Static control flooring: Defending against electrostatic discharge
Electrostatic discharge flooring advice is provided by Polyflor.
Electrostatic discharge (ESD) is a problem you can’t ignore. The scuff of a shoe or the scrape of a chair creates an electron imbalance and, while the human body may not feel it, it can have serious consequences. In electronics manufacturing, pharmaceuticals, healthcare, ordnance manufacture and storage, ESD incidents can cause material, component or system failures, which may prove costly and perhaps even dangerous.
THE NEED FOR STATIC CONTROL
Control of static electricity can be required for a number of reasons, but primarily for:
- protection of microelectronic components during assembly, test or repair
- protection of electronic equipment in use; for example, mainframe computers
- prevention of spark generation where flammable gases are used; for example, hospital operating theatres or areas where explosives are handled or stored
- prevention of charged surfaces to prevent attraction of particles (clean rooms), and
- personal comfort (protection from electrostatic shock).
When choosing a flooring system designed to control static electricity, one must keep in mind that the base components in the contract are of a more specialised nature than normal. Installing static control flooring is usually more expensive than traditional flooring, as the use of specific adhesives and earthing systems is required. The flooring system is usually selected by its static control performance rather than by cost.
The in use performance specification must be agreed upon with the end user at the tendering stage and should include the method of installation and the in use performance requirements, along with the method of testing and the maintenance procedures to be used.
TYPES OF STATIC FLOORING
There are two main groups into which static control floor covering can be divided:
- static dissipative (SD): compliant products will have resistance to earth between 1×10^6 and 1×10^9 ohms, and
- electrostatic conductive (EC): compliant products will have resistance to earth of less than 1×10^6 ohms.
Care must be taken with the lower reading. Most products have a lower limit of 5×10^4 ohms as this is generally accepted as providing some protection against mains voltages. Specialist conductive products are available that have resistance below 5×10^4 ohms. Specification of such products is mainly into areas where explosive materials are handled and, as such, you must liaise with the covering manufacturer to ensure the product and installation method used fully meet the design criteria.
There is another group in which floors are classified by their potential to generate static. Floors in this group limit generation of body voltage and hence reduce the risk of personal shock. The terminology used for floors in this group is antistatic. It does not infer that the product has any capability to dissipate or conduct any charge.
The test method for flooring is EN1815, which is stroll test. Compliant flooring products do not generate static charges above 2kVolts. Some military and medical specifications refer to conductive and dissipative floors as being antistatic. The floor covering manufacturer should be contacted to confirm performance.
Most static control products should be fully bonded using an electrically conductive adhesive. Also check with the flooring manufacturer to confirm suitability. In addition, most static control products require earth bonding strips (grid) to be used. The layout of these strips varies according to the manufacturers and specification requirements.
Due to the very large numbers involved in measuring resistance in flooring systems, a shorthand form is commonly used. Table 1 shows the shorthand representation of some large numbers commonly used.
ACHIEVING STATIC CONTROL
In terms of general flooring performance, the standards as set in BS8203 are usually acceptable. For specific advice, check with the floor-covering manufacturer.
In preparing specification to a new or existing base, the flooring system must consist of components (such as underlay, adhesive, deliberate earthings and floor coverings) that have been tested in combination and have been approved by the floor-covering manufacturer as providing the level of static control required.
The majority of floor-covering types are available in versions suitable for these types of installation. Access panel applications require specific instructions to ensure product performance and achievement of electrical results outlined. Once again, it is recommended that you contact the floor-covering manufacturer for further information.
STATIC FLOORING MAINTENANCE
Incorrect maintenance procedures can have a disastrous effect on the materials as well as the readings. Careful consultation with the flooring manufacturer is, therefore, essential. They will provide details of how their product should be maintained.
Conductive polishes approved by the flooring manufacturer can be used to complement the dissipative or conductive properties of their products. Antistatic polishes to EN1815 for use on insulative surfaces are readily available, reducing personal body voltages or personal shock caused by people walking across the floor. They are designed for use on insulative floors to give temporary protection against the generation of body voltage and hence reduce personal shock.
However, when applied to dissipative or conductive floors, they can have a significant detrimental effect on the static control performance of the flooring. Advice must be taken from the flooring or polish manufacturer.