How much voltage/current is "dangerous"?
From what I've heard:
110 V (or 220 V; household voltage pretty much) is dangerous (i.e. can kill you) I think there's consensus on this, no need to try :)
60 V (old telephone lines) is supposedly dangerous (never tried, only heard it once... probably won't try)
From what I know first-hand:
9 V is not dangerous (I've put a 9-V battery on my tongue, nbd... actually it kinda hurt!)
1.5 V can indeed be quite shocking with enough current (fell for one of those "Do you want some gum?" tricks back in high school...), but they sometimes do not use 1.5 V with the low amperage levels, some use a DC motor to vibrate and complete the trick.
So I guess there's two parameters here, voltage and current... but are there rough numbers on how much of each (or in combination, which I guess would be power) would be considered hazardous?
No old telephone lines have always been 48vDC well at least since from 1950s, if your skin is wet you can feel it slightly, like on your forearm. Now the ring voltage is 90-110vAC with a 2 on 4 sec off cycle (USA). It will ring your bell but good, should you be touching the wires when someone calls. The ring voltage rides on top of the 48vDC, so its present on the same two conductors that the voice voltage(DC) is on. Luckily it's 4 seconds off will give you a chance to get off the conductors with a scream (of pain).
I'll let more experienced users write the whole story, but basically it's power that kills, or better yet, current through vital organs which depends on the current capacity of the source and its voltage (and the needed voltage depends on the resistance through the body which again depends on the skin condition and so on). That's why you don't get killed by static electricity discharges that can go into tens of kilovolts easily and why it's dangerous to touch both terminals of a 12 V car battery.
@AndrejaKo: Ah, interesting; I only thought messing with a car battery is dangerous because of the hydrogen, not because of the current as well! :)
Note that the 1.5V shock devices will use the single cell to power a mechanical vibrator in older designs or a flyback boost converter in more modern deigns to produce high voltages - probably in the 100V - 200V range. Current will be purposefully limited and they will aim to kill approximately zero customers per year.
@endolith Well my grandfather worked as a work safety inspector and according to him one of the causes of car mechanic injuries was accidentally touching both terminals at the same time, especially if wearing rings or having hands covered with say fine metal dust or another agent which can increase conductivity of the skin.
@AndrejaKo: That's a burn, though, not a shock. You're not conducting a current, the metal is, and you are being burned because you're touching the hot metal.
@endolith Well, no. For situations about which I'm talking about, the flesh is actually conductor, so you got me wrong. Metal shavings and metallic dust can get into fingerprints, attract sweat, can cause small wounds and so on. In some cases rings can keep some sweat trapped between the metal part and the skin itself and provide better contact and in some cases may be too tight and provide better electrical contact between the ring and the skin.
When a hand "prepared" in such way touches one pole of the battery, you get increased chances of shock if you touch the other pole, especially if the other hand is contaminated too. Bonus points when touching the positive pole of the battery and then touching exposed part of the car chassis which is of course "grounded" to the negative pole of the battery. So I'm not talking about situations when you have a contact with an overheated conductor short-circuiting causing burns.
@AndrejaKo: I don't think it's possible to be harmed by shock. Even internally, the resistance of the human body only drops to 300 ohms or so.
I have always been told the primary concern with high power sources is that a tool will short across it and the metal will vaporize causing an explosion that actually does the damage.
Years ago I worked in a telephone exchange and we routinely worked on equipment that was powered at 50v DC (via a simple fuse) without a qualm. There was no perceptible sensation at all when touching both -50v and earth. OTOH both back-emf from relay coils and the 70v AC ringing supply definitely were perceptible - but no more than a bit painful - the surprise factor probably being more dangerous if you were working up a ladder on a high equipment rack.
The 2V/400A batteries used to construct the backup 50V supply will deliver a very destructive shock if you get yourself or tooling between 25 of them and a robust short path. This will destroy a substantial piece of a socket wrench in a blinding flash of light, the result of being a dumb ass. It isn't likely to kill at 50V, but I can assure you the burns are nasty.
