Electrostatic discharge (ESD) floor testing serves three different purposes: product qualification establishes conformity before initial use, acceptance testing evaluates the installed floor against the end user’s performance specifications, and compliance verification checks ongoing performance. These stages differ in their requirements, preparation and use of the results. ANSI/ESD S20.20-2021 is the ESD Association’s program standard, approved by the American National Standards Institute (ANSI). The documents cited below include standard test methods (STM) and a technical report (TR).
| Stage | Source framework | Purpose |
|---|---|---|
| Product qualification | ANSI/ESD S20.20-2021 section 7.3 | Establish that the selected ESD control item meets the applicable test methods and limits in Tables 2, 3 and 4, during initial selection and before initial use. |
| Installed-floor acceptance | ANSI/ESD STM7.1-2020 section 6.2 and informative Annex C | Measure the installed or applied flooring system for evaluation against the end user’s performance specifications. |
| Compliance verification | ANSI/ESD S20.20-2021 section 7.4 plan; procedures such as ESD TR53-01-22 | Check ESD control item performance after the control procedures are established and implemented. |
Product qualification under ANSI/ESD S20.20-2021
Qualification plan and permitted methods
S20.20-2021 requires a product qualification plan covering the applicable methods and limits in Tables 2, 3 and 4. Qualification may use product specification review, independent laboratory evaluation or internal laboratory evaluation.
Flooring limits versus footwear/flooring system limits
| Selected item | S20.20-2021 table | Qualification test method | Required limit |
|---|---|---|---|
| Flooring used in an ESD protected area (EPA) | Table 3 | ANSI/ESD STM7.1 | Point-to-point < 1.0 × 10⁹ Ω and point-to-groundable-point < 1.0 × 10⁹ Ω |
| Footwear/flooring system used for personnel grounding | Table 2 | ANSI/ESD STM97.1 | System resistance < 1.0 × 10⁹ Ω |
| Footwear/flooring system used for personnel grounding | Table 2 | ANSI/ESD STM97.2 | Peak voltage < 100 V |
For a footwear/flooring system selected as the personnel grounding method, both Table 2 limits shall be met. The Table 3 limits and test method for flooring become mandatory once the flooring is selected for use in the ESD control program.
Installed-floor acceptance under ANSI/ESD STM7.1-2020
Required measurements
STM7.1-2020 section 6.2 requires both resistance to ground and resistance point-to-point for acceptance of installed or applied flooring.
Preparation before acceptance measurements
Both acceptance procedures are performed at ambient humidity (the humidity of the surrounding air) and require new floors, mats and floor finishes to be cleaned per the manufacturer’s recommendations before resistance testing. For newly installed flooring systems, allow proper cure time, if any, following the manufacturer’s instructions.
Evaluating acceptance data
Installed-floor acceptance results must be evaluated against the applicable end-user performance specifications; taking measurements does not establish a passing result. Informative Annex C of STM7.1-2020 recommends this comparison. The S20.20 qualification limits shown above address a separate stage.
Compliance verification under S20.20-2021 and ESD TR53-01-22
As-found condition
TR53-01-22 recommends verifying an ESD control item where the ESD-sensitive item is likely to reside or be handled, to assess its as-found condition (its condition before cleaning or other changes). It recommends no cleaning, rubbing, moving or other modification of the control item before verification.
Flooring resistance measurement configuration
The TR53-01-22 flooring resistance procedure measures between an electrode on the floor and a previously verified ESD grounding/bonding reference point.
Items, sample sizes and frequency
S20.20-2021 requires a compliance verification plan identifying the ESD control items to be tested periodically and their test frequency. Under TR53-01-22, the organization must determine sample size requirements and the intervals between verifications.
When verification records can count toward qualification
TR53-01-22 excludes product qualification from its scope. S20.20-2021 permits organizations that can verify use of ESD control items before adopting the standard to use compliance verification records for qualification, subject to all of these conditions:
- The records cover at least one year immediately before their use as qualification records.
- Their results meet the compliance verification test limits in Tables 2, 3 and 4.
- The allowance does not apply when a footwear/flooring system is selected as the personnel grounding method.
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Frequently Asked Questions
Under S20.20-2021, qualification establishes conformity of the selected ESD control item during selection and before first use. STM7.1-2020 acceptance measures installed or applied flooring for evaluation against the end user’s performance specifications. Compliance verification checks control item performance after ESD control procedures are implemented, under an S20.20-2021 plan using procedures such as TR53-01-22.
No. S20.20-2021 permits product specification review, independent laboratory evaluation or internal laboratory evaluation as qualification methods. The qualification plan must address the applicable test methods and limits in Tables 2, 3 and 4.
No. S20.20-2021 expressly excludes footwear/flooring systems selected as the personnel grounding method from its allowance for using compliance verification records to satisfy product qualification.
No. STM7.1-2020 notes that resistance-to-groundable-point measurements on qualification samples may differ from resistance-to-ground measurements on installed areas, especially for floor finishes.