Author Topic: What kills people, current or voltage? Or something else? (Read 26602 times)

nadona · « **Reply #50 on:** February 18, 2015, 11:41:43 pm »

Electrical energy kills people.

f5r5e5d · « **Reply #51 on:** February 19, 2015, 02:49:42 am »

http://www.amazon.com/Electrical-Safety-Low-Voltage-Systems-Massimo/dp/007150818X/ref=sr_1_1?s=books&ie=UTF8&qid=1424314216&sr=1-1

really should be on every EE's shelf - chapter on electrical effects on humans, more on world power line distribution and safety grounding practice

LabSpokane · « **Reply #52 on:** February 19, 2015, 06:17:12 am »

Amps only kill who Chuck Norris hasn't already.

Stonent · « **Reply #53 on:** February 19, 2015, 07:32:54 am »

It's WATTS!

Shock · « **Reply #54 on:** February 19, 2015, 09:07:15 am »

I wonder if anyone has been hurt watching his videos yet. Probing wires dangling in the air and PCBs hanging near the edge of the bench will eventually catch up with him.

StarFishPrime · « **Reply #55 on:** February 19, 2015, 10:46:12 am »

Current.
The flow of charge causes local heating and, at surprisingly low level can interfere with the heart and lungs. The former tends to restart itself though the latter will no if the victim is deeply unconscious.

As a physicist this questions throws up the interesting question of how different models such p.d. may be appropriate in differing situations and how the term Voltage becomes conflated with potential & potential difference. From a physics viewpoint electrical potential is a property of a point in space (i.e. within a conductor) and potential difference the difference in potential energy 'twixt two points. A charged particle moving between them will experience an energy change.

However from an electronic viewpoint it may be more useful to think of p.d as a force pushing a charge (current). In the absence of friction such as resistance a particle may move indefinitely without energy change. Thus a particle beam in a vacuum or electrons in a superconductor represents a current without p.d.

Brushing one’s hair on a dry day may built up a potential of thousands of volts, this is not dangerous as the actual quantity of charge that may be pushed is limited causing a small spark and swearing.

We should really use the term potential difference.

VK5RC · « **Reply #56 on:** February 19, 2015, 10:58:06 am »

Only at massive voltages and currents will electrical heating kill you e.g. lightning, usually it is relatively low levels that particularly cross the heart (both V and I) that precipitate lethal cardiac arrhthmias. Skin is not a bad insulator, but once it is broken/penetrated, the body's salt and water make a not bad conductor!

Zero999 · « **Reply #57 on:** February 19, 2015, 12:40:27 pm »

Quote from: Mechatrommer on February 18, 2015, 01:27:50 am

Quote from: helius on February 18, 2015, 01:06:19 am
Quote from: gilbenl on February 18, 2015, 12:53:48 am
People can and do die from licking 9V batteries!
Bullshit. Please stop spreading urban legends.
"urban legend" does exist... http://www.dailymail.co.uk/news/article-2950641/Woman-electrocuted-iPhone-dropped-bath-charging-looked-Russian-version-Facebook.html (sad that lady is a waste)

How does that prove one can die by licking a 9V battery?

It could be a faulty charger leaking too much mains current.

It doesn't even say conclusively the cause of death was electrocution. Li-ion batteries contain some pretty nasty substances and can release hydrofluoric acid under certain circumstances which is a contact poison.

hli · « **Reply #58 on:** February 19, 2015, 01:48:37 pm »

Quote from: timb on February 18, 2015, 10:55:07 am

Actually, there is a US Navy fatality from a 9V battery. During a safety course the instructor was having technicians measure their skin resistance with a Simpson multimeter. One guy got the bright idea to jam the sharp probes INTO his hands to get a really good reading. The blood and salty fluids carried the current right through his heart and as a result, stopped it.

I had read this several years ago in the Darwin awards: http://www.darwinawards.com/darwin/darwin1999-50.html (and the title is on the spot for this forum :-)
So this should make clear its the current, not the voltage (nor power).

bugs · « **Reply #59 on:** February 19, 2015, 07:49:16 pm »

Try to get your hands on the IEC 60479. It is a good indication on what electricity your body can and can not handle.

Zero999 · « **Reply #60 on:** February 20, 2015, 01:43:25 pm »

Quote from: hli on February 19, 2015, 01:48:37 pm

Quote from: timb on February 18, 2015, 10:55:07 am
Actually, there is a US Navy fatality from a 9V battery. During a safety course the instructor was having technicians measure their skin resistance with a Simpson multimeter. One guy got the bright idea to jam the sharp probes INTO his hands to get a really good reading. The blood and salty fluids carried the current right through his heart and as a result, stopped it.

