A footwear/flooring system used to ground standing personnel must meet two qualification limits under ANSI/ESD S20.20-2021: system resistance below 1.0 × 10^9 ohms and peak body voltage below 100 volts. Each footwear and flooring type combination must be qualified during initial selection and before first use, with records identifying the tests, results, limits and environmental conditioning.
Craftsman Concrete helps facilities define their testing scope and organize the resulting reports into project closeout documentation. Floor-resistance testing and person–footwear–flooring evaluations are identified separately so the facility’s ESD program team can see which measurements the documentation covers.
Both system qualification limits must be met
For standing operations, S20.20-2021 requires personnel grounding through a wrist strap or a footwear/flooring system meeting Table 2.
| Qualification measurement | Test method | Required limit |
|---|---|---|
| System resistance, measured with a person wearing the footwear on the flooring | ANSI/ESD STM97.1 | Below 1.0 × 10^9 ohms |
| Peak body voltage generated with the footwear/flooring combination | ANSI/ESD STM97.2 | Below 100 volts |
A passing resistance result alone does not qualify the combination. Body voltage also depends on the footwear, flooring material, environmental conditions and the person’s movement.
The two footwear/flooring qualification limits explain what each measurement establishes.
Floor-only and footwear-only results are different measurements
Table 3 sets separate product qualification requirements for flooring and footwear.
| Component | Test method | Product qualification limit |
|---|---|---|
| Flooring | ANSI/ESD STM7.1 | Point-to-point and point-to-groundable-point resistance each below 1.0 × 10^9 ohms |
| Footwear | ANSI/ESD STM9.1 | Point-to-groundable-point resistance below 1.0 × 10^9 ohms |
These component results do not replace the Table 2 system qualification measurements.
The ESD Association’s March 2024 interpretation bulletin includes foot grounders within the footwear category and directs users to disregard Table 3’s separate foot-grounder requirement.
Qualify each combination before first use
Qualification must be completed for every footwear and flooring type combination used by the organization. A result for one footwear type on one flooring type does not qualify a different pairing.
S20.20-2021 permits three qualification routes:
- Product specification review.
- Independent laboratory evaluation.
- Internal laboratory evaluation.
The same documentation requirements apply regardless of the route. Product specification review can support qualification when the evidence covers the actual combination and supplies the required results.
Routine compliance verification records cannot replace product qualification when a footwear/flooring system is selected for personnel grounding. The guide to supplier documentation and qualification evidence explains how to evaluate the available records.
Establish the qualification conditioning
S20.20-2021 requires qualification using the environmental conditioning specified in the Table 2 test methods or the permitted facility-minimum-humidity route.
The facility allowance applies when its annual minimum relative humidity is above the conditioning level identified in the relevant qualification method. That minimum may be used for items remaining within that facility.
Items leaving the facility must meet the listed test methods’ environmental requirements. The standard’s informative Annex F explains that the site allowance does not extend across multiple sites.
The qualification humidity and conditioning requirements cover the method-specific conditions, the facility allowance and the records needed to distinguish them.
Assemble the qualification record for each combination
Use the following checklist to organize the evidence. S20.20-2021 requires records of the test methods, results and limits, together with the conditioning used; the qualification plan must identify where those records are kept.
| Record item | What to identify |
|---|---|
| Footwear and flooring combination | The footwear type and flooring type covered by the qualification |
| System-resistance evidence | The ANSI/ESD STM97.1 result, measured with a person in the system, and the below-1.0 × 10^9-ohm limit |
| Body-voltage evidence | The ANSI/ESD STM97.2 peak-voltage result and the below-100-volt limit |
| Environmental conditioning | The conditions used, including whether qualification followed the test-method conditions or the permitted facility-minimum-RH route |
| Qualification route | Product specification review, independent laboratory evaluation or internal laboratory evaluation |
| Record location | Where the supporting records are kept, as identified in the product qualification plan |
Which resistance values should compliance verification use?
Table 2 identifies resistance below 1.0 × 10^9 ohms as the maximum allowed compliance verification value. Footnote 7 recommends documenting the footwear and flooring resistance values measured during qualification that satisfied the below-100-volt body-voltage criterion, then using those resistances for compliance verification.
The resistance values used for routine verification explain the distinction between that maximum and the qualification-based values.
A periodic body-voltage generation test is also recommended to verify that voltage remains below 100 volts (Table 2, footnote 6). That recommendation is separate from the mandatory initial qualification of each combination.
What this qualification does not establish
S20.20-2021 excludes electrically initiated explosive devices, flammable liquids and powders. Its resistance measurements must not be used to determine the relative safety of personnel exposed to high AC or DC voltages.
Meeting the footwear/flooring qualification limits therefore does not establish electrical-shock safety or suitability for those excluded applications.
Frequently asked questions
Product specification review, independent laboratory evaluation and internal laboratory evaluation. Regardless of the route, the qualification evidence must identify the test methods, results, limits and environmental conditioning. Each footwear and flooring type combination used for personnel grounding must meet both Table 2 qualification limits.
No. Table 3 addresses the components separately. A footwear/flooring system used for personnel grounding also needs the Table 2 system-resistance measurement with a person included and the body-voltage measurement for that combination. Component test results do not replace those system results.
The ESD Association’s March 2024 Standards Interpretation Bulletin includes foot grounders within the definition of footwear. It directs users to disregard Table 3’s separate foot-grounder requirement, test method and limit because ANSI/ESD SP9.2 was merged into ANSI/ESD STM9.1.