thumb and index finger

[izak]

what is the story behind the human body being able to tolerate voltage from the thumb to the index finger without serious results?
i have seen this adressed on several occasions, and i guess im looking for some kind of medical or physiological explanation to this...

anyone got any ideas?

 

[rattus]

Re: thumb and index finger

Zak, if the thumb and finger are on the same hand, only a tiny current flows through the heart. However, if the thumb and finger are on opposite hands, a much greater current flows through the heart, and then you have big trouble.

My first shock came when I stuck my thumb in a lamp socket--I was a mere child then. The current was concentrated in my thumb, no big deal I thought. I have been nipped many times since, but I have avoided the bad stuff.

 

[augie47]

Re: thumb and index finger

My first shock came when I stuck my thumb in a lamp socket--I was a mere child then.

rattus: me too...even though some of the guys I work with don't think there was electricity when I was a child....
as I recall, I was sitting on a grounded heating register at the time...don't guess anyone wants to address that curent flow

 

[bphgravity]

Re: thumb and index finger

Here's the problem. Most that have a general understanding of shock and the effects of current on the body assume that currents smaller than that which will trip a Class A gfci device will be relatively harmless to a person.

In most cases, this true. Most persons can release themselves from a current of upwards of 6 mA. However, the heart has a vulberable period for about 20% of the cardiac cycle. This is the period when the heart receives the natural electrical signal from the nervous system as to what it is supposed to do. These natural currents are in the order of .1 mA. Any disruption of this signal can result in a loss of heart function or worse, ventricular fibrillation.

Its simply not worth the risk nor makes any sense to test for voltage in this manner.

 

[bthielen]

Re: thumb and index finger

It seems to me that the answer to this question has a lot to do with the voltage applied. At what level of voltage potential applied between the tip of the thumb and the tip of the index finger will one be exposed to a current level capable of serious damage to the hand? Current doesn't have to flow through our heart to cause damage.

Bob

 

[pierre]

Re: thumb and index finger

The practice of using the thumb and forefinger started early, before testers were readily available (readily available meant cost and stocked by suppliers). Now that testers are readily availabe, this practice needs to be stopped. I do believe that it has dwindled down considerably, and as more old timers pass from the industry, it will mostly disappear.

 

[rattus]

Re: thumb and index finger

With some it is the macho thing to do, and nothing will stop them until they burn their fingers off doing something foolish.

If you misplace your tester, your thumb and finger are always handy--get it boy? Handy!

 

[al hildenbrand]

Re: thumb and index finger

Originally posted by izak:
what is the story behind the human body being able to tolerate voltage from the thumb to the index finger without serious results?

I've seen this used almost exclusively on 120 V 60 Hz circuits. The higher the voltage, and the faster the rise time on the voltage, the greater the likelyhood of pain and injury.

The practitioner of this type of voltage detection must first be in no other electrical connection with any point on their body (not trivial), and must have dry fingers and touch the live points lightly. As one increases pressure, the sensation of the voltage increases. The dry skin and light pressure results in a high impedance path through the thumb and finger. When done correctly the starting impedance will be in the 100 K &#8486 range. It is real easy to not do this correctly, as few attain a level of every minute zen that will support the controlled conditions needed to avoid mishap. . .

Edit spelling - Al

[ November 11, 2005, 12:01 PM: Message edited by: al hildenbrand ]

 

[realolman]

Re: thumb and index finger

... through the thumb and finger. When done correctly the starting impedance will be in the 100 K . .

I like that... when done correctly
Is this a great forum or what?


[ November 11, 2005, 03:50 PM: Message edited by: realolman ]

 

[bphgravity]

Re: thumb and index finger

I really wish we would not continue with this discussion. There is really no merit or value in discussing just how dangerous something that is incredibly dangerous and stupid is. I find it very irresponsible and don't think there is place on this Forum for this. Too many people of unknown qualifications and understanding of electricity visit this Forum and read the posts. I just don't think we should be implying there are ways to do something like contacting energized parts in a safe way.

 

[iwire]

Re: thumb and index finger

I agree with Byran, there is no reason to even talk about this in the open.

If the old timers want to continue maybe they could use PMs.

 

[petersonra]

Re: thumb and index finger

I can't even imagine why someone would do such a thing. A volt meter is not all that expensive compared to your life.

 

[rattus]

Re: thumb and index finger

Bob, a neon tester is even cheaper, and it fits nicely in a shirt pocket.

I think none of us is advocating this method, but it is important to understand the dangers.

 

[jimwalker]

Re: thumb and index finger

You can buy a voltmeter for as little as $5 .Why take a shock when its so simple not tne day you might get more than you wanted

 

[pierre]

Re: thumb and index finger

Before purchasing and then using a $5 meter/tester, you should take a look at this.

http://us.fluke.com/usen/Home/Search.asp?txtSearchBox=meter+safety#

Click on Application notes when you get there.

[ November 12, 2005, 03:01 PM: Message edited by: pierre ]

 

[charlie b]

Re: thumb and index finger

Originally posted by izak: what is the story behind the human body being able to tolerate voltage from the thumb to the index finger without serious results?

During a previous life, I worked in the nuclear generation industry. I recall that the limits for radiation exposure to "extremities" (meaning hands and feet) were much higher than the limits for radiation exposure to the whole body. The reasoning, as I remember it, was that the hand is not as vital an organ as, say, the liver.

Perhaps something alonge these lines is what is meant by "without serious results."