Acceptance testing checks the resistance of the completed, installed electrostatic discharge (ESD) flooring system. ANSI/ESD STM7.1-2020 requires both resistance-to-ground and point-to-point measurements, with a separate minimum test count for each. Testing takes place at ambient humidity (the humidity of the surrounding air) after the manufacturer’s required curing and cleaning.
STM7.1 specifies how to take the measurements. The project’s applicable performance specification determines how the results are judged. A resistance limit used to qualify flooring samples in a laboratory does not automatically become the pass/fail limit for the installed floor. Confirm which acceptance limits the project specification requires.
STM7.1-2020 is an ESD Association standard test method (STM) approved by the American National Standards Institute (ANSI). ASTM D2240, cited below, is published by ASTM International.
Where the pass/fail limit comes from
Analyzing results against the performance specification
STM7.1-2020 specifies the measurements. For the criterion, its informative Annex C says the end user should analyze the data obtained under the test method in a manner consistent with their performance specifications for the materials being tested. The pass/fail limit therefore comes from the specification that governs the floor. It has to be read within the scope of the source that sets it: the program, the test stage, and the exact comparison it states.
Flooring product qualification under ANSI/ESD S20.20-2021
ANSI/ESD S20.20-2021 Table 3 lists flooring product-qualification limits using ANSI/ESD STM7.1: point-to-point resistance below 1.0 × 10⁹ ohms and point-to-groundable-point resistance below 1.0 × 10⁹ ohms. Under section 8.3, the requirements for control items selected for an ESD control program become mandatory. Table 3 directs compliance verification of the footwear and flooring system to Table 2. These flooring limits belong to product qualification, not universal installed-floor acceptance.
FAA flooring requirements in FAA-STD-019f
Federal Aviation Administration (FAA) facilities, including air traffic control environments that use ESD carpet, illustrate why acceptance criteria must match the application. FAA-STD-019f section 5.8.9 specifies point-to-point and surface-to-ground resistance greater than 1.0 × 10⁶ ohms and less than 1.0 × 10⁹ ohms for the floor coverings it addresses, including carpet and vinyl. These are application-specific requirements, not universal acceptance limits for every ESD flooring system. This is the October 18, 2017 edition of FAA-STD-019f.
Before testing
Cure time
For a newly installed flooring system, STM7.1-2020 directs the tester to allow proper cure time, if any, following the manufacturer’s instructions. Testing before finishes, coatings, or adhesives are fully cured gives resistance measurements that may differ from those measured after the materials are fully cured.
Cleaning
As part of acceptance testing, new floors, mats, and floor finishes must be cleaned per the manufacturer’s recommendations before resistance testing. Before each measurement procedure, the electrodes are cleaned with an isopropanol-water solution, using a clean, low-linting cloth, and allowed to air dry; the standard gives a 70% isopropanol-water solution as an example.
Ambient humidity
Both acceptance measurements are performed at ambient humidity.
Meter and electrodes
Which meter may be used
Either the product-qualification meter of section 5.1.1 or the acceptance meter of section 5.1.2 may be used to measure installed or applied flooring systems for acceptance testing. The product-qualification meter must be capable of measurements from 1.0 × 10³ ohms to 1.0 × 10¹⁰ ohms. The test voltage each meter must supply depends on the resistance being measured.
| Meter | Measurements | Required test voltage |
|---|---|---|
| Acceptance meter | 1.0 × 10⁶ ohms and above | 100 V (±5%), open circuit |
| Acceptance meter | Below 1.0 × 10⁶ ohms | 10 V (±5%), open circuit |
| Product-qualification meter | 1.0 × 10⁶ ohms and above | 100 V (±5%), under load |
| Product-qualification meter | 1.0 × 10⁴ ohms to below 1.0 × 10⁶ ohms | 10 V (±5%), under load |
| Product-qualification meter | 1.0 × 10³ ohms to below 1.0 × 10⁴ ohms | 10 V (±5%), open circuit or under load |
Disputed results
In case of disagreement over acceptance results, a meter that meets the product-qualification requirements is used to resolve the dispute.
