Flooring - The Primary Control but not a primary concern!
Flooring is sometimes the primary control that a site uses to reduce static accumulation and potential discharge. However it is often disregarded as part of a maintenance or testing program.
Floors that build up a residue or contaminant layer over years of operation may no longer provide the level of static control that they once did when they were first installed.
In environments where very small values of static can cause process issues such as components manufacturing, laboratories, clean room environments etc. ensuring that the floor is operating effectively is critical.
In recent years the amount of forklift related static electricity injuries has increased. This is partly due to the maintenance of concrete floors and the type of wheels used on forklifts. In the pursuit of making the workplace as clean as possible, epoxy or resin has been painted over old concrete floors. The use of certain epoxies or resins can create a highly insulative floor separated from earth. This is combination with certain forklift tyres being insulative has resulted in seriously high values of static with nowhere to earth. The result being that the charge earths to the forklift driver or nearby operators.
There are many types of floors, here are the two most used in industry.
Static Dissipative Flooring including carpet, tiles, raised floors, coatings and resins etc.
Static-dissipative floors are defined in relation to their electrical resistance. Electrical resistance, measured in ohms, is a material’s ability to resist the flow of electricity. A static dissipative floor must have an electrical resistance to ground that’s > 1.0 x 10E6 (one million ohms) AND ≤ 1 x 10E9 (one billion ohms).
The term “static dissipative” should not be confused with the terms “conductive,” “antistatic” or “low charge generating.”
A static-control floor can be dissipative (or conductive) and still generate charges significant enough to cause an ESD event.
Conductive Flooring including carpet, tiles, raised floors, coatings and resins etc.
A floor with an electrical resistance measuring < 1.0 x 10E6 (1 million ohms) is usually considered conductive.
Whilst standards do not specify a minimum electrical resistance, for best practices the industry has historically set a minimum of 2.5 x 10E4. Electrical resistance below 2.5 x 10E4 is considered a potential shock hazard. Conductive adhesive is an electrically conductive glue that forms a sticky plane with conductive properties. Typically copper strips join the adhesive and flooring tiles to ground. Note: the conductive adhesive should always be more conductive than the flooring material.
Flooring Considerations
Installation of a floor and testing the floor meets the resistance requirements is only the first step in a flooring program.
Typically floors are cleaned using detergents and bleaches or waxed or coated. These processes can change the way that a person comes in contact with the floor by providing a barrier to earth through the floor.
Regular maintenance and testing is required for any floor and should be part of your static electricity control plan.