Taking The Mystery Out Of Selecting ESD Flooring

Choices Abound, But Careful Planning Is Essential In Making The Right Choice

Often, the most challenging and anxiety-inducing decisions buyers encounter in the course of creating a world-class electrostatic discharge (ESD) program involve the selection of the ESD floor. Unlike other components in the program, the installation of static control flooring represents a permanent capital investment, with costs of 1 1/2 to 2 times those of a standard non-ESD floor. Because the static control floor affects every aspect of the organization—from performance to image—in most cases, finding the right floor involves a marriage of competing interests, including cost, durability, ergonomics, compliance with safety standards, appearance, company image, maintenance, total cost of ownership and, of course, ESD properties.

When buyers and specifiers contemplate this higher cost of ESD flooring in conjunction with the usual mountain of architectural considerations, it quickly becomes evident that someone involved with the decision-making process needs to understand both static control specifications and the long-term impact that installing an ESD floor will have on the business. To answer their ESD flooring questions, architects and specifiers typically turn to their general contractor or flooring specialist who, in most cases, has meager ESD knowledge and no expertise. Alternately, a buyer might call a supplier of ionizers, grounding mats and heel straps to ask for advice on sub-floor preparation or installation, help which is just as obviously outside that particular supplier’s scope of competency.

Unfortunately, failing to understand the whole picture can yield disastrous results, ranging from a confusion of ESD-industry vocabulary and misapplication of standards to a compromised ESD floor installation. The good news is that the selection of static control flooring needs not be a mystery.

Static Dissipative Versus Conductive
In selecting an ESD floor, understanding the relationship between a floor’s long-term electrical performance and its ability to protect expensive and increasingly vulnerable static-sensitive components and equipment is almost always the biggest problem faced by architects, specifiers and buyers. Several excellent ESD standards, readily available on the ESD Association’s website (www.esda.org), along with a copy of the official ESD Association glossary, should eliminate much of the confusion over electrical criteria.

While these easily accessible documents certainly provide answers to most ESD questions, there is still ongoing and unnecessary confusion over a seemingly basic consideration, that is, the difference between static dissipative and conductive materials and the reasons why one might be more appropriate for use in ESD floors than the other. In the past, the majority of companies selected their particular ESD floor based on the misconception that static dissipative materials were safer than, while still equal in effectiveness to, conductive materials. This widespread fallacy led to the installation of millions of square feet of dissipative flooring that may or may not meet the recommended range of less than 35 megohms for system resistance, as documented in ANSI/ESD-20.20-1999.

It’s important to understand that the definitions of and differentiation between the terms “static dissipative” and “conductive” were originally conceived not for flooring but for the packaging industry. The authors of EIA-541, a standard used by the packaging industry, used sweeping definitions based primarily on surface resistivity in order to simplify the selection and identification of static shielding materials. These standards characterized static protective materials based on their ability to provide shielding from electrostatic fields. Static dissipative materials (1x10⁵ to 1x10⁹) inhibit the generation of static, but they do not sufficiently dampen the penetration of static fields onto enclosed parts. According to the standard, more conductive materials (less than 1x10⁵ ohms) provide better shielding than do less conductive materials. This reasoning proliferated the use of metallized static shielding bags and “faraday cage” tote boxes for the safer packaging of ESD-sensitive circuit boards. EIA-541 recommended a resistivity cutoff point of 100,000 ohms (<1 x 10⁵) for defining adequate shielding. This recommendation effectively drew a line in the sand, which was subsequently “borrowed’ and reapplied to the selection criteria for table covering materials, tote boxes, garments and flooring. However, the unfortunate fallout from these misappropriated definitions is the false belief that materials which are “conductive and capable of providing shielding” are too conductive for safe personnel grounding. The correspondent fallacy holds that, despite their significantly higher resistance to ground, static dissipative materials will inherently prevent the generation of static electricity on mobile workers and moving carts.

In fact, static shielding properties have absolutely no bearing on floors, which are designed to protect sensitive electronic components against walking body voltage, the voltage generated by people walking across their surface. Thus, the consideration of electrical parameters for shielding materials involves entirely different criteria from the parameters that define a functional and long-term effective ESD floor. According to John Kinnear, past president of the ESD Association, one should not choose flooring materials based on their fit into so-called categories of “static dissipative” and ”conductive.” Flooring materials should be approved and installed based on evaluations of properties that apply specifically to flooring.

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