Electrodes
The resistance measurement electrode is a cylinder of 2.27 kg ± 0.06 kg with a diameter of 63.5 mm ± 5%. Its contact is electrically conductive material with a Shore-A durometer hardness between 50 and 70 per ASTM D2240. The resistance between two electrodes must be less than 1.0 × 10³ ohms when measured on a metallic surface.
Power source and leads
Alternating-current (AC) line-powered resistance measuring devices may give erroneous results due to undefined ground paths, and battery-powered equipment is recommended. Unshielded leads, or leads with bad isolation, in contact with the flooring system could also provide erroneous results.
Making the two measurements
Both measurements are required; they differ in how the meter is connected and where the electrodes go, and they share the same voltage sequence.
Resistance to ground
One lead of the meter is connected to ground, as defined in ANSI/ESD S6.1, and the other lead to the resistance measurement electrode. The electrode is placed on the surface of the flooring system a minimum of 1 m from the grounding connection. It is not placed on a seam; if the test position falls on a seam, the electrode is moved slightly off the seam, farther from the ground connection.
Resistance point-to-point
The leads of the meter are connected to the resistance measurement electrodes, which are placed approximately 1 m apart on the surface of the flooring system. If the test location has a seam within the one-meter diameter, the electrodes are placed on either side of the seam, at least 1 m apart.
Test voltage and reading time
At each location, each measurement follows the same sequence.
- Set the voltage to 10 V and energize the measurement equipment.
- If the indicated resistance is less than 1.0 × 10⁶ ohms, record the value after 5 seconds.
- If the indicated resistance is equal to or greater than 1.0 × 10⁶ ohms, de-energize the equipment, energize it at 100 V, and record the resistance after 15 seconds or as defined by the meter electrification period.
- De-energize the measurement equipment.
The standard notes that if switching the test voltage to 100 V results in a reading below 1.0 × 10⁶ ohms, the reading made at 100 V is the value used.
How many locations to test
For each of the two measurements, STM7.1-2020 requires a minimum of five tests in different locations per contiguous flooring system area (one continuous area), or a minimum of five tests per 500 square meters (m²) of flooring system area, whichever is greater. When testing static control floor mats, each measurement requires a minimum of one test per 2 square meters (m²). The minimum is stated separately for resistance to ground (6.2.1.7) and for point-to-point (6.2.2.7), so it applies to each measurement rather than to the two combined.
What the acceptance report contains
STM7.1-2020 requires the report to include the following.
- All resistance values, in ohms, for both measurements.
- The test voltage, the test date, the temperature and relative humidity at the time of testing, and the actual duration of conditioning.
- The test equipment used.
- All components of the flooring system tested, and the substrate to which the flooring sample is applied.
- A summary of the test data giving the minimum and maximum values obtained.
- For applied or installed results, a diagram showing the approximate electrode positions and ground connections used.
- Any conditions other than those the test method specifies, if they were used.
Before arranging an acceptance test, establish the applicable limits, required measurements and reporting expectations for the project.
Craftsman Concrete Floors provides installed-floor resistance testing and a project closeout package documenting the results, test locations and meter calibration records, with reporting prepared in accordance with ANSI/ESD STM7.1 where applicable.
Frequently Asked Questions
No. ANSI/ESD STM7.1-2020 requires both resistance-to-ground and resistance point-to-point measurements for product acceptance of installed or applied flooring systems.
For each measurement, STM7.1-2020 requires at least five tests in different locations per contiguous flooring system area or at least five per 500 m², whichever is greater. For static control floor mats, the minimum for each measurement is one test per 2 m².
STM7.1-2020 directs the tester to allow proper cure time, if any, following the manufacturer’s instructions. Testing before finishes, coatings, or adhesives are fully cured may give resistance measurements that differ from those obtained after full cure.
STM7.1-2020 uses a meter meeting its product-qualification requirements to resolve disputed acceptance results, although either the specified qualification meter or acceptance meter may be used for acceptance testing.
STM7.1-2020’s informative Annex C says the end user should analyze the measured data against the performance specifications for the materials being tested. A criterion must retain the scope of the source that sets it; a product-qualification upper limit and a separate agency’s two-sided range are not interchangeable universal installed-floor limits.