I think what people don't consider in the whole "it's not the volts that kill, its the current" debate is that they are largely orthogonal factors when talking about electrocution. Yes, they are related through Ohm's law, and maybe we could even solve the entire function space describing voltage/current for any two (or more) points of contact on a human body if we knew enough about it... But simply, voltage is potential difference. Human skin acts somewhat like a dielectric (depending on humidity, etc) and so does the air between it and whatever energized conductor may be present.
I feel (just viscerally speaking here) that high voltage sources are more dangerous than high output low voltage ones. Like for example imagine that you are in a spherical, conductive room with an energized sphere suspended in the center of it. (somehow.) As the voltage increases, at some point, you are going to be electrocuted no matter what you do, when there is enough of a voltage difference between the room and the energized sphere to ionize the atmosphere, lead to dielectric breakdown of your skin, and establish a path through your body, which is basically a sack of saline.
OTOH, if you drive a steel nail into your left shoulder and another into the back of your right thigh, and connect two poles of a lab power supply to them, then I guess you could really say that it's the current that kills. but in that case Ohm's law really would be R=V/I, (or really close to it anyway) and "current/voltage/power" are all given by one another. I'm guessing the conventional wisdom that "current kills" comes from the fact that most electrocution injuries happen when someone comes in (near) direct contact with an energized conductor, so the dielectricity of skin is negligible
How much voltage is dangerous is not really a static number as it depends on your body resistance, time of exposure and source "stiffness" (i.e. how much current it can supply). You get figures like 60V (or as low as 30V) which are an attempt at an average figure above which "caution should be taken".
However, depending on how "conductive" you are at any one time, sometimes e.g. 50V might be quite safe and other times it may kill you.
DC or AC (and what frequency) seem to make a difference too, female or male, etc - this table is very instructive:
Figures as low as 20mA across the heart are given as possibly capable of inducing fibrillation - here is another table from the same source that gives body resistance based on different situations:
You can see that as low as 20V may be dangerous given the right conditions.
Here is the reference the tables came from, I think it is quite accurate based on some experiments I have done myself measuring body resistances. The rest of the site seems to be generally very well informed and presented from the bits I have read, so I think this may be quite a trustworthy source.
Your reference actually references other references: The MIT safety group and a Bussman publication *Deleterious Effects of Electric Shock* - http://www.allaboutcircuits.com/vol_1/chpt_3/10.html, first paragraph.
Most of the painful data dates back to second world war. Thinking of which ruins my appetite for todays breakfast.
Some of this data doesn't make sense. How can "Threshold of perception" be highre current than "slight sensation"?
Hi Olin. Yes - I wondered about that too. Maybe they got them the wrong way round?
10000 Hz requires higher currents than 60 Hz? Or have I misunderstood something?
12 VDC CAN kill and has killed people.
While 12V is almost always safe, worst case situations can and have lead to death.
Mechanism may be ventricular fibrillation BUT paralysis of the respiratory muscles occurs at about 20% of the current needed to introduce fibrillation.
See discussion and references at the end of this answer.
12 VDC applied across the chest has killed volunteers despite medical experts standing by !!!
(From memory - volunteer prisoners participating in medical research).
Carry a car battery with exposed terminals on a hot day when you are sweating and press the terminals to your body (as could happen worst case when lifting the battery etc) and you may end up repeating the experiment.
Once conduction into the body starts you get a very low impedance / resistance circuit into what is essentially a large bag of dilute saline solution.
There are two mains "what kills" issues.
One is general trauma - burns etc, and that is obviously very situation and person dependant. I've had shocks from 1200 VDC, 230 VAC, 50 VDC, RF and miscellaneous other sources. No major burns. I'm still alive
Enough current for long enough to stop your natural heart rhythm and throw it into fibrllation.
At typical domestic voltage levels you are USUALLY safe if the current flows for well less than one ventricular heart valve cycle and at "low enough" current.
Earth leak circuit breakers (ELCB) also called ground fault interrupters (GFI) and other names aim to trip at currents somewhere under 10 mA and from memory (references later - rushing) in about 10 mS = well short of a heart cycle.
A shock from a circuit protected with an ELCB / GFI device will be felt but will USUALLY not be fatal.
A 9v battery on the tongue almost certainly won't kill.
A 9v battery across the chest with saline solution (or sweat) just might - probably not.
