Footwear/Flooring Qualification Under ANSI/ESD S20.20-2021

For standing operations, S20.20-2021 requires personnel grounding through a wrist strap or a footwear/flooring system meeting Table 2.

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.

Table 3 sets separate product qualification requirements for flooring and footwear.

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.

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.

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.

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.

Table 2 identifies resistance below 1.0 × 10⁹ 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.

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.