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.
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.
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.
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.
On this subject, does anybody know if AC or DC is more dangerous
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.
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.