A 12V "car battery" or any high current source from a few volts up MAY kill in the very worst case. Hand to hand I havve never heard of shock occurring or being felt.
110 VDC (not AC) routinely killed Edison's linesmen.
50 VDC MAY not be felt with dry hands on a dry day. On a high humidity day brushing the back of the hand with terminal strips with 50 VDC on causes annoying minor shocks (as experienced in eg Telecom wiring frame jumper running (based on my long ago experience)
75 VAC imposed on 50 VDC gives a very nasty shock sometimes. Worst case this could kill.
High current 1200 VDC hand to body somewhere may not kill - I'm still alive.
Can 12 Volts kill?
Probable? - no.
Possible? - yes.
Data point: Note that this is a completely true and non-fabricated account. I have a friend (still alive) who built a lamp to take flounder fishing. It used a 12V SLA battery and an Aluminum pole with the light at the top. Flounder fishing involves wading through shallow salt water. In the course of fishing he discovered that an electrical fault existed - in some manner he was exposed to 12 VDC between his hand holding the pole and the water he was standing in. He was completely unable to release his grip - the current flow exceeded his "let go" threshold. regardless of how "worst case" this may have been and what various tables and standards say, it was clearly possible to reach his personal can't-release level. The literature states that respiratory paralysis can occur at currents not significantly greater than the can't release level. If he'd been by himeself (never a wise idea with such activities) he may have found himself floundering :-). Note that this was a hand to leg current path. Chest to chest worst case can be reasonably expected to be potentially higher.
this is not a primary reference source but the figures used have been obtained from an "official" source. See above page.
Note that for 60 Hz Ac ventricular fibrillation is stated as occurring at 100 mA but paralysis of respiratory muscles occurs at 20 mA . These limits are very much user and situation dependant but give an order of magnitude indication.
With very informal equipment I measured 1500 ohms resistance across two areas on my abdomen. I decided not to measure across my chest in the vicinity of the heart. I used flat contacts with no skin penetration. At 12V, if resistance did not change with current flow (and I'd expect it to probably drop) a current of 8 mA would be produced. Measurement with skin penetrating electrodes may reasonably be expected to increase this significantly.
A superb discussion of electrical safety, current levels in various situations and consequences can be found here. The writer's competence and bona fides are above reproach*. The discussion relates to the provisions of standard IEC60990 'Measurement of touch current and protective conductor current'. This is a "for money" standard that I do not have access to, but excerpts from it are provided in the above reference and elsewhere.
- '*' P E Perkins PE.
Convenor IEC TC108/WG5, IEC 60990 'Measurement of touch current and protective conductor current"
A careful but less than exhaustive examination of the above document and other related web material makes it very clear that
"Electrocution" from a 12 Volt DC source would be extremely unlikely
In worst case situations it could happen.
Accounts of two deaths by electrocution. One at 12V. One at 24V. Note that BOTH these are unsupported heresay reports and actual cause of death may not have been electrocution.
Table 1. Estimated Effects of 60 Hz AC Currents
1 mA Barely perceptible
16 mA Maximum current an average man can grasp and "let go"
20 mA Paralysis of respiratory muscles
100 mA Ventricular fibrillation threshold
2 Amps Cardiac standstill and internal organ damage
15/20 Amps Common fuse or breaker opens circuit*
* Contact with 20 milliamps of current can be fatal.
As a frame of reference, a common household circuit breaker may be rated at 15, 20, or 30 amps.
Interestingly - this answer has 1 downvote, and surprisingly few upvotes considering the undoubted truth it tells. Maybe the downvoter and anyone who doesn't think it is a good answer would like to tell me why? The aim is to be balanced and objective and as factual as possible. If it falls short please advise.
I have also touched 50VDC(48V) and it just annoyed me and gave me a tickle. I know a guy whom had a 100kW power supply turned on while he was working on it, he lived without long term consequence. I do have some lead acid 9V batteries though.
@endolith - My certain memory that I read about it long ago BUT you could find it and other references and do us all a service BUT I'll do so if I get time if you don't do so first. While there you could add references for all the other did and didn't claims. eg 1200 VDC didn't kill me, 230 VAC often doesn't / often does etc. Edison's linemen dying (something he tended to hide) ... .
