Some time back, I think on BBC, they carried out an experiment on the man in the street. A box with a red button on top, a cameraman, a sweet young lady with a microphone who asked people passing if they would like to take part in a 'scientific' experiment to test when they could feel an electric tingle! They kept the button pressed as long as they could as the voltage was increased in increments. Conductive button, one hand, other hand on the box, (this is year's back so details little fuzzy). The object was to check on people's sensitivity via skin resistance. The insulation resistance of people's skin depends not just on moisture or sweat glands but on depth of nerve endings under the epidermis, the dead layers of skin.Turned out that the sensitivity to feeling of a mild tingle ranged from 12-15 volts up to 600 volts. Test was very subjective but a general cross section of people on the street. I personally have 'ruddy' complexion, a sign of thin epidermis, <30 layers. A thick skin, especially on hands and soles of feet can be many layers thicker. My experience with feeling electric effect is that I can sense as low as 15-20 volts DC on back of hand. Single cell 1.5volt on tip of tongue. Once had 630 volts pulsed DC hand to hand, capacitor discharge, 0.1uf non resistance limited, very painful, Ouch! On Jun 7, 2017 2:54 AM, "Neil Benson" wrote: > Thankyou very much, Sean. > > This is the info I was after. > > On Tue, Jun 6, 2017 at 11:37 PM, Sean Breheny wrote: > > > For anyone wanting to read more in depth about this, beyond what is > > available on the web, one good book is: > > > > https://www.amazon.com/Applied-Bioelectricity-Electrical-Stimulation- > > Electropathology/dp/0387984070 > > > > It has a lot of data from experiments done on volunteers (!) in the ear= ly > > 20th century. Those experiments only went up to the "no let go" point > > (thank God!) but they reveal a lot about what variables affect the > severity > > of an electric shock. > > > > > > On Wed, Jun 7, 2017 at 12:31 AM, Sean Breheny wrote: > > > > > The body is roughly a "bag" of moderately-conductive (10 to 100 ohms > > point > > > to point) liquid with a decently insulating outer coating (stratum > > corneum > > > of the skin) which has tiny holes in it. Sweat can provide a conducti= ve > > > path through these holes (sweat ducts), although the resistance is > fairly > > > high because the hole diameter is small and the density of holes isn'= t > > very > > > high. > > > > > > There is also capacitance across the skin and within the > > > moderately-conductive fluid inside. This does allow AC to cause more > > > current flow than DC. > > > > > > The water in the tub is also only moderately conductive. When the > > contacts > > > from the cord get immersed, there is a distributed current flow throu= gh > > the > > > water and (if you are in the water) through you. The large contact ar= ea > > of > > > the water (with dissolved ions) and your skin means that many of the > > sweat > > > ducts are in contact with the water and the overall resistance offere= d > by > > > the skin is reduced. At this point, you essentially look like an equa= l > > > volume of impure water and become part of the current path. > > > > > > Likewise, it is MUCH easier to be killed or injured by low voltages i= f > > you > > > break the skin and allow direct contact with the fluid inside. 9V cou= ld > > > definitely kill you given the proper attachment points to direct the > > > current flow through vital organs. > > > > > > Higher voltages quickly cause breakdown of the skin due to heating an= d > > > electrochemical effects from the high current density in the tiny swe= at > > > ducts. After the breakdown the current grows to a value only limited = by > > the > > > internal 10 to 100 ohm resistance and often causes burns. > > > > > > The nerves are the most sensitive to electrical disruption since they > > rely > > > on electrochemistry to send signals and they normally work with only > 10s > > of > > > millivolts of signal. Current flow through nerves causes pain and als= o > > > muscle contraction. Higher current levels can also directly stimulate > > > muscle contraction. DC tends to cause continuous contraction. AC tend= s > to > > > cause vibration and loss of voluntary control. > > > > > > A current path through only a limb is likely to be painful but not > > > permanently damaging unless it causes thermal damage or nerve damage. > > Very > > > violent muscle contraction can also tear muscles or tendons/ligaments= .. > > > Thermal damage can rupture blood vessels if the current is very high. > > > > > > A current path through the brain will often cause an immediate seizur= e > > and > > > can lead to nerve damage in the brain. Death can result - especially = if > > the > > > brain stem is affected. > > > > > > A current path through the heart will often cause a disruption in the > > > rhythm which can degenerate into ventricular fibrillation. > > > > > > A current path through the abdomen can paralyze the diaphragm muscles > and > > > prevent breathing. > > > > > > Generally, due to the increased impedance (no capacitive effects) and > the > > > slightly reduced disruption of nerves due to continuous rather than > > pulsed > > > stimulation and also the greater chance of a muscle contraction > throwing > > > you away from the source of the current, DC is somewhat safer. > > > > > > For DC current, about 1mA is the threshold of perception and also > > > generally considered a maximum acceptable safe level. 10mA is quite > > > painful. 