ANSI/ESD STM7.1-2020 laboratory qualification tests at least five representative flooring samples (referred to as specimens in STM7.1). Each sample undergoes resistance-to-groundable-point and point-to-point testing after low-humidity conditioning, then both tests are repeated after moderate-humidity conditioning.
The procedure uses six numbered electrode positions and two reference positions for each measurement configuration. Each reading starts at 10 volts, with a switch to 100 volts when the indicated resistance reaches 1.0 × 10⁶ ohms or more. The steps below cover preparation, electrode placement, measurements and reporting.
ANSI/ESD STM7.1-2020 is an ESD Association standard test method (STM) for electrostatic discharge (ESD) flooring, approved by the American National Standards Institute (ANSI). The ASTM documents cited below are published by ASTM International.
Equipment for the qualification measurements
The qualification meter
The meter used for product qualification must be capable of making measurements from 1.0 × 10³ ohms to 1.0 × 10¹⁰ ohms (Section 5.1.1). Its test voltage depends on the resistance being measured:
| Measured resistance | Required meter voltage |
|---|---|
| 1.0 × 10⁶ ohms and above | 100 volts (± 5%) while under load |
| 1.0 × 10⁴ ohms to less than 1.0 × 10⁶ ohms | 10 volts (± 5%) while under load |
| 1.0 × 10³ ohms to less than 1.0 × 10⁴ ohms | 10 volts (± 5%) open circuit or under load |
Battery-powered equipment is recommended, because alternating-current (AC) line-powered resistance measuring devices may give erroneous results due to undefined ground paths.
The electrodes
Product qualification uses conductive rubber electrodes (Section 5.2). Each is a cylindrical electrode of 2.27 kg ± 0.06 kg with a diameter of 63.5 mm ± 5%, having a contact of electrically conductive material with a Shore-A durometer hardness between 50 and 70 as per ASTM D2240. The resistance between two electrodes must be less than 1.0 × 10³ ohms when measured on a metallic surface.
The support surface and the flooring samples
Flooring sample support surface
A planar (flat) surface used for flooring sample support must have a surface resistivity greater than 1.0 × 10¹¹ ohms/square when measured per ASTM D257, or a surface resistance greater than 1.0 × 10¹⁰ ohms when measured per ANSI/ESD STM11.11 (Section 6.1.2.1).
What the flooring samples must include
- Count: a minimum of five flooring samples, labeled from 1 to 5 (6.1.3.2).
- Size: each flooring sample large enough that a 300 mm by 600 mm test area can be defined as in Figures 1 and 2.
- Makeup: each flooring sample representative of, and including, all the system components as they would be used in an installation (6.1.2.2.2). Tests of tiles installed with an adhesive, for example, must include the tile, the appropriate adhesive, the grounding system, and the substrate (the underlying surface to which the flooring is applied) that would be used.
- Groundable points: two on each flooring sample, simulating end-user grounding methods (6.1.3.3).
- Seams: if the installed product has seams, the flooring sample must include a seam.
Preparing and cleaning the flooring samples
Mounting the flooring sample on its substrate
Mount each flooring-system sample on the defined substrate material using the manufacturer’s recommendations (6.1.3.1), such as:
- cure time
- pressure applied
- rolling direction
- adhesive thickness/application method
- grounding location
A floor finish or similar product may require an alternative substrate to accommodate the test; if required, mount the manufacturer’s recommended substrate material, according to the manufacturer’s instructions, to the support material described above (6.1.2.2.1). If the flooring sample under test is a floor finish, apply or coat the recommended substrate according to the manufacturer’s instructions.
Cleaning before conditioning
Clean each flooring sample before humidity conditioning, by the type of material (Section 6.1.4):
| Flooring sample type | Cleaning method |
|---|---|
| Flooring, mats, or other hard surface materials | Follow the manufacturer’s instructions. |
| Carpet or similar textile materials | Clean with standard hot water extraction cleaning procedures, such as those described in ANSI/IICRC S001 or AATCC 171 and AATCC 138, or follow the manufacturer’s recommendations. |
| Floor finishes | Remove any surface contamination by wiping with a clean, dry, low-linting cloth. |
IICRC is the Institute of Inspection, Cleaning and Restoration Certification; AATCC is the American Association of Textile Chemists and Colorists.
Humidity conditioning and the order of testing
Under STM7.1-2020 Section 6.1.5, after cleaning, place the flooring samples in the low humidity environment for 72 hours minimum, then perform the resistance to groundable point and resistance point-to-point tests in that conditioning environment. At the conclusion of the low humidity testing, place the flooring samples in the moderate humidity environment for 72 hours minimum, then repeat both tests in that conditioning environment.
| Conditioning stage | Environment | Minimum preconditioning |
|---|---|---|
| Low humidity (first) | 12% ± 3% relative humidity and 23°C ± 3°C | 72 hours |
| Moderate humidity (second) | 50% ± 5% relative humidity and 23°C ± 3°C | 72 hours |
Taking each reading
Every reading, in both configurations and at every electrode position, follows the same voltage and timing sequence (6.1.6.4 to 6.1.6.5 for resistance to groundable point, 6.1.7.4 to 6.1.7.5 for resistance point-to-point):
- Set the voltage to 10 volts 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 volts, 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 volts results in a resistance reading of less than 1.0 × 10⁶ ohms, the reading made with the 100-volt test voltage is used.
