Should I choose a conductive or static-dissipative floor?

This is one of the most common questions we hear from buyers and specifiers. Most of the time, when people ask – or assume, incorrectly, that they should use one or the other – it’s because they don’t really understand the difference. Technically, conductive and static-dissipative are descriptive terms, defined by the electrical resistance of the floor, as measured by an ohm meter, according to ANSI/ESD Standard Test Method 7.1.

Conductive floors measure below 1.0 x 10⁶ ohms to ground.

Static-dissipative floors measure above 1.0 x 10⁶ and below 1.0 x 10⁹ ohms to ground.

Floors measuring above 10⁹ are insulative (with little to no measurable conductivity)

Okay, you’re thinking. That’s all well and good – in practical terms, what does this mean?

Pretend for a moment that you’re emptying water from a large jug to a smaller container. To control the flow of water, you grab a funnel. As you pour, water collects in the cone then moves through a hose that’s narrower than the cone. The narrow hose slows the rate at which water leaves the cone and flows into the container.

Enlarging or shrinking the diameter of the hose will either increase or restrict the rate at which water is “discharged” from the funnel.

The rate at which static charges flow is determined by the degree of conductivity or static dissipation.

Like a funnel with a large open hose, the conductive elements in a conductive ESD floor allow static electricity (or any form of electricity) to flow quickly across its surface or through the thickness of the flooring material.

Static-dissipative flooring, on the other hand, is more like a funnel with a narrow hose. With less conductivity, static flows across and through the thickness of the flooring material at an appreciably slower rate.

How ESD Flooring Works

The conductive elements in a properly performing ESD floor draw static away from a charged person or object, and through the thickness of the flooring material. From the floor tiles, static charges move to and across the underlying ground plane – conductive adhesive or underlayment – to copper strips placed at the perimeter of the room. From the copper strips, charges move to an A/C outlet or other type of ground connection to ground.

The graphic below shows the flow of static electricity from a person on an ESD floor to ground.

Conductive Floors

A conductive floor is more conductive – or less resistant – to the flow of electricity. A highly conductive floor – measuring 2.5 x 10⁴ ohms to ground or below, for example – provides too little resistance. Like water gushing through a funnel with an overly large hose, static charges will race across or through an overly conductive floor.

Electronics Environments

In electronics manufacturing and handling environments that follow protocols set out in ANSI/ESD S20.20-2014, everyone in or walking through the space is required to wear special ESD footwear. As part of its design, ESD footwear has built-in electrical resistors. The resistors slow the rate at which electricity passes between the floor and soles of shoes to the person wearing the ESD footwear (toe, heel or sole straps or ESD shoes). This electrical resistor is intended to protect the wearer from electrical hazards if the floor is too conductive.

End User Spaces

The protocols in data centers, flight control towers, telecom spaces, 9-1-1 dispatch centers and other end-user spaces are different from those for electronics manufacturing and handling spaces.

In end-user spaces, people are not usually required to wear ESD footwear. In environments like critical call centers, 9-1-1 dispatch operations, and FAA flight towers, where people work with electrified equipment – i.e., equipment plugged into a power source – conductive flooring is generally prohibited. That’s because if a highly conductive floor were somehow exposed to an A/C power source – from a short circuit, for instance – the floor could become part of a dangerous electrical circuit, exposing people in the space to a significant shock hazard.

The chart below shows the results of tests performed by an independent lab on overly conductive flooring.

As you see in the chart, both static-dissipative carpet and EC (electrically conductive) rubber restrict the flow of electricity sufficiently to prevent the floor from becoming part of a dangerous circuit. An overly conductive carpet, on the other hand, could expose the same person in the same scenario to a significant shock hazard.

Like water in an overflowing funnel, when a person is carrying excess static electricity, the charge has to go somewhere.

If the electrical resistance of the floor is too high – > 10⁹ ohms – , static cannot flow to ground quickly enough to prevent static charges from accumulating on people. These charges stay in place, on the body, and jump to the first person or object people touch. This transfer of static electricity is called electrostatic discharge, or ESD.

A minute static discharge (ESD event) – a discharge so small that humans can’t even perceive it – can damage or destroy static-sensitive electronic equipment and components.

The Sweet Spot

Is there an ideal range for conductivity or static dissipation?

