ANSI/ESD STM7.1 and ASTM F150 both measure flooring resistance, but they use different procedures and cover different flooring applications. Their requirements for test samples, conditioning, electrode placement and readings are not interchangeable. This page compares STM7.1-2020 with F150-25.
ESD means electrostatic discharge, and STM means standard test method. ANSI is the American National Standards Institute; ASTM International publishes F150.
Where each method applies
STM7.1-2020: ESD-control flooring systems
STM7.1-2020 covers flooring systems including floor mats, floor coverings, coatings, paints, raised access panels, and floor finishes, and it provides a method for measuring resistance greater than 10⁴ ohms and less than 10⁹ ohms. It does not apply to facilities where ordnance, flammables, or explosives are stored or handled, and it refers those concerns to ASTM F150.
F150-25: resilient tile or sheet flooring
F150-25 covers the determination of electrical conductance or resistance of resilient flooring in tile or sheet form. The method names applications such as hospitals, computer rooms, clean rooms, access flooring, munition plants, and any other environment concerning personnel-generated static electricity.
Laboratory qualification samples
STM7.1-2020 qualification flooring samples
STM7.1 qualification uses a minimum of five flooring samples (referred to as specimens in the standards). Each flooring sample must be representative of the flooring system and include all the system components as they would be used in an installation, such as the tile, adhesive, grounding system, and substrate for tiles installed with an adhesive. Each flooring sample must be large enough to define a 300 mm by 600 mm test area, and each must have two groundable points that simulate end-user grounding methods. If the installed product has seams, the flooring sample must include a seam (STM7.1-2020 sections 6.1.2.2 and 6.1.3.2–6.1.3.3).
F150-25 qualification flooring samples
An F150 qualification flooring sample is a portion of floor covering 48 in. by 48 in. (1.22 m by 1.22 m) in area. If a qualification test is required, one flooring sample is tested unless otherwise specified. Unless otherwise specified, five measurements are made on the flooring sample, with the electrodes at different locations for each measurement, and each value is recorded to two significant figures (F150-25 section 6.1).
Conditioning and test environment
STM7.1-2020 specifies two conditioning stages for laboratory qualification and ambient humidity for installed-floor acceptance. ASTM F150-25 specifies conditioning and testing in a defined environment whenever possible.
STM7.1-2020: two humidity stages of at least 72 hours each
STM7.1 qualification conditions cleaned flooring samples in a low-humidity environment of 12% ± 3% relative humidity and 23 °C ± 3 °C for at least 72 hours and tests them in that environment. The flooring samples are then placed in a moderate-humidity environment of 50% ± 5% relative humidity and 23 °C ± 3 °C for at least 72 hours and retested there (section 6.1.5).
F150-25: at least 24 hours at 23 °C ± 1 °C, whenever possible
Whenever possible, the F150 flooring test sample is conditioned for at least 24 hours at 23 °C ± 1 °C (73.4 °F ± 1.8 °F) and 50% ± 5% relative humidity and tested in the same environment (section 7.1). The F150 instruction is conditional, and it specifies a single environment rather than the two humidity stages that STM7.1 requires.
Electrode placement
Both methods measure between the floor surface and a ground connection and between two points on the floor surface. STM7.1 calls these measurements resistance to ground and resistance point-to-point; F150 calls them surface to ground and surface to surface.
STM7.1-2020 resistance to ground in acceptance testing
For resistance to ground in acceptance testing, the STM7.1 electrode is placed on the surface of the flooring system a minimum of 1 meter from the grounding connection. Do not place the electrode on a seam. If the test position falls on a seam, move the electrode slightly off the seam, farther from the ground connection (sections 6.2.1.4–6.2.1.5).
STM7.1-2020 resistance point-to-point in acceptance testing
For resistance point-to-point, STM7.1 places the two electrodes approximately 1 meter 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 meter apart (sections 6.2.2.4–6.2.2.5).
F150-25 surface to surface in qualification and installed testing
F150 places the electrodes at least 1 in. (25.4 mm) in from an edge and 36 in. (914.4 mm) apart in both its qualification and its installed surface-to-surface procedures. The same placement applies to conductive floors and to static-dissipative floors. In qualification testing the edge is an edge of the flooring sample; in installed testing it is an edge of the area being tested (F150-25 sections 8.1.1.1–8.1.1.2 and 8.2.1.1–8.2.1.2).
F150-25 surface to ground in installed testing
ASTM F150-25 section 8.2.2 does not clearly explain how its two-electrode spacing instructions apply when the meter’s positive lead connects directly to ground. For projects requiring this test, Craftsman Concrete Floors works with the facility’s ESD program lead or project team to agree on the test setup before fieldwork begins. If no testing protocol has been established, we help develop one around the project specification and flooring manufacturer’s instructions, with the agreed setup documented in the test report.
Test voltage and reading time
STM7.1 acceptance testing uses the voltage sequence below for both resistance measurements (sections 6.2.1.5 and 6.2.2.5). F150 specifies separate sequences for conductive floors and static-dissipative floors (sections 8.1.1.1–8.1.1.2, 8.2.1.1–8.2.2.2). VDC means volts of direct current.
| Procedure | Voltage sequence | Reading time |
|---|---|---|
| STM7.1-2020 acceptance resistance measurements | Energize at 10 V. If the indicated resistance is less than 10⁶ ohms, record it. If it is equal to or greater than 10⁶ ohms, de-energize, re-energize at 100 V, and record. | After 5 seconds at 10 V; after 15 seconds, or as defined by the meter electrification period, at 100 V. |
| F150-25 conductive floors: qualification surface to surface, installed surface to surface, and installed surface to ground | Set the meter to 10 VDC. If the reading is below 10⁶ ohms, record it. If it is higher than 10⁶ ohms, change the voltage to 100 VDC, take the reading again, and record it. | 15 seconds after the voltage is applied, or once the reading has reached equilibrium, at either voltage. |
| F150-25 static-dissipative floors: qualification surface to surface, installed surface to surface, and installed surface to ground | Apply the prescribed voltage, either 100 VDC or 10 VDC. If the floor is known to be greater than 10⁶ ohms, use 100 VDC. | 15 seconds after the voltage is applied, or once the reading has reached equilibrium. |
The threshold at 10⁶ ohms
STM7.1 assigns a reading equal to 10⁶ ohms to its 100 V branch. The F150 conductive-floor procedures specify readings below 10⁶ ohms and readings higher than 10⁶ ohms, and they do not assign a reading of exactly 10⁶ ohms to either branch.
Installed sampling
STM7.1-2020 acceptance testing
For acceptance testing of an installed or applied flooring system, STM7.1 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 m² of flooring system area, whichever is greater. This minimum is stated separately for resistance to ground and for resistance point-to-point (sections 6.2.1.7 and 6.2.2.7). Static-control floor mats require a minimum of one test per 2 m².
F150-25 installed testing
On an installed floor, F150 requires a minimum of 5 tests per floor surface material, or a minimum of 5 tests per 5,000 ft² of floor material, whichever is greater. For an existing floor, or a floor that has had its initial test, a minimum of three of the five tests should be conducted in areas that are subject to wear, that have chemical or water spillage, or that are visibly dirty (F150-25 section 8.3).
F150-25 test areas after installation
For testing after jobsite installation, F150 defines each test area as a portion of the floor not exceeding 20 ft by 20 ft (6 m by 6 m). This test-area size is distinct from the total-area sampling requirement (F150-25 section 6.2).
Frequently Asked Questions
Their scopes differ. STM7.1-2020 covers ESD-control flooring systems, including mats, coverings, coatings, paints, raised access panels, and finishes, with resistance greater than 10⁴ ohms and less than 10⁹ ohms. F150-25 covers resilient flooring in tile or sheet form. STM7.1 excludes facilities storing or handling ordnance, flammables, or explosives and refers those concerns to F150.
STM7.1-2020 requires at least five representative flooring-system samples. Under F150-25, if qualification testing is required, one flooring sample is tested unless otherwise specified; unless otherwise specified, five measurements are made at different locations on that flooring sample and recorded to two significant figures.
No. STM7.1-2020 qualification tests cleaned flooring samples after at least 72 hours at 12% ± 3% relative humidity and 23 °C ± 3 °C, then after at least 72 hours at 50% ± 5% relative humidity and 23 °C ± 3 °C, testing in each conditioning environment. F150-25 calls for at least 24 hours at 50% ± 5% relative humidity and 23 °C ± 1 °C whenever possible, with testing in that same environment.
In STM7.1-2020 acceptance testing, a 10 V reading equal to 10⁶ ohms requires de-energizing the equipment and re-energizing at 100 V; record after 15 seconds or as defined by the meter electrification period. The F150-25 conductive-floor procedures compared here (qualification surface to surface, installed surface to surface, and installed surface to ground) specify readings below or higher than 10⁶ ohms without assigning the equality case.