Electrostatic Discharge

Electrostatic Discharge (ESD) is common in the course of everyday life. Walking across a carpet and touching a door handle can produce a painful zap. Removing laundry from a clothes dryer is often accompanied by a crackling sound. What you feel or hear is electrostatic discharge. Electrons are often transferred when dissimilar materials are separated from each other. After separation the materials have a net charge. The process is known as Triboelectic Charging. Some objects, such as dry skin and wool, tend to become positively charged. Others, such as polyester and vinyl, become negatively charged. An ESD event occurs when a Triboelectricly charged object looses its charge suddenly to an object at a different potential. The potential differences between Triboelectrically charged objects can be quite high. A person's threshold of detection of an ESD event is about 3000V. A painful zap will have several times that voltage.

Static buildup of charge is much more than the minor annoyance of a zapped finger or static cling. It can be destructive and even deadly. An ESD event from a person, charged to several thousand volts, will produce peak currents of several amps. A discharge of this magnitude through an integrated circuit can melt silicon or cause oxide damage. An ESD event to an operating electrical system can cause problems even if no physical damage occurs. Large electrical currents from an ESD event can change the state of internal logic. The system can subsequently lock up or behave in an unpredictable manor. A dangerous situation can be created by a metal gasoline can become charged sliding on a plastic bed liner of a pickup truck. Touching the charged can with a grounded gas nozzle may result in a spark that can ignite gasoline vapors, causing a serious fire. (Always place a gas can on the ground before filling it with gasoline. Never leave a gas can inside of a vehicle when refilling it.)

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