We’re glad you asked. Yes. We call it “the sweet spot” – that is, between 1.0 x 10⁵ and 1.0 x 10⁸.

Standard ANSI/ESD S20.20-2014, governing electronics manufacturing and handling facilities, allows resistance up to 10⁹ ohms to ground. While, in some cases, a floor measuring 10⁹ may provide adequate static control, ambient humidity and other environmental factors can affect the ESD properties of a floor. If a floor measuring at the upper end of the acceptable resistance range were to lose any conductivity at all, it could too easily become out of spec, ineffective or even insulative.

Resistance measurements between 10⁵ and 10⁸ fall within the acceptable range for any ESD application. This range offers adequate tolerance against external variables like changing humidity and surface contamination.

Questions? We’re here to help. Call today: 617-923-2000

Here’s a short cartoon video using a slightly different water analogy to demonstrate The Sweet Spot.

No industry standard rates ESD (static-control) floors based on levels or classifications of static control.

You may have heard a sales or customer service rep (or flooring contractor) refer to ESD flooring by level, rating the floor Static Control Level 1, 2 or 3. Smart marketing strategy! A system of levels or classifications simplifies the scientific data used for standards and specifications. As psychological research shows, Easy = True.

If you’re an ESD buyer or specifier who has not mastered or doesn’t care to wade through complex technical data, defining static control by level is a welcome strategy. And why not? It makes your job easier. There’s no shame in choosing a quicker, easier option when it’s offered.

No, really.

Some engineers we meet don’t know much more than the average Jane or Joe about the electrical resistance properties of an ESD floor. And don’t care to know.

We get it. It’s time consuming to learn and digest new, unfamiliar concepts. The problem is, for static control floors, levels and classifications are manufactured terms. People certainly don’t use those terms with any malicious intent. The goal is simply to make static-control flooring easier to understand; therefore, their ESD floor an easier sell.

What are “levels” of static control anyway?

Marketing terms. That’s all they really are.

While, in some cases, a conductive floor is a superior option – for example, EC (electrically conductive) rubber outperforms static dissipative rubber; that’s because the conductivity in dissipative rubber comes from a liquid additive that leaches out over time. With ESD carpet, depending upon the actual resistance readings, the opposite is often true. In critical applications – such as FAA flight towers, E-9-1-1 call centers, telecom spaces, for example – industry standards require dissipative flooring and, in fact, don’t allow for resistance readings below 1.0 x 10⁶.

To claim that more conductivity is better or that a conductive floor provides greater – or a higher level of – static protection than a static-dissipative floor is an oversimplification, and – as shown above – can be misleading. (Despite perceptions, easy is not always true.) Properly evaluating/specifying an ESD floor is more complicated than that.

Depending upon the material and how it’s manufactured, a floor can be more or less conductive—have higher or lower electrical resistance. Higher conductivity does not mean the floor is more static protective. In fact, some highly conductive floors are static generators. More on this later.

The required electrical resistance – how conductive the floor should be – varies by industry. In some cases, it depends upon whether or not people in the space are required to wear static-protective shoes. In others, it depends upon the application or type of equipment in use.

Certain applications—explosives manufacturing, for example—prefer conductive flooring; that is, flooring materials that measure in the lower range of electrical resistance (below 1.0 x 10⁶ or 1,000,000 ohms).

Applications such as FAA flight towers, telecom, and E-9-1-1 call centers—require flooring materials to measure in the mid to upper range of electrical resistance: above 1.0 x 10⁶ (1,000,000 ohms) and below 1.0 x 10⁹ (1 billion ohms). These standards are meant to ensure the safety of the people working with or around electrified equipment.

• Please note: conductivity is the opposite of electrical resistance.
  • A floor with higher resistance (measuring in the upper range) would be less conductive, therefore correlating to a “lower level” of static control.

We’re not telling you a less conductive (“lower level” or static dissipative) floor is better for mission-critical environments.

What we’re telling you is: the people who write the industry standards and specifications for flight towers, telecom, E-9-1-1 call centers and other mission critical spaces require the use of less conductive flooring.

As we hinted above, conductivity/resistance is only one of the parameters necessary for specifying an ESD floor. The other crucial factor—having no relationship to conductivity or electrical resistance—is charge (or body voltage) generation.

