Dangerous Voltage

If I understand your question correctly, whe had a considerable discussion of this question last November. In the "Search all of CR4" box, type "danger AC" to get there. The short answer is that for a given voltage, with equal source current capabilities, DC is more dangerous, because the AC voltage will drop to zero every half cycle, giving an opportunity to pull away.

i will not agrre with your answer the amplitude of AC is high , say at zero it is ok, the AC voltage is higer than DC by ten times and less by 5times. how can you say DC is very dangerous

Yogindranath,

Please explain, as it makes no sense as written:

"the AC voltage is higer than DC by ten times and less by 5times. how can you say DC is very dangerous"

Regards, Greg

True, I did it when I was a kid... OWW it's like an 155 pound man sitting on my hand

which is more dangerous: voltage or current???

Current through your body, that is the danger.

My friend was cuting limbs from a tree. He cut a highline wire and it knocked him to the ground.He was told that he had been hit by 72000 volts of electricity .Wouls this usually kill a man ?

AC has a capacitive effect and current can be injected even from a distance. AC is more dangerous. For coming in contact DC is more dangerous as average energy is greater for same voltage.

so is it current or voltage?

NFPA annually addresses electrical safety specifically by local region, voltage, and human accidental cause.

Electrical hazard deaths are Second only to auto accidents in most states annually.

Portable electtric heaters (110/220 VAC) cause most electrical deaths and house fires.

Annual electrical House fire damage exceeds the damage done by Katrina and Rita combined.

Direct human contact with electrical voltage results in primarily two types bodily damage classified as either burns or heart failure. Burns can usually be repaired and heal to some degree in time. The higher voltages are more likely to result in body burns.

Death by heart failure results from required amperage to freeze the heart muscles irregardless of the voltage necessary to provide required amps. Fortunately, heart muscles subjected to low and higher amps will "clamp" closed and prevent permanent damage.

Unfortunately, 110-220 VAC is the most likely voltage to result in heart fillerbration damage and almost certain death assuming human skin as the only insulator. Once the heart goes into fillibration, death is certain unless quick CPR action is readily available. Unfortunately, CPR is usually not readily available and/or adequate to reverse heart fillibration. The higher KVA power supplies in skin contact result in major body burns and temporary heart clamping, each of which is very painful but fortunately, recoverable and unforgettable.

It has been unfortunately demonstrated that a single 1.5 vdc household flashlight battery will provide the required amps and certain death if the human skin insulating factor is defeated. Further details intentionally withheld to prevent intentional devious duplication.

Excellent and detailed answer.

I would only like to add that in contradictions to the belief that a non-lethal shock has no consequences is falls. It has been proved that a heart that was subject to fillibrations at some times tends to produce "scars" that may lead to cardiovascular diseases at a later stage.

Wangito.

To my view it is not the voltage but the amplitude of the resulting current (discharge) which is danger. Apart from the current there is also the time of the discharge which seems important to me.

You can touch without danger 100kV, if there is no path for the current to flow. Think of a birth on high voltage wires or the spark you can get from a cat by freezing weather. This discharge can be the result of a voltage build up of more than 10kV.

The danger is that you're never sure how good your skin and clothes you will isolate and protect you from a discharge.

In human body which is made of cells with protected boundary and then linked with blood supply, which is mainly fluid for exchange of resources. Cells exchange desired chemicals by controlled opening and closing of gates in the lipid membrane. These gates are opened and closed by electrical potential caused by Sodium and Potassium ions and also by calcium ions. These flow in small channels is called signal transduction. With heavy potential applied to human body, these gates open too much and blood and cell protoplasm come in contact, and some time puncturing the cell boundary permanently. Our cells can be repair and need to replace with new one and again need proper blood supply in controlled to healthy cells. This link is broken by cell damage to massive level. What you see as burn fluid or wound is the after effect of the cell damage. For more details you can look into electrical injury biological research papers.

This is a useful link to UK regulations on electrical things including earth leakage protection against electric shock.

http://www.tlc-direct.co.uk/Book/1.1.htm

Basically the product of current and time are linked.

