When does DC voltage become dangerous?

**BatteryCharger** · 02-11-2010, 04:43 AM

Ok, theoretically in the right place you could probably be killed with 1ma @ 1v. More realistically speaking, when does DC voltage become dangerous to touch with your bare hands? 36v? 48? 75? How high does it need to be before you should be afraid of it like 120v sockets?

Just curious...

**timberwolf** · 02-11-2010, 04:50 AM

It varies, you usually start feeling it at about 50Volts, which also is about the limit in safety regulations. And as with any powersource, not the Voltage is dangerous but the current.
I may check this in more detail when I'm back at home.

**endreein** · 02-11-2010, 05:09 AM

IF you drop down 1 metre you could die
if you drop down 25 you could survive !!

same goes for voltage ,,don't be afraid for sockets They hurt but, normaly you wont die unless you put some wet steel rods in them and grab them with your hands for a long time !! ,,,, has somthing to do with how easy the current goes through You.

**endreein** · 02-11-2010, 05:13 AM

also you can touch 10000v electrical fenses , but they only hurt like **** and won't kill you same reason: not enough current !!

**Wiggle** · 02-11-2010, 05:46 AM

Probably not going to find an exact number people can agree on, but I'd say 60+ VDC.

**jhellwig** · 02-11-2010, 05:51 AM

36-48 is where you might start feeling it. It depends on varying conditions. 50v is where you start to have to aboe3y different wiring standards per the National Electric Code.

You must remeber that dc is much more hazardous than ac of the same voltage. Dc will sustain an arc at much lower levels than ac. If you get shocked by dc you will likely not let go of what you touch. Ac will trow you away.

**Mr Happy** · 02-11-2010, 06:43 AM

It depends how sensitive you are, whether you have sweaty hands, and so on. I can certainly feel a tingle from 24 V, and in the wrong circumstances 12 V could be enough to kill you.

If you always assume electricity is dangerous you won't go far wrong.

**Apollo Cree** · 02-11-2010, 07:01 AM

Originally Posted by jhellwig

You must remeber that dc is much more hazardous than ac of the same voltage. Dc will sustain an arc at much lower levels than ac. If you get shocked by dc you will likely not let go of what you touch. Ac will trow you away.

Conventional wisdom in electrical engineering is exactly the opposite. The most common form of electrocution death is from stopping the heart. 60 Hz AC is much more likely to cause heart stoppage than DC current of the same voltage.

AC voltage is quite good at causing muscle contractions and causing you to "clamp on" to an exposed wire as well.

**Magic Matt** · 02-11-2010, 07:26 AM

The position of the shock, and distance between entry and exit points is critical. A voltage of 60V per cm across your body will cause tissue damage. If the entry and exit points are somewhere like your leg, you can survive even the frighteningly high voltages from lightning. If the voltage goes across your heart, even 100VDC could be fatal and stop it.

**Apollo Cree** · 02-11-2010, 07:27 AM

Here's some info from the CDC.

http://www.cdc.gov/niosh/docs/98-131/overview.html

It lists around 16 mA as a current level where you may not be able to let go.

Around 20 mA can paralyze your respiratory muscles and stop breathing.

100 mA can cause ventricular fibrillation and stop the heart. This is particularly dangerous because even if you get disconnected from the current, your heart won't necessarily restart.

**Magic Matt** · 02-11-2010, 07:40 AM

Good info... just a word of caution though... the figures you've quoted are at ~600VAC 60Hz though, not DC.

**JohnR66** · 02-11-2010, 07:44 AM

I heard somewhere that low DC voltages that you may not notice can do electrolysis damage to cells. Supposedly, a person was killed while working on a vehicle with a 24 volt battery and some how manged to get pinned with part of his body in contact with one of the terminals and another to the body (ground) of the vehicle. He was trapped that way for a while (hours?) and died later due to the damage to his cells from the current.

I can't attest to the validity of this story, but it sounds plausible as electric currents passing through chemicals can break down the molecules or form new ones.

**Apollo Cree** · 02-11-2010, 08:15 AM

The problem with such a question is that the answer is so complicated. It's mostly the amount of current flowing into a vital organ that causes death.

If you run a current between two fingers on the same hand, only a small percent of the current will flow through, for instance, your heart. If you run the current from your left hand to your right hand, a larger percentage of the current will flow through the heart. A medical patient with, for instance electrodes for a heart monitor could have a much lower current threshold if there's some sort of electrical problem because .

Even though we say current is the problem, what we see most of the time is voltage. We are usually dealing with what we consider to be "constant voltage" sources. This would be something like a battery. It produces 1.5 Volts most of the time. If you have 0.01 mA flowing, it's 1.5 Volts. If you pull 500 mA out of it, it's still close to 1.5V.