How to Rate or Evaluate an ESD Floor

Let’s be clear: ESD (Static-control) floors are neither rated nor specified by levels.

ESD flooring should be tested and evaluated using industry-specific standards and universal test methods. Flooring should be selected and specified based upon these electrical metrics:

Resistance, measured in ohms
Charge generation, measured in volts

Electrical Resistance

Electrical resistance readings are taken with an ohmmeter and measure the electrical resistance of flooring material from point to point or point to ground. Electrical resistance tests tell you how fast a static charge can be expected to travel across the floor and how quickly (or slowly) static electricity will bleed from the surface of the floor to ground.

This information is important because if static charges bleed – or dissipate – too slowly, the floor may be incapable of preventing random ESD events from damaging electronic components. If charges bleed too quickly, under certain circumstances the floor could pose a safety risk.

Resistance Testing

Resistance tests follow the specific procedures outlined in ANSI/ESD S20.20-2014, test method STM 97.1. The diagram below shows how the test should be performed.

Note: though measurement requirements differ by industry, every industry uses the identical – universal – test to measure the electrical resistance of static-control flooring materials.

Resistance Measurements – or Facts About Conductivity

As previously noted, electrical resistance requirements vary from industry to industry.

To adhere to safety protocols, any floor installed in the above applications should be verified – after installation – that it does not measure above or below this resistance range. Floors with resistance readings higher than 1.0 x 10⁹ may not dissipate static quickly enough to prevent damaging ESD events; under the right circumstances, floors with resistance readings below 1.0 x 10⁵ could pose a safety risk.

Charge Generation, also called Body Voltage Generation

Many specifiers don’t realize this: a floor can be electrically conductive (or dissipative) and still generate enough of a static charge to damage or destroy sensitive electronics.

In most work environments, static is primarily generated when people walk on the floor. That’s because walking creates friction (between the shoe sole and the floor) and friction generates static electricity. That’s why it’s so important to test charge generation.

Charge generation tests, performed with a voltmeter, measure the static charge generated by a person walking on a flooring surface, wearing a particular type of footwear. (The test should be performed multiple times with subject wearing every type of footwear that may be worn in the space.)

Body voltage tests predict how much static a person will generate – and accumulate on his or her body – as he or she walks across the floor wearing a particular type of footwear.

As noted above, this is important because a floor that generates static can be the source of damaging static events – even if the floor measures in the highly conductive range.

Charge Generation Test

Charge generation—or body voltage—tests are performed according to the procedures outlined in ANSI/ESD S20.20-2014, test method ANSI/ESD STM 97.2.

Body Voltage Measurements

ESD flooring should be chosen to address critical operations based on the sensitivity classification of the electronic components, assemblies and systems. That is, tests should be performed to predict charge generation and measurements should align with the static-control needs of the electronic equipment that’s to be protected.

How much static a component can tolerate depends upon various factors, such as its speed and sensitivity, the way it’s manufactured, or environmental factors it’s subject to.

Here are the basic requirements:

ESDS Component Sensitivity Classification for the Human Body Model (Per ESD-STM5.1)

* Note: Sensitivity increases as Class number decreases

Bottom Line: What’s Wrong with Levels or Classifications of Static Control?

Nothing. there is absolutely nothing inherently wrong with describing a floor by level or classification – assuming the terms correspond directly to industry standards.

To have any relevance to standards or specifications, “levels” or classification must refer to very specific electrical resistance readings. Level 1, for example, would need to mean that this particular flooring material measures between X number and Y number of ohms – for instance, from 1.0 x 10⁸ to 1.0 x 10⁹ ohms.

Even then, to say a particular “level” of static control – or degree of resistance or conductivity – is “better” than or superior to another is meaningless.

What is wrong is using marketing terms as an easy shortcut for specifying an ESD floor.

Why?

Because no legitimate industry standard or specification refers to levels or classifications. Every standard and specification, in every industry, refers to specific electrical resistance parameters measured in ohms.

Furthermore, conductivity tells only part of the story. To ensure your ESD floor will protect your equipment, the material must also be tested for charge generation.

