When an electrically charged object is brought near an object that conducts electricity but is separated from the ground, there will be a discharge as the electrons jump across.

If the charge is strong enough, there may be a spark or 'crack' sound.

But even a tiny discharge, too small for a person to notice, can disturb sensitive electronic components or cause equipment failures.

This is why floors in areas that house sensitive electronic equipment need to be 'ESD safe'.

In critical applications, ESD floors are used in conjunction with other measures, such as humidity controllers and 'static controlled' clothing and footwear.

Dealing with static electricity

Resilient floor coverings can be grouped into three basic categories to describe their ability to deal with the problem of static electricity - anti-static, static dissipative and static conductive.

Anti-static

Anti-static floors are made from materials that do not generate a static charge.

In that sense, an ordinary linoleum floor is 'anti-static' under certain conditions, and so is bare concrete as long as the relative humidity in the floor and air are balanced correctly.

But there is also a wide range of tile and sheet products specifically marketed as anti-static because they do not contribute to the build-up of static electricity, unlike many normal vinyl and carpet products.

They are often used in the picking and packing areas of warehouses and around automated carousels.

Although anti-static floors overcome the problem of people building up a static charge as they walk across the floor, they won't actively attract or control a charge before it has a chance to discharge somewhere else.

For this reason, they are not classified as 'ESD flooring'. This term is reserved for static dissipative and static conductive flooring.

Static dissipative

Static dissipative floors allow static electricity to 'dissipate', or discharge in a controlled way.

They're used where a higher level of static control is necessary, such as in computer rooms, x-ray suites, operating theatres and some electronics manufacturing facilities.

In technical terms, a static dissipative floor is defined as having a surface resistance of between 1 x 10⁶ ohms and 1 x 10⁹ ohms. (See below for details on surface resistance in floors.)

Static conductive

These floors are at the top level of ESD flooring, and are more conductive than static dissipative floors.

They are used in places where very sensitive components are being handled, such as on electronic assembly lines.

Conductivity is improved by installing the floor over a grid of copper tape and earthing it to the ground.

The surface resistance of static conductive floors is defined as being between 4 x 10⁴ ohms and 1 x 10⁶ ohms.

What does surface resistance mean?

The surface resistance of a floor refers to how easily an electric charge can travel across its surface.

The higher the resistance, the more 'insulative' it is.

The lower the resistance, the more 'conductive' it is.

An insulative material is one that has a surface resistance of greater than 1 x 10¹² ohms.

10¹² is another way of saying one trillion (that is: 1,000,000,000,000 - or 1 with 12 zeros after it).

An ohm is the unit of measure for the electrical resistance between two points. Its symbol is Ω.

To remove the problem of electrostatic damage to sensitive equipment, a floor needs to have low electrical resistance so that any static electricity generated is able to be discharged before it has a chance to build up.

This is what characterises an ESD floor.

Unlike ESD floors, anti-static floors aren't officially described in terms of surface resistance, because their purpose is not to control the discharge of static electricity - it's simply to reduce the build-up in the first place.

Nonetheless, the floor coverings that can be classed as anti-static are generally in the range 10¹⁰ ohms to 10¹² ohms.

For floors that do need to be ESD safe, engineers often specify actual surface resistance levels rather than simply calling them 'static dissipative' or 'static conductive'.

For example, hospitals typically have ESD floors specified at somewhere between 5 x 10⁴ ohms and 2 x 10⁶ ohms.

Computer companies have varying requirements depending on what they do, but the specifications tend to go up to 1 x 10⁹ ohms.