Yeah, car batteries can do about a kiloamp into a dead short so we can treat them as ideal voltage sources for this ‘application’. However, even with wet hands and solid contact, 12 volts is too low to get much current flowing.
Soaking my hands in saturated salt water got my hand to hand resistance down to 10-20kohm (0.5-1ma), which is still at least a factor of 250 above the 40 ohm resistance you’d need to draw 300ma, which is the lower figure wiki gives for DC caused fibrillation. Putting one hand on either terminal didn’t get me so much as a tingle.
I know tingle levels are possible when soaking for longer (hours) and 9v will tingle your tongue (2-4milliamps), but it seems exceedingly hard to get to a dangerous level, considering that most models I’ve seen had the internal resistance of people at hundreds of ohms (350 is the number that sticks in mind). Also nerves are somewhat AC coupled, which brings the fibrillation limit up and makes people push away from the source instead of clinging on.
I guess it might be possible for someone with thin skinned thoroughly soaked hands making good contact and having a poorly shielded sensitive heart, but I’d call it a ‘freak accident’.
It’s worth noting that the reason we use clamps on the ends of the jumper cables is because pressure increases surface area in contact, which decreases resistance for the simple reason of Ohm’s law applied to parallel resistors. (Three 1k Ohm resistors have a parallel resistance of only 333 Ohms. It’s meaningless to give a single figure for copper → wet skin resistance without also giving the surface area for which the figure is valid.)
This means that incidental touching of metal is extremely unlikely to kill anyone, but accidentally clamping your finger, gripping metal tightly, or anything else that applies pressure to your skin will dramatically raise the risk.
Yeah, car batteries can do about a kiloamp into a dead short so we can treat them as ideal voltage sources for this ‘application’. However, even with wet hands and solid contact, 12 volts is too low to get much current flowing.
Soaking my hands in saturated salt water got my hand to hand resistance down to 10-20kohm (0.5-1ma), which is still at least a factor of 250 above the 40 ohm resistance you’d need to draw 300ma, which is the lower figure wiki gives for DC caused fibrillation. Putting one hand on either terminal didn’t get me so much as a tingle.
I know tingle levels are possible when soaking for longer (hours) and 9v will tingle your tongue (2-4milliamps), but it seems exceedingly hard to get to a dangerous level, considering that most models I’ve seen had the internal resistance of people at hundreds of ohms (350 is the number that sticks in mind). Also nerves are somewhat AC coupled, which brings the fibrillation limit up and makes people push away from the source instead of clinging on.
I guess it might be possible for someone with thin skinned thoroughly soaked hands making good contact and having a poorly shielded sensitive heart, but I’d call it a ‘freak accident’.
It’s worth noting that the reason we use clamps on the ends of the jumper cables is because pressure increases surface area in contact, which decreases resistance for the simple reason of Ohm’s law applied to parallel resistors. (Three 1k Ohm resistors have a parallel resistance of only 333 Ohms. It’s meaningless to give a single figure for copper → wet skin resistance without also giving the surface area for which the figure is valid.)
This means that incidental touching of metal is extremely unlikely to kill anyone, but accidentally clamping your finger, gripping metal tightly, or anything else that applies pressure to your skin will dramatically raise the risk.
Upvoted for experimenting!