Quick answer: ESD epoxy flooring specifications are verified by measuring resistance with a megohmmeter and two weighted electrodes under ANSI/ESD STM7.1, both point to point and from the floor to the building ground. Under ANSI/ESD S20.20 the floor and footwear system together must then measure below 1.0 × 10⁹ ohms, and the walking body voltage must stay under 100 volts peak. A passing result needs a defined test grid, recorded temperature and humidity, and a written report.
Facility engineers and quality managers usually ask about the test after the floor is already in, when an auditor asks for the data. This guide covers the method in enough detail to write it into a specification. If you are still choosing a system, our ESD anti-static epoxy flooring page covers the installation side, and the sections below cover what a requirement for the floor actually means and how it is proven. We keep the material decision, conductive against dissipative, out of this post because it has its own guide, linked in the grounding discussion below.
What S20.20 Actually Requires of a Floor
ANSI/ESD S20.20 does not certify a floor by itself. It is a standard for an entire ESD control program, and it sets requirements for the floor only where the floor is part of how people are grounded. The floor is checked in two ways: the material is qualified, and the installed floor and footwear system is verified together.
Material qualification uses ANSI/ESD STM7.1, which defines the resistance measurements for floor materials. System verification uses ANSI/ESD STM97.1, which measures resistance through a person, their footwear and the floor, and ANSI/ESD STM97.2, which measures the voltage a person generates while walking. The current limits are a system resistance below 1.0 × 10⁹ ohms and a peak walking body voltage below 100 volts. Older practice used a tighter 3.5 × 10⁷ ohm shortcut to assume the voltage would pass, but the 2014 revision removed that shortcut, so a resistance reading alone no longer settles it.
Two practical points follow. First, the floor's own target range comes from the facility's ESD control plan, not from one universal number, which is why specifications should name the range. Second, the footwear is part of the test. A floor that passes on its own can still fail as a system if the shoes are wrong. Where fueling or flammable vapors are involved, the requirement may be tighter still, as covered in our aircraft hangar floor guide.
Point to Point Against Resistance to Ground, and Why Both Are Measured
Point to point resistance measures the electrical path across the floor between two electrodes, and resistance to ground measures the path from one electrode to the building ground, so you need both to know the floor is uniform and actually connected. They answer different questions, and a floor can pass one and fail the other.
| Measurement | Measured Between | What It Shows | Typical Cause of a Fail |
|---|---|---|---|
| Point to point (Rpp) | Two electrodes on the floor surface | Uniformity of the conductive layer across the surface | Insulating film, worn topcoat, localized damage |
| Resistance to ground (Rg) | One electrode on the floor and the groundable point | Whether charge has a continuous path to building ground | Disconnected or poorly tied ground strip or ground point |
| System resistance (STM97.1) | A person in footwear standing on the floor, to ground | The floor and footwear working together | Footwear not rated for ESD, contaminated soles |
The ground connection is the one most often missed. A floor can read a perfect resistance across its surface while the copper grounding strips under it were never tied back to building ground, and only the resistance to ground reading exposes that. Our guide to conductive against static dissipative epoxy covers how the grounding network is built, which is why it has to be verified at commissioning and not assumed.
The Test Method: Electrodes, Voltage, Electrode Weight and Dwell Time
The method uses two 5 pound electrodes with a rubber contact surface, a megohmmeter that applies a defined test voltage, and a clean, dry floor. Each step is controlled because small changes in contact change the reading.
- Electrodes: each weighs 5 pounds (about 2.27 kg) and has a conductive rubber contact surface about 2.5 inches (63.5 mm) in diameter. The weight and surface area set the contact pressure, which is why substitutes do not give comparable numbers.
- Meter and voltage: a calibrated megohmmeter applies the test voltage. Qualification reports for ESD floors commonly cite test voltages between 10 and 100 volts, chosen by the procedure for the resistance range being measured.
- Placement: for point to point, the two electrodes sit a fixed distance apart on the surface, commonly about 3 feet (0.9 m). For resistance to ground, one electrode sits on the floor and the lead connects to the groundable point.
- Dwell time: the procedure defines how long the voltage is applied before the reading is taken. Record the reading only once the display settles, and use the same method every time so retests are comparable.
- Surface condition: the floor is clean and dry, and the spot is not recently wet-cleaned, because residues change the reading.
Before a test day, check the electrodes themselves. One common electrode set lists a pair reading below about 1,000 ohms at 10 volts when placed on a clean metal plate, which confirms the leads and contact surfaces are sound. A worn or dirty electrode gives a falsely high reading that looks like a floor failure. Record the meter's model, serial number and calibration date, since an auditor will ask for them.
Building a Test Grid: How Many Points and Where to Place Them
Test at least five locations per contiguous floor area, or five per 500 square meters (about 5,400 square feet), whichever is greater, and place them where they tell you something. That is the recommended minimum for an installed floor, and the facility's control plan can require more.
| Floor Area | Recommended Minimum Test Points | Notes |
|---|---|---|
| Up to about 5,400 sq ft (500 sq m) | 5 | Per contiguous area, spread across the floor |
| About 10,800 sq ft (1,000 sq m) | 10 | Five per 500 sq m |
| About 27,000 sq ft (2,500 sq m) | 25 | Add points near each ground connection |
Number matters less than placement. Good grid points include the spots where people walk and work, the far end of each grounding strip from its ground point, doorways and transitions where the coating is most likely to wear, and corners and edges. If the floor is the primary personnel grounding path, test where people actually step.
