A shocking discovery

[vk6zgo]

I was told at school that it was possible to kill 500 people from the mains without blowing a 5 amp fuse if you got them all to hold hands, I am not sure if this is possible as I cannot find any reports of such an experiment being conducted.

I once got a nasty shock from a 2 volt lead acid battery when connecting the terminals up.

The maximum power allowed by law on an electric fence unit in the UK is 15 joules this is considered the maximum that will not be lethal to a normal person and I would assume that there is a safty factor there as well.

You are either the most sensitive person to voltage in theworld,on there was some kind of inductor in the circuit you were connecting to.

[cybergibbons]

You are either the most sensitive person to voltage in theworld,on there was some kind of inductor in the circuit you were connecting to.

Stranded wire piercing the skin can cause small voltages to feel quite powerful...

[G7PSK]

there was no wire, self capacitance is more likely

[IanB]

there was no wire, self capacitance is more likely

It just isn't possible to get a plain ordinary shock from touching a 2 V cell.

Mostly what happens is that a pointy wire penetrating the skin hurts. If that pointy wire happens to be electified it hurts way more. 2 V will hurt a bit, 12 V will hurt like crazy. Psychologically it tends to make you jump out of your skin.

[G7PSK]

I can assure you that at the time I got the shock there was no wires connected to the cell. I was just wiping the terminals with petroleum jelly after it had come of charge preparatory to using it. I have also had belts of car batteries in the past.

[sacherjj]

I don't particularly care that they are not made anymore. I have a few CRT monitors that work really well and intend on using them because LCDs suck (you only get one resolution and that resolution isn't very high either). OK, well, I care a bit because I will have to use old monitors instead of being able to buy a new one, but it is not that big a deal.

I've never seen a CRT that can touch my 24" Dell 1920x1200 IPS panel.  I'm sure they were made.  But I'm also sure they cost more than my first few cars.  That isn't even a high res panel.  Nothing like the 3,840 x 2,400 that are out there.

[slateraptor]

Please watch this.  It explains exactly why it's not true.

Ironically, that video is off too.

There are 2 ways to die by electric shock:
1) death by ventricular fibrillation, and
2) death by power dissipation.

He's trying to justify death by point (1) using the physics behind point (2).

[alm]

Yes, some of his arguments only focus on power dissipation, but his point that a high current 12 V supply will deliver insufficient current to cause ventricular fibrillation due to skin resistance at 12 V stands. I'm not sure about the minimum duration of the current to induce V-fib, but it's almost certainly much more than 1 us, since polarization of the heart is based on ion transport, and typical timescales are much longer.

[Pentium100]

I've never seen a CRT that can touch my 24" Dell 1920x1200 IPS panel.  I'm sure they were made.  But I'm also sure they cost more than my first few cars.  That isn't even a high res panel.  Nothing like the 3,840 x 2,400 that are out there.

I have Sony GDM-FW900 (24" widescreen): 2305x1440, maybe more if I set the timings correctly. My Dell P1130 (21" 4:3) supports up to 2048x1536, but 1600x1200 or 1920x1440 is good enough
I don't think there is a 24" LCD that can support higher resolutions. The 3840x2400 ones probably are something like 30".

[Randall W. Lott]

Please watch this.  It explains exactly why it's not true.

Ironically, that video is off too.

There are 2 ways to die by electric shock:
1) death by ventricular fibrillation, and
2) death by power dissipation.

He's trying to justify death by point (1) using the physics behind point (2).

I'm not an expert, but wouldn't you agree that the video has a better explanation than the whole "current kills, not voltage" saying?

[slateraptor]

I'm not an expert, but wouldn't you agree that the video has a better explanation than the whole "current kills, not voltage" saying?

I don't agree. Ventricular fibrillation is the main cause of death by electric shock, which is induced by sufficient current passing through the heart. It's not about frying your innards via energy discharge, which is what the video consistently alludes to.

[Randall W. Lott]

I'm not an expert, but wouldn't you agree that the video has a better explanation than the whole "current kills, not voltage" saying?

I don't agree. Ventricular fibrillation is the main cause of death by electric shock, which is induced by sufficient current passing through the heart. It's not about frying your innards via energy discharge, which is what the video consistently alludes to.

You can die from burns or heart failure.  Aren't higher voltages needed to penetrate your flesh to pass current through your heart?  There's a huge amount of resistance unless the skin is penetrated.  Of course, if you stab your chest with wires, you can reduce resistance enough to pass lethal current.  High voltages will greatly reduce the resistance of your body.

I had a professor that was working with a woman that touched a high voltage supply.  The arc passed through her finger and blasted a hole through her elbow.  They claimed that it was that her arm was bent that saved her.  I'm not sure about the truth in that.

Attaching jumper cables to each hand likely won't kill you, but attaching mains voltage could possibly.

[IanB]

I don't agree. Ventricular fibrillation is the main cause of death by electric shock, which is induced by sufficient current passing through the heart. It's not about frying your innards via energy discharge, which is what the video consistently alludes to.

I didn't infer that from the video at all. The risk of ventricular fibrillation is higher when there is more energy in the electric shock, which could be a higher current for a shorter time or a lower current for a longer time. The video correctly talks about current in mA and energy in joules. Both are relevant to the amount of danger present. I'm not sure at all where you think the video talks about frying your innards?