I had read this several years ago in the Darwin awards: http://www.darwinawards.com/darwin/darwin1999-50.html (and the title is on the spot for this forum :-)
So this should make clear its the current, not the voltage (nor power).

That's been posted before but as of yet it has never been verified as genuine.

It's very unlikely a 9V battery would cause death, even if the resistance of the skin was removed. The internal resistance of the battery itself would've been over 18R on top of the body's internal resistance.

According to the article he tried to measure his internal resistance with a meter. He didn't just connect the battery directly to some metal spikes and push them into his thumbs. The meter would've limited the current to a safe level.

electr_peter · « **Reply #61 on:** February 20, 2015, 03:41:29 pm »

Don't underestimate low voltages. If low voltage is coming from low impedance source (impedance level of 9V battery is questionable), it can be very painful and dangerous. There were cases in US where 0.5-1 VAC were felt as very strong painful sensation (rural area with ground-neutral voltage difference and pool near the house).

Marinas/harbours can be deadly to swimmers because of ground problems. While voltage gradient may not be high enough to completely paralyse/kill a person in water, it may be enough to restrict muscle movement and drown a person. Fresh water is more dangerous than salty water.

free_electron · « **Reply #62 on:** February 20, 2015, 04:00:33 pm »

falling piano's. definitely falling piano's.

that, and rampaging elephants.

0xdeadbeef · « **Reply #63 on:** February 20, 2015, 04:40:45 pm »

Just in case that nobody mentioned this before, but in most of the cases it's frequency that actually kills people - at least when working with mains.
The (ion based) conduction from the sinoatrial node to the heart muscle can be quite easily affected in certain vulnerable phases (even a punch on the heart can kill you if the timing is right).
It's known that lower frequency in the 50Hz region are especially likely to cause a depolarization that stops the continuous rhythm of excitation/conduction (partly bad luck, as the mains frequencies were defined before this was known).
If a current is running directly through the heart (e.g. during surgery or due to implants), the current needed to stop the heart from beating is actually pretty low.
If the (dry) skin has to penetrated and a lot of tissue, bones etc. is between the current source and the heart, higher currents are needed of course.
BTW: that also the reason why defibrillators measure the ECG to time the depolarization and do make sure they are only used in case of ventricular fibrillation and not if the hearts is either working ok or not at all (as this would be either fatal or pointless).

oldway · « **Reply #64 on:** February 20, 2015, 05:00:26 pm »

What kills people, current or voltage? Or something else?

Something else: stupidity, negligence and distraction

Excavatoree · « **Reply #65 on:** February 20, 2015, 05:12:54 pm »

Quote from: free_electron on February 20, 2015, 04:00:33 pm

falling piano's. definitely falling piano's.

that, and rampaging elephants.

Those audio stones that improve the flavor, cut and clarity of one's music are just as effective at repelling rampaging elephants.

helius · « **Reply #66 on:** February 20, 2015, 05:20:31 pm »

Quote from: Hero999 on February 20, 2015, 01:43:25 pm

That's been posted before but as of yet it has never been verified as genuine.

It's very unlikely a 9V battery would cause death, even if the resistance of the skin was removed. The internal resistance of the battery itself would've been over 18R on top of the body's internal resistance.

According to the article he tried to measure his internal resistance with a meter. He didn't just connect the battery directly to some metal spikes and push them into his thumbs. The meter would've limited the current to a safe level.

Who's to say it wasn't a megger?

mikerj · « **Reply #67 on:** February 20, 2015, 06:04:44 pm »

Quote from: helius on February 20, 2015, 05:20:31 pm

Who's to say it wasn't a megger?

Exactly what I was going to say. The old meggers could generate around 2.5kv and would give you a very unpleasant shock even on dry skin.

Quote from: Mechatrommer on February 18, 2015, 01:27:50 am

"urban legend" does exist... http://www.dailymail.co.uk/news/article-2950641/Woman-electrocuted-iPhone-dropped-bath-charging-looked-Russian-version-Facebook.html (sad that lady is a waste)

This iPhone was connected to the mains, very probably via a faulty (or Chinese knock off) charger. She won't have been the only person to have been killed by a faulty phone charger either.

edy · « **Reply #68 on:** February 20, 2015, 06:52:07 pm »

I think the OP was trying to say that if POWER kills you or P=VI... Then 1,000,000 V x 1 mA would be equivalent to 100 V x 10 A. Both situations the power is the same = 1000 Watts. Then you could say "1000 Watts can kill you". There is a big problem with this argument. It is not even POWER that kills you... it is POWER x TIME or ENERGY that kills you.