Anybody who has had a painful 'poke' off a spark plug will know that 12,000 volts does not kill you. Somebody mowing a wet lawn with a 230 v faulty mower will not know - they will be dead.

With a good ground you are dead either way - AC or DC.

The statement that 1-1/2 volt can kill you, that seems to be a bit much! When I went AIT (Advanced Individual Training) in the Army (many years ago) we were taught that it took a minimum of 47 volts to kill you.

If you grasp an object, a wire, a pipe, or whatever and you are completing a DC circuit, your muscles will contract making it impossible to turn loose. AC will often knock you loose.

I remember this 47V from the army too. However, with dry whether and a leader like skin, this 47V wil not harm you much. Again, it is the current that kils you.

Perhaps in wet condition, smaller voltage can give shock. Try to touch 9V battery to your tongue and you will get shock while 15kV from Piezo Electric Gas Lighter will make only tizzy feeling.

Having worked on my boat while covered in salt water, I know you can get a shock from 12 volts, however, I don't believe it will kill you.

Also holding a nine volt ni-cd or a ni-mh or other high capacity battery will get you a burnt spot on your tongue. Not good!

Now, we discussed the question whether and at which amplitude DC or AC currents (or voltages) might hold some danger for people.

On a lazy Sunday I become always a bit philosophic. Therefore: how about the danger of a pulse?

Let us consider a lightning strike. Such a strike results from the discharge of very high voltages build up in the sky or between the sky and earth. The currents during the strike can induce high voltages on a cupper wire of a view meter with sufficient energy to damage electronic circuits. The current in the air due to the strike is normally a pulse of a no more than milli seconds, with rise time often faster then nanoseconds.

Also in our body, from head to foot, a voltage difference will build up during this strike due to induction, resulting in a current flowing through our body. We may expect a high voltage (hundreds of volts) and probably relative high currents too. I expect high currents because the salt content of our body fluids are high. If this hypothesis is holds, why are we not killed by just a strike in the neighbourhood (above us in the sky)? Is it the fast pulse arising from a discharge, which is too fast for our body to react on? If it is the fast discharge, than we may conclude that we are only in danger if the current, either AC or DC, is high and slow enough to have impact on our body. Than the danger for AC or DC currents (voltages) depends on how sensitive your body is to currents flowing through it. This might depended on your condition and health. The current will probably cause shaking of the muscles. If it is your heart it will not suffer from missing a bead or two or having a few more. If the current is holding for longer, your heart might give up or the muscle will be damaged. So probably it is also the time the current holds on that will cause danger.

It is still hard to say, but in any case the danger depends on the isolation of your skin, the condition of your body, the speed of the current and the amplitude of the voltage applied.

how much current is needed to hurt you?

Go back and read posts#15,18, 24, etc!

The key, as noted by others, is current; particularly current through a critical path. According to the National Safety Council, around 300 people die in the US each year from electrical shocks on 120 and 277V circuits. An electric shock from as little as 50VAC for as little as 1 second can disrupt the heart's rythm, causing death in a matter of minutes. Electrical shock thresholds can be described as follows: Tingle sensation occurs at about 0.25 to 0.5 milliamps for an adult female and between 0.5 and 1.0 milliamp for an adult male. Current greater than 1 - 2 milliamps is uncomfortable for either gender. The maximum let-go threshold level for a female is about 9 milliamps and about 15 milliamps for a male. The let-go threshold is defined as the level at which humans lose muscle control. The current flow causes muscles to contract until current flow is removed. The fibrillation level is a function of current and time For example, fibrillation will occur at 500 milliamps over 0.2 seconds or 75 milliamps over 0.5 seconds.

According to IEEE std 60, the maximum safe shock duration can be determined by the formula T = 0.116 / (E / R ) where T is the duration in seconds, E is the voltage and R is the resistance of the person (which is assumed a constant 1,000 ohms).

Ah, thanks Bluestone for this answer (thought it was not I who has put the quetsion). So indeed the time is in the formula, and yes it is the current and the muscles.

Bluestone, you correctly point out the combined factors of time as well as current, comment on the heart muscle (as others have done) without directly mentioning path, and comment on the voltage without differentiating the AC versus DC physiological effects. All the factors mentioned by the various commentators are important: voltage, current, path, time, source type and frequency, local environment, and person's own condition.

