Charged Questions Archives

First, it is important to understand that an ESD floor should never be purchased based upon whether it is called dissipative or conductive. These terms are inappropriate for specifying permanent static control flooring. (See article: Taking the Mystery Out of Selecting Static Control Flooring) Ideally, a floor should be specified based upon both its propensity to tribo-charge people and its electrical resistance to ground (measured in ohms or meg-ohms) when installed. Descriptions like dissipative and conductive do not adequately describe these properties. When evaluating an ESD floor for its ability to control static, ESD engineers verify that:

1) The floor will not generate more than 100V when someone walks on it;

2) The total system resistance of the person, footwear, walking surface and ground is less than or equal to 3.5 x 10⁷ or 35 meg-ohms maximum.

The answer to this question is similar to that of the previous question. The word antistatic does not designate some special electrical resistance range. Antistatic merely refers to a material's propensity to charge other materials during contact and separation. If a floor has antistatic properties, it means that under a particular set of circumstances—say, a person walking across the floor wearing Rockport walking shoes—a significant static charge does not build up. If that same person walked across that same antistatic floor wearing leather-soled or athletic footwear, however, a static event might occur. If we were to focus on a particular set of conditions, as just described, we could end up with a floor that works only under those conditions, creating a situation that would be difficult to monitor or control. For this reason, we look at antistatic properties as part of a much bigger picture that includes electrical resistance to ground and tribo-charging performance at low relative humidity.

Most ESD floors are rendered electrically conductive by adding, blending or weaving carbon and graphite into standard flooring materials. Vinyl tile is made conductive by adding conductive carbon chips or veins into the vinyl raw materials used in standard vinyl flooring. Carpets are made conductive by weaving in thousands of carbon-coated conductive fibers. Rubber is made conductive by adding either carbon powder or adding chemicals that reduce electrical resistance of regular rubber flooring. Epoxy coating manufacturers utilize several different methods for making the coatings conductive, including: fiber technology, conductive aggregate additives, carbon and graphite particulate blending and sometimes a combination of several in the same coating.

This is an interesting question. A quality product should provide a lifetime of service. Likewise, conductive properties should last for the life of the product. Some "dissipative' vinyl products, however, require regular recoating with antistatic floor finish in order to maintain acceptable electrical properties. These should be avoided unless the solution does not need to be a long-term one. Some ESD carpets require periodic applications of a topical treatment containing antistat. The problem with applying the antistat is that the maintenance crew doesn't always know when it is time to reapply the antistat or when the humidity conditions might be too low for adequate performance from a surface additive. Fortunately, there are many products that will provide unlimited electrical performance without any use of maintenance additives. Make sure you read the fine print.

As stated in the earlier question, antistatic and conductive are mutually exclusive terms. Antistatic has to do with properties involved in charging of materials when they contact and separate. Conductive properties refer to the ability of a material to conduct an electrical charge.

As long as the ESD flooring has a resistance to ground of over 25,000 ohms, the floor can be used in most factory and hospital situations. Operating rooms, which often house electrical defibrillation equipment, require floors to have resistance to ground ratings of over 25k ohms. A simple calculation that takes into consideration the highest voltage and current of electrical equipment used in a particular application will determine what is and what is not safe. But most standards recognize the 25k ohm number as a safe lower parameter.

Electrical bonding between ESD floor tiles is achieved from the conductive adhesive and not as a result of individual tile to tile contact. The adhesives used in conductive installations is highly conductive and provides excellent continuity across the entire floor. Conductive adhesives take the place of so-called copper grounding grids beneath the floor. The conductive adhesive must be attached to some form of ground to meet relevant specifications.

Static generation occurs more easily when the climate is dry. Static also stores better on surfaces when the air is dry. Sometimes an ESD floor will appear to perform when the humidity is over 40 percent. This is quite normal with carpet. Any ESD carpet should be tested at least as low as 12 percent relative humidity. Unless the carpet is loaded with carbon fibers, most carpets will fail below 20 percent RH.

