If you’ve ever touched a metal doorknob after walking across a carpeted floor or pulled your laundry out of the dryer and experienced a mild jolt of electricity, you’ve been in direct contact with a phenomenon known as Electrostatic Discharge (ESD). This everyday occurrence is experienced when two materials come into contact with and then separate from each other, and results in static electricity, which is a completely harmless event in the majority of cases.
However, static electricity and ESD have created serious industrial problems for centuries, dating back as early as the 1400s, during which European and Caribbean forts were using static control measures to prevent inadvertent electrostatic discharge ignition in their gunpowder stores1.
In fact, nearly every imaginable industry from agriculture, medical, printing, petrochemical, pharmaceutical, textiles, and plastics are affected by ESD issues2. Today, thanks to the rapid proliferation of electronic devices with increasingly more compact circuitry, the sensitivity to ESD occurrences has never been higher, and the trend is only expected to accelerate. In fact, according to the Electrostatic Discharge Association’s (ESDA) 2010 report, “Electrostatic Discharge Technology Roadmap,” ESD impacts productivity and product reliability “in virtually every aspect of the global electronics market. It is imperative that companies begin to scrutinize the ESD capabilities of their handling processes.” The report concludes that “It is unlikely that any company which ignores static control will be able to successfully manufacture and deliver undamaged electronic parts.”
Further, the effects and annual losses attributed to ESD are estimated to run into the billions of dollars in the electronics industry alone. Despite a great deal of effort during the past 30 years to minimize the impact of ESD, it still interrupts production yields, manufacturing costs, product quality, product reliability, and profitability across the board3. The cost of damaged devices themselves ranges from only a few cents for a simple diode to thousands of dollars for complex integrated circuits. When associated costs of repair and rework, shipping, labor, and overhead are factored into the equation, the need for dissipative flooring solutions takes on new significance4.
As a result, many flooring manufacturers have developed products that can help effectively address ESD problems in a variety of applications. In order to fully appreciate the solutions that the flooring industry offers, it’s imperative to first understand the nature of ESD, what causes it, and the risks associated with it.
esd 101: a primer
Effectively managing ESD starts with the knowledge of how electrostatic charges occur in nature. Let’s take a closer look at the science behind electrostatic charges and why it’s important for designers and specifiers to establish a thorough understanding of it.
An electrostatic charge is simply defined as an “electric charge at rest,” which is most commonly created by the contact and separation of two materials. Depending on the type of materials in question, the charge can be relatively high if they are dissimilar (similar materials can produce a charge, but at lower thresholds). Table 1 below illustrates a number of common materials that may carry an electrostatic charge.
As a person walks across a carpeted floor, the soles of the shoe come into and out of contact with the surface, creating an imbalance of electrical charges within or on the surface of the floor. The imbalance of electrons produces an electric field that can then be measured. The amount of charge generated in each case depends upon factors such as the area of contact, the speed of separation, relative humidity, and chemistry of the materials, among others5.
The process of creating electrostatic charge by contact and separation of materials described in the example above is known as “triboelectric charging.” The word “triboelectric” comes from the Greek words, tribo—meaning “to rub”—and elektros—meaning “amber” (fossilized resin from prehistoric trees). It involves the transfer of electrons between materials during which the atoms of a material with no static charge have an equal number of positive (+) protons in their nucleus and negative (-) electrons orbiting the nucleus6.
Once a charge has been established, a material becomes electrostatically charged if it is not grounded or dissipated naturally over time. This charge can then be transferred from the material, creating an electrostatic discharge or ESD event. Electrostatic discharge, then, is defined as “a swift discharge of electric current between two objects with different charges and different numbers of electrons. This exchange of electrons creates a large electromagnetic field buildup, resulting in ESD.”7
ESD has the potential to disrupt the normal operation of an electronic system and cause equipment malfunction or failure, or degrading or even destroying it in some cases. The level of the charge that is released depends upon factors such as the resistance of the actual discharge circuit and the contact resistance at the interface between contacting surfaces8. Typical voltage levels of static generation are illustrated in Table 2 below, as well as the role that relative humidity plays in the accumulation of static charges.
In addition to the financial costs associated with ESD events mentioned earlier, safety is another big concern. As noted, most electrostatic charges are harmless, naturally dissipating into the atmosphere or through contact with a grounded object. In fact, ESD events happen all the time but mostly go unnoticed because human beings are unable to feel charges at a threshold of 3,000 volts or lower9.
However, when charges accumulate and rise above 3,000 volts, they can become dangerous. A significant ESD event may cause a worker to recoil from the shock, creating a potentially dangerous situation for workers in confined spaces or near moving machinery. In fact, any ESD event greater than 80,000 volts can generate sparks that can knock a person to the floor and cause injuries, and many workplace fires, explosions, and injuries have been linked to a static spark ignition of vapors, gases, and dust10. The National Safety Council notes that such high ESD voltages are often found in and around high-speed web-processing equipment, and in workplaces where employees handle solvents, petroleum, gases, sugar, flour, chocolate powder, and other potentially flammable materials.