@RussellMcMahon: You could have impeccable memory and the original source could still be wrong. I'm skeptical is all. Minimum human internal resistance is still 300 ohms.
"Peng and Shikui (1995) presented 7 cases of electrocution by AC or DC voltages ranging from 25-85 Volts. In all cases, the contact site was on or near the chest, the contact time was “long”, and skin burns were observed. In addition the authors note that all victims were working in an enclosed, high humidity and high temperature environment" That's the lowest I've ever heard of.
@endolith - Please see added "Can 12 Volts kill?". Note summary - Probable? - No. Possible? - yes.
Prolonged exposure to even very low DC currents can kill body tissues by electro-chemical effects. Medical devices with electrodes that attach to the body (e.g., heart monitors) are rigorously tested to insure that DC current can not flow in the leads.
@jameslarge Yes. A good point which is seldom mentioned when this subject is discussed in forums like this one.
@RussellMcMahon , links in the body of your answer appear to have disappeared. Are you able to recover them?
If the victim relies on a cardio pacemaker, and 100 mV is applied to the device in the wrong way, it is advisable to have a gorgeous, liberal, and unattached CPR-trained nurse nearby to keep him going and motivated to live until he reaches technical help. I wonder if pacemaker electronics can go into fibrillation with just the right current pulses... Can defibrillator machines supply pacemaker pulses?
When I had radio-electronics in grade 8, lesson #1 was how to safely disconnect a victim from voltage and apply CPR. In those days (1953) we did not do it mouth to mouth, so it was ok for 13 year old boys. But now days... they are probably glad that most electronics is low voltage! That same teacher came back to me in grade 12 grade physics.
It's not the voltage but the current that kills.
About 60V is considered the level at which you can start getting an electric shock.
According to Joseph J Carr's. "Safety for electronic hobbyists. Popular Electronics." October 1997:
In general, for limb-contact electrical shocks, accepted rules of thumb are: 1-5 mA is the level of perception; 10 mA is the level where pain is sensed; at 100 mA severe muscular contraction occurs, and at 100-300 mA electrocution occurs.
Electrocution becomes fatal when the current passes through the heart and causes fibrillation - the current causes the heart's beat to get out of sync and it can't pump blood any more.
Another thing that's sometimes omitted but is also extremely important is that electrocution also causes burns which themselves may be enough to cause death. Here are a few videos demonstrating how the system works: http://www.youtube.com/watch?v=ehHo_P4O3FA http://www.youtube.com/watch?v=u-IbdeZW2PQ http://www.youtube.com/watch?v=gMEDcvmoAfI http://www.youtube.com/watch?v=eyuT4B6ZZpk
see my answer to this question: http://electronics.stackexchange.com/questions/9222/safe-current-limit-for-human-contact/9244#9244 which is a pretty much a duplicate of this one.
@Matt, I really really hate people saying "its not the voltage, it is the current". Measure the 9V battery when on your toungue and you will find it is a lot less then 9V. Yes, we often rate things by their open circuit voltage, which does not tell you much, but it is the power that kills, that little 9V battery cannot deliver much. I have a 400 Amp 3V source at work, It will stay 3Vs up to 400A. This makes 3V dangerous because it is able to deliver high power. The 9V battery has a big series resistor, a 9V lead acid would be dangerous as it does not have as big a series resistor.
@Matt, not to say that often the current rating of a source is a good way to tell if it is dangerous, you need to know the voltage to know what on your body it will conduct through. 110 will conduct through your skin, 5V is going to need something like a tongue or water on your skin. 480 is going to conduct through clothing very easily.
@Kortuk Knowing the voltage doesn't provides enough information to determine the chance of damage, knowing current does (as measured through the body). Now you can argue that if you know one, you know the other based on some model of the resistance of the human body. However that pretty much impossible to determine in the general case. The resistance varies extremely widely based on contact location, moisture conditions, duration of application, frequency, etc. Thus the only term which is a consistent measure of damage, is current or current at 'x' frequency/duration more accurately.
