Electrostatic discharge and antistatic coverings
Raised access flooring has many usage areas: cloud-computing, laboratories, telecommunication, clean-room, hospital, industry etc.
The floor is used to hide plumbing, cables, and ventilation. Computers and servers generate a lot of heat and raised access flooring is used to manage the cooling in a dependable manner. Raised access flooring can be an advantageous solution in many areas to achieve optimal use of available space by hiding cables and plumbing etc.
The floors can be used with practically any kind of covering, but ESD coverings are necessary in areas where ESD sensitive electronics are produced, operated, or serviced. Also highly flammable/explosive areas, surgery wards etc to avoid operational disturbances in electronic equipment.
Standard we adhere to:
IEC61340-5-1 and ANSI/ESD20:20 are international leading standards. The
former is primarily used in Europe and Asia and the latter is used
primarily in North America. These standards are highly compatible and
they specify ESD control requirements and guidelines generally,
Terms for ESD-coverings are specified in electrical resistance (Ω) and upper resistance limit to ground is set to be R<1×109 (1 billion Ω). When the covering is used to provide grounding for personnel, the maximum allowed body charge is <100V.
The coverings are divided into the categories: Antistatic, electrostatic dissipative, and electrostatic conductive. The term antistatic coverings is often used in error and misunderstood.
A common misconception when people talk about antistatic coverings is that they really mean a covering in the category “electrostatic dissipative” or “electrostatic conductive”, that are usually referred to as ESD-coverings.
An antistatic main property is that it reduces the triboelectric charge between footwear of the personnel moving on the covering and the covering itself, this will in turn avoid uncomfortable discharges upon touch, but no more than that.
NB: The human sensitivity threshold for static electricity is approx 3000V.
Antistatic coverings can not be grounded and therefore can not remove surplus charge. The effect is determined from its ability to reduce triboelectric charge and varies with humidity.
This covering is unsuitable in ESD-sensitive areas, where raw electronic components are exposed or in explosive/flammable areas. For areas such as these use ESD-coverings belonging to the categories electrostatic dissipative/conductive which are grounded. Typical areas are electronic production/service and within certain industries such as telecommunication, IT, hospitals, technical clean rooms, X-ray/MRI, laboratories etc.
Please note that the terms static dissipative and conductive are no longer used in the ESD standards, but are still used within the covering industry.
Electrostatic dissipative coverings have a resistance (R) between 1×106 (1MΩ) and 1×109 (1GΩ).
Electrostatic conductive converings have a resistance (R) <1×106 (1MΩ).
There are no apparent advantages with conductive coverings compared to dissipative. But, in explosive areas a shorter discharge time is an important property.
Within the electronics industry or in areas where sensitive electronics are exposed the max allowed body charge (<100V) according to the aforementioned standards. This is almost impossible to enforce without introducing mandatory requirements for ESD-footwear/heel-straps. In this context the phrase “system resistance” is used, which signifies the total resistance to ground measured from person to earth through footwear and coverings. Max allowed system resistance is <3.5 x107 Ω (<35MΩ). Both practical tests and mathematics proves that body charge never exceeds 100V when system resistance is kept below this level. Also, coverings with resistance (R) between 35MΩ and 1GΩ are able to cope with the requirement of a max body charge of <100V but only if it is documented through a standardised test (Walking test) which simulates a realistic movement pattern on a covering. The humidity also affects the properties of dissipative/conductive coverings. Low humidity reduces the conductivity and high humidity works in reverse.
In sectors and industries where it’s not practically possible to introduce mandatory ESD-footwear requirements, it is especially important to not only analyze the covering’s resistance (R) but also the covering’s triboelectric properties. A covering with a lower resistance to ground is not necessarily a better choice than a covering with higher resistance, i.e. 1×108 compared to 1×109 Ω.
In a “controlled” environment the triboelectric charge can be a deciding factor.
Study the product sheet and do not only choose a covering based on a single parameter. Generally it can be said that coverings based on rubber generate less charge than vinyl.
For security reasons it is necessary with a lower resistance limit to avoid dangerous electric discharges upon touch i.e. when its a high main voltage. A minimum resistance (R) of 100kΩ (1×105) is recommended. Personnel safety is always the top priority.
Grounding of the coverings
Electrostatic dissipative/conductive covering tiles must be grounded through the raised access floor construction to have the desired effect. ESD-tiles are glued on the panels, i.e. Gammacore, by using an electrically conductive glue. The panels are electrically connected to the supporting steel-construction. The coverings should have at least one connection to electric ground for each 100m2 area. Usually the supporting steel construction is already connected to electric ground for other reasons. If they are not, this can easily be fixed by an electrician. Important: Always make sure the conductive glue is at least as conductive as the ESD-tiles and that the glue’s conductive properties do not deteriorate for many years. Check the electronic continuity between the tiles and the steel construction. Adhere to the installation-guide from the covering manufacturer.