ESD Library

Managing Static With ESD Flooring

Similarly, certain excellent conductors—conductive vinyl, for instance—are comprised primarily of ordinary static-generating materials (standard VCT) with a small distribution of carbon or graphite chips or veins to provide conductivity. Although the embedded conductors do make the floor groundable, the regular VCT in the floor is highly static generating. When shoe soles contact and separate from the VCT, static builds. To prevent static buildup, everyone who walks on the floor must wear special conductive shoes or conductive heel straps, a requirement that would be difficult if not impossible to enforce in a call center: Can you imagine the local sheriff putting on heel grounders every time she touches her computer?

Static Control Carpet
Intuitively, it makes sense that conductive carpet would be less effective than conductive vinyl in preventing static buildup, but in fact the opposite is usually true. Conductive carpet tiles contain thousands of grounded conductive fibers that sweep off static from shoes, safely discharging the static to ground, much the way small brushes eliminate static on high speed copiers as the paper is fed into the collator. This does not mean that conductive vinyl is an inferior product. It simply means that conductive vinyl works best in applications, such as electronic manufacturing and assembly, where footwear and traffic are monitored and controlled.

Conductive carpet resembles standard carpet except for the addition of special carbon fibers that are woven throughout the surface and backing. (see figure 1, how carpet works) When a person walks on the carpet, the conductive fibers extract excess static build-up from the shoe sole, before it damages components, and safely discharge the static through the conductive backing. The charge is then routed through a conductive release adhesive that secures all of the tiles in place. The release adhesive, also known as pressure-sensitive adhesive, contains millions of conductive fibers. These fibers create a conductive network below all of the tiles in the installation. The adhesive is connected to ground along the edges of the room through 18 inch copper strips (1 ground strip per 1,000 square feet) that bridge the gap between the perimeter floor tiles and electrical conduit. When properly installed, every single floor tile is at the exact same electrical potential as all of the others. This condition is called "electrical continuity." This procedure may sound technically challenging but in actuality requires no more skill than a standard carpet tile installation. The key to success is doing the homework up front and specifying carpet tile products manufactured with conductive fibers in conjunction with conductive adhesive and grounding strips.

Rubber Flooring
Carpet may be the wrong choice for certain applications. Entry areas can become a maintenance nightmare during inclement weather. Carpet could become unsightly or stained if continuously exposed to salt and chemicals used to control ice and snow buildup. Sometimes carpet is seen as a collector of dust and dirt. Although closed loop carpet tiles are easily vacuumed and steam cleaned, some facilities managers prefer floors that can be broom cleaned or damp mopped. Other people choose resilient flooring simply because a resilient floor was installed when their facility was built and no other flooring material has ever been tested or used. Some people see carpet as inferior to vinyl or other hard surfaces and there is no way to alter their thinking. Fortunately, it is possible to meet the same static protection level of conductive carpet with certain rubber flooring alternatives. Dissipative nitrile rubber flooring, in particular, provides static inhibiting properties similar to conductive carpet tiles, but for very different reasons. From high school physics, we know that whenever two dissimilar surfaces are rubbed together, they generate static. The corollary is also true: Similar materials generate less static when they interact. The base compound used in rubber flooring sufficiently resembles most shoe soles to the degree that it inhibits the buildup of static by preventing static generation in the first place. Unlike conductive vinyl, nitrile rubber is a homogenous dissipative material with conductive properties distributed across one hundred percent of the surface and throughout the thickness of the tile. The full distribution of conductive properties means that shoe soles will never contact anything on the surface of the floor that can generate static. And, like all effective conductive flooring options, rubber meets the second critical criterion: it can be grounded.

A typical rubber installation relies on the same conductive adhesive as carpet tiles. Without conductive adhesive, the rubber tiles cannot reach electrical continuity or be grounded and an ungrounded floor has no means of dissipating static away from the floor.

*This article originally appeared in the May '04 issue of Emergency Number Professional Magazine.