ANSI/ESD S20.20 has three garment categories with the following names and required limits:
Category 1 – Static Control Garment < 1 x 1011 ohms
Category 2 – Groundable Static Control Garment < 1 x 109 ohms
Category 3 – Groundable Static Control Garment System < 3.5 x 107 ohms
The primary purpose of a smock is to create a faraday cage around the torso and arms of an operator to shield ESD charges from operators’ clothing from damaging ESD sensitive devices. The general rule for ESD control in an ESD protected area (EPA) is to ground all conductors including people. So personnel are to be grounded and since ESD smocks are conductive, they should also be grounded.
Desco recommends Statshield ESD Smocks which are Category 3 Groundable Static Control Garment Systems. Typically a Category 1 or Category 2 Static Control Garment would be used for a visitor or for employees who do not handle ESD sensitive items. In addition to personnel being grounded, the ESD Smock should be grounded. If the ESD Smock is not grounded, the electrostatic charges on the Smock will not be taken to ground. This charge can discharge to ESD sensitive items. That is why the ESD Handbook cautions:
“After verifying that the garment has electrical conductivity through all panels, the garment should be electrically bonded to the grounding system of the wearer so as not to act as a floating conductor.” [ESD TR20.20 section 188.8.131.52.6 Proper Use]
Statshield ESD Smocks that have a hip-to-cuff grounding can be tested using a regular Wrist Strap Tester per Compliance Verification ESD TR53. If personnel are grounded via a wrist strap, then the company would test each day using a Wrist Strap Tester, and, in addition, periodically perform Compliance Verification testing on the Category 1 Static Control Garment. Another savings can be selecting Statshield ESD Smocks with conductive cuffs which replace needing a wristband.