This is one of those questions that should be answered only by a qualified flooring professional, based upon either a site inspection or a lengthy conversation. Almost any floor can be installed over an old floor as long as the old floor is in good condition and well-bonded to the sub floor. Some floors are much easier and less risky to install over old floors. Vinyl, for example, can be installed over existing vinyl. However, vinyl is stiff and unforgiving—it could delaminate if the adhesive does not cure well or if the surface is slightly uneven. The possibility of failure is much greater installing vinyl over vinyl than it would be if ESD carpet were installed over old vinyl. Carpet tiles are flexible and the release adhesive bonds extremely well to old vinyl and epoxy. Many installers prefer installing carpet tiles over old vinyl rather than over new concrete. Often, the choice of installing over old floors involves a decision to avoid removing old vinyl because it contains asbestos and the cost of removal might be a budget buster.

Moisture permeation through concrete slabs can wreak havoc with all types of flooring. Several years ago, the Rubber Association determined that levels exceeding 3 pounds of moisture per 1000 square feet per 24 hour period caused serious problems, such as delamination, adhesive breakdown and adhesive oozing. High moisture can also lead to the development of bacteria and molds, which, in addition to causing foul odors, contribute to sick building syndrome. The industry standard test for moisture permeation is the calcium chloride test. The test is simple and accurate. For the reasons stated above, high readings must not be ignored.

Add conductive drag chains and casters to materials and carts to ground them to esd flooring.

The photo to the right shows a recently completed Conductive Vinyl tile installation. This client plans to use "wire shelf carts" to move electronics assemblies around the floor. Even though this floor is grounded and conductive, the cart will not be grounded as its wheels are insulators. Static cannont drain through an insulator even if that insulator is resting on an esd, anti static floor. The cart shown in the photo does not have a conductive drag chain or conductive casters. Adding conductive wheels or drag chains to the cart provides a path for charge in the cart to drain to ground, in this case the conductive floor.

A chain is only as good as its weakest link. In an electrical chain, a weak link creates a breach in conductivity. A loose or disconnected wire is the simplest example: If a wire is loose or a cord is unplugged, the chain ends; the electrical current does not reach its intended target. With static control, the idea is to discharge the built-up (static) electrical current to ground. A person can wear a wrist and/or heel strap and sit on an ESD chair, but if the floor cannot discharge the static generated by friction-walking across the floor, moving in the chair-the charge cannot flow to ground. It has no way to get there.

Remember: a static charge cannot discharge through plastic or other electrically insulative flooring materials.

Think of a person's body as an isolated conductive object (AKA a capacitor) capable of storing static electricity. Kind of like a two-legged Van-de-Graff generator. When the static-charged person approaches and then sits in the conductive chair, the static charge on the body immediately flows to the chair-until both the body and the chair share the same charge. We call this sharing potential.

An electrical charge can flow only between conductive objects. Since the floor is non-conductive, the charge remains static. In the scenario you have described, the chair and the person remain ungrounded because they are isolated from ground. There is no conductive path through the floor. If either the person or the chair make contact with electronic equipment - both will discharge to the equipment simultaneously. Without a conductive floor, a conductive chair is nothing more than another charged body looking for a place to discharge. Kind of like an accident waiting to happen.

What you're really asking is this: how do I ensure continued conductivity across the static control floor? The answer must involve your choice of static control flooring.

First, there are several different types of static control floor covering. All possess different properties and some of the floor coverings have limitations. For example, Armstrong manufactures a product called SDT. Armstrong SDT requires special waxes to make it perform. Some antistatic broadloom cannot be grounded at all because it is not conductive.

Staticworx® vinyl tile is a permanently conductive material that requires no special care to remain conductive. Waxes are not needed. Our vinyl tiles can be grounded using a simple 24 inch long, 2 inch wide, copper strip under one tile. We provide the strips as part of our package. The other end of the strip is attached to an electrical outlet using one of the screws in the outlet box.

Only one ground connection is needed per 1000 square feet. The other tiles are bonded via our conductive pressure sensitive adhesive-Groundtack-which contains conductive coated fibers.

Questions about the differences between what we commonly call “antistatic carpet” versus “permanent static control carpet” (also known as ESD carpet) usually get raised at some point in every project. The distinction is critical. Numerous flooring products are bought with the belief that they are antistatic when in fact - they often are, or become, static generators. When that misapplication involves the choice of flooring for common office space or a hotel lobby, it’s no big deal. But if the flooring is for the command center of a public utility or the server room for a stock exchange, not understanding the technical differences can be catastrophic.

