Problems Caused by Electrostatic Charge

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Generically speaking, here are the fundamental static-related problems encountered in industrial environments:

  • Electrostatic Attraction
  • Electrostatic Discharge
  • Electromagnetic Interference (EMI)

In today's industry, highly-insulating synthetic materials, such as plastic powders and insulating liquids, are used in large quantities in an ever-increasing number of applications. Such materials charge up readily, and large quantities of electrical energy develop with an attendant risk of incendiary discharges. When, for example, powder is pneumatically transported across pipes, charge levels of up to about 100 microcoulombs per kilogram can develop and potentials of thousands of volts are generated within powder layers and the powder cloud. Energetic sparking from charged powder may initiate an explosion of the powder cloud. Similar problems occur when insulating liquids, such as certain fuels, are pumped along pipes, and it is essential that strict grounding procedures are followed during the refueling of aircraft, ships, and other large vehicles.

The capacity of a person for retaining charge depends on stature, but is typically about 150 picofarads. Even the acts of removing items of clothing or sliding off a chair can lead to body discharges to ground of about 0.1 ┬ÁC, which are energetic enough to ignite a mixture of natural gas and air. Human body capacitance is sufficiently high that, if poorly conducting shoes are worn, body potential may rise to 15,000 volts so above ground during industrial operations such as emptying bags of powder. Sparking may then occur with energy exceeding the minimum ignition energy of powder or fumes, so causing a fire or explosion. Conducting footwear may be used to prevent charge accumulation on personnel in industrial situations where triboelectrification may occur.

In the microelectronics industry, extremely low-energy discharges, arising from body potentials of only a few tens of volts, can damage microelectronics systems or corrupt computer data. During the handling of some sensitive semiconductor devices, it is imperative that operators work on metallic grounded surfaces and are themselves attached to ground by conducting wrist straps.

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