2. Electrical Safety

60 hz vs 10 khz individual body chemistry why is

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Unformatted text preview: ric arc, which is a discharge of electricity through air or another gas, involves extremely high temperatures (up to 50,000 K), which ignite all types of clothing fibers; the heat energy can kill and injure personnel at surprisingly large distances, 30 feet or more from the discharge. Even low- voltage systems have significant arc hazard if they can produce high currents: for example, a 12- V car battery can produce currents up to 300 A, which can cause an arc. <Sidebar> Electric arc is a powerful discharge through the air that can occur at low voltages such as 12 V produced by a car battery; it involves extremely high temperatures that ignite all clothing and heat energy that kills personnel. 4. The Electric Safety Handbook [1] warns: “When an electric arc occurs, the vaporization of solid metal conductors into gas is an exotermic or heat- releasing reaction that leads to rapid superheating of the surrounding air. The metallic vapor can be toxic exposure to respiratory or lung tissue because of its chemical composition and high heat. The superheating of the surrounding air can create a blast effect leading to acoustic trauma or tissue destruction from explosion. The rapid expansion of the air creates a wavefront that can reach pressures of 100 to 200 lb per square foot (lb/ft2) (4.79 to 9.58 kPa). Such pressure is sufficient to explode switchgear, turn sheet metal into shrapnel, turn hardware into bullets, push over concrete walls, and propel molten metal and superheated plasma at extremely high velocities.” <Sidebar> Blast created by electric arc creates a high- pressure wavefront; combined with high temperatures, it is extremely dangerous. © 2013 Alexander Ganago Page 4 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 Harmful effects of electric currents on the human body Figure 2- 1 lists the harmful effects of external electric currents of the human body. The magnitude of currents found in different sources varies for the same type of harm. As always in safety issues, we must be conservative: for example, if some sources listed 7 mA as a hazardous current, consider it a hazard. Current Effects Below 1 mA Barely perceptible 1 – 3 mA Pain 7...
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