ESD shoes – what are they and when are they necessary?

Why do you need ESD shoes?

ESD stands for the English term “electrostatic discharge“. As certain electronic components and electronic devices are so sensitive that they would be damaged by an electrostatic discharge – for example if touched by a worker – there are electrostatically protected areas for the production of such objects in which electrostatic discharges should be avoided as far as possible. The abbreviation EPA to designate these areas is derived from the English term “electrostatic protected area”.

However, it is not only important to protect highly sensitive electronic components from irreparable damage caused by uncontrolled discharges. In some factories and other places, highly flammable substances are used that can ignite in the event of a spark caused by an electrostatic discharge. This can even lead to explosions if the spark hits a gas or coal dust, for example. ESD shoes can offer a certain degree of preventative protection here, whereas normal work shoes cannot.

How an ESD shoe works

To prevent uncontrolled electrostatic discharge – for example near an electronic component – from occurring in the first place, ESD shoes are designed to dissipate electrostatic charges from the wearer’s body in a controlled manner via the sole of the shoe, which is done by earthing the wearer when standing on an ESD floor. The risk of uncontrolled discharges, for example when touching sensitive components, can therefore be reduced by wearing ESD shoes.

The sole of ESD shoes is usually made from a polyurethane plastic, also known as a PU sole. Areas of application for ESD shoes include

• Electrical engineering production
• Semiconductor technology production
• Microchip production
• Battery production
• Aviation industry
• Manufacturing of medical devices
• Watch industry
• Research facilities
• Hospitals

Descriptions of ESD shoes often state that they are antistatic. However, antistatic properties and the ESD capability of shoes are not always the same thing. A shoe is said to be antistatic if the contact resistance is between 100 kiloohms and 1 gigaohm. If the resistance is lower, it is referred to as a conductive shoe. If the contact resistance is higher, it is known as insulating footwear. This follows from the EN ISO 20345 standard.

The contact resistance that an ESD shoe must have is defined in another standard, IEC 61340-5-1, which states that a shoe is ESD-capable if the contact resistance is between 100 kiloohms and 35 megohms. An ESD shoe is therefore always antistatic, but an antistatic shoe does not automatically have ESD capability. Whether the ESD requirements of the IEC 61340-5-1 standard are met can be recognized, for example, by the yellow ESD symbol on the shoe.

• Sneaker
• Cleanroom shoes
• Boots
• Ankle boot
• Low shoes
• Sandals
• Sandals
• Clogs
• Slipper
• Mules
• Ballerinas
• Street shoes
• Finches
• Overshoes (with ESD tape for dissipation)

For them to be fully effective, the soles of the ESD shoes must be clean. Dirt on the contact surfaces can change the electrical resistance. The same applies to the climate at the respective place of use, i.e. in terms of humidity and temperature. For example, ESD shoes conduct better in the summer months than in the winter months, when the ESD shoes and the wearer’s feet are often cold. A small splash of water on the inside of the shoe usually helps to improve conductivity again. So if you want to be sure that the ESD footwear you are using is working properly in the respective working environment, you should regularly carry out an on-site measurement of the electrical contact resistance at an ESD footwear test station.

In addition to ESD footwear and an ESD floor, other ESD equipment can be used to prevent uncontrolled discharges, such as ESD furniture, ESD wristbands and ESD clothing. However, the easiest way to ground a person is with ESD shoes, as their soles are always in contact with the ESD floor when working in a standing position, provided that the floor has been laid and is functioning correctly. ESD shoes are therefore the main grounding measure.