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While playing with mosquito racket in my home, I unscrewed the racket and touched the 2 wires with my hands. I felt that my bones were dislocated, I got shocked, but I am not dead.

My calculations say that I should die:

the output voltage is 5 kV to 10 kV, my body resistance is approx. 50 kΩ, the current through my body is 0.1 A if 5 kV to 0.2 A if 10 kV.

According to the table at https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html I should die; I tried this many times but I am still alive.

I think my interpretation regarding current, voltage and my body resistance is wrong (if right I would be dead by now) - please tell me why I am not dead?

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6 Answers 6

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The circuit is not quite as you have described. As stated in the comments (amongst the sea of humor), is that a bug zapper is not an ideal voltage source. It can't deliver very much power, even though the voltage is high.

You can consider the circuit more like this:

schematic

simulate this circuit – Schematic created using CircuitLab

(values are guestimates).

The net result is you will get an initial current spike of maybe a few 10's of milliamps, but only for a few microseconds. After that the bug zapper simply cannot sustain the current, and so the terminal voltage will drop, and the current will most likely end up being less than a milliamp.

It's not the peak current that kills you, but a current sustained long enough to deliver enough energy to kill you.

As to why it kills the bugs, that is simply a case of bugs being smaller than you. It will take far less energy to cook a small bug than it will to stop a human heart.

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    \$\begingroup\$ Two continuous miliamps is enough to kill you :) \$\endgroup\$
    – Long Pham
    Commented Jun 7, 2018 at 15:14
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    \$\begingroup\$ Isn't it also partially an issue of the probes (cathode and anode) being close to one another, hence the current doesn't travel through your body? \$\endgroup\$
    – Ken - Enough about Monica
    Commented Jun 7, 2018 at 17:06
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    \$\begingroup\$ @horsehair Yes, that is also a factor. Current has to pass through a sensitive organ, such as your heart muscles or your diaphragm, for there to be a risk of death. And the source in this case is isolated from e.g. local ground, so even if the OP is touching a good ground with a foot or the other hand, current won't be flowing to there from this source. It can only return to the supply in the zapper so its return path must be very close to the source. \$\endgroup\$
    – Jamie Hanrahan
    Commented Jun 7, 2018 at 17:28
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    \$\begingroup\$ @JamieHanrahan you are right about the current path for an ''immediate death''. To add up a bit on your comment, some of the electric death toll occurs a long time after the actual shock because of burn related complications. In all honesty, it is a gruesome way to die in both cases \$\endgroup\$
    – Simon Marcoux
    Commented Jun 7, 2018 at 19:50
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    \$\begingroup\$ I'd argue that the proximity of cathode and anode is much more relevant to the question than the current. I've touched mains voltage (120VAC @ 60Hz, US) several times -- but I had contact with hot and neutral both with a single hand, so the current primarily dumped through my hand instead of traversing my body. Hurt like hell, but since I had contact with the source before it was energized, I didn't even get burned. My hand was numb for a while after one particularly unpleasant jolt... but still here typing :) \$\endgroup\$
    – Doktor J
    Commented Jun 7, 2018 at 20:44
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  • Passing the current through a finger is relatively safe, as there is not enough current to burn you, and it's far from your heart.

  • Passing the current from hand to hand puts the heart somewhere "in the middle" of the path, but clearly not in direct series. Plus your skin can still present a large resistance.

  • If you pass the current across your chest, the chance of death is higher.

  • If you had probes that went deep into your chest, and passed the current through the probes, you'd dramatically increase the risk.

As others have stated: The bug zapper has a very limited amount of power that it can deliver. There is enough energy to fibrillate a bare heart, but yours is protected in your body.

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  • \$\begingroup\$ Isn't your skin surface resistance also much lower due to humidity? This would lead the current just over your skin, and not through your body. \$\endgroup\$
    – chthon
    Commented Jun 8, 2018 at 13:18
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    \$\begingroup\$ @chthon: There are several layers that make up your skin, and they have different electrical properties. I seem to vaguely recall that the dermis has much smaller resistance, possibly due to all the blood vessels and whatnot. (Which is why touching say a 9V battery with your finger does not hurt, but if you stick needles deep into your skin, and connect the battery to those, it hurts like heck. Don't ask me how I know.) \$\endgroup\$
    – Nominal Animal
    Commented Jun 8, 2018 at 13:45
  • \$\begingroup\$ @NominalAnimal There's a story going around about a guy who stuck two probes in each of the thumbs and did in fact die from it. Perhaps you were lucky. Was a 9volt powered multimeter I believe. \$\endgroup\$
    – htmlcoderexe
    Commented Jun 12, 2018 at 7:34
  • \$\begingroup\$ @htmlcoderexe - The key to that story is that the probes were in his thumbs, as in his blood. Regardless of the legitimacy of that story: OP, I'm assuming, did not have a direct path to their innards with the zapper. \$\endgroup\$
    – Bort
    Commented Jun 12, 2018 at 11:19
  • \$\begingroup\$ @Bort I guess it depends on just how deep is "deep into your skin" for Nominal Animal's case specifically. For OP, that was obviously not the case. \$\endgroup\$
    – htmlcoderexe
    Commented Jun 12, 2018 at 11:22
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To put this more like an electrical engineer would put it: this high-voltage source has a high internal resistance, and understanding what that means answers your question.

