Operator Earthing - Are you doing it correctly?

Thank you guys for such an awesome response to my last blog post on Partial Inerting. It was made clear from the responses, that it is rather an unexplored topic in many parts of the world. Keep sharing your thoughts and keep sharing the blog with your colleagues, friends and students.

For today's blog post, I am picking up a basic concept of OPERATOR GROUNDING and what is the correct way to actually do it. There are many industries who provide Safety Shoes (maybe antistatic/ static dissipative) to their employees working on the shop floor, however, a substantial misconception regarding grounding practices exist in the industries that "If I have provided my operator dissipative shoes he has been grounded adequately." Also, there are many who purchase shoes with higher resistance to the ground then what is recommended by the standards.


As per IEC standards, the overall resistance of operator to ground should be less than 100 megaohms in order to prevent a probable spark discharge of sufficient energy from the operator. As discussed in my previous blog posts, spark discharge is a kind of Electrostatic Discharge (ESD) which is possible by an ungrounded conductor and the human body is a good conductor. Hence, an ungrounded operator or operator with resistance more than 100 mega ohms can result in a spark discharge which can, in turn, ignite flammable atmosphere with MIE of up to 30mJ.

Operator grounding involves the following:

1. Static Dissipative Shoes
2. Static Dissipative Insoles
3. Static Dissipative Socks (can be cotton)
4. Static Dissipative Flooring (can be grounded Static Dissipative Mats or grounded SS platform)

Even if one of the components is not dissipative, the operator would not be grounded completely.

For Example:

• If an insulative powder is spilled on the ground where an operator is standing, then it can hinder operator grounding. 
• If there is some insulative liquid which is stuck to operator shoes, then it can also hinder operator grounding. 
• If there is an insulative paint coating or non-dissipative flooring, then it can hinder operator grounding even when the operator is donning dissipative shoes with dissipative insoles and socks.

In order to ensure adequate resistance to ground, the overall resistance of operator can be verified at the plant entrance itself using a simple device as shown in the figure below:

Ref: Static Dissipative Footwear Tester on https://www.newson-gale.com/product/sole_mate/

The device is designed to test the condition of static dissipative footwear prior to entering safety critical hazardous areas exposed to potentially ignitable atmospheres. All International Standards recommend regular testing of static dissipative footwear. It is imperative to ensure that electrostatic charge is not accumulating on operator bodies.

The device shown above tests the condition of the shoes by measuring the resistance of the electrical loop through the operator and their footwear. If the resistance of the shoes is too high, the device will indicate that the shoes have failed the test via a red lamp and buzzer alarm. If the shoes pass the test a green lamp will indicate to the operator that the shoes are fit for purpose. Additionally, users can interlock the tester with audible alarms or entry doors into hazardous areas so that personnel not wearing suitable footwear cannot enter the hazardous area.

P.S.: Although the operator can be grounded with a wrist-band or flying lead and clamp, but that is something that hinders the operator's movement.

Do share this with your friends and colleagues. It is important that we improve the basic understanding of operator grounding to prevent Electrostatic Discharges.