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DC or AC is more dangerous?

Which is more dangerous, AC or DC?

The argument about which is more dangerous, AC or DC, has gone on for a long time, possibly starting with rivalry between Edison and Westinghouse. In the early days it was like a political/religious argument. Edison believed that DC was the way electricity should be done, and would not have any other views heard. However, despite the merits of DC, it has the downside that for transmission over a distance, there are problems. AC is much better for this as it can be transformed to higher voltages, sent, and then transformed back again, thus saving a lot of wastage as per I2R. Nevertheless, part of Edison's publicity campaign to make AC appear more dangerous was to have public executions with AC electric chairs termed "To be Westinghoused".

One of the reasons it's tricky to have a reasonable comparison of AC and DC at the same voltages and current specifications, is because AC and DC are manifested in quite different situations. AC is ideal for transforming to different voltages, so mains at 240 volts or 110 volts is typical, whereas the 12 volts supply in a car is at a much higher current.

I have done an experiment myself in putting DC mains into an AC mains system. This showed an additional danger which DC has. In effect, DC is more difficult to turn off. Switches which are of the old style are OK, but modern switches tend to spark across if the supply is DC.

One way to get a comparison of AC with equivalent DC is to construct a battery of the same voltage as the mains and see how the electricity behaves. Batteries are always DC, and there's no such thing as an AC Battery. The electricity from the DC battery of the same voltage as the AC mains which you're accustomed to, tends to behave in ways which are more dangerous. However, most of the dangers are through arc and carbonisation of surfaces, rather than the electrocution risk.

This raises an interesting question, which is: For the equivalent voltage, which is more dangerous in terms of electrocution risk only? You'd have to compare a constant voltage DC with its RMS equivalent AC. (RMS = root mean squared, the equivalent "average voltage"). Many people misunderstand this, and I've even seen statements that AC is twice the voltage because it goes from minus peak voltage to plus peak voltage, etc.

Another myth I've seen popularly bandied-about is the idea that AC is safer because there's a fraction of a second where you can let go (where it crosses the zero line). Although this will stop an arc across a gap, it's no help at all if you're made of flesh and you've got stuck across a high voltage. You can't let go in so-many milliseconds.

What's more likely to save you from death through electrocution is the involuntary muscle action upsetting the configuration of things that led to the shock in the first place. This also backs up the idea that if you handle electrical items gently like broken glass, you have a better chance of survival.

Statements about electrocution risk comparison such as "DC is more dangerous than AC" or "AC is more dangerous than DC" are yet to have the scientific credibility of evidence. However it would be possible to perform some experiments and get a conclusive result. It may be a reasonable assumption that the "ouch" factor has a good correlation with the actual dangerousness, in which case a set of non-lethal experiments could be done. It's the sort of experiment which student volunteers get paid various amounts of money for. In a double-blind experiment, voltage and volition can be correlated, and the AC or DC can be recorded without volunteers or experimenters knowing which it is at the time.