Electrical Shock - Current and Voltage

As far as I know, the voltage is immaterial, it is the current that matters to kill.

And as far as I remember (may be wrong it is not in mAs rather in μAs : somewhere around 50-60 is a heavy shock and 100 or so is fatal.

Yes I was almost right, checked google

http://books.google.co.in/books?id=sPVj4zx_VzkC&pg=PA55&lpg=PA55&dq=shock+fatal+current&source=bl&ots=UQqoJ-MEou&sig=aOdYZ6kJWUvPV0onTUbYg-iGxrA&hl=en&ei=WVq-SZL-L5SM6gPulOzcBA&sa=X&oi=book_result&resnum=3&ct=result

http://homepages.udayton.edu/~hardierc/EGR101/safety.htm

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

Here's a short one from OSHA--

http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html

The last paragraph touches on the relationship of voltage--Higher voltage breaks down the bodies restsistance easier to deliver the the amps. Way more dangerous as the voltage increases. K T

Thank you for the hyperlinks..

It's helpful..

As per my knowledge, the current magnitude is derived by Ohm's law i. e. current (I) = Voltage (V)/Resistance (R). Here, the Resistance is the body resistance of the person exposed to the voltage.

Also the current path is important - if it passes thru the heart nerve, will cause adverse effect on heart functioning.

A very small magintude current flows from brain to different parts of the body in the form of signal, and the relative part reacts to that signal to perform the designated task. The high amount of current damages the nerves thru which it passes for a relatively longer time.

The exact value of current produced because of the voltage has been answered by previous replies.

I would just like to add on is the reason why their is a shock because of the current- It is I^2R factor, which produces heat.

The Resistance of human body is suppsoe to be high (do not know the exact figure) so even a small amount of current produces lot of heat which comes as a shock to the body.

Hi,

a current of 5mA is estimated to be safe, this will protect nearly all people.

And a voltage of 42V too, this is only working if in dry conditions with no injuries on your skin.

Some facts:

the "resistance" of our body is nearly totally only in our skin. (no injuries!)

My skin resistance varies between some few KOhms to more than 50 MOhms depending on conditions.

The 42 V is not causing a breakdown of the resistance of a healthy skin.

The action that will harm you is not by heat but by exciting nerve action and muscles.

You can easily break any of your bones including the spine by electrically activating your muscles, may be the muscles and more will be damaged.

You will not be able to loosen the grip of your fingers if muscles are excited by a current as the closing muscles are much stronger than the opening muscles. So if you suspect a damage in a power line, do not touch, and if touching is inevitable than touch with the tip of one finger: if excited then the closing action will withdraw your finger and hand.

If working on maybe dangerous lines then make a double check if anything is disconnected to high voltage. I once experienced some molten copper droplets on my spectacles as connected the two wires of a 220V line - the fuses were taken out before, but somebody had installed an additional loop that was fused from wherever but not from the place where fuses should be. And by short circuiting the two wires I protected myself against this - not thinking about molten droplets near my eyes.

Most critical is a current that may flow through the heart region: from head or neck to lower parts of the body or from right to left side, as this is directly affecting the pulse generator that commands the heart.

There have been a lot of spectacular accidents with low voltage (12 to 24V) equipment: the Baptist priest who dropped his microphone into the baptising basin did not survive the next second as he grabbed at it, the fun-boat owners - with batteries onboard to facilitate motor start- that went swimming and touched non-insulated conductors or the poles of the batteries.

Everybody should have fault current protection switches in the electrical installation that break any circuit if a current is not flowing back along the power line.

Protect yourself and your nearest others.

RHABE

I have seen damage to humans in both ways discussed, and more.

Electrical disruption of the rhythms of the heart kills if not corrected, and can happen at surprisingly low voltages.

As a youth, my father and a workmate were checking a circuit for an intermittent problem. The workmate put his index finger on one of the two insulated wires strung along a flume for lighting, 277 volt if I remember, to put a bit of tension to try to cause the intermittent problem. When he did, his finger tip was blown off at the first joint. The end of his finger was cauterized (cooked) and did not bleed. The investigation could only surmise that there was a harmonic spike since there was no other cause apparent, but the instant boiling of the fluids in the joint where he touched the insulation was determined to be the cause of the injury.

I have also seen first-hand the effects of high voltage contact (7kV) and though the man survived, he was badly burned, cooked actually.

