January 2018

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There is a very common misconception that if a person is wearing a wrist strap, an ESD garment (ESD smock, ESD shirt, ESD coat etc.) is unnecessary. Operators falsely believe that any charge on a person and their clothes will find its way to ground via the wrist strap.
Today’s blog post will explain the importance of ESD smocks and why they should be considered for your ESD Protected Area (EPA).

Purpose of ESD smocks
The main reason people wear ESD smocks is to shield their insulative clothing and minimize the electric fields generated from their clothing. As we learned previously, all process essential insulators should be kept at a minimum distance of 12 inches from ESD susceptible items. Clothing fabric, particularly when made from synthetic fibres, is a significant charge generator. Non-ESD clothing fabric is an isolated charged insulator which cannot be grounded and the resulting charges can threaten ESD control.
An insulator (like clothing) will not let charges flow and holds the charge until either neutralized naturally over time (hours or days) or with an air ionizer (artificially under a few seconds). Until the charges are neutralized, your clothing may have several thousand volts that could suddenly discharge and damage nearby static-sensitive items.
The ESD Standard does not require ESD smocks, however they are a very practical solution for minimizing ESD events from a person’s clothing. ESD smocks can be an important step to demonstrating commitment to an ESD control program.

Example of an ESD Smock
Example of an ESD Smock

Garments are intended to attenuate electrostatic fields that may be present on personnel clothing. The need for ESD protective garments is generally determined based on the sensitivity of the ESD items being handled where ESD control is a requirement.
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. Personnel clothing usually is electrically separate or isolated from the body.” [ESD TR20.20 Clause 5.3.13 Garments]

ESD smock properties
Most smocks are constructed of a dissipative material which incorporates texturized polyester and carbon nylon fibres. The conductive nylon fibres are woven in a chain-link design throughout the material, providing continuous and consistent charge dissipation.

ESD Smocks are an ESD protective product that should possess the following ESD control characteristics:

  • Antistatic low-charging so they minimize the generation of electrostatic charges;
  • Dissipative so when grounded they will remove charges to ground;
  • Shielding creating a “Faraday Cage” effect so they will restrict charges generated on the user’s clothing to the inside of the ESD Smock and
  • Groundable so the user can easily and reliably connect them to ground.

The majority of ESD smocks on the market are single-wire ESD smocks meaning they provide one electrical connection to ground.
The all-new SCS Dual-Wire Static Control Smocks are designed for use with dual-wire grounding systems. The smock’s dual-wire circuit loop closes when its two conductive cuffs are bridged by the skin on the wearer’s wrists.

  • One conductive cuff is electrically bonded to the dissipative garment and one snap stud at the hip.
  • The second conductive cuff uses an isolated conductive path to bond to a second snap stud at the hip.

When used in conjunction with a dual-wire continuous monitor, SCS Dual-Wire Static Control Smocks provide assurance of a proper dissipative path from operator to ground at all times.
For more information on the differences of single-wire and dual-wire systems, please review this post.

Installation and grounding of ESD smocks
Follow the directions below for proper installation and grounding of the ESD smock.

  • Put on the smock, and close the garment by fastening all of the snaps on the front. Verify that no clothing is exposed outside of the smock.
    Installation of Smocks - Part 1
  • Fit the conductive knitted cuffs over the wrists. Ensure that the cuffs make contact with the skin. They should never be worn over the shirt sleeves.
    Installation of Smocks - Part 2
  • Ground the ESD smock. A popular way to ground an ESD smock is with a coiled cord either attached to a snap on the waist area of the smock or via a wrist strap snapped to the inside cuff of an ESD smock. If none of these methods are suitable, the smock should be grounded via the person’s wrist removing charges via ESD footwear to ESD protected flooring.
    Installation of Smocks - Part 3

 

Using Hip-to-Cuff Grounding with the SCS Dual-Wire Static Control Smock and SCS Iron Man® Plus Workstation Monitor
Using Hip-to-Cuff Grounding with the SCS Dual-Wire Static Control Smock and SCS Iron Man® Plus Workstation Monitor

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. This can be accomplished by several means:

  1. Ground the garment to the body through a wrist strap-direct connection with an adapter
  2. Ground the garment through a conductive wrist cuff in direct contact with the skin of a grounded operator
  3. Ground the garment through a typical separate ground cord, directly attached to an identified groundable point on the garment
  4. 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 TR20.20 Clause 5.3.13.2.6 Proper Use]

ESD Garments are a conductor and therefore should be grounded. If not grounded, the ESD smock can be a potentially threatening isolated charged conductor. If an operator is wearing a smock but is not electrically connecting the smock to either their body’s skin or ground, then charges on the smock may have nowhere to go or discharge to.

