Without special footwear, some ESD floors cannot prevent static discharge. Learn why, how options differ, and how footwear interacts with flooring materials.
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Preventing Static: ESD Flooring the First Line of Defense
Regular floors are insulators. This means they can’t be grounded. With a regular floor, static charges stay on its surface. They have nowhere to go. They’re stuck. Instead of providing a path to ground, regular floors create charges on people as they walk across the floor.
With ESD floors, conductive elements are added to the flooring material in the manufacturing process; these conductive elements draw static downward, away from the surface of the ESD floor, through the thickness of the material, across the underlying conductive ground plane, to copper strips connected to ground.
While conductivity is vital to protecting static-sensitive electronics, providing a path to ground does only part of the job. When people walk across the floor, the friction between the soles of their shoes and the surface of the floor generates a triboelectric—or static—charge, called walking body voltage. This is true of regular, as well as with certain—in some cases, very effective—static-control floors.
The charge stays in place until the person touches someone or something, then releases to that person or object. This sudden rush of electrical current, called an electrostatic discharge, or ESD, can wreak havoc in any environment where sensitive electronics are manufactured, handled, or used.
ESD floors are designed to discharge static electricity to ground and eliminate charges from building as people walk—protecting electronics and electronic equipment from damage caused by ESD.
Footwear and Charge Generation
Say “static,” and most of us think about static cling or the pesky zing we get from doorknobs. In fact, static is an invisible threat. To feel a static shock, the charge must be at least 3500 volts. But a charge as low as 20 volts can disrupt data or damage or destroy the microcircuits inside electronic components.
To prevent damage caused by random static events, an ESD floor must perform two functions:
1) Provide a safe and effective pathway to ground;
2) Prevent the generation and accumulation of static when people walk on the floor.
Without the use of special ESD footwear—heel straps, toe straps, sole straps or ESD shoes—some static-control floors meet only the first requirement: they do not prevent static from accumulating as people walk.
The type of footwear used in the space also affects charge generation. Shoes with PVC soles, for instance, generate more static than shoes with leather soles. Because of its triboelectric propensities, leather is naturally low-charge generating; leather also absorbs moisture, which acts as a conductor to reduce static charges.* However, the anti-static tendency of leather is not reliable; in lower humidity ranges, leather shoes are not always anti-static.
Leather shoes generate too much static to meet the body voltage limits for ANSI-certified electronics manufacturing and handling.
That’s why, when selecting an ESD floor, it’s crucial to determine what type of shoes people will wear in the environment—and, if the floor is not low charge generating, mandate the use of ESD footwear.
What is ESD Footwear?
Footwear is the meeting point between the floor and a person walking on the floor. When shoe soles come into contact with the floor, the conductive elements in ESD footwear form an electrical bond or bridge between a person’s body and the carbon veins in static-dissipative or conductive floors, discharging static to ground.
Used in conjunction with floors, such as static-dissipative or conductive vinyl, that do not inhibit static generation, ESD footwear prevents static generation when people walk.
ESD footwear comes in several forms: heel straps, toe straps, sole straps, and shoes. Benefits and performance vary, with buyers selecting footwear based on their needs and priorities.
Made of conductive material, heel straps cup the heels of the shoes. The conductive strap forms an electrical bond with the conductive fibers or filaments in the ESD floor. An attached conductive ribbon tucks into the shoe and is inserted into the sock (if worn), making contact with the skin, which is mildly conductive. The conductive ribbon (or band) bleeds static from the surface of the skin, preventing charges from accumulating.
Heel straps are inexpensive and can be used with regular footwear. For those with a tight budget or transient workforce, who may not wish to invest in costlier ESD shoes, or with workers reluctant to wear industrial-type footwear, heel straps are a good choice.
Conductive toe straps cup the toe of the shoe. As with heel straps, an attached conductive ribbon or band tucks into the shoe, bringing the person, shoe and floor to the same electrical potential, and discharging static to ground.
Like heel straps, toe straps are inexpensive and can be used with regular footwear. Typically worn with high- or thin-heeled shoes, conductive toe straps create an electrical contact point between the floor and sole of the shoe.
Conductive sole straps cover the full sole of the shoe, providing electrical contact with the ESD floor as long as some portion of the shoe sole is in on the floor. Like heel and toe straps, sole straps come with an attached conductive ribbon that tucks into the shoe, drawing static away from the wearer, through the conductive sole strap to the floor, dissipating charges to ground.
Less expensive than ESD shoes, conductive sole straps provide the same full electrical contact with the ESD floor—even when the feet are partially lifted or one foot is off the ground. If a person is squatting, for instance, the heels of his or her shoes are generally lifted, rendering heel straps ineffective. With sole straps, conductive contact would still occur through the toes of the shoes. The surface area of ESD sole straps is also large enough to make electrical contact even on floors with a low density of conductive particles.
Continuity ensures constant protection.
ESD shoes are no longer your grandfather’s—or grandmother’s—hideous, orthopedic-looking footwear. Today, ESD shoes come in a variety of styles to suit both men and women. More expensive than heel, toe, or sole straps, conductive or dissipative shoes are typically used in electronics manufacturing and assembly applications, and selected to help to ensure compliance with ANSI/ESD footwear protocols.
