Why Does 32V AC Pose More Risk Than 32V DC for Electric Shock and Injury?

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Why can 32 V AC be more dangerous than 32 V DC for electric shock, especially for causing ventricular fibrillation?

AC is more dangerous than the same nominal DC voltage because it can trigger ventricular fibrillation at much lower current, around 60 mA for 60 Hz AC versus about 300–500 mA for DC [#21660344][#21660347] The main factor is current through the body, since voltage is what pushes that current [#21660350] Also, 32 V AC is usually an RMS value, so its peak is about 45 V, which is not the same as 32 V DC [#21660349][#21660350] One reply notes that DC can cause muscle lock-up instead, and the heart may restart after the current is removed, while AC reverses 50 or 60 times per second and is more likely to disturb the heart’s rhythm [#21660347] Even low voltages can be dangerous if the current path crosses the heart, because much of the body’s resistance is in the skin and internal tissue can be around 500 ohms [#21660347]

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#1 21660343 15 Dec 2011 18:16

Richard Bosanquet Richard Bosanquet

Anonymous

Post #1
21660343 15 Dec 2011 18:16

Hi all
In my text book is says : contact with voltage as low as 32v ac or 115v dc can lead to asphyxia , ventricular fibrillation etc
My question is why does it matter if it is ac-dc ? If 32v ac can hurt wouldn't 32v dc do the same damage ?

Just started studying so sorry for the stupid question
Thanks

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#2 21660344 15 Dec 2011 18:29

Cody Miller Cody Miller

Anonymous

Post #2
21660344 15 Dec 2011 18:29

It has been shown that to cause fibrillation which leads to cardiac arrest, that it takes less AC current to do so than DC current. "60 mA of AC (rms, 60 Hz) or 300–500 mA of DC can cause fibrillation":http://en.wikipedia.org/wiki/Electric_shock
#3 21660345 15 Dec 2011 18:32

Richard Bosanquet Richard Bosanquet

Anonymous

Post #3
21660345 15 Dec 2011 18:32

Is that because alternating current is causing more damage on the heart ?
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#4 21660346 15 Dec 2011 18:33

Cody Miller Cody Miller

Anonymous

Post #4
21660346 15 Dec 2011 18:33

Yes...It sounds like it causes more tissue damage.
AC more dangerous due to fibrillation risk
#5 21660347 16 Dec 2011 00:36

Steve Greenfield Steve Greenfield

Anonymous

AC more dangerous due to fibrillation risk
Post #5 21660347 16 Dec 2011 00:36

I don't think it is damage, I think it is that it causes fibrillation because it is reversing 50 or 60 times a second.

A DC current can cause the muscle to lock up, and the heart may restart after the current is removed.

When a doctor tries to restart your heart, they use a big pulse of current in one direction, not AC. The idea is to cause the non-coordinated fibrillating heart muscle cells to all lock up for a moment, then naturally restart together.

That Wikipedia page agrees with my testing, in that most of your body's resistance is in the skin and the internal tissues can be around 500 ohms, depending on where and how deeply you puncture. At 5V, that is 10mA, which as the Wikipedia page points out can be lethal if the current is directed across the heart.

Fortunately it is highly unlikely that you'll somehow puncture one hand on your computer's 5V or 12V buss while simultaneously puncturing the other hand or opposite foot on a ground.
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#6 21660348 16 Dec 2011 01:04

Richard Bosanquet Richard Bosanquet

Anonymous

Post #6
21660348 16 Dec 2011 01:04

Haha
Thanks guys for ur answers
Richard
#7 21660349 16 Dec 2011 05:48

BHARADWAJ ACHARYA BHARADWAJ ACHARYA

Anonymous

Post #7
21660349 16 Dec 2011 05:48

When you say 32v ac it means RMS value . So the peak value would be 1.414 tmes of rms voltage , well that shoots up the voltage !! So 32v Dc is not same as 32v Ac.
#8 21660350 16 Dec 2011 09:32

Steve Greenfield Steve Greenfield

Anonymous

Post #8
21660350 16 Dec 2011 09:32

Good point, but 32Vrms x 1.4 ~ 45Vpk, hardly 115Vdc.

It is the current that determines damage. Voltage is required to push the current.
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#9 21660351 16 Dec 2011 11:20

BHARADWAJ ACHARYA BHARADWAJ ACHARYA

Anonymous

Post #9
21660351 16 Dec 2011 11:20

True! Current determines the damage so will be the voltage! Current and voltage are two Different things , we may argue Voltage is directly proportional to current (Ohms law) .
The 10v Dc may be Small to cause a current in the body , but the 5amps(say) it is producing is enough to give the body a shock!!
#10 21660352 22 Dec 2011 21:35

bob Lin bob Lin

Anonymous

Post #10
21660352 22 Dec 2011 21:35

Thanks for sharing!
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Topic summary

The discussion explains why 32V AC poses a greater risk of electric shock and injury compared to 32V DC. AC current at typical mains frequencies (50-60 Hz) can cause ventricular fibrillation at much lower currents (around 60 mA RMS) than DC, which requires significantly higher currents (300-500 mA) to induce fibrillation. This is because AC reverses direction multiple times per second, disrupting the heart's electrical signals and causing fibrillation, whereas DC tends to cause muscle contraction or "locking" without fibrillation. Additionally, 32V AC is usually specified as an RMS value, meaning its peak voltage is about 1.414 times higher (~45V peak), increasing its potential to drive harmful current through the body. The severity of electric shock depends primarily on the current flowing through the body, which is influenced by voltage and body resistance (typically around 500 ohms internally). Lower voltages like 5V or 12V DC are generally safer due to insufficient current to cause lethal effects. Medical defibrillation uses high-energy DC pulses to reset the heart rhythm, not AC. Overall, AC is more hazardous at lower voltages due to its alternating nature and higher effective peak voltage compared to DC at the same RMS voltage.
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Why Does 32V AC Pose More Risk Than 32V DC for Electric Shock and Injury?

Why Does 32V AC Pose More Risk Than 32V DC for Electric Shock and Injury?

Why can 32 V AC be more dangerous than 32 V DC for electric shock, especially for causing ventricular fibrillation?

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