Statshield ESD Smocks and ESD Control
By Penny Butler and Gene Felder

               Why use ESD Smocks in a company’s ESD protected area? ESD control procedures need to be followed all the time. It does not help that an ESD sensitive item is protected from damaging electrostatic discharges (ESD) most of the time, it has to be all the time. Discipline is needed from each and every worker handling the ESD sensitive items, and outfitting a company’s workforce in special ESD smocks is demonstrable proof a company considers ESD control important.

               Wrist Straps reliably remove charges from a person via the moisture layer on their skin; charges on insulative clothing cannot be removed via the Wrist Strap. “While a person may be grounded using a wrist strap or other grounding methods, that does not mean that insulative clothing fabrics can dissipate a charge to that person's skin and then to ground. Clothing usually is electrically separate or isolated from the body.” (ESD Handbook TR 20.20 section 5.3.13.1 Introduction and Purpose/ General Information)

               The primary purpose of ESD Smocks is to shield ESDS items from charges on operators’ clothing. In a sense, the ESD Smock creates a Faraday Cage shielding the ESD sensitive items from electrostatic charges and discharges on the person’s clothing. It should be part of a company’s ESD Control Plan that all smocks are to be closed and regular clothing does not extend beyond the smock cuff. Otherwise, you are defeating the primary purpose of the ESD smock. For the smock to perform properly, it must make intimate contact with the operator’s skin. Then it becomes grounded when the operator is. “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]. Garments should be worn with the front properly snapped or buttoned to avoid exposure of possible charges on personal clothing worn under the garment.” (ESD Handbook TR 20.20 paragraph 5.3.13.2.6 Proper Use)

               The recommended technical requirement range per ANSI/ESD S20.20 Table 1 for ESD Garment is10E5 to 1x10E11 ohms tested per ESD STM 2.1. But when specifying, we suggest selecting garments with lower resistance as they are better quality products, and the resistance may tend to increase over time due to wear and laundering. Also if the ESD Garment is used to ground the worker, via Statshield’s patented hip-to-cuff feature, the total resistance should be less than 35 megohms or 3.5 x 10E7 ohms (the Table 1 Wrist Strap System recommended range). Good quality smocks will typically measure in the 10E5 - 10E6 range when new. The hip-to-cuff designated operator ground connection can allow for the elimination of worker’s wristband as the coil cord can be attached directly to the smock for positive operator grounding and “hands-free” operation.

               Make sure to specify smocks that are identified as ESD protective with the ESD protective symbol. “A label should be considered with the manufacturer’s name or logo and date or lot code and ESD identification. This will identify the smock as an ESD protective garment and provide information as to the manufacturer and date of manufacture. The label should be legible after 50 commercial cleanings (washings).” (ESD Handbook TR 20.20 paragraph 5.3.13.3.1.6 Labels)

               A company’s Compliance Verification Plan should include testing to see that the ESD Garment measures in the recommended electrical resistance range of 1 x 10E5 ohms to 1 x 10E11 ohms.” A Surface Resistance Test Kit can be used for this test, and data can easily be used to determine when a garment should be removed from service prior to becoming out of spec.

               ESD Garments are an optional ANSI/ESD S20.20 technical requirement, but many leading companies use them as a key for superior ESD control.