This may not be what you wanted to hear. If not, we apologize. We don’t like making your job any more complicated or time-consuming than it needs to be. But – if you’re specifying a floor with electrical properties, you need to reference metrics. This is the only way to be sure your new floor meets the code, parameters and specifications defined by your industry. And to do the job right, you’ve got to put in the time.

Excerpt from FAA 019f, governing flight control towers and flight support:

From FAA 019f

5.8.9 Electrostatic Discharge (ESD) Control Flooring and Floor Coverings
ESD control floors and floor coverings shall have a point-to-point resistance and a surface-to ground resistance of greater than 1.0 x 10⁶ ohms and less than 1.0 x 10⁹ ohms (ANSI/ESD STM7.1). ESD control flooring, floor coverings, and floor tile laminates include materials such as vinyl tile, vinyl sheet, carpet, carpet tile, and carpet tile with positioning buttons, but not the applied coatings on the material.

You’re constructing a new facility, covering an old floor as part of a renovation project, or repurposing a workspace, and need to install a floor with ESD protection. You’re smart; you’ve done the research. To comply with the personnel grounding parameters in the 2014 version of ANSI/ESD S20.20, the ESD standard for electronics manufacturing and handling facilities, you know the floor must have an electrical resistance measurement no greater than 1.0 x 10⁹ ohms, and it must generate no more than 100 volts in a walking body voltage test.

Because you want a floor with a clean, hospital-like shine, you’ve settled on ESD vinyl. The supplier you’ve chosen has given you a spec sheet stating that the floor meets ANSI/ESD S20.20 and you’ve done your own resistance and walking body voltage tests on site.

You’ve covered your bases. Right?

Not necessarily.

First, spec sheets don’t always tell the whole story. Many manufacturers do resistance testing in house (and some ignore body voltage testing altogether). These resistance tests may not be performed rigorously, according to the standard test method outlined in S20.20, may not be done in the required 12% humidity-controlled environment, and the test subject may or may not have worn all the various types of footwear that will be worn in your facility.

Even if the manufacturer performed the tests properly, in a controlled lab environment, and did the proper body voltage testing, it cannot be assumed from one resistance spec that both point-to-point and point-to-ground resistance tests were performed (as mandated by the test method). Point to point tests measure resistance from one point on a floor to another. Point to ground tests measure resistance from a particular point on the floor to a ground connection.

Why do these tests matter?

Let’s take a hypothetical example: Suppose you lay a highly conductive copper tile on a highly insulative sheet of plastic. You decide first to measure point to ground resistance (Rtg). In this scenario, there is no ground connection – that is, despite its being highly conductive, when laid over plastic the copper tile cannot be grounded. To measure resistance to ground, you’d create a ground connection by attaching one end of a ground cord to the copper tile with an alligator clip, the other end to some sort of ground point – an electrical outlet, for instance. Let’s say the ground cord, like a wrist strap, has an electrical resistance of 1 megohm (1.0 x 10⁶) to ground.

Next you place a five-pound weight on the copper tile and another weight on the ground cord. Basic physics tells us that circuit resistance can never be lower than the resistance of the most resistive element in the chain, in this case the ground cord with the 1 megohm resistor. In this setup, the resulting point to ground (Rtg) resistance of the circuit will be 1 megohm, which meets the ESDA definition of a static-dissipative floor material (≤ 1.0 x 10⁹).

Electrical Pathway: Safety Considerations

Suppose, as STM 7.1 requires, you also measure point to point resistance (Rtt) – that is, the tile’s surface resistance, measured within a single tile and also across a seam, from one copper tile to another. Performing the test using both variables can help determine the grounded pathway – whether electrical charges will move across the floor/across seams or through the thickness of the floor. Without testing both ways, it’s impossible to know what might happen if the surface of the floor were to become grounded by contact with grounded equipment.

To perform this test it is not necessary to ground the tiles, so there would be no need for the ground cord or 1 megohm resistor. Without the resistor, you’ll get a measurement that’s much lower, quite likely below 2.5 x 10⁴, the lowest resistance permitted – for safety reasons – by any standards organization.

Keep in mind that 1.0 x 10⁶ is the minimum recommended resistance in the telecom industry, FAA, 9-1-1 dispatch, and Army Corps of Engineers, for use in areas where personnel will be in contact with electrified equipment.* In electronics manufacturing facilities, because people typically wear ESD-protective shoes with built-in resistors that are tested every shift, this may not be an issue – unless, that is, there’s ever an electrical short or ground loop in the building, while people are walking on the highly conductive floor and not wearing shoes with built-in resistance.

