The Problem of ESD

If you've ever ordered computer hardware or any electronic part, you likely received it in an anti-static bag. This special type of packaging is exactly what its name implies, a means to protect against static electricity; specifically electrostatic discharge, or ESD

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Electrostatic discharge, or ESD, has been a safety and productivity issue in industry for many, many years. It has been the culprit behind numerous explosions as well as countless product failures and defects in solid state electronics.

What Is ESD?

ESD is the release of static electricity from one object to another. Most people know it as the sparks induced by the Van de Graaff generator in science class, or the shocks they gave their friends after scuffing their feet across the carpet or rubbing a balloon on their head. The sparks are the result of a difference in electric potential between the two objects in contact (Credit: Industrial Plastic Supply, Inc. -->). The charge difference is created through friction, known as the triboelectric effect.

(The magical effects of static electricity. Credit: thebeautybrains.com)

ESD is not limited to sparks and shocks that we can feel, however. It also can come in more subtle forms, namely invisible corona or brush discharges which occur in the presence of highly curved electrodes. These are the ESD events that plague production efforts in electronics manufacturing and industry. A majority of the defects aren't realized until they reach the customer, and resulting costs can be high.

Prevention and Control

Preventing ESD events and the resulting damage requires engineers to consider the potential for charge buildup in an area or part, and the electrostatic sensitivity of components.

In regards to electrostatic sensitivity, studies have been done to determine the cost effectiveness of increasing ESD resistance of manufactured products. In most cases, profits do not improve above an effective resistance of 4 kV HBM (per Human Body Model). Unfortunately, many components lose performance as ESD resistance is increased, so a compromise is often required.

Manufacturers also can define an EPA (electrostatic protective area) for areas workstations where ESD prevention is critical. In these areas all conductive materials are grounded, workers are grounded, and charge build-up on sensitive products is prevented. Grounding (connection of an object to earth) helps limit and dissipate any charge buildup in an object that may otherwise have the potential to induce an ESD event. Connection to ground is important for preventing ESD in any application or setting, not just for electronics.

ESDs and Explosions

ESD is a particular nuisance for electronics, but what about applications involving explosive materials? A lack of understanding or consideration for static buildup could have devastating results in these situations, where it takes only a small spark to make for a very bad day.

(Cell phones may not be dangerous at the pump, but an unusual high static buildup could be. <-- Credit: ESD Journal)

Such was the case at the Barton Solvents facility in Valley Center, Kansas. According to the Chemical Safety Board (CSB), at about 8:30 am on July 17, a tanker unloaded a non-conductive solvent through a feed leading to one of the facilities storage tanks. A device for measuring the liquid level in the tank, suspended from pulleys and connected to a metal float, was connected to a grounded metal tape assembly. When air entered the line during the filling of the tank, it caused turbulence which rocked the assembly's loose connections and created a space between the float and the linkage assembly. The charge that had built up in the liquid caused a spark to arch in the gap, igniting the flammable vapors from the solvent.

The explosion set off a chain reaction through a number of adjacent storage tanks, and the tops of some of the tanks became projectiles which caused offsite property damage in addition to extensive on-site destruction. The incident destroyed 36 storage tanks of over 660,000 pounds of chemicals, and resulted in an evacuation order for residents in the area.

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While this is the CSB's best guess, the actual details of what caused the explosion are unknown. Regardless, the case is an example of the potential dangers of ESDs when volatile compounds are present. In these situations, proper understanding and control of ESDs is essential for ensuring safety. In industries where ESD is mostly a quality assurance concern, better design and operating techniques could mean substantial cost savings and less instances of catastrophic or latent product failure.

References

ESDA.org

The "Real" Cost of ESD Damage - In Compliance Magazine

Electrostatic Discharge Explained - Electronicspub.com