Shocking: Mitigating the Risk of ESD in Controlled Environments

Everyone has felt electrostatic discharge – or ESD – as the mild shock when you touch something or someone. Static is a natural occurrence. Your skin naturally builds up static electricity from friction and contact with various materials, especially in dry environments. If your skin builds up a positive electrical charge, that charge will seek to correct the imbalance by discharging to another object upon contact. While this discharge is amusing when you rub a balloon on a child’s head and then watch their hair stand on end, it's potentially disastrous in controlled environments with sensitive electronics, hazardous chemicals or stringent cleanliness requirements.  

Three Reasons to Control ESD

The concerns around ESD pose significant risks to personnel, operations and profitability. 

1. Safety: ESD can ignite flammable or combustible substances. This can range from a tiny spark igniting flammable gases to an arc flash event triggering an explosion of high-voltage equipment. 
2. Product damage or failure: ESD can damage sensitive electronics, including semiconductors, electrical circuits, medical devices and other microelectronics. Damage can be catastrophic or latent. Catastrophic damage results in a non-functioning device from the start. Latent damage results in enhanced degradation over time and normal use.
3. Cleanliness requirements:  A cleanroom operator can attract particles if they build up a positive charge that is not appropriately discharged through proper grounding. This can expose substances and processes in the operator’s area to a higher-than-acceptable concentration of particles.

Strategies to Safely Discharge Static Electricity

There are strategies to control ESD for facilities and for operators. At the facility level, controlled environments are designed and constructed with conductive flooring, grounding straps, points and mats, and other grounding systems to dissipate static electricity from surfaces and equipment.

Low humidity increases electrostatic buildup on surfaces and clothing and should be monitored and managed to reduce ESD risk. At the operator level, ESD-compatible garments ensure operators are grounded and wearing products that dissipate static buildup. 

How do ESD Products for Operators Work? 

ESD-compliant garments can cover head to toe, but gloves, finger cots, and shoe covers are the most important since hands and feet regularly come into direct contact with products, equipment, and surfaces in a controlled environment. Here’s a look at these important ESD wearable products and how they work to effectively control ESD:

Shoe Covers: 

ESD-compliant shoe covers are crucial in managing  ESD since they ground the operator. Shoe covers are typically made of polypropylene fabric with stitched seams to meet cleanliness requirements. A conductive black carbon ribbon is stitched into the bottom seam of the shoe cover with sufficient length for the other end of the ribbon to tuck securely inside the operator's sock or shoe.

One end of the ribbon maintains contact with the operator’s skin near the ankle, and the other end is on the bottom of the shoe cover, contacting the floor. This carbon ribbon conducts static buildup on the operator’s skin to the conductive cleanroom floor instead of to product, materials or equipment.

Vinyl and nitrile gloves naturally dissipate static electricity. These gloves don’t ground the operator by conducting static electricity to the ground like ESD shoe covers, they prevent discharge by dissipating static electricity over the large surface area of the glove.

Gloves

Cleanroom glove substrates are latex, vinyl, or nitrile. Vinyl and nitrile gloves naturally dissipate static electricity. These gloves don’t ground the operator by conducting static electricity to the ground like ESD shoe covers, they prevent discharge by dissipating static electricity over the large surface area of the glove. For cleanrooms with ESD requirements, nitrile gloves offer the highest standards in cleanliness, comfort, chemical resistance, durability, and ESD compliance. Vinyl gloves offer ESD compliance but are inferior to nitrile in comfort and chemical resistance. Latex gloves are not ESD compliant, as the material is an insulator (versus dissipative or conductive).

Nitrile finger cots are inherently static dissipative, and latex finger cots can be treated with a conductive black carbon application to mitigate ESD risks.

Finger Cots

Finger cots are not typically used in cleanrooms since they do not encapsulate particles from the operator’s entire hand and wrist area. They can, however, comply with ESD prevention requirements for other controlled environments.

Finger cots have the same substrate options as gloves (latex, vinyl, or nitrile). For ESD-sensitive environments, nitrile finger cots are inherently static dissipative, and latex finger cots can be treated with a conductive black carbon application to mitigate ESD risks.

Require ESD Packaging

Proactive controls reduce the risk of static contamination. When sourcing these products for your organization’s controlled environment, ask your supplier what measures are taken during packaging to reduce friction so products do not introduce static electricity in your facility. Products with the highest ESD requirements should be available in static shielding metalized packaging instead of poly bags.

Final Words: Ground and Dissipate

Explore More Resources:

How to Avoid Electrostatic Discharge (ESD) in a Cleanroom - Video

An Introduction to ESD by the EOS/ESD Association

Learn more about the EOS/ESD Association which advances the understanding of EOS and the theory and practice of ESD avoidance