[slateraptor]

I can wet my hands and hold the leads of a high-voltage, current-limited power supply all day, but nothing happens if the current is insufficient to induce the involuntary muscle contractions that lead to v-fib. Energy is irrelevant in this obvious scenario.

Energy is indirectly relevant in a capacitor discharge model because of the impulse potentially exerted on the heart by combination of sufficient current offload and just the right RC time constant. That 11.2J is significantly greater than 0.0072J doesn't make a bit of difference for a sufficiently large time constant; the argument is donuts vs dynamite. A defibrillator pumps way more energy directly through the heart than the cap example in that video, yet it saves lives, not kills.

[Pentium100]

A defibrillator pumps way more energy directly through the heart than the cap example in that video, yet it saves lives, not kills.

Try using it on someone who does not need it and it is very likely that you will kill him.

[Bored@Work]

There are 2 ways to die by electric shock:
1) death by ventricular fibrillation, and
2) death by power dissipation.

We got taught an additional way, but years later health professionals told me they aren't sure it is possible. Toxic substances created by electrolysis of the blood during the shock, killing you days after the shock.

And of course there is the proverbial falling off the ladder because of the shock.

[Uncle Vernon]

There are 2 ways to die by electric shock:
1) death by ventricular fibrillation, and
2) death by power dissipation.

We got taught an additional way, but years later health professionals told me they aren't sure it is possible. Toxic substances created by electrolysis of the blood during the shock, killing you days after the shock.

And of course there is the proverbial falling off the ladder because of the shock.

Don't forget at HV and beyond, vaporisation is a real possibility! Whether the heart stops a microsecond before the smoke has never been accurately measured.

[Blofeld]

I can wet my hands and hold the leads of a high-voltage, current-limited power supply all day, but nothing happens if the current is insufficient to induce the involuntary muscle contractions that lead to v-fib. Energy is irrelevant in this obvious scenario.

Energy is indirectly relevant in a capacitor discharge model because of the impulse potentially exerted on the heart by combination of sufficient current offload and just the right RC time constant. That 11.2J is significantly greater than 0.0072J doesn't make a bit of difference for a sufficiently large time constant; the argument is donuts vs dynamite. A defibrillator pumps way more energy directly through the heart than the cap example in that video, yet it saves lives, not kills.

This is what Tony Kuphaldt has to say about it in his allaboutcircuits e-book (I don't know if it's true and I have no intention to try it out on myself):

http://www.allaboutcircuits.com/vol_1/chpt_3/2.html
"AC's alternating nature has a greater tendency to throw the heart's pacemaker neurons into a condition of fibrillation, whereas DC tends to just make the heart stand still. Once the shock current is halted, a "frozen" heart has a better chance of regaining a normal beat pattern than a fibrillating heart. This is why "defibrillating" equipment used by emergency medics works: the jolt of current supplied by the defibrillator unit is DC, which halts fibrillation and gives the heart a chance to recover."

Anyway, I think the whole chapter on electrical safety is worth reading:
http://www.allaboutcircuits.com/vol_1/chpt_3/index.html

[Randall W. Lott]

Speaking of the heart.  It's an amazing organ because independently beating myocytes grow to form a unified mechanism to pump blood.  The physics of the human body is incredible.

[grumpydoc]

...the jolt of current supplied by the defibrillator unit is DC...

Not quite any more - modern defibrillators use a biphasic shock, basically one cycle of AC.

The principle is the same though - depolarise ALL of the hearts myo-fibrils and conducting system together and hope that organised electrical activity starts up once more.

As to causing fibrillation the main danger is an electric shock when the heart is trying to repolarise - in fact not just electrical energy can do this. Mechanical shock can do it as well which is why it is not a myth that a cricket ball landing on one's chest can kill.

In some cases a shock is used to try to convert other rhythms back to normal such as certain fast rhythms which prevent the heart working well (eg ventricular tachycardia) - in this case the shock is synchronised to the "R" wave so as to avoid causing ventricular fibrillation.

Although energies as high as 200J are used in de-fibrillation that's mainly because the body doesn't conduct nearly as well as you'd like in this situation - in open heart surgery paddles are used directly on the heart and only a couple of Joules is needed.

To be honest I'm not sure that it's volts or amps but enough Joules will kill you.

[sacherjj]

I have Sony GDM-FW900 (24" widescreen): 2305x1440, maybe more if I set the timings correctly. My Dell P1130 (21" 4:3) supports up to 2048x1536, but 1600x1200 or 1920x1440 is good enough
I don't think there is a 24" LCD that can support higher resolutions. The 3840x2400 ones probably are something like 30".

IBM has a 22.2" at 3840x2400.  If course, I think it is around $1.5k.     Although that was probably more in the ball park of the GDM-FW900 when it was available.

[G7PSK]

If you read this it states that a minimum of 1.25 amps is required for stunning pigs this is passed directly through the brain it does not cause death but epilepsy. Pigs are very similar to humans and are frequently used for training surgeons.

http://www.grandin.com/humane/elec.stun.html

[siliconmix]

haven't pigs got a really fatty skin though ?

[grumpydoc]

haven't pigs got a really fatty skin though ?

Dunno - they do have pretty massively thick skulls though.

[entereev]

What's the average weight today? Aren't we nearing the pig fat thickness?