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Name: michael
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 1999-2001


Question:
All things being equal, which is more harmful to the human body. AC or DC? ALL THINGS BEING EQUAL. (length of exposure, amps, voltage, area involved, etc...) The important thing here is which one is the most damaging (causes more harm)or is more fatal.


Replies:
It depends on the frequency of the AC. All AC is not equal. It's also hard to directly answer your question, because we can't experiment with electrocuting human subjects. The "let-go" current is the best experimental measure we have of the effect of electricity on humans. The "let-go" current is the lowest level of current passing through a human subject through an electrode held in the hand that makes the subject unable to open his hand and drop the electrode. (From what I understand, the experiment hurts, but it isn't permanently damaging to the subject.)

It turns out that the "let-go" current starts at some finite value at a frequency of zero (DC), passes through a minimum, and then increases as the frequency gets higher. (At high frequencies, the only known harm from AC is the resistive heating of the subject's tissues.) This means, that, using "let-go" current as the measure of hazard, there is a frequency of AC that is more dangerous than others. Ironically, this most dangerous frequency is around 60 Hertz, which is the frequency of the AC supplied by electric utilities in the US.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois


This is a very general question since it does not discern between the possible harmful secondary effects of the electrical source EMF and is not clear whether it is referring just to electrocution. I will briefly respond to just the electric shock difference between the two.

The amount and kind of injury depends on six things - voltage, amperage, resistance, type of current, path of current, and duration of exposure.

Voltage is a measure of electrical force. The greater the voltage, the greater the tissue damage. Voltage typically ranges from a house current of 120 volts to a high-tension wire current of 1,000 volts or more.

Type of current means whether the charge is AC or DC. Lightning is a direct current (DC) which possesses much stronger voltage than a high-tension wire. Generated electricity packs far less power and is an alternating current (AC).

In humans, since AC is an alternating current, if a person is shocked by AC they will be seen to be shaking in sympathy with the frequency of the alternating current. If the current passes through the heart, by a person holding a live wire in their left hand and their right foot is in water and not their left, then there is a much greater chance the current will effect the pacemaker of the heart and possibly cause fibrillation (where the heart pumps little to no blood). DC current, tends to jolt the person with no shaking but still can have the same effect in that if the current runs through the heart it can have serious consequences. In both these situations the amount of current is of course very important.

Amperage is the flow of the current and, when combined with voltage, is what causes the most damage. The greater the amperage, the greater the damage to tissue.

Peter F



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