Testing of ESD smocks
Panel-to-panel conductivity is essential to ensure portions of the smock are not left as isolated charged conductors. A Resistance Test Kit can quickly measure resistance of the fabric and ensure panel-to-panel conductivity by placing five pound electrodes on different fabric panels.
To ensure that the fabric is low tribocharging, a Static Field Meter can be used to measure charges generated by causing contact and separation with other materials. In addition, the Static Field Meter can demonstrate shielding by measuring a charged object and then covering the charged item with the ESD smock. Being shielded, the measured charge should be greatly reduced.

Static control garments that electrically bond to the test subject and provide a path to ground for the test subject (Category 3) shall be evaluated by all three methods:

  • the resistance point-to-point test method (Fig Sa, 5b and 5c);
  • the resistance point to groundable point test method (Figures 4, 6a, 6b and 7); and
  • the system test to determine the resistance from the person, through the garment

groundable point of the garment to the groundable point, including the ground cord (Figures 8a and 8b).” [ANSI/ESD STM2.1 Clause 1.3.2]

Using the SCS 701 Analog Surface Resistance Megohmmeter to test panel-to-panel conductivity
Using the SCS 701 Analog Surface Resistance Megohmmeter to test panel-to-panel conductivity

Cleaning of ESD smocks
Smocks must be laundered periodically for proper operation. The proper method to clean a smock is to:

  • Wash the garment by hand or with a standard household washing machine in cold or warm water.
  • Only use non-ionic liquid softeners and detergents when laundering. Do not bleach your ESD smocks!
  • Tumble dry with low heat or hang dry.

Do not use:

  • Hot water
  • Dry detergent
  • Bleach
  • Fabric softener
  • Industrial laundry machines

Please also note that smocks should not be altered in any way. The smocks effectiveness is in fully covering the human body and street clothes – especially at the wrists and front of the body. Altering the smock in any way will nullify its effectiveness.
The typical useful and effective life of an ESD smock under normal wearing and recommended washing conditions is a minimum of 75 washings. Under the same conditions, SCS smocks will maintain their usefulness and effectiveness for a minimum of 100 washings

Wrist straps are generally straight forward with what they do and how they work, but when it comes to foot grounders there is still a lot of confusion out there – something we want to address in today’s post. So, let’s get started.

Introduction
An Electrostatic Discharge (ESD) flooring / footwear system is an alternative for grounding standing or mobile workers. Sitting personnel are usually grounded via a wrist strap, but this method is not feasible for operators moving around in an ESD Protected Area (EPA).
ESD foot grounders are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic charges from personnel. ESD foot grounders are easy to install and can be used on standard shoes by placing the grounding tab in the shoe under the foot.
Per ANSI/ESD S20.20 Clause 8.2 Personnel Grounding: “For standing operations, personnel shall be grounded via a wrist strap or by a footwear/flooring system meeting the requirements of”:

  • the total resistance of the Footwear / Flooring system shall be less than 1.0 × 109 ohms
  • the maximum body voltage generation shall be less than 100 V.

Structure of Foot Grounders
Foot grounders discharge static from a person to ground by connecting the person to a grounded walking surface. A conductive ribbon placed inside the wearer’s shoe or sock makes electrical contact with the skin through perspiration. The ribbon is joined to a resistor which limits electrical current should accidental exposure to electricity occur. The other end of the resistor is joined to a conductive sole. The sole contacts a grounded ESD floor mat or ESD flooring system.

Structure of a Foot Grounder
Structure of a Foot Grounder

Foot grounders must be worn on both feet to maintain the integrity of the body-to-ground connection.
Wearing a foot grounder on each foot ensures contact with ground via the ESD floor even when one foot is lifted off the floor. This will more reliably remove static charges generated by human movement and more reliably protect ESD sensitive devices (ESDS).

Installation of Foot Grounders
1. Standard Style Foot Grounders
Standard D-ring heel grounders are equipped with an elastic D-ring fastening system which provides adjustable cinching of an ankle strap and allows “flex” during walking. They are designed for use on most types of shoes and boots.

  • Place the grounding tab in the shoe so that it will lay under the heel. Once heel is repositioned inside tied shoe, tuck excess ribbon material into side of shoe.
  • Place heel cup onto the shoe. For models with a non-marking interior, install so that the lined cup surface is making contact with the shoe.
  • Pull the strap through the D-ring and cinch down for snug, comfortable fit.
  • Test each heel grounder to confirm proper installation.
Installation of Standard Style Foot Grounders – more information
Installation of Standard Style Foot Grounders – more information

2. Cup Style Foot Grounders
Cup Style Foot Grounders are heel grounders designed for use on standard shoes and can be easily adjusted to fit the individual wearer.