All muscles are contracted by the application of an electrical impulse from the nerves or by an electric shock. There are different types of muscle cells. Heart (cardiac) muscle cells have to contract in a coordinated pattern to pump the blood, so there are carefully set-out pathways for this to occur, along with backup pathways, etc. A heart cell's contraction is followed for a very brief time with its inability to respond to another nerve (voltage) pulse. This allows the nerve paths within the heart muscle to properly propagate the signal for contraction throughout the entire muscle. However, an AC shock with its typical 60 Hz waveform, catches each portion of the muscle as it first becomes ready to contract and sends it into contraction. Thus the coordination is lost, and remains lost after the shock stops, because the signal paths are now being triggered in a chaotic manner. Application of a strong DC shock to the heart muscle causes all the muscle fibers to contract at the same time, thus momentarily stopping the chaotic quivering which had been happening--known as fibrillation. Then the normal conduction pathway can take over, if it was not damaged or destroyed.

Within the body, a shock's current flow has to go through the heart muscle to cause fibrillation, so a shock on one extremity only is very unlikely to cause any direct heart problems. However, an AC shock from one arm to the opposite leg is quite likely to do so. Therefore, in evaluating the danger of a shock, the point of entry and point of exit are important. Also, the level of voltage applied is important, because lower voltages can make a person grip or hang onto the energized source while higher voltages cause stronger contractions of more muscles to typically throw a person away from the energized source.

Low levels of current mean low levels of energy imparted to the person, so damage is typically limited to what the muscle contractions caused the body to do--jump, move the arm, have the hand hit the face, etc. At more severe levels of muscle contraction, you see tears within the muscles, tearing of the muscle or ligaments from the bones, breaks in the bones because of very high stress, and damage to nerves. At higher levels of energy, you see thermal effects such as deep tissue burns, local burning and destruction of cells and tissue, and boiling of cellular or extra-cellular fluid. At still higher levels of energy, you see cooking, carbonization, and vaporization.

Healthy, intact, dry skin is a very good insulator. Thick skin can have a dielectric strength of over 200 volts. Therefore, factors which reduce the skin's resistance-- such as wetness, salt content, sweating, age, location on the body--all influence how much injury a shock at moderate voltage levels causes.

As mentioned above, only AC will cause fibrillation of the heart muscle, but all shocks can cause the other types of damage, regardless of frequency. Very high frequencies will treat the human body as they do any other type of inductor, with penetration depth being less as the frequency increases. I suspect the number of high frequency shocks are fairly low overall, as the potential exposure is low.

Lightning strikes are a pulsed DC, and have enough energy to cause serious harm. Lightning has cooked the potatoes in a field and blown the bark off a tree. It can do similar things to us.

AC voltage is the RMS (root-mean-square) average of the instantaneous voltage of the sine wave, so its instantaneous value varies each cycle from zero to a peak of 1.414 of its RMS value and then through zero to its negative peak, and then back to zero. Therefore, a 12-VAC shock will have a peak voltage of +17 and -17 volts compared to its zero midpoint. Although the energy contained in AC or DC circuits is the same at identical voltages and currents, I suspect that a low-level AC shock is more likely to break through the skin's resistance because its peak voltage is higher.

In summary, I believe that an AC shock is more likely to be dangerous and harmful at low to moderate voltage levels. At higher voltages, I believe that they are nearly equal.

Work safely, y'all. John M.

thanku you answer is right sq 2 RMS value will be high at max , hence AC is very dangerous than DC, 10 times.

Thanks heavens for fast earth leakage switches.

Sounds like you fell asleep in AIT.

Looks like you failed to comprehend what you read.

Feels like there is no way you will see the truth.

Obviously, not every contributor is professionally capable of handling facts.

According to extensive testing, the exact details of which will be with held -

A specific known amperage through the human heart kills. The voltage is only a factor in precisely delivering the exact amperage. More amperage as well as less amperage will not kill.

AIT training specifically stated the voltage to be quantitified as "across normal dry skin" delivering amperage through the heart as a conductive path. Amperage does not kill through other parts of the body rather than the heart.