So then, electricity can harm us in several ways, at very low and very high voltages, both in the I²r effects and in the fibrillation of the heart. There is also the collateral damage that we do to ourself and to others as a reaction to feeling the buzz. We jump, throw things, drop hot wires, say things, fall off ladders etc, when the electrical contact was relatively harmless in itself.

The best advice is not to leave any avenue open for accidental electrical contact. Wear your safety gear and use your head. CJM

"It's the volts that jolts and the mills that kills."

Dear All,

All above replies are one to one co related, I related like this,

every human body having its own body resisitance and frequency of internal nerve system which working on smll electrical signal. Voltage is only factor which braeks the body resistance, as far as shock concern, Ampere contributing more as IsqR basis.

when ever we come across contact, if it is only touching, our body responding quickly and retracts on lower voltages with small current . if we hold conductor firmily, same can catch untill died .

whenever current flows through our body, external current waveform disturbs internal signals and frequench, our brain reacts for this , that why we feel jolts, taste change in tongue. weak point open and heart stop working etc.

It is very difficult to find shock voltage/current, level of voltage and current.

Bye

As some may have surmised, the basic problem in setting "safe" voltage and current standards comes from the multitude of uncontrollable variables; human body resistance changes from person to person, when a person sweats the surface resistance drops, current discharge path inside the body changes damage possibilities, discharge timing with cardiac cycle. So to accurately answer the OP question, no there is no formula for determining the safe condition numbers. Ohms law is still valid to predict current with a known impedance, but the impedance is not really known. This is why defibrillators are not calibrated and adjusted to how many volts or current gets produced, but to how many Joules will be delivered per shock.

But still safety boards everywhere must set some plausible voltage and current standard to make electrocution less likely. Thus the rule of thumb 50 volt standard here at work.

But we should not for get that electrocution is not the only hazard electricity can produce. There is also the arc flash problem so often forgotten. I've witnessed the effect of a small 4-40 nut shorting out the +5V buss of an underpopulated VME crate. I was monitoring the +5V buss at the time with a storage oscilloscope. The voltage dropped only briefly to +4.7V as the nut liquefied and exploded. Fortunately I was not in the line of fire of the spraying molten metal. It did make for an entertaining day.

The current is critical no doubt .But conditions under which one gets a shock is more critical.For the same current if u are on a dry fllor and wet floor can make things different.If ur body is wet shock for same current can be more fatal .If u are standing in a puudle of water and are wet then same current can be more dangerous.Also depends on how ur in contact for example if one hand is touching alive conductor the other is not touching any conductor or eath current has to pass thro the body and thro legs to ground .but if ur other hand is touching a wall current flow can be across the body and thro the heart .So that can be a killer.There are many factors under which a current which is harmless in one condition can be more fatal in other cases.I have seen people escaping after contacting a 33 kv live terminal but die on 6.6 kv.

What I have been told that it is the current that kills. 500ma (0.5 A) thru the heart is enough to stop it. 200 ma can do damage, the voltage does not matter. Higher voltage just makes it easier for the current level to be made. In Ontario the electrical authority is concerned about voltages greater than 300V.(this is peak voltage-- multiply RMS (AC-Voltage) by 1.414 for peak). Numerous rules regarding personnel protective equipment, training and a real aversion to "live work" are on the books. Arc flash is the new hot topic with new rules again coming in. Working at 1200 V you should have serious training to prevent injury. MIKE L.

there are more chances of passing current thru Kidney... burning the same.

The limit is 30 mA

Below 30mA, human body is normally safe.

Above 30mA, we are not safe.... paralysis between 30 - 70 mA, depends upon the current path in our body.

Above, fatal death.

Some seem to be very fixated on the fact that it is current that causes the disruption of signals causing mucles jerks, heart stoppage etc... That fixation is causing some to believe that voltage is insignificant. We have to keep in mind that regardless of the available current you still need the voltage to push it. I can set a power supply to a few volts with a 10A current limit and touch both terminals with no adverse effects. I don't know all of the limits but I have heard the current limit is very low in the order of a few mA. Voltage requirement will change with conditions. Human skin is designed to protect the body and does a pretty good job but when the voltage get high enough current flows. Just don't get overly focused on current and forget voltage. I had a collegue that did so and was afraid to to a 5V power supply that had a high current capability. A double A size battery could deliver the current required to kill a human but it can not do so in a human because it lacks the necesary voltage to force the current into human skin.