@Mark, if you know current through the body then you already have a complete picture. I know too many people whom will tell me it is the current that matters and think that means voltage can be ignored. I have a cable at work that looks like a completely normal wire that runs from the Power room down 2 stories to the first floor. That cable can deliver less current then a wall socket but it is running at 18kV. It has an output ripple capacitor so if you were to touch it and have it arc through you, you are cooked.
Just find that a lot of the common folk that read information like this can end up misunderstanding and thinking that voltage does not play a part. The issue on this forum is that almost every user with rep understands in detail as they are active in the field even as a hobby.
It's not the current, either. When your body builds up a static electric charge and discharges into a doorknob, there are thousands of volts driving several amps, but nothing bad happens, since the duration is only a fraction of a microsecond and the total energy built up is in the millijoules.
I just *love* these "It's not the voltage but the current that kills" statements. It is not wrong, but it's like saying "it's not a lack of food which kills people, it's the low blood sugar." What, in your opinion, makes the current flow !?
@PeterA.Schneider The voltage is like willpower. If you can overcome the resistance with enough voltage (or if you can overcome the urge to eat with enough willpower) then current can flow (or you can starve yourself). If enough current can flow (or if you're not a walrus) then you are dead (either way).
It's not the voltage but the current that kills, is a popular yet
still incorrectincomplete answer. It is the ENERGY that kills. With static electricity you will will be exposed to voltages much, much, much higher than 110/230V and that is not dangerous. So obviously high voltages are not that dangerous in some cases. Why? Because the time is so short that the total energy you are exposed to is so low. Please see the video It's not the volts that kill you, it's the amps at youtube that explains this topic in more detail.
Thanks for the answer! A few notes: (1) Energy? Are you sure you don't mean *power*? (2) If it's not the current that kills, then why does the YouTube video say the opposite (amps = current)?
Your statement about the energy being the issue is incorrect from everything I've heard and reasonable logic. It *is* the current that kills. The volts only matter in how much current they can cause, which depends on how well the potential is coupled to your body. That's why wet skin is a lot worse, because you get more current for the same volts. Energy can kill in some situations by cooking your tissue, but that's way more current than would kill you for other reasons in most cases. A few extra Watts is no big deal for the body to dissipage.
Maybe calling it incorrect is wrong, but my point is that _only_ considering current is incomplete without also considering the time. With a static discharge you might be exposed to 8A at the very start. 8000mA is a magnitude above the dangerous levels already mentioned, and yet still only annoying.
@hlovda: Yes there is a time component to causing harm, but thats current and time, still not energy. Energy is simply the wrong metric unless you're doing damage by cooking.
@Olin, I disagree, for there to be high current you need the voltage. I agree that 480V with 1mA rated current will not be dangerous, but is .1V with 1000000A rating? Only if you can get it to conduct. You need to know both conditions to have a complete picture. I hate that people act as though you only need to know current and hlovdal is making the same point here. You are not at danger with a 1000A source and 1V unless you touch it with something that will conduct alot of current at 1V. But a 40kV source with 100mA is actually pretty dangerous.
I think it would be fairest to say that an electrical event is not dangerous, regardless of peak voltage or current, if the total energy is below a certain level. Likewise, if the current and voltage are below a certain level, a person can--given enough time--safely absorb an arbitrarily large amount of electrical energy. Further, if voltage is sufficiently low, the amount of current that can flow as a consequence of such voltage will be too low to cause harm.
@supercat, in general my point. There is no perfect way to be sure something is safe.
@Kortuk: While there's no perfect way of knowing something won't pose some unanticipated type of hazard, there are essentially-perfect ways of knowing a particular kind of electrical event won't be dangerous. One can achieve safety by limiting current, voltage, or energy. Limit any one of those three, letting the other two do what they will, and one can completely avoid electrical hazards. To be sure, sometimes it may not be practical to limit one of them to the level which would be required to ensure safety if the other two were unlimited...
@Kortuk: ...in which case one will have to worry about how parameters interact, but if one can limit any one of the factors to a low enough level, the other ones really won't matter.
All the answers given are correct to an extent :
- Electrical current will cause muscles to contract and can lead to respitory and cardiovascular seizures.
- The electrical energy imparted on the body will burn and cause serious internal injury.
But this only holds true for a given voltage, a certain voltage is needed to traverse the skin and this of course is a function of the impedance. For example the 9V battery on the tongue gives a slight shock but you wont feel anything if you hold the battery in your hand.