Voltage results in burns rather than kills except that the applied voltage results in delivering the precise exact amperage to stop heart action.

Artificial electrical triggers to heart function are often substituted in lieu of a properly functioning heart signal.

To whom are you yelling? I didn't fall asleep in AIT, but you and I both know that "There's the right way, the wrong way, and the Army way." The Army way is to put everything into a means which can be hammered through the skulls of many trainees with many different backgrounds and levels of education, all at once. There are errors, omissions, and simplifications in what they teach, but you will never succeed in an argument with a Drill Instructor!

The current flow through the heart muscle, to put it into fibrillation, is an approximate minimum threshold, not a doorway. You have stated: "More amperage as well as less amperage will not kill." I have never heard this before, so please check your references.

To my knowledge AC is more dangerous than DC when compaired in the same voltage. An AC cycle has a peak value that is √2 the nominal value.

Safety level is 50V AC - 75V DC, below is safe- above is dangerous (and lethal)

18mA can kill you (there is no time frame given)

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

It should be clear to the originator that one should try and avoid working on (or coming in contact with) any energized electrodes regardless of the voltage or frequency. If it is necessary to hot work, proper procedures must be followed. Depending upon the voltage and geometry, those procedures could include the use of insulating blankets, coverups, personal safety mats, etc. or even bare hand live line working techniques for HV, EHV and UHV. When working on smaller, lower voltage energized devices, machines, appliances, etc. it is good practice to avoid creating a critical path to ground through the heart and other internal organs in the event of accidental contact. That is accomplished by using only one hand (with no rings or jewelry) to do the work and making sure that any path to ground is through the leg and foot on that hand side (keeping the other leg and foot isolated from ground if possible).

There is a whole industry built around electrical safety and many international and national standards address proper work procedures, equipment and training.

My advice: if you don't know what you are exactly doing (and ask questions like this one): never work on live electrical systems.

Always check the network before touching it. (even if you personally switched it of a minute ago)

On HV systems it is a good advice to ground the lines before you enter the local/premises. (the vaporisation of your grounding wire is a clear sign that something went wrong)

Many highly skilled electricians have been killed by relying on a switch.

I have hired some local lads to gather up some stray dogs, cats, and a large turkey. I am planning a demonstration where I will shock these animals to death in a public display to prove that AC is dangerous. Oh, wait, Thomas Edison already did this about 80 years ago to prove that Tesla and Westinghouse's AC was more dangerous than his DC generating scheme.

Hasn't this been settled for about 80 years?

http://staff.fcps.net/rroyster/war.htm

They are both dangerous, don't know if there is anyway to quantify danger. It's like comparing falling off a 200' building or off a 200' cliff, your screwed either way.

electricity obeys the laid down laws of physics, so power will only be disipated in resistance. If a man touches a 10kV supply and a resultant current flows through his body any power will be proportionaly dissipated according to the multitude of resistive pathes the current takes.

For example around the joints are areas of high resistance, typically around 1 kohm so if a current of 20Amps flows through this joint then (I squared R) 40kWatts will be disipated in the joint/s and result in them exploding a bit like a fuse.

All forms of electricity are dangerous.

Hi,

20 squared is 400 so it would be 400Kw for direct current.

V x I x Cos(phi) = W in A.C. circuit where phi is the angle the current lags or leads the voltage waveform and it is known as the power factor.

Besides 10Kv is probably the line voltage and not the phase voltage.

Vph or phase voltage is Vl / square root of ( 3 ).

So if person touches 1 10Kv line it is at 5773.5 volts.

5773.5 times 20 x 20 = 2309401 watts or approx 2.3Kw assuming a unity power factor.

Still enough to explode the joint....probably provided the current has a path to ground or earth ( terra in Latin, also used in electrical engineering ).

Regards,

Dr M.

Both doc's are throwing numbers around carelessly.

Docrobgar in his first paragraph uses the example of 10kV; then in the second paragraph uses a resistance of 1 kOhm, which would produce a current of 10 Amps (not 20, as indicated), if that is the only resistance in the circuit. I^2R would then be 100kW. Dr. Marten correctly indicated that the 20A would produce a power of 400kW.

