When I was in apprenticeship, they taught us that 50 milliamps was enough to stop your heart. When I quoted that the other day, an engineer corrected me by saying that it was 5 milliamps. We both volunteered our confidence in our figures, so I was wondering if the figure had changed.

I was always taught that 100 mA would do you in. Here is a link to a website that talks about the effects of current on the heart.

http://www.tpub.com/neets/book2/5j.htm

It is dependent of the body's resistance and the voltage (determines amperage) and the level of luck the victim has. This is why some die from the slightest shocks and others get the snot shockout of them and live.

A lot depends on the path through the body. A shot down your leg hip to foot is not nearly as dangerous as one from hand to hand or directly into your chest (the reason pool lights need to be 18" underwater).
Of course a small shot through one finger can kill you if you fall off the ladder.

You do not even need to be shocked. You can be the unlucky one at the bottom of the ladder when the sparked sparkie gets it in the finger...

5ma will not stop your heart. 5ma is "safe", which is why GFCI is set to not allow any more than that.

Just like radiation levels, there is no actual current level that is garunteed to kill you- but at somewhere around 20-100ma through your heart, it will stop beating properly. In this range, muscle action is also inhibited, preventing the victim from escaping the shock.

FYI, there was a man once killed himself with a 9V battery during a classroom exercise. He pierced his skin with the ohmeter probes, lower the contact resistance to the point where he recieved a lethal shock through his heart. It does not take much!

"one hand rule", anyone?

5mA is generally considered the 'annoying shock' level, where you feel it, but no real harm results. As others have mentioned, nothing is certain in this world.

The electrocution I witnessed - breathing and heart stopped cold, WAS able to re-start manually - was almost certainly at a very low current level. The current exited the mans' temple ... apparently causing the brain to shut down. This path would call for much less current that 'through the heart.' Through means not quite understood by medicine, the body actually does a pretty good job of directing current around the heart.

Not to be a doubting Thomas here, does anyone have any actual info on the 9volt battery story? I do believe it is and urban myth but I am not sure. I could go to these sites like snoops.com (I think that it is what it is called) but It would take away from my time here.

I'm skeptical too, but I swear I read at as confirmed on snopes... Can't seem to find it, though, and Darwin considers it "unconfirmed", which probably means "********":
http://www.darwinawards.com/darwin/darwin1999-50.html

Well, the math is reasonable and it's completely plausible, like something one of us would do in a lab. I would not try this at home.

I believe it was a USN sailor in electricians Mate "A" school. I think it was after learning about "internal resistance" with respect to batteries.

Larry C

Our Safety Trainer has always stated that the number is close to 50 milliamps to stop your heart. The path thru your body definitely matters as to if your heart is affected by the shock. A shock from hand to hand, is alot worse than from the fingers to the forearm of an arm. Also, if the skin is wet or dry affects the severity of a shock. As wet skin conducts much better than dry skin.

I found the following on the OSHA website.
http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html

Current level (in milliamperes) Probable effect on human body
1 mA Perception level. Slight tingling sensation. Still dangerous under certain conditions.

5 mA Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.

6-30 mA Painful shock, muscular control is lost. This is called the freezing current or "let-go" range.

50-150 mA Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible.

1000-4300 mA Ventricular fibrillation (the rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely.

10,000 mA Cardiac arrest, severe burns and probable death.

Bob

Coincidently regarding the 9 volt battery. I was very surprised yesterday when I took a 9 volt battery off the truck because I was going to change out the old one in my tracer. I put it in my pocket and then locked up the truck and put my keys in the pocket. I went upstairs and all of a sudden my pocket started feeling real hot. I reached in and pulled out my keys and evidently the clip that holds them together had crossed the terminals on the battery and it was very hot. Never had that happen before.

That happend to me once. It scared the poo-poo out of me.

Yes it was, I was in the Navy when this happened and we all had to read about the incident.

If you want to talk about the effects of current flow through the human body you need to define all of the other factors.

AC or DC
Hz?
Path
Time
Voltage
Male or Female
Body weight
Body resistance (Determined by moisture level, contact area, and pressure)

The IEC did some resaerch at the U of IL back in the late 60's, they had volunteers willing to take electric shocks. From that some basic values were published.

A LV AC(60hZ) shock of an average weight (Was 140lbs in 1968) male for 1/2 second will cause

1mA - Sensation of shock (Like a 9V Battery on your tounge)
2-10mA - Mild shock not painful, still maintain muscle control
10-20mA - Loss of muscle control, AC causes muscles to contract, can cause you to clench down on the conductor and not be able to let go, the increased pressure causes body resistance to go down, so current goes up, time becomes a factor because fibrilation can occur at these levels if the duration is long enough, if not removed from circuit this can be a fatal shock. this is why most electricians are taught to touch things with the back of thier hand. (DC no let go currents are closer to 75mA)
20-50mA - Lungs collapse - causing victim to pass out due to lack of O2 many times
50-100mA - 5% chance to go into Ventricular Fibrilation
100-200mA - 95% chance to go into Ventricular Fibrilation
(Someone earlier said 100mA is the fatal current, if I had to pick 1 value to answer this question, it would be 100mA, however there are several other factors, it is not really a question that can be answered with a simple current level)
>200mA - I2R heating of the conductive parts of the body (circ and nervous system) are damaged, there are no degrees of electrical burns, all electrical burns are 3rd degree because the cook you from the inside out, nerves are also damaged causing permanant damage.

5ma is considered a safe level for adults, but infants and toddlers can be killed at this level. I do not know the reasons.

On this subject, does anybody know if AC or DC is more dangerous, or is there a difference at all. It seems that, just by having been hit by AC so many times, that AC is the kicker.

The body uses AC as its internal nervous signaling system and muscle actuation. This would include the heart. It also seems to me that the difference in frequency and added voltage of AC would throw the body into much more distress than the same voltage in DC.

Any thoughts? Any facts?

AC is dangerous at lower currents than DC

AC has the "advantage" of having a current zero at every 2 sine wave "crossings" per cycle, as if that will help, but with DC, you don't have a chance to let go!.
DC will make all of your muscles tense and I mean ALL of them.
DC is what is used to tenderise cattle in slaughter-houses.

There are a few things to consider here.

1st, the #1 cause of death from electric shocks is ventricular fibrilation, around 100mA or so (Depending on several factors) of 60hZ AC will cause the heart to go into fibrilation, to survive usually the victim will need, drum roll.... a DE-fibrilator, which uses DC to stop the heart, after the heart has stopped CPR is more effective and many times the heart starts beating normally again. This makes SC more dangerous.

2nd- AC has a skin effect, meaning the center of the conductor is not used, think of the curretnt flow cross section looking like a donut. DC uses the entire cross section of the conductor, now when that conductor is an arm or a leg the center of the "conductor" is bone (Poor conductor) which increases the effective resistance of the limb for DC compared to AC that flows around the bone and through the circulatory system and nervous systems, both of which are excellent conductors. Another reason AC is more dangerous.

3rd - the biggest factor in determining how much damage is done by a current flow is duration. For AC it takes about 10-20mA to cause a loss of muscle control, and AC causes the muscles to contract (Hence the time honored practice of using the back of your hand), so with AC, at around 15mA or so you can become stuck on the circuit and then duration increases, many times you will be stuck until someone kills the power. DC is very different, it takes around 75mA of DC to cause a loss of muscle control, and it causes your muscles to stiffen, rather than contract like AC does, so it is very hard to get hung up on a DC circuit. The 3rd and last reason AC is more dangerous than DC.

However, speaking from experience, DC hurts more.