Many currents in our household appliances are much

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Many currents in our household appliances are much higher, for example: ü 1,600-W hair dryer uses more than 13 A (do the math yourself) ü If 0.2% of this current enters your body, you are in mortal danger. <Sidebar> External electric currents disrupt the normal functioning of the nervous system of the human body and override its protective mechanisms. The currents as low as 30 mA can stop the breathing, and currents above 500 mA can stop the heart. Secondly, internal organs of the human body are good conductors of electric currents, because they contain fluids with high concentrations of ions. An external electric current that flows through the human body generates heat ࠵? ! ࠵? , which leads to internal burns that are extremely difficult to heal. <Sidebar> The internal organs of the human body may be severely burned by the heat ࠵? ! ࠵? generated by the electric current through the human body. These burns are extremely difficult to heal. Book Page 93
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EE for the 21 st century 1-2 Safety: Avoid electrocution 1-2-1 Harm from currents © 2015 Alexander Ganago Page 3 of 8 Last printed 2015-07-24 11:59 AM File: 2015 1-2-1 Harm.docx Even if electric currents do not enter the human body, they may still present danger. Electric arc, which is a discharge of electricity through air or another gas, involves extremely high temperatures (up to 50,000 K) ü Such temperatures ignite all types of clothing fibers ü The heat energy can kill and injure personnel at surprisingly large distances, 30 feet or more from the discharge ü Even low-voltage systems have significant arc hazard if they can produce high currents: for example o 12-V car battery produces currents up to 300 A, which can cause an arc. o If you drop a screwdriver onto the terminals of a car battery, the heat of electric arc discharge might weld it to the terminals… <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. The arc involves extremely high temperatures that ignite all clothing and heat energy that kills personnel. The Electric Safety Handbook [1] warns: “When an electric arc occurs, the vaporization of solid metal conductors into gas is an exothermic 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/ft 2 ) (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.
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  • Fall '07
  • Ganago
  • Electric charge, Alexander Ganago

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