Desco - Questions And Answers

Does the human body have electrical resistance? What amount of electrical current is harmful to people? - Anonymous, Chino, CA

The resistance of the human body (skin) will vary greatly; from 1,000 ohms to well over 10 Megohms. The ESD Association uses a resistance of 1.5 kilohms in it’s ESD-STM5.1-1998, HBM (Human Body Model).ESD control products that ground static charges are not recommended where equipment electrical power is over 250 VAC. At 250 VAC, a 800 kilohm resistor [1 megohm +/- 20%] will limit the electrical current to the level deemed a safe level according to MIL-STD-454: Using Ohm’s Law l = E/R or 250 VAC divided by 800,000 ohms equals 0.0003125 amps or 0.3mA. All personnel ground straps should have sufficient resistance to ground to limit current to the perception level as shown in MIL-STD-454, Requirement 1, DOD-HDBK-263, Section 7.3.1.3, Table VIII. Human “skin” is a conductor. Static does not travel “through” but rather across on the skin’s surface. AC electrical current [60 hertz] will have various effects on humans. The results are generally: perception at less than 1 mA, surprise from 1 to 4 mA, reflex action from 4 to 21 mA, muscular inhibition from 21 to 100 mA, respiratory block at 40 to 100 mA, and generally death over 100mA.

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