the fall ends.

Despite the fact that you’re experiencing the same gravitational acceleration from both, a one meter fall, while being potentially dangerous if you’re not prepared and allowed to land right, is not likely to kill you. A 100 meter fall, on the other hand, is likely not survivable by any means.

This seems like the opposite situation. Gravity doesn’t kill you from a fall (just like voltage doesn’t kill you from electricity). Gravity makes possible the sudden acceleration that kills you, which is analogous to the voltage-induced current.

The ground technically kills you. People have fallen for months, even over a year, without harm

What they're getting at is that while it is the amount of amperage that goes through your heart that determines your likelihood of dying, you need a certain voltage to overcome the resistance of your skin to achieve such an amperage. Anything under around 50v is generally safe to touch, and often high amperage applications are under that limit.

So the reason high voltage is more dangerous, if it has sufficient amperage backing it up, is that the higher the voltage, the better its ability to pierce your skins resistance and flow through your body to begin with.

It's the Ohm's law: V=IR. Amps (I) kill you but your body has rather high resistance, at least kilohms (even when wet), and it depends on the voltage partly. So low voltage even with high amps current do nothing to you.

And the corollary is high voltage with low amps do nothing to you too, neither amps nor voltage kill you alone.

The issue is that low voltage is guaranteed not to shock, can burn of course.

High voltage is inherently dangerous.

High voltage is not inherently dangerous. In a dry climate you can easily develop ten thousand volts by lying down in a bed without bedsprings with a long acrylic blanket and pulling the blanket over your head hair with your feet. You can get multiple-centimeter-long branching sparks of static electricity from your finger. The only danger of the activity (to you) is that you might produce enough ozone to irritate your lungs. But the energy of those sparks is limited by your body's capacitance to the blanket.

If you do this in a vacuum you could get X-rays, and if you do it near your cellphone or laptop you can kill them. But it's not dangerous to your body.

However, high voltage with enough power behind it to burn a Lichtenberg figure through your body can kill you pretty darn quick.

electronics die off ESD w/o the xray. I didn't mentioned ESD on purpose as indeed what really matters is energy/joules. If you have a source capable of high power but for too short time it won't be that dangerous either.

Thanks for clarifying, I didn't mean to imply that X-rays were necessary to kill electronics with ESD, just that they could be dangerous to a human, physically, even at low power levels. Killing electronics with ESD indeed does not require vacuum.

High amperages are really only dangerous (in terms of electrocution) with higher voltages. As voltages get low enough, our bodies' resistance means that there won't be enough current passing through you to hurt you. The dryness of the contact point makes a big difference (several orders of magnitude), but even with wet hands, it is pretty much impossible to hurt yourself with < 12 volts.

The risks with low voltages and high amperages are from shorts causing rapid heating.

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