Easiest type of footwear to use
ESD shoes are superior to heel, toe and sole straps in that shoes are easier to put on, so more likely to be used properly. Shoe straps can slip or slide, be attached incorrectly, or—if the conductive band is incorrectly inserted—straps can fail to make electrical contact with the skin.
Compliance is easy to monitor.
ESD footwear should never be worn outside the facility. Upon entering the workspace, people should be required to put on static-protective heel, toe or sole straps, or change to ESD shoes. Requiring people to change shoes makes compliance relatively easy to police. With the ESD symbol on the back or side of the shoe, ESD shoes are easy to spot in the work area. As they’re bigger and bulkier, ESD shoes are also easier to see than heel, toe or sole straps.
Full, continuous contact with the ESD floor
In terms of static protection, ESD shoes are similar to conductive sole straps: both types of ESD footwear provide full contact with the ESD floor, and protect against static even when one foot is off the ground or the feet are partially lifted. Continuity ensures constant protection.
Flooring Materials and ESD Footwear
Standard, non-ESD flooring
As noted above, regular, non-ESD flooring is an insulator and cannot be grounded. Special ESD footwear will neither ground nor prevent static generation on regular, non-ESD floors.
ESD Vinyl and Epoxy
With ESD Footwear
Some very high performing static-control floors—conductive vinyl, for example—are made from ordinary static-generating materials (in this case, regular vinyl) with a small distribution of carbon or graphite particles. The floor is groundable and the embedded conductors provide a safe pathway to ground. Because the material itself generates static, ESD vinyl does not reduce walking body voltage on a person wearing ordinary footwear.
For the floor to be effective, protocols must be in place mandating that every person in or passing through the environment wear static-protective footwear religiously.
This does not mean conductive vinyl is an inferior product. It means that static-control vinyl works best in applications, such as electronic manufacturing and assembly, where footwear and traffic are tightly controlled and regularly monitored.
ESD epoxy, recommended for applications requiring extreme durability—where forklifts are used, for example—is highly susceptible to static. For this reason, ESD epoxy should never be used without tightly enforced protocols requiring the use of ESD footwear.
With Street Shoes
In environments, such as server rooms, 9-1-1 dispatch operations, FAA flight towers, or mission critical data centers, where there are no protocols for ESD footwear—or in environments where protocols are in place but footwear is not regularly monitored or mandates can’t be enforced—and people wear regular street shoes, ESD vinyl and epoxy will not prevent static buildup and should not be used.
ESD Carpet and Rubber Perform Well With or Without Special ESD Footwear
In environments where people wear regular footwear, static-dissipative carpet tile and ESD rubber are the best ESD flooring choices. Static-control carpet and ESD rubber provide a safe pathway to ground while also reducing walking body voltage—regardless of footwear.
Because of their ability to provide redundancy—a.k.a. belt and suspenders—ESD rubber and carpet are also superior choices for electronics manufacturing facilities. If footwear protocols are haphazardly followed, ESD rubber and carpet still provide a high level of protection that ESD vinyl and epoxy are incapable of providing.
An independent study, conducted by MIT Lincoln Laboratories, found conductive rubber to be the only ESD flooring material that protects against static regardless of footwear.
Static-Dissipative Carpet Tiles
Static-dissipative carpet tiles contain thousands of dissipative fibers that sweep static off the soles of shoes as people walk, and direct the charge safely to ground—much the way small brushes eliminate static on high-speed copiers as paper is fed into the collator.
Static-dissipative rubber is a naturally low static generator. Because rubber is similar to the material used in the soles of regular shoes—and since similar materials generate minimal static when they interact—ESD rubber also inhibits static without the need for special footwear.
ESD Footwear: Essential to Meet Electronics Industry Standard ANSI/ESD S20.20
For electronics manufacturing and assembly applications, industry standards require that resistance to ground (RTG) including the person, footwear and floor be < 1 billion ohms or ≤ 1.0 X 10E9, and the static generated in a standard walking body voltage test (while wearing special ESD footwear, per ANSI/ESD STM97.2) < 100 volts.
With regular footwear, rubber and carpet minimize static generation. But when people walk on the floor wearing regular street shoes, these materials do not keep charges under 100 volts. Since 100 volts is the maximum allowable charge, all electronics applications involving ANSI/ESD S20.20 require the use of ESD footwear.
- 7 Common Mistakes Selecting an ESD floor
- Choosing ESD Flooring for:
- ESD Footwear: What Is It and When Is It Necessary?
- Facility Managers’ Guide to Selecting ESD Flooring
- Keeping Architects Grounded
- The Need for Due Diligence in Specifying Static-Free Flooring
- Standard of Care for Specifying Floors in Mission-Critical Spaces
- Static-Control Footwear for Electronics Manufacturing and Handling Applications
- Understanding the Hidden Costs of ESD Flooring
With Staticworx ESD flooring, you never have to choose between performance and aesthetics. Our beautiful, high quality ESD carpet tile, vinyl, EC rubber tile and sheet goods, and ESD epoxy floors are as beautiful as they are functional.