Now, assume you have an exposed voltage of 50 V somewhere. If you walk up and touch it and have on shoes with rubber or plastic soles, the electrical resistance of your shoes is so high that you might only get a few micro amps. Change to leather soles, you still probably don't get much current. Now, assume you're touching a metal piece of furniture with one hand and touch the 50V circuit with the other. You get considerably more current. Now, consider if you have sweaty hands and are making really good contact with a grounded metal table. Now, assume you're standing in a decorative fountain with wet hands working on the water pump and you don't realize that the 50V DC power supply isn't turned off.

The threshold of "safe" voltage varies widely in these different situations because the electrical resistance varies so widely.

In the electrical engineer safety discussions, a "nightmare" scenario was something like "A technician is working on a piece of low voltage electronic equipment. The equipment has energized components with sharp edges, for instance voltage test pins. The technician slips and manages to spear a finger on each hand with a pin and pierce the skin. What's a safe voltage level here?" The answer was that there probably was no safe level.

With all that said, you mostly worry about voltages above 50V. You understand that lower voltages can still be dangerous in certain conditions. You become more concerned in wet conditions, or any kind of medical situation. Me, I start getting nervous above 12V, and ratchet up the nervousness as voltage gets higher.

You also understand that a lower voltage high current situation can cause thermal burn problems. For instance, shorting out a car battery with your class ring can cause a really nasty burn.

By the way, telephone wiring is around 48 Volts when the phone is on the hook, and we normally don't worry about that too much. However, if you're messing with some phone line connection and thoughtlessly decide to hold the connector in your mouth to free both hands, it can be an unpleasant or even fatal surprise. Especially if the phone rings, when the voltage jumps to around 90V.

**Apollo Cree** · 02-11-2010, 08:37 AM

Originally Posted by Magic Matt

Good info... just a word of caution though... the figures you've quoted are at ~600VAC 60Hz though, not DC.

In terms of the hazards listed, the voltage is irrelevant. 100 mA will tend to cause fibrillation no mater whether it's 50 VAC with wet hands or 500VAC with dry hands.

AC vs. DC is mostly relevant to the ventricular fibrillation.

Normally, you "play it safe" with AC vs. DC and just assume they're equally dangerous. e.g. DC is less likely to cause fibrillation, but you treat it as if it were equally dangerous.

By the way, I think we tend to think of AC as more dangerous than DC because the common AC power sources we are familiar with are higher voltage than DC power sources.

House wiring is 120 VAC or higher. Electrical distribution lines on power poles are 7000VAC or higher. Car batteries are usually 12V. Batteries are commonly 1.5V or 9V. Electronic circuitry in consumer electronics is commonly under 5V.

**Apollo Cree** · 02-11-2010, 08:39 AM

Originally Posted by JohnR66

I heard somewhere that low DC voltages that you may not notice can do electrolysis damage to cells. Supposedly, a person was killed while working on a vehicle with a 24 volt battery and some how manged to get pinned with part of his body in contact with one of the terminals and another to the body (ground) of the vehicle. He was trapped that way for a while (hours?) and died later due to the damage to his cells from the current.

I can't attest to the validity of this story, but it sounds plausible as electric currents passing through chemicals can break down the molecules or form new ones.

Entirely plausible. I'll bet the 24V current was still painful and he would have done something to stop it if he wasn't pinned down.

**uk_caver** · 02-11-2010, 08:49 AM

Originally Posted by Apollo Cree

In the electrical engineer safety discussions, a "nightmare" scenario was something like "A technician is working on a piece of low voltage electronic equipment. The equipment has energized components with sharp edges, for instance voltage test pins. The technician slips and manages to spear a finger on each hand with a pin and pierce the skin. What's a safe voltage level here?" The answer was that there probably was no safe level.

At some voltage, there'd presumably be an equal risk of damage from other factors (the technician jumping back after stabbing their fingers (from pain rather than electric shock), and tripping over something on the floor, etc), and at some lower voltage, even if the electrical risk was nonzero, it would be so relatively small compared to other factors as to be beyond worrying about.

**InHisName** · 02-11-2010, 01:11 PM

Originally Posted by Apollo Cree

The technician slips and manages to spear a finger on each hand with a pin and pierce the skin. What's a safe voltage level here?" The answer was that there probably was no safe level.

That is what I heard back in my Engineering days. They referred to an Everready cell killing one. Needing only 10+ ma to do it. Imagine one Eneloop and above stiuation and 210 lb technician being brought down. Gives me the willies.

**Apollo Cree** · 02-11-2010, 02:01 PM

Originally Posted by uk_caver

At some voltage, there'd presumably be an equal risk of damage from other factors (the technician jumping back after stabbing their fingers (from pain rather than electric shock), and tripping over something on the floor, etc), and at some lower voltage, even if the electrical risk was nonzero, it would be so relatively small compared to other factors as to be beyond worrying about.

The point wasn't necessarily that the exact scenario was likely. It was more of a reminder to not make any assumptions that a particular voltage is safe in all conditions. There's one urban legend about some teacher demonstrating to his students that a car battery wouldn't electrocute you. Bare foot in a bucket of salty water, and a hand in another bucket of salty water. Oops, bring in a new teacher and counseling for the kids.