In this case, according to repeated independent lab tests, resistance below 1.0 x 10⁵ might create a safety hazard. (Note: 10⁵ = 100,000 ohms is four times higher than 2.5 x 10⁴ or 25,000 ohms – as illustrated in the example above and as is common in conductive flooring materials.)

* Standards for many industries prohibit the use of floors with resistance below 1.0 x 10⁶. Standards include: Motorola R56, for 9-1-1 dispatch facilities; ATIS-0600321.2015, for telecommunications rooms; FAA STD 019f, for flight-control applications; and Army Corps of Engineers UFGS 09 62 38, for static-control flooring in government facilities.

So there are practical considerations – safety issues – to evaluate as part of this process. The point is, it matters – a lot – which tests are performed and how those tests are conducted.

But I tested the floor myself. Isn’t that good enough?

If a manufacturer gives you test results – or test results appear on a spec sheet – rather than assuming the tests were performed properly and accepting the results at face value, it’s smart to ask questions.

Once you’ve properly qualified your chosen floor or narrowed your choices to a few properly qualified floors, then, and only then, it is time to evaluate the materials based on how they’ll perform in your environment. Again, this is the time to ask questions:

Is the environment dirty or clean?

Built-up dust and dirt can affect the ESD properties of some floors, particularly those with a lower concentration of conductive material on the surface. Vinyl, for instance, can measure in the conductive range, but because the base material is insulative (static generating PVC) and the conductive particles are not distributed contiguously across the tile surface, a layer of dust and dirt on the floor could prevent contact with a conductive heel or toe strap, rendering the floor less effective.

That’s not to say vinyl is a poor ESD flooring choice, but it does mean that any conductive floor that relies on contact between ESD footwear and randomly-dispersed conductive particles on the surface may require excessively frequent maintenance to eliminate dust and dirt from impacting the readings. When regular cleaning cannot be reasonably assumed, it may make sense to consider a different type of flooring material.

Will people be using chemicals or soldering equipment?

If so, ESD epoxy, which is generally impervious to damage from solder or chemicals, may be the optimal choice. On the other hand, epoxy surfaces can be loud and noise will echo across the room. If noise attenuation is an objective, ESD rubber may be a better option.

Is ergonomics or slip-resistance important?

If so, flooring materials like extreme-duty carpet tiles and rubber, designed with ergonomics in mind, may be the best options. Carpet with a non-directional design will greatly minimize wear patterns and tiles made with mergeable yarns are easily replaced without worry about color matching or dye lots.

If you’re getting the idea that each flooring material has its own set of benefits and drawbacks, bravo! You’re absolutely right! In fact, an ESD floor that performs well in one environment can fail miserably in another. The only way to be sure you’re choosing the right floor for your application and environment is to consider every scenario and be sure you ask all the right questions.

Before even thinking about how a material will perform in your environment, be sure you’ve qualified the floor, following the qualification procedure outlined in ANSI/ESD S20.20. Unless an ESD floor has been properly tested, ideally by an independent lab, following test methods to the letter, it is not safe to assume it will perform properly after it’s installed.

You’re smart. You’re prepared. You do your homework. To be sure you end up with the ESD floor you purchased, you have to be smarter and better prepared – by ensuring, before selecting or purchasing a ESD floor, that the floor has been properly qualified.

You finally received your new portable ohm meter with the five-pound probe and someone showed you how to use it. Just drop the two five-pound probes on the floor, connect leads to the meter and hit the test button. That’s all you need to do. Right?

Not even close.

Let’s start with your mission. What are you doing and why are you doing it?

Hopefully your goal is to identify flooring options that meet standards like ANSI/ESD S20.20-2014. To meet standards, you need to utilize standard test methods. When it comes to ESD flooring, the test method you need to follow is ANSI/ESD STM 7.1-2013. Do you have a copy of this test method? If you don’t have a copy, you can order it here on ESDA.org.