But then Dr. Marten introduces the AC equation P=V x I x cos(phi) (also correct), but does not use that equation to calculate power. I'm not sure about line versus phase voltage... My impression is that line voltage is the potential difference between any single wire and ground, while phase voltage is the voltage between two of the three-phase wires. If a person touches a 10kV line (as I have, fortunately through a rather dry branch I was cutting off), they are much more likely to touch one wire and ground than two phase wires.

Since a person is essentially resistive, the power factor is going to be essentially unity, so the power equation reduces to P=V x I. Using Dr. Marten's 5773.5V, and Docrobgar's 20A, the power would be 5773.5V x 20A = 115470W, or 115kW.

"5773.5 times 20 x 20 = 2309401 watts or approx 2.3Kw" Wrong twice! The current is squared in I^2R, not in V x I. "2309401 watts" is approx 2.3MW, not kW. BTW Watt was a person, and should be capitalized. kilo should not. M must be capitalized to indicate Mega- as above; m indicates milli-

Speaking of milli-, all the above numbers have very little meaning, since only a few milliAmperes of current is sufficient to kill a person, if that current passes near the heart. I am only alive today due to the high resistance of that dry branch, which only gave me a brief tingle. On the other hand, as a child I was thrown across a small room by contact with 120V through my body to wet plaster on the floor. Obviously I survived that too, as well as several accidental contacts with CRT anodes, and multiple carelessnesses (is that a word?) with 120, 240, and even 480VAC.

As at least a couple of others have pointed out, we really should not be working on live circuits, and indeed its Volts that Jolts, but mills that kills!

The truth is they are both equally dangerous and there is nobody left alive to dispute fact.

The DC current is constant and does not fluctuate, the shock results in severe trauma to the body and has a tendency to throw the body away from point of contact as the muscles go in to an involuntary spasm just like the act of using a defibrillator to start somebody's heart.

DC current values are the equivalent to the RMS value of the the AC cycle which is 0.707 times the peak value and there is no variation.

The maximum AC peak value is 1.414 times the DC value and therefore for that part of the cycle the shock would be much worse and it occurs 100 times a second for 50 Hz supplies.

It is true that it also falls to zero 100 time every second, but this little comfort after having the full whack anyway. The human body does not feel any relief at any time during the cycle.

At the 50 Hz frequency the AC current has a gripping effect on the body with all muscles contracting in the gripping or severely contracted condition. If the Live part is being grasped in the hands it is therefore very difficult to let go, thereby by prolonging the agony and increasing the chances of fatality.

At nominal house voltages the AC current is the most like to prove fatal, but at higher voltages of 11KV, the question is irrelevant - fatality and injury is likely to be sustained by burns. Some people are still alive after coming into contact with 11Kv and 33Kv but have lost arms and legs either die to burnt flesh or the body being cooked by microwave energy. The skin looks OK but the inner flesh is like well done roast beef, feels numb and has no sensation.

Many people might find this whole question irrelevant after reading this.

Indeed. Vandals climbing onto the roofs of electric trains and coming into contact with the conductor wire at 25kVac usually don't survive to tell the tale. Assuming there is enough remaining after the event to indicate it was once a vandal.

However, a person standing on the top of a glass-legged stool can use a Van der Graaf generator to achieve charges far greater than this nominal voltage, and the only effect will be a bad hair day.

So it's the volts that jolts and the mills that kills.

Next!

Anybody knows what voltage (AC or DC) is used in shock treatment in ER?

DC. The medical term is cardioversion. They typically use a pair of paddles with a conductive gel applied to the metal surface against the patient's body. The equipment is calibrated for a specified amount of energy in joules (up to a maximum of about 400j), so the person running the "code" will request the size of shock and the person with the machine will make sure that everyone is clear of the bed and patient when the discharge trigger is pressed on the paddle. Failure to apply conductive gel results in skin burns--I've seen this happen a few times.
I don't know the actual voltage of DC applied, but the muscle contraction from it causes the patient to arch his/her back and lift his/her torso (along with your hands and the paddles) a few inches off the bed. --JMM