One of the discussion points for my thesis is the safety when using direct current to transport electricity. Especially when touching cables the risks should be bigger, so I was told.
Is this really true?
Lucky for us, I’m not the first one to have this question. Already in the 1940’s this debate was solved by the only right way. Yes, you thought correct, by testing it on humans.
Charles Dalziel was an American scientist, interested in everything that had to do with electricity, which included safety. To test the effects of electric shock on men, he used the 115 men to test the effects of DC and 167 men to test the effects of AC on the human body and wrote this article about it.
His interesting conclusions were that both systems lead to contraction of the muscles up to the point where the subject looses control, meaning not being able to let go of the conductor the subject is holding. The interesting point of this is that the current needed for this to happen is much lower for AC (between 6 and 24 mA, with an average of 16 mA), than for DC (300 mA on average).
However, a normal power plug kicks out at currents over 16A, meaning that you’ll not be able to retell the story when you stick your fingers in the plug in both cases.
Also, the risks for the heart are very different between the two systems. This is mainly since the alternating current will put the heart into fibrillation (uncontrolled contraction), whereas DC will just put the heart to a standstill, which apparently has a better survival rate (restart use a defibrillator, which uses, surprise surprise, a short DC shock to restart the heart).
Also in this case the current that’s needed to trigger a heart attack turned out to be lower for AC (2s 50mA) vs. DC (2s 150mA). However, when a current of 500mA is flowing through the body, the heart attack takes place after 0,2s for both systems
So, we can simply conclude from here that both systems are dangerous (so don’t try the experiment at home), but that the DC system shows to be hazardous only at a higher current compared to AC.
+1 for DC.
Header photo: Determination of the let-go current. Fig 10a, Dalziel, 1956