Electric Shock

Current is what kills you!

The static shock from your car door is a high voltage but it won't kill you!

That's why we have earth leakage circuit breakers which trip on current.

Voltage is the first part, if the voltage is (very low 50V or less) because dry skin has a fairly high Resistance little or no current will flow. as the voltage goes up the risk goes up due to ohms law current is dependent on voltage for a constant Resistance. If the skin is wet then it is much more dangerous because the resistance is very low.

There is no voltage that is totally safe! The reason why a shock is dangerous is because it can cause the heart to arrest, or go into fibrillation an erratic beating that does not pump any blood. A current as lows as 35mA can do this. Residual current devices RCD's that are to protect from shock should be rated at no more than 30mA trip current. The 100mA versions are for fire protection. You will have heard of defibrillator these give a controlled shock directly to the heart to reset it back to a normal rhythm. DC voltage is dangerous because it causes muscles to lock up and it can be impossible to let go of the live terminal. Death is often a result of the severe burns that occur. AC tends to throw you away from the source of contact, injuries from the sudden jolt can include broken bones. Respiration can also be affected so causing death by oxygen starvation. If in doubt do not go near any live equipment!

If you find any one that is connected to a live terminal DON NOT TOUCH THEM! Use an insulator to pull them free, or to seperate them from the source of contact. Plastic wood, or a rope can be used. Disconnect the supply. Give CPR phone for medical help. Act quickly but be safe. If you can get to switch off the power first do so. So long as this will not injure any one else. Do not delay seconds count.

Its the volts that jolt and the mills (milliamps) that kill

Well said.

an electrical shock occurs when you become part of a circuit making yourself a resistor under short circuit conditions. Because our bodies have a high concentration of water saturated in electrolytes we make very good resistors. So the characteristics of what the body receives become akin to ohms law. This is not uniform though as different parts of our body have different resistances depending on many conditions so the "shock" characteristics is unique to each situation. With this there is no general situation with it and both values play a key.

Looking at how electricity works you have voltage which is amount of energy per unit(charge) and current being how many charge units there are over a period of time. (how ohms law works) Charge is what gives the jitters and familiar effects but the amount of it and how strong is what does the damage. Time here is also a value (since current is a time dependant value) so the longer your "hooked up" the worse the effects. you can feel a small current of half an amp or more between your fingers with no effects but can be killed by a 50 microamp current directly across the heart. It is all in the circuit mechanics.

Because of the body making the short circuit the electricity will travel through the body to lowest charge or ground taking the path of least resistance depending on what part of the body falls on that path. People can survive high electrical events like lighting strikes because of the path traveled by the current. Your critical point is the thorax/chest area which contains the sensitive internal organs and heart. The heart is the most critical point because of its own electrical system. Any charge on that can cause fatal effects as it will conflict with the system there.

I'm afraid one of the contributors has got things slightly mixed up

AC current tends to cause muscle contraction and their in ability to release contact.

DC current tends to throw the victim at the moment of contact due to one single muscle reaction.

Anyone who as an apprentice has had the old 500v dc insulation tester trick played on them will know that it is impossible to hold the connections in their hands when the tester is operated.

DC is the worst in terms of initial shock and burns as the maximum current is constant and there is no relief from the reduction of the current value as the sine wave passes though zero, as there is in AC.

In theory you should be able to release an AC contact as the wave passes though zero, but as it happens at 50 times second the human reactions are not fast enough in practice.

To answer the question it really is a matter of both - current low as 10mA can cause fibrillation of the heart. So 10mA at 230v could be fatal, but 10mA at 12v will not be as the low voltage cannot overcome human skin resistance.

A car battery is 12v DC at 300A, but you will not receive a fatal electric shock from it. At this current however you can receive serous and possible life threatening burns if you short out the terminals holding the shorting link in your bare hands.

When I was a kid, the local garage man used to test car and Xmas tree lamps by using a pair of metal dividers to bridge the contacts to the battery posts after placing one lamp contact on one post, and using the dividers to make the other contact.

One day when I was in the garage and he was testing a lamp, the dividers slipped and shorted between the two battery posts. The battery exploded and blew the cell tops out of the battery, covering him with acid, and he carried the burn imprint of the dividers on his hand for the rest of his life.

Despite spending most of my career in the supply industry I never knew of anybody in the companies who died from electric shock due to HV contact.