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  • \$\begingroup\$ I don't think "internal resistance" is a term hard to understand if you google for it, to be completely honest :) \$\endgroup\$
    – Marcus Müller
    Commented Jun 7, 2018 at 20:29
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    \$\begingroup\$ @MarcusMüller You might just want to elaborate a bit upon it (thus making the answer more self-contained), since this answer just seems so small. :) \$\endgroup\$
    – EKons
    Commented Jun 7, 2018 at 20:30
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    \$\begingroup\$ Nope, I think the main strength of this answer is is shortness. I could re-explain internal resistance, but I'd do that worse than wikipedia or a million other sources. I honestly, not out of laziness, refuse to reproduce "common knowledge" that can be found easily enough – for quality reasons. \$\endgroup\$
    – Marcus Müller
    Commented Jun 7, 2018 at 20:30
  • \$\begingroup\$ a great answer, but IMVHO requiring one correction: this high-voltage source, not the high-voltage source... there definitely are high-voltage sources with internal resistance low enough to kill a human (e.g. lightning, HV lines, any high-power source in general) \$\endgroup\$
    – user20088
    Commented Jun 10, 2018 at 1:16
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    \$\begingroup\$ I find this answer fairly unhelpful. If you prefer not to explain the answer fully, then it could be improved by at least including links to sources where the OP can learn the topics he needs to be able to understand it. Doing so takes care of your concern that you will not do as good a job at explaining it as those sources. If all Stack Exchange answers consisted of "You will know the answer once you learn topics X and Y" then the site would be useless. \$\endgroup\$
    – JBentley
    Commented Jun 10, 2018 at 18:28
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It is not only current and voltage that matter, but duration. 10kV at 1A for a microsecond is about 10 microjoules. You might feel a shock, but it is not enough to actually tense all your heart muscles into paralysis long enough to make you unconscious, or even cause physical damage from heating or muscle contraction.

On the other hand, IF you have a bad heart it might be enough to upset the rhythm and send you heart into fibrillation, which can be fatal. Maybe you are just lucky

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    \$\begingroup\$ What energy (in Joules) would be enough to cause any damage to heart / death? \$\endgroup\$
    – Marki555
    Commented Jun 7, 2018 at 20:25
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    \$\begingroup\$ @Marki555 - Energy is not normally a consideration. For instance, back in the 60s there was a case of a patient in a hospital with a wall-powered pacemaker. Unfortunately, the unit was not properly isolated, and when the patient touched the (grounded) bed frame, the (estimated) 47 uA which was applied directly to his heart did the job. \$\endgroup\$
    – WhatRoughBeast
    Commented Jun 8, 2018 at 0:44
  • \$\begingroup\$ @Marki555 No idea, but medical defilrillators can run into the hundreds of joules. Again, duration is the key \$\endgroup\$
    – Dirk Bruere
    Commented Jun 8, 2018 at 7:25
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Death from electrocution occurs mainly in two situations and is not directly correlated with the actual current/voltage values:

1) Enough current and energy passed through your body to actually burn you inside out 2) A voltage passed through your heart and put you into a fibrillation state.

Both can come into play at the same time!

The first is mainly caused by excessive current into your body. Once the skin is penetrated, it is easy to pass a surprisingly high current into your body. This is why wet + electricity is so bad. It reduce drastically your skin resistance.

Before venturing into the 2nd part, you need also to understand that electricity will have an entry point and an exit point. You can often see a burnt mark at those points when it occurs (in hard situation).

Directly related to that: if the current pass through your heart with a voltage high enough or with some weird frequency, it can put your heart into fibrillation: desync it. When this occurs, you need to reset your heart using a defibrillator like in all poorly written medical drama. A shock does not so much when the heart is flat-lining, but help fibrillation cases.

As for your question, you didn't die because the current entered finger and exited through your finger. It didn't pass through your heart. Also, the current in play we're not enough to cause any significant burns. Specific injuries prediction is on a case by case basis.

In a nutshell, your heart either fail or you burn to death when you die from an electric shock...you might also survive and be severely burnt or maimed by the aftermath. Losing limb is unfortunately not so uncommon.

If you want to know more, the wikipedia article is well written.

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    \$\begingroup\$ You missed one: 3) Enough current passed through your diaphragm to prevent you from breathing effectively, for long enough for you to suffocate. It takes less current to paralyze the diaphragm (or paralyze it "enough") than it does to induce fibrillation, but of course this route takes longer to have a lethal effect. \$\endgroup\$
    – Jamie Hanrahan
    Commented Jun 16, 2018 at 3:55
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    \$\begingroup\$ I shivered at how painful it must be to die like this. You are off course right that I missed this one @JamieHanrahan \$\endgroup\$
    – Simon Marcoux
    Commented Jun 16, 2018 at 4:02
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    \$\begingroup\$ And damned frustrating, since you'd be conscious for part of it - but, depending on the path the current is taking, unable to move to fix the problem. Shivering indeed. \$\endgroup\$
    – Jamie Hanrahan
    Commented Jun 16, 2018 at 6:19
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    \$\begingroup\$ There is a table in this page: allaboutcircuits.com/textbook/direct-current/chpt-3/… that shows current levels for various detectable and deleterious effects, broken down by male vs. female and for DC vs 60 Hz AC vs 10 kHz AC. \$\endgroup\$
    – Jamie Hanrahan
    Commented Jun 16, 2018 at 9:05
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Another aspect to consider is frequency. Mosquito zappers are DC, but they don't supply constant DC. After the voltage is stepped up from 3-6 VDC from the batteries through a voltage multiplier, it comes out in rapid pulses. As soon as voltage is applied and your body begins to take the energy, the current is stopped. I don't know exactly at what frequency mosquito zappers operate, but at high enough frequencies, the human body can simply absorb the shock in the skin before it reaches deeper into the nervous system and your heart. That's why you're able to be shocked by a tesla coil without dying. You still feel it, but it doesn't penetrate far before the pulse ends and simply dissipates before the next pulse comes along.

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