**march.brown** · 02-12-2010, 02:30 AM

A friend of mine (many years ago) was changing a battery on a truck ... He made two mistakes ... Firstly, he left his wedding ring on ... secondly, he used a non-insulated spanner.

As he tightened the live battery terminal, the spanner was in contact with his wedding ring ... The ring unfortunately came into contact with the bodywork of the truck.

The ring suddenly became extremely hot and luckily did not weld itself to the spanner and the bodywork ... He was left with a ring shape burn on his finger and the ring had to be cut off due to the swelling of the finger.

Where you have an almost infinite ammount of current (as in this case), it can be very dangerous.

I worked for many years on 48 volt and 110 volt DC systems and you actually get used to these voltages ... I found that the back-EMF, off highly inductive devices (such as electro-magnetic relays), really makes you jump though ... You never really get used to that.
.

**jtr1962** · 02-12-2010, 05:31 AM

Originally Posted by JohnR66

I heard somewhere that low DC voltages that you may not notice can do electrolysis damage to cells. Supposedly, a person was killed while working on a vehicle with a 24 volt battery and some how manged to get pinned with part of his body in contact with one of the terminals and another to the body (ground) of the vehicle. He was trapped that way for a while (hours?) and died later due to the damage to his cells from the current.

Well, they use the principal of electrolysis to kill hair cells, so there is some validity here. I think what happens is the electrolytic reaction produces lye, which in turn kills the hair cell. Something similar probably happens to other types of cells subjected to low but continuous current.

Also, everyone here is talking about voltage and current, but it's total energy in joules from the charge which actually kills. I think you need around 100 joules to stop the heart, give or take, although I've heard figures as high as 200. Accidentally discharging a 10,000 µF capacitor connected to a full-wave bridge across a 120 VAC would be enough ( stored energy = ½CV² = ½ ( 0.01 ) ( 169 )² = 142.8 joules ). However, accidentally discharging a 1000 µF cap wouldn't be, although it might cause some really nasty burns, plus a heck of a jolt. Notice however the squared term with voltage. A seemingly small value capacitor at a high enough voltage could be deadly. If you're working on CRT TVs, for example, all it takes is a cap of 0.3 µF charged to 25 kV to kill you. I think the capacitance of the picture tube is more than this. On the flip side, you would need HUGE capacitances at 12 VDC to kill you, roughly on the order of 1.5 Farads.

Obviously almost any battery can store well in excess of 100 joules ( a AA Eneloop stores roughly 9,000 joules, for example ), so given a low impedance path through the heart, even a 12 VDC battery can kill.

**tino_ale** · 02-12-2010, 05:48 AM

IIRC your kidney can also fail from current in your body. There has been occurence where someone sustained an electric shock, was well minutes after but would be found dead the next morning because the kidney were damaged during the process.

After any electrical incident where you suspect current has gone through your body you should seek medical assistance. Now, I agree it's not easy to define in what case the incident was "significant" enough to decide whether to have a check-up or not

**Apollo Cree** · 02-12-2010, 11:26 AM

Originally Posted by jtr1962

Also, everyone here is talking about voltage and current, but it's total energy in joules from the charge which actually kills.

I think joules is only going to matter for burns or tissue damage. A short shock without many joules can easily stop the heart and it may not restart on its own. A long shock below the dangerous current levels will tend to not do any damage except in extreme situations, even though it accumulates a lot of joules.

The amount of current and length of time actually flowing through the various organs is usually the most important factor.

**65535** · 02-12-2010, 11:55 AM

While it's true the lethal amount of current across the heart is very low, it takes a whole lot of voltage to allow that amount of current to flow through your heart.

Also joules is a measure of energy per time, the longer the time the more joules that flow, shorter time, less joules.

DC reacts to resistance more than AC, it takes a fair bit more DC volts to generate lethal current across the heart than it does AC. 24VAC will cause muscle contractions and some pretty bad feelings. It takes around 50VDC to feel the current flowing through your body.

You're more likely to die from higher voltages than low because they will travel farther through your body.

The actual chances of being electrocuted from normal circumstances of the average person is very low. It's hard to generate a short across your heart with current electrical codes. Sure you could burn yourself very badly, or cause muscle damage and soft tissue damage, but death is unlikely.

**Mr Happy** · 02-12-2010, 03:01 PM

It's worth bearing in mind that the electronic muscle stimulators with sticky pads that are sold to increase muscle tone use a pretty low voltage of about 12 V. If that voltage can cause muscle contractions around your body, it is not difficult to imagine it doing the same kind of thing to your heart muscle.

There is always a statistical variation where people are concerned. Just because 99 healthy people are unharmed by an electric shock, it does not prove that 1 person might not have an undiagnosed heart condition or genetic predisposition that causes a fatality.

To be safe, never get glib with electricity.

**Apollo Cree** · 02-12-2010, 03:46 PM