The standard method for evaluating the slip
resistance of footwear is by determining its
dynamic coefficient of friction (COF).
According to Introduction to Plastics Engineering (2018), the coefficient of friction is defined as “the ratio of the force required to move two sliding surfaces over each other, and the force holding them together.”  The COF can be either a static or dynamic measurement.
The difficulty in determining the slip resistance of occupational footwear in real-world environments comes from the three factors that, in combination, affect the scoring of COF:
Floor Type • Contaminants • Footwear
Dynamic COF measures the force between surfaces when one or more of the objects are in motion, but herein lies the complexity. Reliable testing protocols must yield reproducible standardized results, taking into consideration the relationship among the footwear, the contaminant and the floor type.
ASTM F2913 Slip Resistance Testing
ASTM International, formerly known as American Society for Testing and Materials, is one of the largest voluntary standards organizations in the world. Its F2913 testing standard, developed in 2012, provides the current basis for measuring the slip resistance of footwear in action.
ASTM F2913 testing produces a measurable, reproducible result, though there is no or universally agreed-upon “magic safety number” when evaluating the slip scores themselves. But it provides valuable data in evaluating footwear slip resistance.
Though it is true that “to date no study has been performed that defines the safe threshold COF…for all combinations of footwear, contaminant, and floor type,”  ASTM F2913 offers a strong directional guideline for evaluating the effectiveness of slip-resistant footwear for the workplace and has become the gold standard in determining the dynamic COF of footwear and outsole. Here’s ASTM’s description of F2913:
This test method determines the dynamic coefficient of friction between footwear and floorings under reproducible laboratory conditions for evaluating relative slip performance. The method is applicable to all types of footwear, outsole units, heel top lifts and sheet soling materials, also to most types of floorings, including matting and stair nosing, and surface contaminants on the flooring surface, including but not limited to liquid water, ice, oil and grease.