Dear Friends,
I always insist “while a safetyman advises others on safety issues he is not to assume things and say I think……..” He has to give a definite answer -either yes or no. Often a safety issue becomes a matter of life and death as in the case of a confined space entry or a heavy lift. We can not take chances. We have to be certain in such issues. With regard to electricity also we have to be quite serious. If one is not sure he need not be ashamed to ask for experts/consultants.
As I mentioned electrical engineers are often not trained in safety. For sure they should be trained in safety and CPR. From the replies provided by them you can see where they stand and why they consider DC is more dangerous than AC. It is their opinion only. They are not sure.
The comparison on the effect of DC and AC is attached, (current in milliamperes)
1. AC is more dangerous than DC.
2. If our AC power supply is 220 Volts (RMS) then the actual peak voltage is about 310 V.
(To get same effect of say DC 220 volts we require peak voltage of 310 in AC and we call it AC 220 V.)
3. Interference with the normal rhythm of heart causes the condition called ventricular fibrillation. In this condition fibers of the heart muscles instead of contracting in coordinating manner (which causes heart to act as a pump) contract separately and at different times. When this happens, the heart's lower (pumping) chambers contract in a rapid, unsynchronized way. (The ventricles "flutter" rather than beat.) The heart pumps little or no blood. Blood circulation ceases and (unless proper resuscitation efforts made) death ensues. Heart cannot spontaneously recover from the condition. It is estimated that 50 ma is sufficient to cause Ventricular fibrillation.
4. 1.5 volts, a pen torch cell if touched with your tongue you feel the effect of current.
5. Average resistance of human body is considered as 1000 ohms. Internal resistance 400 – 600 ohms.
6. 6, 00,000 ohms. Skin on the palm of a village blacksmith who never used gloves in his life who can take a heated iron piece with his bare hands and sole of an old man who never used foot wear in his life. Callus – the dead cells or thickened skin on their hands and sole has that resistance.
7. Between the ears we have the least resistance of around 100 ohms only.
8. Minimum voltage required to pass sufficient current to kill a person is around 60 volts.
If the frequency is increased to thousands probably we may not even feel electricity. The normal supply frequency of 50 0r (60 as in USA) is all the more dangerous.
Regards,
Kesava Pillai