The effects of both on the human body differ, but one is more hazardous than the other.
No matter what, if either AC or DC comes in contact with the human body, it can be hazardous. The actual effect varies, though, as it depends upon several different factors, including the amount of current administered, duration of which it was in contact with the body, pathway of the current, voltage applied, and impedance of the body itself.
All of that being said, if it comes down to one or the other, AC can generally be viewed as the more dangerous of the two currents — here’s why:
1) To start off, in order for both currents to have the same effect on the human body, the magnitude of DC flow of constant strength needs to be two to four times great than AC; that is, more DC current is needed to induce the same amount of physical damage as AC current. This is because the effect of the currents on the body is a direct result of the excitatory actions of its magnitude — specifically, the actual making and breaking of the current itself. Such excitatory actions include nerve / muscle stimulation, induction of cardiac atrial or ventricular fibrillation, and more.
For DC to produce the same effect as AC on the human body, its flow of constant strength must be two to four times that being administered by the AC.
2) When death by electric shock occurs, it’s typically due to ventricular fibrillation, and the likelihood of a human suffering this sort of life-ending injury is much higher when coming in contact with an AC than a DC due to the fact that the human body’s threshold of DC-caused ventricular fibrillation is several times higher than for AC.
3) Generally speaking, the human body’s impedance is higher for DC, and it only decreases when the frequency increase. As such, the severity of electric shock is less when in contact with DC than it is with AC.
4) It’s easier to let go / remove contact with “live” parts in the case of DC than AC. This runs counter to the popular belief that because the alternating cycles of an AC current pass through zero, the individual is afforded enough time to pull their limb / body away from the part itself, whereas with the constant flow of the DC current, there is no frequency oscillations that afford the brief moment for the person to pull their body away. The basis for this argument can be sourced in the “let-go” experiment, which was reported in the same aforementioned IEC publication 60479. In it, the lowest level of current that could safely pass through a human body was administered through an electrode held in a test person’s hand; it was enough current to make the person unable to open his hand and drop the electrode.
Without getting into all of the details of the actual experiment, the conclusion was that the test subjects found it easier to release the electrode when DC was administered rather than AC.
Now, while it can be surmised that AC is more dangerous than DC, the safest solution is to avoid contact with any and all high-voltage electrical conductors, no matter the type of electrical current. As mentioned at the beginning of the article, any contact with an electrical current can be hazardous.
No matter what, if either AC or DC comes in contact with the human body, it can be hazardous. The actual effect varies, though, as it depends upon several different factors, including the amount of current administered, duration of which it was in contact with the body, pathway of the current, voltage applied, and impedance of the body itself.
All of that being said, if it comes down to one or the other, AC can generally be viewed as the more dangerous of the two currents — here’s why:
1) To start off, in order for both currents to have the same effect on the human body, the magnitude of DC flow of constant strength needs to be two to four times great than AC; that is, more DC current is needed to induce the same amount of physical damage as AC current. This is because the effect of the currents on the body is a direct result of the excitatory actions of its magnitude — specifically, the actual making and breaking of the current itself. Such excitatory actions include nerve / muscle stimulation, induction of cardiac atrial or ventricular fibrillation, and more.
For DC to produce the same effect as AC on the human body, its flow of constant strength must be two to four times that being administered by the AC.
2) When death by electric shock occurs, it’s typically due to ventricular fibrillation, and the likelihood of a human suffering this sort of life-ending injury is much higher when coming in contact with an AC than a DC due to the fact that the human body’s threshold of DC-caused ventricular fibrillation is several times higher than for AC.
3) Generally speaking, the human body’s impedance is higher for DC, and it only decreases when the frequency increase. As such, the severity of electric shock is less when in contact with DC than it is with AC.
4) It’s easier to let go / remove contact with “live” parts in the case of DC than AC. This runs counter to the popular belief that because the alternating cycles of an AC current pass through zero, the individual is afforded enough time to pull their limb / body away from the part itself, whereas with the constant flow of the DC current, there is no frequency oscillations that afford the brief moment for the person to pull their body away. The basis for this argument can be sourced in the “let-go” experiment, which was reported in the same aforementioned IEC publication 60479. In it, the lowest level of current that could safely pass through a human body was administered through an electrode held in a test person’s hand; it was enough current to make the person unable to open his hand and drop the electrode.
Without getting into all of the details of the actual experiment, the conclusion was that the test subjects found it easier to release the electrode when DC was administered rather than AC.
Now, while it can be surmised that AC is more dangerous than DC, the safest solution is to avoid contact with any and all high-voltage electrical conductors, no matter the type of electrical current. As mentioned at the beginning of the article, any contact with an electrical current can be hazardous.
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