And how did they figure out that AC is specifically 5 TIMES more dangerous?
In: 5
It’s alternating current, which means it changes voltage levels all the time (usually at 50 or 60 high-low-high cycles per second, depending on the grid). Nerves also use changes in voltage to transmit signals, so the alternating current messes that up much more than a constant (DC) voltage. It thus causes muscle spasms (making you unable to get away from the thing you just touched) and heart arrhythmia which ultimately kills you.
The “5 times” figure is likely very speculative since there is no absolute scale for danger. It may come from a study like “we gave mice a shock of X volts DC or AC, and they died about equally often at 5x the voltage with DC than they did with AC”, or it may be completely made up.
It’s not exactly AC, it’s the common frequencies of AC that we run into.
Electricity makes your muscles contract. With DC it’s all one direction which tends to cause one big spasm that throws you away from the thing you touched.
With AC it’s pulsing back and forth. This causes rapid repetitive contractions of muscles, and at 60 Hz it’s faster than your limbs can react, which effectively “freezes” you in place holding/touching the thing that’s electrocuting you.
Both will hurt you, both can cook you from the inside and screw up your heart, but AC is “worse” because it’s more likely to result in sustained contact and that contact is going to cycle your muscles a whole bunch more.
DC current forces electrons to flow in a complete loop around the circuit. The electrons only flow in one direction, at a constant pace. As a result, the effects of electrical resistance are far greater on DC current, as it is pusing all of the electrons through everything. Our bodies aren’t great resistors, but they’re better than nothing, so this winds up being important.
AC current makes the electrons vibrate back and forth rapidly. Rather than pushing them in a full loop, it uses the fact that moving electrons create magnetic fields which move nearby electrons almost immediately to propagate very short currents down a wire, before reversing the direction of flow and pulling them back the other direction. This significantly reduces electrical resistance, as only the electrons flowing through resistors will be impacted by them. The rest will just keep vibrating. This is why we use AC current for all long-distance transfer, as it is far less lossy over those distances due to only caring about local resistance rather than the resistance of the entire circuit. Most appliances (except simple things like lightbulbs) need DC to run, but that’s not really an issue. That’s what AC/DC converters are for.
So AC has much less resistance going through the body, but there is another far worse issue. Your nerves don’t quite work on electricity, but they can be activated by it just fine. With DC current this will mean electrocution will make all your muscles activate at once, which is a problem, but with AC current the rapid fluctuations will cause all of them to spasm randomly. Including the heart. DC current will stop the heart entirely as it all contracts, but we can recover from that. It will start itself up again if completely stopped, once the current is removed. That’s what defibrillators do, actually, basically turn the heart off so it can turn itself back on again. But AC current makes the heart muscle spasm along with everything else, which is also known as fibrillation. That’s the thing which de-fibrillators are supposed to de, and we don’t recover from that on our own. The random spasms will continue even after the current is removed, leading to rapid death if you don’t get immediate medical assistance.
So it’s both that AC goes through the body easier and does something far worse to our bodies which makes it more dangerous.
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