The rule of thumb is 50 VAC or 120 VDC is considered the danger limit, take these as guidelines as the limits will change with humidity and other environmental factors.
Whether or not these voltages are lethal really depends on the situation. For example, if you are working inside and power cabinet and you touch 1000 VAC with your elbow resting on the earthed shell, you will most likely BBQ your forearm and need an amputation. Do the same thing with 1000 VAC in your left hand and earth in your right hand and its game over.
I agree with the other answers about that is the current that kills, but most off the other answers forget that the internal resistance of a body is not constant.
- How big is the body, a child, a small woman and a big man do not have the same mass.
- Contact area, i.e. how moist is the skin and how thick is it.
- How far shall the current travel in the body, longer distance means higher resistance (just like any other cable out there). So there is a big difference if you have 2 wires connected directly to your chest or if one cable is attached to your hand and the other to your foot.
Then with this input you can calculate how big the current will be at the different voltages.
Yes these are certainly factors but once current reaches the nerves resistance becomes incredibly small. However the initial voltage required to cross the skin into the nerve system of our bodies remains relatively constant despite age, size and contact area with the conductor.
@Johan - I'm being picky, but I'm not sure I agree with your opening comment, the fact that body resistance is not constant is the main theme of my answer? also Russell mentions varying risks dependent on internal resistance.
The resistance of the human body depends on voltage, too. :) Larger voltages reduce the resistance of the body and increase the current more than if the body had a fixed resistance.
What I need is something like an electric dog bark trainer, but with a much higher shock energy. I can barely sense the output of the dog collars, so canines must be much more sensitive to electric shock than humans. (The purpose of this training is to break a bad vocalization habit I have acquired when playing the flute.)
From my experience;
Once, I connected output of a transformer to a voltage doubler to obtain 65V DC voltage. When I touched it with my two hands, it didn't shock me, it didn't even made me feel it. If I hold my breath and stay really calm like a training Buddhist monk, I barely felt a very tiny vibration at my fingers.
I didn't measure current then. I am a male with an average body, and my hands were not dirty at that time.
I know some will probably frown at this, but +1 for the vision of a buddhist monk trying to measure electricity with mindpower, a la Shaolin Temple kung fu flick training scene.. :-)
And, on some other occasion, you'd be unfortunate and die. Dry hands at 65 VDC is most often non fatal. Wet hands and bad luck and you could have a bad day.
From my experience.
I have built a single-pulse high voltage source that charged a 6 uF capacitor to 600 Volts and discharges it through a transformer's primary winding so that it's about 30 kV at the secondary. I got a shock from it through a 1 cm air gap, and it caused me to lose hearing and vision for a few seconds. Fortunately both recovered completely, but it was scaring even to switch this circuit on. I was lucky not to have bought a 400 uF capacitor battery for that voltage.
I don't think the voltage means much above a certain threshold, but the energy does definitely.
The worst shock of my life was 700 VDC for a moment. It was only a moment because the involuntary jerk quickly broke the connection. But I had a nifty little burn blister punched through my skin and into my meat that took a long time to heal. I was in high school at the time, and my dad never found out (or my electrical engineering career would have been redirected into something productive like law, accounting, or dentistry).
From the above answers, it is not just the voltage and not just the current. For every voltage and current there is a time of exposure that is required to give an effect. However, I was taught in middle school electronics that 100 mA is lethal to half of the population and that 60 Hz is about the worst possible AC frequency. (In those days, the unit of frequency was CPS, named after Charles Proteus Steinmetz.)
So what we need is some function of voltage, current, frequency, and time for each effect given in McMahon's response above, as well as additional effects of incineration and explosive destruction.
The good thing about such shocks is that they provide an accelerated learning curve. Once you get a bite like my big one, you will take extreme care to avoid a repeat! I guess that is why electric shock is such an efficient training device. However, I do not recommend that others repeat this as an experiment, especially with both feet in grounded buckets of salt water. Then you will for sure never repeat the experience. Clearly Edison's great invention incorporates measures to increase the contact area and maximize the current flow.
Does anybody here remember the Caltech lightning lab?