Two guys who I did know lost limbs, both in a similar fashion due to PTW foul ups, both started to climb on top of HV transformers in substations ( different incidents) . one of them lost an arm from burns as he climbed up and put his paint tins etc, too close to an insulator, the other seemed to have a miraculous escape after kicking his metal paint scuttle across the top of the transformer causing it to arc with an insulator. The man had little visible effects but began to complain of a numb foot after several days. He had an exploratory operation which revealed that his foot and ankle had been microwaved to a very well done piece of roast beef and obviously required amputation.

In both cases they attempted to paint transformers which had been incorrectly identified on the PTW paperwork or had been wrongly isolated.

Good post! I saw a few odd occurrences in the service, related to radar. (I was in Ordnance, but supporting the site). We had an older "electrical" guy join the missile battery (unit). He used to, some years previously, test electron tubes by touching the grid-caps on top of large tubes. Only now, they were plate caps. He touched one cap, which carried a pretty hefty voltage, and literally was thrown away from the console. On another occasion, there was an outage on a missile trailer, during a rain storm, and no one could find the problem. A Lt., standing in a puddle, kicked the panel door, out of frustration... the outage was due to a faulty interlock, and he made the connection!! I also had to inspect missiles for readiness, and in one event, two "trained" missile workers got into serious trouble. The fuel lines had aluminum screw caps that were flush with the missile body. Inside the caps were Teflon plugs, to protect the Al caps from RFNA (red fuming nitric acid), which was part of a hypergallic starting charge. The two men removed the Al plug, then decided to sit down and take a break. It was hot in the sun, so they removed their acid-resistant suit hoods, and sat on the edge of the missile trailer. The missile had come from a cool, underground silo. The solar radiation heated the oxidizer tank, popping the Teflon plug out, and the two men were sprayed from behind with RFNA. I believe they lost their ears and much of their hair and scalp.

"10-mA at 12V -will not be (fatal)" IF you can get 10-mA from 12V, it would kill you just the same as from 200-Volts. Two ways - interrupting current through an inductive path (not really 12-Volts when it gets you, of course, but still needs considering if you are writing a safety manual) Or you could place each arm in a bath of salty water to lower the skin resistance enough.

Both as well as frequency

High voltage alone is not as dangerous as high current.

115 60 hz is dangerous both because of the high current, and the fact that the 60hz will disrupt the signal to the heart.

RF frequencies will do cellular damage, especcially the HF frequencies band.

Think of High voltage(potential) and low current (flow)as a high dam with only a trickle of water coming over the top.

Think of low voltage, high current as a 2 meter dam with a million cubic meters of water going over it.

Now answer your own question. Which will do the most damage?

The voltage plus current kill, the minimum range are 75 volt ac at 25 mA, 60 Hz.

Refer to thread "Dangerous Voltage" posted by yogindranath in Electrical Engineering on 02/24/07.

Do you know who (experimentally) found the dangerous current to be 8 mA and above?

Hitler's "scientists" in Konzentration Kamps!? Shock? At 50 Hz!

What are parameters of curing el-shocks applied to mentally ill people? Or to restore heart beats?

The first company Geartz in Austria began to apply this knowledge.

The question is simple. So the answer also should be simple . But not so . In electrical circuits potential difference (voltage) and flow of electricity (current) are related terms and cannot exist independently . So cause of shock is dependant on both voltage and current .The quantum of electric shock depends on the flow of current through the affected person and is is dependant on potential difference and resistance of connectivity.Then the question is how much voltage or how much current can do the harm? That also depends on to whom it is applied .That means there is so fixed formula. I have seen people allowing to pass 230 volts through their body and burning a bulb and still not getting a shock. In one of our quarters one lady got electrocuted and died when she was putting wet cloths for drying on steel wire . on investigation it was found that there was 36 volts leakage potential on that wire and earthing of the building was not proper. The insulation resistance of the body vary from person to person and depending on wet or dry conditions.So there is no fixed formula for death or burn due to electric shock.Certain standards are followed by the manufactures of ELCB and RCD depending on studies conducted. Proper earthing should be done for electrical wiring and shock guards must be installed to protect personnel working on electrical equipments .Power supply can be cut off if they come in to direct contact with live supply.To protect personnel working on electrical system adequate protective clothing and insulated tools should be provided and all safety rules and permit system should be followed to avoid electrical accidents.

Actually, the main factor for electric shock is resistance. It is the current which will kill you, but the resistance of your body (for a given voltage) determines the current through your body. Thus if your body presented a very low resistance, you could be killed by a 9 volt battery. I heard a story once, where a sailor (in the US navy) decided to measure the resistance across his body with an ohm meter. The battery voltage (I believe was 45v.) Of course he managed to penetrate his skin with both probes... and it zorched him.

In any case I will vote for current (and I am not a cardiologist).

Bill