Electrostatic discharge is a very common everyday electrical phenomenon which can not be avoided or prevented, however, it can be controlled.
All materials carry some quantity of electrons which give the material a net charge. This charge is said to be static since the charge carriers aren't going anywhere. The Electrostatic Discharge event occurs, when any two materials are put together, or brought near to each other, or are separated. During this movement of materials relative to each other, electrons will migrate from one material to the other. This movement of electrons (which are charge carriers) is an electrical flow or current and is considered a discharge, hence the name Electrostatic Discharge
In many cases, Electrostatic Discharge events of only a few volts is enough to cause serious permanent damage to semiconductor devices. At the microscopic level, the damaged area looks like a moon crater or a welded spot where the silicon materials where melted and fused together. Electrostatic Discharge events do not always destroy an electronic component immediately on the first occurrence. Sometimes, many events occur over a period of time. Each occurrence adds a bit more damage until the component finally fails. Any damage is always permanent and cumulative. Once the device finally fails completely, the failure is referred to as a catastrophic Electrostatic Discharge failure. Electrostatic Discharge damage which is not catastrophic leaves the component operable, but damaged, such that it will fail at a later time under normal stresses.
The worst part of Electrostatic Discharge is that the damage occurs deep within the device at a microscopic level, so you cannot ever see it to verify that Electrostatic Discharge was the culprit.
Despite a great deal of effort during the past decade, Electrostatic discharge still affects production yields, manufacturing costs, product quality, product reliability, and profitability. Industry experts have estimated average product losses due to static to range from 8-33%. Others estimate the actual cost of Electrostatic discharge damage to the electronics industry as running into the billions of dollars annually. The cost of damaged devices themselves ranges from only a few cents for a simple diode to several hundred dollars for complex hybrids.
As a result it is vital in clean rooms and other technical sensitive areas that these Electrostatic Discharges are controlled. One common Electrostatic Discharge event occurs simply when a person walks across the floor. Static electricity is generated as shoe soles contact and then separate from the floor surface.
By definition for a material to be antistatic or electrostatic dissipative (ESD) it must have a electrical resistance between the limits of 1x105 Ohms/square and 1x1012 Ohms/square. Anything over 1x1012 Ohms/square is considered insulative and not safe.
When used in conjunction with ESD flooring, ESD footwear is a very reliable method of grounding personnel. The charge goes to ground rather than being discharged into a sensitive part. To prevent damaging a charged device, the rate of discharge can be controlled with static dissipative materials. No special socks are needed as the electric path from sole to body is made through natural perspiration
Electrostatic discharge footwear is designed to ensure constant drainage of static charges from the body to ground. For ESD footwear to be effective both inner soles and outer soles need to be static dissipative and provide continuous electric contact of the foot to ground as required by ESD standards.
Replacing the ESD insole that is found in ESD footwear with a standard non ESD insole will nullify the ESD properties of this footwear.