Resistance to groundable point
Resistance to groundable point (Section 6.1.6) is measured between a groundable point and a single electrode placed in turn at the six numbered positions, following Figure 1.
Electrode positions in STM7.1 Figure 1
Figure 1 shows groundable point A at the upper-left and groundable point B at the upper-right of the flooring sample, with the six electrode positions on a nominal 600 mm by 300 mm test area:
| Electrode position | Location in Figure 1 |
|---|---|
| 1 | Lower-left |
| 2 | Middle-left |
| 3 | Upper-center |
| 4 | Middle-right |
| 5 | Lower-right |
| 6 | Lower-center |
The figure dimensions the electrode-position grid with 50 mm edge offsets, 150 mm intermediate offsets, and 300 mm half-widths; all of its dimensions are nominal.
Setting up the first reading
- Place the flooring sample on the insulating support surface described above (6.1.6.1).
- Clean the resistance measurement electrode with an isopropanol-water solution, for example a 70% isopropanol-water solution, using a clean, low-linting cloth, and allow the electrode to air dry (6.1.6.2).
- Connect one lead of the meter to groundable point A and the other lead to the resistance measurement electrode (6.1.6.3).
- Place the electrode at position 1 (6.1.6.4), not on a seam: if the test position falls on a seam, move the electrode slightly off the seam, further from the ground connection.
- Take the reading and de-energize the equipment as described under Taking each reading (6.1.6.4 and 6.1.6.5).
Completing all positions, both groundable points, and every flooring sample
Repeat the placement and reading steps (6.1.6.4 and 6.1.6.5) for electrode positions 2 through 6 with the meter still connected to groundable point A (6.1.6.6), applying the same seam rule, voltage sequence, and de-energizing at each position. Then connect one lead of the meter to groundable point B and repeat those steps for electrode positions 1 through 6 (6.1.6.7). Repeat the whole measuring sequence (6.1.6.1 to 6.1.6.7) for all flooring samples (6.1.6.8).
Resistance point-to-point
Resistance point-to-point (Section 6.1.7) is measured between two electrodes placed on the same flooring sample used for resistance to groundable point, following Figure 2. The groundable points, while shown in Figure 2, are not used for the resistance point-to-point measurement.
Electrode positions in STM7.1 Figure 2
In Figure 2, the measurement electrode positions A and B lie inside the flooring sample near the upper-left and upper-right; they are distinct from the separately labeled groundable points, which the figure marks as not used for point-to-point measurement. Numbered positions 1 through 6 are in the same lower-left, middle-left, upper-center, middle-right, lower-right, and lower-center arrangement as in Figure 1.
Setting up the first reading
- Place the flooring sample on the insulating support surface.
- Clean the resistance measurement electrodes with an isopropanol-water solution, for example a 70% isopropanol-water solution, using a clean, low-linting cloth, and allow the electrodes to air dry.
- Connect the leads of the meter to the resistance measurement electrodes.
- Place one electrode at position A and the other at position 1 (6.1.7.4), not on a seam: if the test position falls on a seam, move the electrode slightly off the seam, further from the other electrode.
- Take the reading and de-energize the equipment as described under Taking each reading (6.1.7.4 and 6.1.7.5).
Completing all positions, both electrode positions A and B, and every flooring sample
Repeat the placement and reading steps (6.1.7.4 to 6.1.7.5) for positions 2 through 6, with the other electrode remaining at position A. Then repeat those steps (6.1.7.4 through 6.1.7.6) with one electrode at position B and the other electrode in positions 1 through 6. Repeat the whole measurement sequence (6.1.7.1 to 6.1.7.7) for all flooring samples.
What the report must contain
Report all values in ohms for resistance to groundable point and resistance point-to-point (6.3.1). Also report:
- the test voltage
- the test date
- the temperature and relative humidity at the time of testing
- the actual duration of conditioning
- the test equipment used
- all components of the flooring system tested
- the substrate to which the flooring sample is applied
Summarize the test data by reporting the minimum and maximum values obtained. If conditions other than those specified in the test method are used, such as flooring systems being installed to stainless steel substrates, they must be reported (6.3.3).
Frequently Asked Questions
Both resistance-to-groundable-point and point-to-point tests are performed on every flooring sample in the low-humidity conditioning environment and then repeated in the moderate-humidity conditioning environment. STM7.1-2020 requires at least 72 hours of conditioning at each stage: 12% ± 3% relative humidity first, then 50% ± 5%, both at 23°C ± 3°C.
No. In STM7.1-2020 Figure 2, electrode positions A and B are inside the flooring sample near its upper-left and upper-right corners. They are distinct from the separately labeled groundable points, which are not connected during point-to-point measurement.
For both STM7.1-2020 qualification configurations, an indicated resistance equal to or greater than 1.0 × 10⁶ ohms requires de-energizing the equipment, re-energizing it at 100 volts, and recording the resistance after 15 seconds or as defined by the meter electrification period. De-energize after the reading. The standard’s note says to use the 100-volt reading even if switching produces a value below 1.0 × 10⁶ ohms.
STM7.1-2020 qualification electrodes must not be placed on a seam. Move a seam-coincident position slightly off the seam: farther from the ground connection for resistance-to-groundable-point testing, or farther from the other electrode for point-to-point testing.
Under STM7.1-2020, take readings with one electrode at position A and the other at positions 1 through 6, then with one electrode at B and the other at positions 1 through 6. Repeat the full measurement sequence for every flooring sample, applying the voltage, timing, de-energizing, and seam-placement steps at each position.