2. Electrical Safety

The rapid expansion of the air creates a wavefront

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Unformatted text preview: – 10 mA Let- Go threshold Above 15 mA Respiratory paralysis Above 50 mA Ventricular fibrillation Above 50 mA Muscle paralysis Above 500 mA Can stop the heart Figure 2- 1. The effects of external electric currents on the human body. The Let- Go threshold is one of the least intuitive and the most dangerous effects of electricity. When excited by external electric currents exceeding this threshold, the muscles on the inner side of the human hand involuntarily contract so that the person clenches his/her fist and cannot open it until the electrical excitation is removed. It means that if you accidentally touch a “hot” wire with your palm so that the current starts flowing through your body, your hand will grasp this “hot” wire and you will find yourself incapable of letting go of it. The professional jargon expression is that the person “froze on the circuit.” <Sidebar> When the external electric current exceeds the Let- Go threshold (7 – 10 mA), it causes the human to clench his/her fist until the electric excitation is removed. This is an extremely dangerous and potentially lethal condition. This is an extremely dangerous situation, because, as the current keeps flowing, it causes more and more harm, and eventually gets lethal. To avoid being trapped, experienced electricians first touch the suspicious wire with the outer side of the hand so that if the fist gets clenched the hand will not hold the wire. Moreover, the muscular paralysis caused by electric current does not end immediately after the source of excitation was removed: it may take a few minutes © 2013 Alexander Ganago Page 5 of 28 Last printed 2013- 07- 07 12:28 AM File: 2013 EEW 1- 02 Electrical safety.docx Engineering in the Electrical World (EEW) Part 1 Unit 2: Electrical safety until the person regains control of his/her body. Therefore, Tasers and other “stun guns” can immobilize the person for several minutes. The exact magnitude of the current at the Let- Go threshold is reportedly higher for males than for females, widely varies among individuals, and depends on the frequency of the electric voltage. Ironically, the Let- Go threshold is the lowest (see the numbers in Figure 2- 1) at the frequencies, which are chosen for industrial and household...
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This note was uploaded on 12/06/2013 for the course EECS 314 taught by Professor Ganago during the Fall '07 term at University of Michigan.

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