Obviously the 2 situations are not the same as it depends on the resistance since V is related to I by R. You can't just arbitrarily assign the voltage and amperage and say "here hook yourself up to this" and expect V and I to be arbitrary values without knowing the resistance.

The VI relationship given by Ohm's law is V=IR, or V/I = R.

So in the first situation, 1,000,000 V/1mA = 1,000,000,000 ohms resistance would be needed.
In the second situation, 100 V/10 A = 10 ohms resistance would be needed.

Although the "Power" calculation is the same if you put 1,000,000 volts across a 1,000,000,000 ohm, or you put 100 volts across 10 ohm resistance... P=1000 W.... You can't ask if "power" kills you because your body resistance (or the lack of it) in the presence of a high electromotive force or potential (volts) and an unlimited source of electrons (current) is what will kill you.

For example, high voltage alone is not enough. Although the more volts obviously the more amps given a FIXED resistance (according to V=IR). When you get a static shock you could have thousands of volts but because there is a very small source of electrons available it is extremely short in duration. If you had a large reservoir of electrons continuing to flow for a long period of time then yes you would get a considerable amount of energy deposited in your body which would likely burn and boil you.

Similarly, try shorting the ends of a car battery. Yes it is only 12 V but it can deliver a huge amount of current and keep on doing that for a considerable amount of time. The 12 V in a car battery cannot overcome the resistance in your skin, that is why you have very little current going across you. But put a low-resistance device across it (like a screw-driver handle) and watch it spark and glow and get dangerously hot!

So I would say it is neither voltage or current, but BOTH since they are proportionally related by resistance. It is RESISTANCE (lack of it) that kills you in the presence of either a large voltage or current (neither one is independent of the other) and TIME (since power x time = energy which is what is needed to kill you).

Zero999 · « **Reply #69 on:** February 20, 2015, 08:19:12 pm »

Quote from: helius on February 20, 2015, 05:20:31 pm

Quote from: Hero999 on February 20, 2015, 01:43:25 pm
That's been posted before but as of yet it has never been verified as genuine.

It's very unlikely a 9V battery would cause death, even if the resistance of the skin was removed. The internal resistance of the battery itself would've been over 18R on top of the body's internal resistance.

According to the article he tried to measure his internal resistance with a meter. He didn't just connect the battery directly to some metal spikes and push them into his thumbs. The meter would've limited the current to a safe level.

Who's to say it wasn't a megger?

If it was a megger then it wouldn't be 9V then would it?

And what's the test current used by a megger? Normally it's too low to be lethal, even if it does cause a painful shock, so perhaps the person who did it already had a heart condition?

G7PSK · « **Reply #70 on:** February 22, 2015, 09:24:36 am »

I don't have a Simpson to check but I do have an old AVO 7x. It uses two 4.5 volt cycle lamp batteries in series to give it 9 volts for the 10 Meg ohm range, it only uses a 1.5 volt cell on the lower range's. I measured the current on the 10 Meg range with a Fluke and an Amprobe and a Uni T 61E they gave mw a range of 1.3 to 1.6 m amp feeding straight into the meters shunts (ie) the AVO was effectively seeing a short and delivering the maximum current it could or would. There is no way that you could electrocute yourself with that current unless you applied the probes directly onto the heart itself, which would require opening up the chest. I have read in the past and heard it said that it takes at least 5 mA to kill. The meter that is mentioned in the Navy report is either an insulation tester of the old school variety or some form of bonding tester to deliver a deadly current or the story is just that a story.
As for the AVO to kill some one with it you would do better to batter them around the head with it than try and electrocute them with the probes on the ohm range.

VK5RC · « **Reply #71 on:** February 22, 2015, 09:38:02 am »

There are several, usually congenital, variants of myocardial cell voltage dependant trans-membrane ion channels that lead to easier than usual triggering of arrhythmias. Eg congenital prolonged QT syndromes, these can lead to apparently healthy young people 'dropping dead' sometimes precipitated by otherwise trivial stimuli eg exercise (well documented) and POSSSIBLY a very small electrical insult.
Could the 'sailor' have had one of these?

G7PSK · « **Reply #72 on:** February 22, 2015, 04:47:41 pm »

Interesting articles on electric shocks.

http://www.medwelljournals.com/fulltext/?doi=ijepe.2010.177.181

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763825/

https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

And to ensure it is fatal.

http://hypertextbook.com/facts/AprilDunetz.shtml


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Author Topic: What kills people, current or voltage? Or something else? (Read 26602 times)

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