Don’t even think about making decisions without first testing the material, following procedures in this test method. It isn’t as simple as measuring samples right out of the box. Let’s go through the entire process step by step:

There are two distinct phases to evaluating and selecting ESD flooring:

1. The qualification phase
2. the acceptance phase.

In this post, we’ll cover the qualification phase.

The qualification phase requires you to install 12″ x 24″ samples of the proposed flooring on an insulative support material like rigid plastic sheet stock. You should install the test specimen on the support sheet in the same way the flooring would be installed in your factory. If the flooring uses an adhesive, then you need to secure it with the specified adhesive.

Most ESD flooring is sold in tiles or sheets. You must create one seam in your 12″ x 24″ sample to duplicate the kind of seam that might exist on the floor after it is installed. This will enable your tests to measure resistance values as current moves from one tile or section to the adjacent tile or section.

Last and most important: The installed samples must be conditioned at 12% +/- 3% humidity for at least 72 hours before the tests begin. The tests must be performed inside the 12% +/- 3% environment.

Why must the humidity be so low?

Resistance to Ground Testing (RTG)

To qualify a flooring product, you will need five 12″ x 24″ samples with two groundable points per sample. The samples should be numbered from 1 to 5. All five samples must be conditioned for the full 72 hours at low humidity. Each sample will be tested 6 times from both ground points per the diagram below. This will yield 60 measurements in total.

Note If you look closely at the diagram below, you’ll note that some of the test points are very close to the ground locations; some are in the opposite corner; and at least 2 tests will probably cross the seam you created when you prepared the samples. These are important details because the purpose of this test is to determine, among other things, if the floor has any shortcomings under different circumstances. One shortcoming might be wide variances across seams vs resistive properties within the same tile.

Point to Point Resistance Testing (RTT)

RTT testing examines the surface of the floor. The qualification phase of RTT testing will tell us if the surface of floor is more or less conductive than the resistance though the thickness of the floor. Like the previous tests, each sample is tested 6 times from 2 fixed probe locations. The fixed probe locations are marked as position A and B in the illustration below.

This test will tell us what might happen if the floor were inadvertently grounded by equipment placed on top of it. In most cases resistance values are a cumulative measurement involving a less conductive surface and a more conductive adhesive or underlayment. However, the surface of some materials is more conductive than the underlayment the material is bonded to. In this scenario, the surface of the floor could form a ground circuit with a piece of nearby energized equipment, with much less resistance than intended. Standards like FAA 019f call out this and other surface tests for this very reason.

We never want an ESD floor to become grounded at a lower electrical resistance than a particular standard prescribes.

To satisfy safety concerns, we need to account for intended and unintended ground connections.

Whether or not bare concrete prevents static is a common question—and one any facility manager with a concrete floor should ask. If bare concrete grounded and inhibited static reliably, with measurable results, it would certainly be an inexpensive ESD flooring option.

First, let’s be clear about the material: by bare concrete, we mean breathable—in other words, concrete that has not been sealed. Sealers are typically made with an acrylic, polyurethane, or regular (non-ESD) epoxy base—all insulative, static-generating materials.

Once the concrete is sealed, it too becomes an insulator. Glass, plastics, dry air, and wood are all examples of insulators. Insulators block the flow of electrical current. Because electricity can’t move through them, insulators—like sealed concrete—cannot be grounded.

Environmental Considerations

A bare concrete floor below grade can create an unsuitably damp environment. Above grade, a bare concrete floor will generate particles, likely contributing to constant contamination and poor air quality. That’s why concrete is almost always sealed.

Technical Terms

What is an anti-static or static-free material?

The terms “static-free” and “anti-static” simply mean the material in question will not contribute to triboelectrification. Triboelectrification, or tribocharging—is the result of frictional contact between two materials with different electrical potentials.

When people walk—or chairs or carts roll—across a floor, the frictional force between the two materials (the shoe soles or casters rubbing against the floor) strips electrons from one material and transfers them to the other. The material that gave up electrons is left with an overabundance of protons, or a positive charge. The material that accepted electrons is left with too few protons, or a negative charge. This electrical charge stays in place—in other words, static—and continues to accumulate as the person/object moves across the floor.

The static that accumulates on the body as people walk is called “walking body voltage.”

The electrification that results from frictional contact is called charge generation.

Walking Body Voltage = the static charge that accumulates on the body when people walk.

Charge generation = the static charge that results from frictional contact.