20mA can cause some muscle paralysis which may make breathin= g > > > difficult and may make it impossible to let go. Around 50mA is where > > death > > > is possible, but 100mA is considered the point where ventricular > > > fibrillation is likely if the current path is right for it. > > > > > > For AC, I've seen various figures but it seems like AC is about 3x > worse > > > than DC when you consider the RMS current value of the AC (peak value > is > > > about 40% higher). So, 300uA can be felt, 3mA hurts but is unlikely t= o > > kill > > > you. 6mA can cause inability to let-go. 20 to 30mA is where things ge= t > > > really dangerous and 50mA is likely to kill you if untreated. > > > > > > As you can see, if the skin is broken, only 5V is needed, under optim= al > > > conditions, to produce 50mA with a point-to-point body resistance of > > about > > > 100 ohms. > > > With the skin intact, it depends greatly on the contact area, contact > > > pressure, how much sweat is present. The effect is also very non-line= ar > > > because there is a positive feedback effect that more current causes > more > > > heating which causes lower resistance due to skin beginning to break > > down. > > > > > > > > > On Tue, Jun 6, 2017 at 11:18 PM, Neil Benson > wrote: > > > > > >> My question is the HOW of electrocution: my understanding is that > while > > >> standing in a grounded tub of water, if a live extension cord is > dropped > > >> into the tub--I die. > > >> > > >> What is the physiology? (I can understand sterilization), why death= .. > In > > >> fact, why anything? Is the body CAPACITANCE so large that significan= t > > >> current flows? In this case I would not expect that the tub needs to > be > > >> grounded. > > >> > > >> Is DC safer? > > >> > > >> I've read the story of a guy killed when he attached a 9 volt batter= y > > >> between his hands--INTERNALLY, not just surface. But is DC safer in > the > > >> 'standing in water' case? > > >> > > >> I'm aware that most forums prohibit health advise (other than: See a > > >> doctor), so this is a science question. > > >> > > >> > > >> > > >> On Tue, Jun 6, 2017 at 9:28 PM, John Gardner > wrote: > > >> > > >> > ...will his genes be passed on to another generation? > > >> > > > >> > They got this far - Probably more involved than one idiot... > > >> > > > >> > On 6/6/17, Sean Breheny wrote: > > >> > > The worst electrical shock I've gotten was from plugging in an > > 120VAC > > >> > cord > > >> > > which had a single strand of the stranded line cord sticking out > > where > > >> > the > > >> > > plug met the cord. This was outdoors and I was standing barefoot > on > > >> > > concrete. > > >> > > > > >> > > A close second was the time I was doing ESD testing at 15kV, was > > >> > > accidentally touching the unit under test AND was holding the > ground > > >> clip > > >> > > against a bolt in the floor to ground it (and happened at that > > >> instant to > > >> > > have unknowingly lost contact with the bolt). So, it was a direc= t > > >> > > across-the-chest hand to hand 15kV shock, thank God it was from > > just a > > >> > 1nF > > >> > > capacitance or I'd be dead. Definitely woke me up! > > >> > > > > >> > > I also once had a funny experience where two of us were debuggin= g > a > > >> motor > > >> > > drive which used 20kHz, 50V PWM. We were feeling around the PCBA > on > > >> the > > >> > > tops of components to feel how warm things were getting. My > coworker > > >> > asked > > >> > > why a particular IC was getting so very hot when it wasn't > supposed > > >> to be > > >> > > a major heat dissipating component. I also went to feel that par= t > > and > > >> > > initially it didn't feel warm but I moved my finger a bit and it > > >> suddenly > > >> > > felt very hot. After more investigating I discovered that it > wasn't > > >> hot > > >> > but > > >> > > it was right next to an exposed terminal which was connected to > the > > >> PWM. > > >> > If > > >> > > your finger happened to touch that adjacent terminal, it produce= d > a > > >> > > sensation unlike any other AC or DC electric shock I've ever fel= t. > > It > > >> > felt > > >> > > just like touching a hot object. I guess the high frequency > caused a > > >> > > different kind of nerve stimulation. > > >> > > > > >> > > > > >> > > > > >> > > On Tue, Jun 6, 2017 at 6:18 PM, James Cameron > > >> wrote: > > >> > > > > >> > >> Either way, he was electrocuted by his choice to use his phone, > and > > >> > >> that matches an anticipated narrative, feeds the fear, and is > > >> > >> therefore good click bait. We should expect no less from story > > >> > >> writers and editors because that's how they are funded. > > >> > >> > > >> > >> I'm reminded from my own experiments that submerging is not > > required; > > >> > >> condensation is enough to make a path. > > >> > >> > > >> > >> -- > > >> > >> James Cameron > > >> > >> http://quozl.netrek.org/ > > >> > >> -- > > >> > >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archiv= e > > >> > >> View/change your membership options at > > >> > >> http://mailman.mit.edu/mailman/listinfo/piclist > > >> > >> > > >> > > -- > > >> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > >> > > View/change your membership options at > > >> > > http://mailman.mit.edu/mailman/listinfo/piclist > > >> > > > > >> > -- > > >> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > >> > View/change your membership options at > > >> > http://mailman.mit.edu/mailman/listinfo/piclist > > >> > > > >> -- > > >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > >> View/change your membership options at > > >> http://mailman.mit.edu/mailman/listinfo/piclist > > >> > > > > > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .