Some electrostatic discharge (ESD) flooring materials give different resistance readings at different test voltages. The same flooring system can therefore fall on opposite sides of STM7.1’s conductive/dissipative boundary when measured at 10 volts and 100 volts. This change in classification does not necessarily indicate a meaningful change in static-control performance.
STM7.1-2020 is an ESD Association standard test method (STM), approved by the American National Standards Institute (ANSI).
Why the reading can drop at 100 V
STM7.1-2020 discusses one possible explanation in informative Annex C. Depending on the material, 100 volts or higher may cause breakdown within the material, creating a lower-resistance path. This may produce a misleading picture of the flooring system’s electrostatic performance. A lower reading at 100 volts does not, by itself, establish that breakdown occurred.
Which reading counts
If switching the test voltage to 100 V results in a resistance reading of less than 1.0 × 10⁶ ohms, the reading made with the 100 V test voltage is the value used.
How STM7.1-2020 defines conductive and dissipative
STM7.1-2020 classifies flooring systems by their resistance to groundable point. A conductive system measures below 1.0 × 10⁶ ohms. A dissipative system measures at or above 1.0 × 10⁶ ohms and below 1.0 × 10⁹ ohms. A floor whose resistance to groundable point reads at or above 1.0 × 10⁶ ohms at 10 V but below it at 100 V is therefore classified from the 100 V reading and meets the conductive definition.
How much the boundary matters
Negligible difference near 1.0 × 10⁶ ohms
Informative Annex C states that the difference in a flooring system’s actual static-control properties is negligible between 9.5 × 10⁵ ohms and 1.5 × 10⁶ ohms, so slight variations at 1.0 × 10⁶ ohms have negligible effects on static-control properties.
Specifying a range at a defined test voltage
When specifying a flooring system for use, Annex C says it is more reliable to specify the required resistance range at a defined test voltage than to use the terms conductive or dissipative.
What a resistance reading does not show
Resistance is one property that can be used to evaluate a flooring system’s electrostatic performance, but it does not fully characterize the system. Triboelectric charge generation (static charging through contact and separation) with personnel and mobile equipment is an additional property to consider, and ANSI/ESD STM97.2 is the test method for voltage generation in combination with a person.
Frequently Asked Questions
A floor measured to its groundable point can register at or above 1.0 × 10⁶ ohms at 10 volts and below 1.0 × 10⁶ ohms at 100 volts. Informative Annex C of STM7.1-2020 identifies material breakdown at 100 volts or higher as one possible cause, depending on the material. A lower reading alone does not establish breakdown.
Under STM7.1-2020, the 100 V reading is used when the prescribed switch gives a result below 10⁶ ohms. If that measurement is resistance to groundable point, it meets the standard’s conductive definition.
Informative Annex C of STM7.1-2020 says the difference in actual static-control properties between 9.5 × 10⁵ and 1.5 × 10⁶ ohms is negligible. It recommends specifying the required resistance range at a defined test voltage rather than relying on conductive or dissipative labels.