In order to answer this question clearly there are a few pieces of information you’ll need to know.

Never rely on the AATCC-134 specification to judge a floors' static control protective properties. To protect electronic devices and equipment, static control floors must:

1. Be antistatic - the floor must prevent the generation of static electricity
2. Be capable of being grounded. A ground wire alone does NOT ground the floor. The ESD flooring material must be made with conductive elements such as carbon, carbon fibers or other conductive materials
3. Must have permanent static control properties - independent of environmental conditions such as temperature or humidity.
4. Be traffic-resistant — traffic and chair castors should not diminish the static control performance of the floor.
5. Perform without the need for special maintenance procedures such as waxing, spraying or buffing with antistats.

Conductive properties are easily measured with simple, inexpensive ohm-meter.

Random static discharge will wreak havoc inside your data or call center causing lost or corrupted data, dropped calls, pc lockup and blown headsets. Designers of 24/7/365 mission critical spaces such as data centers, 911 call centers, command centers, server rooms and flight control towers routinely design their spaces to withstand external threats such as weather, power outages, earthquakes and, in some cases, even biological threats. An invisible internal threat that is sometimes overlooked, electrostatic discharge (ESD) can wreak havoc inside any mission-critical space. Dropped calls, blown headsets, PC lockup and lost or corrupted data represent just a few of the problems.

Although we appreciate your interest in our epoxy ESD flooring, we need to caution you about the limitations of static dissipative or conductive epoxy coating in a data center/server room application.

All ESD coatings are formulated to eliminate static build-up by providing a ground path. The ability to be grounded is achieved by adding either conductive fibers or carbon and graphite particulate. The fibers and particulate enable us to create an electrical bridge through a material that otherwise, is an insulating static generator. However, conductivity is the only static control property provided by a coating. The coating is not antistatic. In other words, ESD coatings will only eliminate static if they are used in conjunction with special static control footwear. If people walk on them with standard footwear (dress shoes, sneakers, hiking boots etc.) the coating will neither prevent the generation of static nor remove the charge after it is generated. You would still need to bridge the electrical gap between your body and the floor by wearing special footwear special. Walking on any ESD coating in street shoes would be the same as walking across a sheet of plastic. The result would be the generation of thousands of volts and an increased likelihood of an ESD event!

In data centers we recommend the following conductive materials:

1. Conductive rubber that also has anti-static properties.
2. Conductive vinyl tile with anti-static properties.
3. Conductive carpet tile with anti-static properties.

We often supply floor finishes for use on soiled ESD vinyl sheet flooring. The application of a polish or finish usually becomes necessary a few months after installation; as you probably know, when vinyl ages and is exposed to foot traffic, it becomes porous and begins to collect dirt. A good ESD polish will re-seal the pores without hurting the static control properties of the floor.

Additionally, if the flooring in the MRI suite is only static dissipative and not a conductive product, it would not be unusual for people to generate static when they walk on that floor with ordinary footwear – as opposed to special static footwear. Keep in mind, a person would not even realize they were generating charges because it takes at least a 3500 volt zap before the human body can sense a static discharge. The electronics inside MRI equipment is sensitive to a lot less than 3500 volts – hence the reason for installing the ESD floor in the first place. The static control coating would deal with that problem as well.

If you encounter flooring applications for these types of areas in the future, we strongly recommend installing 2 layer Staticworx® EC Rubber. A recent study done by MIT demonstrated the near impossibility of generating appreciable amounts of static on 2 layer rubber – no matter what footwear was worn. As a comparison they measured fewer than 200 volts on rubber versus over 3000 volts on the dissipative vinyl. And because 2 layer Staticworx® EC Rubber flooring is plasticizer-free, it presents none of the maintenance issues associated with vinyl.

From a purely technical perspective, a floor’s ESD properties can be evaluated:

1. by measuring the floor’s resistance to ground;
2. by measuring the total resistance ground of the system including the person and the floor;
3. by using a walking test to measure voltage generation on a person;
4. or by testing some combination of the above.

According to the recommendations of ANSI/ESD S20.20, it is acceptable to install a floor with a resistance to ground (RTG) that is =1.0 X10E9. But, to comply with ESD standards, the floor must not allow body voltage generation over 100V.