In state-of-the-art technology, each and every delicate component needs to be protected from a wide range of risks. While physical impacts and viruses might seem to be more immediate dangers, sensitive circuitry can just as easily be ruined by a single touch from one statically charged finger.
In fact, many components can be destroyed by a discharge of only 300 volts. However, one person walking across the floor can quickly build up a negative charge through a process called triboelectric charging. If the person is not insulated then this charge increases the more they move around, up to 3000 volts.
If the charge is large enough, then when the person nears an earthed person or object, the charge will jump through the air to go to earth, resulting in a spark. If the earthing object is a person, this will be experienced as a mild static shock. However, if it is a piece of equipment, then it could just have been irrevocably damaged.
This obviously has significant implications for any facility that relies on delicate computer equipment, such as data warehouses, R&D sites, clean rooms and laboratories. It’s a particular problem for the electronics manufacturing industry, which loses significant amounts of money every year in damaged goods.
In some sectors, such as munitions manufacturing, hyperbaric chambers, oil and gas facilities and military installations, static electricity poses an even more dangerous risk. If there are any explosive substances, gases, vapours, fogs or dust present then a small electrostatic discharge can be an ignition source.
To avoid these problems, anti-static floors can be installed, which actively removes any charge being built up in a person and safely takes it away to an appropriate earthing point.
Anti-static floors are ordered into categories depending on how quickly electricity can move through them, a property measured in ohms. Conductive surfaces are those with the least resistance, dissipative surfaces allow electricity to flow through them at a controlled speed, and insulative surfaces are the most resistant.
Anti-static floors work by incorporating specialised conductive materials that take away any charge a person has built up as soon as the person’s foot comes into contact with the coating. This contact kicks off a chain reaction that results in the charge being safely removed down through the floor and away from the sensitive working environment.
Next, the charge hits a conductive primer that has been filled with carbon to ensure a very low level of resistance. Finally, the charge goes into a copper tape buried under the floor coating, which is connected to a safe earthing point.
In practice there may be more or fewer steps. For example, it is possible to create a floor that removes static charge without using copper tape; however, it won’t be as conductive as a floor that does.
One thing that the floor definitely needs is the earthing point; without this it cannot be considered anti-static, as charges that go into it will simply build up. In practice an earthing point is usually a highly conductive metal rod driven deep into the building’s slab; however, other options include using the building’s steel beams or using a plug socket.
Typically, one earthing point per 200m2 should be sufficient, but the exact requirements need to be specified by an electrical engineer to ensure that the resistance measurements are appropriate.
To determine if the floor is up to the task at hand, its electrical resistance should be tested at each stage of the application. The BS EN 61340-5-1 standard includes a method for determining the resistance of a floor through point-to-point conductivity testing. The result will determine whether the floor can be categorised as conductive, dissipative or insulative.
When testing the floor, it is best to move the contact points around to ensure that a footprint sized space has been checked, as this is the practical contact area through which any charge held by a person will be transferred.
Making sure that a floor finish meets a site’s anti-static needs requires an understanding of the location’s operational activity, how the floor build-up works to remove this threat, and the role that other factors such as testing and personnel clothing play.
To get a full picture of all of these factors and how they interact, it is important to talk through the flooring specifications and materials with the manufacturer and contractor to ensure that the final coating will provide the required standard of conductivity.
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