Choosing the Right ESD Floor

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For example; a floor that generates body voltages below 100 volts when tested per ESD STM-97.2 may generate several thousand volts on a person who forgets to wear heel straps. A dissipative carpet that measures between 1.0 X 10⁶ ohms and 1.0 X 10⁸ ohms may become insulative from conductive fiber fractures in situations involving chair casters constantly roll back and forth over the surface. These potential scenarios represent serious liabilities to any ESD program and yet they are an everyday reality. As previously stated, engineers and lab technicians are least likely to comply with proper ESD personnel grounding policies and yet these individuals test and handle their company’s most important and expensive items. For any of these reasons it may make sense to identify “contingency or adaptive features” during any product selection process. In the case of ESD flooring that logic may constitute identifying ANSI/ESD S20.20 compliant floor systems that also demonstrate low tribocharging characteristics on people wearing standard insulative footwear. Low tribocharging characteristics (triboelectric compatibility) may not entirely prevent walking body voltage but a conductive floor with antistatic properties will significantly minimize the liability associated with peak voltages in uncontrolled environments.

Most ESD Flooring Performs Differently In the Installed Environment
Some processes used during tile and carpet manufacturing operations alter finished flooring surface in one way or another. Some processes generate residues. The processing of high vinyl content PVC tiles may create temporary glazes for shine and appearance. These inadvertent surface alterations may temporarily impact the static control performances of new flooring. For example, PVC tiles have a shiny wear layer that disappears after scuffing and heavy use. Eventually the PVC surface must be revitalized through high speed buffing or often, waxing with ESD finishes. The new walking surface may exhibit entirely different tribocharging characteristics from the original factory wear layer. Rubber flooring may be contaminated with silicon mold release that will hinder the product’s dissipative performance until it has been cleaned several times. Data collected in the present study showed a significant improvement in tribocharging characteristic between cleaned rubber flooring and freshly installed flooring that was still contaminated with factory applied mold releases. In the case of carpet, antistatic coatings are often incorporated into fibers that reduce static during manufacturing. Although antistatic coatings are not permanent, simple washing will not remove them. However, the coatings disappear over time from traffic and humidity changes. Coatings may remain on the carpet just long enough to prevent walking body voltages over 100 volts during lab testing and initial floor certification. A few months after installation, that same carpet may generate thousands of volts on mobil personnel.

Accelerated Life Testing Can Reveal Product Weaknesses
Conductive carpets should always be tested before and after the “chair caster test.” The chair caster test simulates approximately one to two years of task chairs rolling over a carpet’s surface in a normal lab or assembly environment. The test had been previously used by carpet mills to evaluate surface wear and appearance of yarn systems. The test revealed significant weaknesses in carpet tile designs with PVC backing. Rolling chair casters destroy or “mash” the carbon fibers in conductive carpeting and render a once conductive product into an insulator. Only one conductive carpet design met the recommended requirements of ANSI/ESD S20.20 after the chair caster test. A Properly conducted test should expose floors with conductive yarn systems to at least 100,000 cycles. Our testing demonstrated that a lifetime-time electrical warranty can not be interpreted as immunity to caster rolling damage.

Many conductive PVC floors are purchased by buyers with no intention of ever applying waxes of any kind. This belief may be short lived since it costs more to mechanically burnish floor tiles than it does to wax them. Despite the beautiful look of a factory shine –it would be wise to evaluate ESD floor finishes and glazes at the same time as the overall ESD floor tile evaluation. One embarrassing experience from a plant tour by unimpressed visitors could initiate an overnight philosophy change in maintenance practices. Before buying any resilient floor it is usually a good idea to install a small patch in a high traffic area and monitor performance and appearance. This inexpensive test drive could prevent a costly miscalculation in total cost of ownership and worse - compromised ESD performance due to unanticipated performance problems caused by maintenance and normal abuse.

Test Flooring Based On Real World Conditions
Will the operation require the use of heel straps or other types of conductive footwear? Many labs and technical environments can not mandate or monitor compliance with the use of heel straps. Unfortunately, these environments still require some form of ESD mitigation due to the use and handling of extremely sensitive electronic equipment. It may be prudent to purchase flooring based upon meeting not three but four electrical testing parameters:

Resistance to ground, total system resistance, voltage measurement in combination with a person with conductive footwear and voltage measurement in combination with person wearing uncontrolled footwear. Our testing demonstrated that certain materials can meet the first three criteria and perform reasonably well in the fourth test. The decision to address or ignore the fourth criteria is strictly a function of confidence in procedures. A periodic analysis of heel strap compliance in similar operations usually predicts what can be expected in similar operations.