Like all electrical current, static seeks its quickest path to ground. When the charged person or material comes into contact—or within close enough range to another person or object—the static charge jumps, like a tiny lightning bolt, to the other person or object.

This phenomenon is called electrostatic discharge. The rush of electrical current from an electrostatic discharge—or an ESD event—can damage or destroy the internal circuitry of sensitive electronic components. In electronics manufacturing or handling environments, random ESD events can disrupt production or cause latent product failure. ESD can ignite flammable chemicals. In mission-critical spaces, like data server rooms, mission-critical call centers, 9-1-1 dispatch operations, flight control towers, and other similar spaces, ESD can cause equipment to malfunction, disrupt data, and damage or destroy components.

Electrostatic discharge (ESD) = the static charge that jumps from a charged person or object to another person/object, potentially causing equipment damage and malfunction.

Does an antistatic or low charge-generating floor ground static charges?

In ESD flooring, conductive elements, like carbon fibers, particles, or filaments, are embedded in the base material in the manufacturing process. The conductive elements are distributed throughout the material, creating a conductive surface. The conductive elements at the surface pull static charges through the thickness of the material to ground.

Conductivity and Environmental Variables

An engineer in Florida once asked why he should use a static-dissipative mat instead of covering his workbenches with back issues of the Miami Herald. On that beautiful, very humid day, the Herald performed marginally better than a static-protective table covering. On a dry day, when the newsprint wasn’t soggy, we’d have seen notably different results.

The same is true of concrete. Concrete draws its conductivity from moisture in the environment. Water, including underground vapor, is electrically conductive: i.e., water promotes, rather than resists, the flow of electricity. We measured the conductivity of a concrete floor on a humid summer day and found it to be overly conductive—only to see that same concrete floor measure almost insulative in drier weather later that same year.

Environmentally-dependent, the conductivity of bare concrete relies on numerous variables, including moisture permeation, geological conditions, subterranean activity, aquifers, weather, and ambient humidity (RH). Due to environmental instability, bare concrete will not, and cannot, meet industry standards with any degree of reliability.

Concrete and Electrical Resistance

We evaluate the conductivity of a flooring material by measuring its opposite: electrical resistance. By evaluating the rate at which current passes across the surface of a floor tile, resistance tests—measured in ohms—predict how effectively the floor will resist—or conduct—the flow of electricity to ground.

According to Ohm’s Law, as resistance increases, charge dissipation decreases.

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ANSI/ESD S20.20 recommends resistance readings below 1,000,000,000 (1 x 10⁹) ohms, using test method STM7.1. As mentioned above, the conductivity in bare concrete comes from moisture in the soil below the slab. As concrete dries (for whatever reason), its electrical resistance increases, making the floor less conductive. That’s why a floor with decent conductivity in humid conditions can be insulative in a drier environment.

The same is true in reverse. As concrete absorbs vapor from the soil, its resistance decreases, potentially turning the concrete floor into a dangerously conductive plane.

If any areas of your factory are used for “hi pot” testing, you should procure and install electrically insulative rubber mats to cover the concrete and protect your personnel from electrical shock hazards.

Advisory

If you choose to use concrete as your static-protective floor, you should set an absolute minimal flooring resistance—100,000 (10⁵) ohms for a factory environment. For end-user spaces, such as mission-critical call centers, server rooms, or 9-1-1 dispatch operations, housing operational equipment, resistance should be no lower than 1,000,000 (10⁶) ohms.*

Since the resistance of a bare concrete floor is cyclical, we strongly suggest testing its resistance with an ohmmeter on a regular basis. We also recommend performing ANSI/ESD S97.2 body voltage tests to determine if the concrete floor will maintain walking voltages below 100 volts, as required by ANSI/ESD S20.20-2014.

The electrical resistance of bare concrete can vary by up to 2 orders of magnitude in either direction. Broad performance differentials caused by unpredictable site conditions would be a hard sell to a knowledgeable customer or any auditor as part of an ISO certification.

* While these are Staticworx recommendations, requirements for the communications and telecom industry and flight control towers are set by independent industry standards: Motorola R56, FAA 019f, and others. For safety reasons, these standards all recommend resistance ≥ 1 x 10⁶ in areas where energized equipment is used.