Mark every point on a site plan and label it, then test the same points at every retest. A dated log of readings at fixed points is what makes a drift visible, because a reading that creeps upward over three years is a maintenance problem you can fix before it becomes a failure. Take both a point to point and a resistance to ground reading at each location so the two can be compared.
Humidity, Temperature and Cleanliness: Why Readings Move
ESD floor readings move with humidity, temperature and surface cleanliness, which is why test conditions are recorded with every reading and not treated as background. Two readings on the same floor can differ by an order of magnitude for reasons that have nothing to do with a defect.
| Factor | Effect on the Reading | What to Do |
|---|---|---|
| Low relative humidity | Resistance runs higher, especially on systems that rely on surface moisture | Record RH; test in realistic winter conditions, not only summer |
| Temperature | Shifts resistance, typically higher when cold | Record air and floor temperature at each test |
| Cleaning residue, wax, polish | Builds an insulating film, so resistance climbs | Use only cleaners approved for the installed system |
| Dust and contamination | Raises contact resistance at the electrode | Test on a clean, dry spot |
| Floor age and wear | Gradual drift as the topcoat wears | Retest on a schedule and compare to the baseline |
Humidity matters more in Denver than in most places. Heating-season air can drop below 30 percent relative humidity, and a floor that tests acceptably in a humid summer week can read higher in January. Laboratory qualification of floor materials is often done under low-humidity conditioning, around 12 percent relative humidity at 23 degrees Celsius, precisely because dry air is the harder case. For an installed floor, the practical answer is to record temperature and relative humidity with every reading and to schedule at least one retest in the dry season.
When a reading fails. A single high reading is a prompt to investigate, not a verdict on the floor. Work through the likely causes in order of how often they turn out to be the answer:
- Check the test equipment first. Recheck the electrodes on a clean metal plate and confirm the meter is within its calibration date.
- Clean and retest the same point. Wipe the spot dry with a cleaner approved for the installed system and test again, then compare the result to the first.
- Test the neighboring grid points. A cluster of high readings points to a surface film or a worn area, while one isolated reading points to local damage.
- Compare point to point with resistance to ground. If the surface passes but the ground reading fails, inspect the ground strip and its connection to building ground.
- Look for recent changes. A new cleaning product, polish, recoat, spill, or change in equipment and cart traffic is the usual trigger.
- Strip and retest if residue is the cause. Use an ESD-compatible stripper, allow a full dry period, and retest before the area returns to normal operation.
That sequence usually costs far less than replacing a floor, because most failed readings on a correctly installed system come from contamination and not from the coating itself. Whatever the cause, write down the failed reading, the fix and the retest result. A documented failure that was found and corrected tells an auditor the program works, while an undocumented one looks like a gap.
What Belongs in a Commissioning Report, and the System and Footwear Qualification
A commissioning report should contain enough data that a stranger could repeat the test and compare the result years later, and that includes the footwear and walking tests, not only floor resistance. Our ANSI/ESD S20.20 compliance guide covers the certification process, and this is the checklist for what the report itself must hold.
- Floor system identification: product names and codes, data sheets, and the installation and cure dates, since testing happens after a full cure.
- Site plan with test points: every grid point labeled and located, with the ground points shown.
- Instrument details: meter model, serial number and calibration date, plus the electrode type and weight.
- Method and conditions: the standard followed, the test voltage, and the air temperature and relative humidity at the time.
- Results: point to point and resistance to ground readings at every point, with the acceptance limits from the control plan and a pass or fail for each.
- System qualification: the footwear and flooring system resistance under STM97.1 and the walking body voltage under STM97.2, run with the facility's actual footwear.
- Sign-off and retest schedule: who tested, who accepted, and when the next verification is due.
Footwear deserves its own line. Qualify the specific shoes or heel straps staff will wear, and retest when the footwear changes, because a different sole can move the system result. Facilities with broader commercial flooring needs will find the surrounding options in our commercial epoxy flooring page. Keep the report and the baseline readings on file, since the first retest is only meaningful against them.
Frequently Asked Questions
Under ANSI/ESD STM7.1 (formerly S7.1), using two five pound electrodes with a defined contact surface and a megohmmeter applying a set test voltage. Point to point measures between two electrodes on the floor, resistance to ground measures from one electrode to the building ground point.
S20.20 requires the floor and footwear system together to measure below 1.0 times ten to the ninth ohms, and the walking body voltage must also stay under 100 volts peak. The floor's own target range comes from the facility's ESD control plan rather than a single universal number.
Annual verification is the common interval, with additional testing after any change to cleaning products, after a recoat, or when a process audit requires it. Keeping a dated log of readings at fixed grid points is what makes a trend visible.
Yes, significantly for some systems, which is why test conditions including temperature and relative humidity are recorded with every reading. In Denver's dry air readings tend to run higher, so testing in realistic winter conditions rather than only in summer matters.
It is one of the most common causes. A standard floor polish, wax or residue leaving detergent builds an insulating film over the surface and resistance climbs out of range. Only cleaning products approved for the installed system should be used.