When a shoe fails on low resistance after continuos wear after having passed previously, this usually means the shoe is saturated with either water from walking in a wet area or from extreme sweat. Just as electrical hazard shoes should not be worn in wet conditions prior to work on hazardous voltages, ESD shoes should not be used for work situations after such exposure until they have dried. Testing shoes while being worn is at best difficult. One fact that must be remembered when shoes are tested in a store or van environment is that the person wearing the shoes is very important to the results. This is even more so than when a person tests his worn shoes on a daily basis.
People dump a least a pint of water in the form of sweat into their shoes daily.
If a shoe is designed not to be dangerously conductive taking this fact into account, then the resistance when it is dry on a dry skin person wearing fresh polyester socks will of course be very different than expected for normal use. A few of these factors involve just the shoe resistance especially in its dry state. Shoe outersole resistance and its contact with the measuring plate 2. Shoe insole and mid sole resistance with sufficient sweat involved and dry 3. Shoe sock liner resistance with sufficient sweat involved and dry 4.