  • Place the foot grounder on the shoe so that the lining is contacting the shoe.
  • Insert the grounding tab inside of the shoe and under the foot. Make sure that solid contact is made between the sock and body. Cut contact strip to desired length.
  • Fasten hook and loop straps together, securing the foot grounder firmly on shoe.
  • Test each foot grounder to confirm proper installation.
Installation of Cup Style Foot Grounders – more information
Installation of Cup Style Foot Grounders – more information

3. D-Ring Toe Grounders
Toe Grounders with the elastic D-ring fastening system are designed for use with a variety of men’s and women’s shoes including high heels, cowboy boots, flat shoes, loafers and safety shoes.

  • Insert the grounding tab inside of the shoe and under the foot. Make sure that solid contact is made between the sock and body. Cut grounding tab to desired length.
  • Place rubber toe material under toe area of shoe sole. Pull hook-and-loop strap over top of shoe and cinch down until snug. Install so that the lined surface is contacting the shoe.
  • Pull elastic strap around the back of the heel. Adjust D-ring plastic loop for a comfortable fit.
  • Test each toe grounder to confirm proper installation
Installation of D-Ring Toe Grounders – more information
Installation of D-Ring Toe Grounders – more information

4. Disposable Foot Grounders
Disposable Foot Grounders are designed for applications where the use of permanent foot grounders are not economical or practical. They are constructed so that it may be used once and then discarded.

  • Remove shoe. Wipe any excess dirt from underside of heel. Remove release paper from heel grounder.
  • Apply the adhesive end of the heel grounder to the underside of heel of the shoe. Wrap the tape snugly around the outside of the shoe.
  • Insert the non-adhesive end of the heel grounder inside the shoe so that the black dot is over the middle of the heel area facing upwards.
  • Put the shoe on.
  • Test each foot grounder to confirm proper installation.

NOTE: This product is not recommended for use on equipment with operating voltage.

Installation of Disposable Foot Grounders – more information
Installation of Disposable Foot Grounders – more information

Advantages of ESD Foot Grounders
ESD foot grounders are often preferred over ESD shoes for several reasons:

  • One size fits many foot sizes, reducing stock holdings and simplifying operations.
  • ESD foot grounders usually pass the mandatory resistance test as soon as worn, whereas some ESD shoes require a ‘warm-up period’ in order for the operator’s Resistance to Ground (RG) to drop below 35 megohms.
  • The operator is allowed to wear their own footwear, increasing their comfort in the workplace and not limiting footwear selection to available ESD shoe styles.
  • Less initial investment cost in comparison to ESD shoes if outfitting all operators in an EPA.

Disadvantages of ESD Foot Grounders
ESD foot grounders have a useful life that is dependent on the floor and it’s surface roughness, which can make them seem like they have shorter useful life in comparison to ESD shoes. However, there are a few simple tricks to avoid a quick ‘burn-out’:

  • We recommend ESD foot grounders only to be used indoors where floors are usually smoother (and where the ESD foot grounder is less likely to become wet, thereby short circuiting the resistor). The rougher the floor the greater the wear.
  • The manner in which the wearer walks can also affect the life span of the grounder.

In summary, with reasonable care and if used only indoors, ESD heel and toe grounders can last several weeks.

Testing of Foot Grounders
Proper testing of your foot grounders involve testing:

  • the individual foot grounder
  • the contact strip
  • the interface between the contact strip
  • the wearer’s perspiration layer

There are personnel grounding testers on the market designed to properly test foot grounders. For more information, check out our selection chart.
If you obtain a fail reading from the tester you should stop working and test the foot ground and contact strip individually to find out which item has failed. Replace the foot grounder or replace the bad component if possible. Retest the system before beginning work.

Ensure your Foot Grounders are working before handling ESDs
Ensure your Foot Grounders are working before handling ESDs

Cleaning of Foot Grounders
Foot grounders are used to ground static charges, however dirt provides an insulative layer adversely effecting reliability. For proper operation, the foot grounder and its conductive strip must be kept clean.
The rubber portion of the foot grounder should be cleaned using an ESD cleaner. Ensure that your ESD cleaner is silicone free. This is critical as silicone is an insulator. An alternative would be to clean using isopropyl alcohol. ESD cleaners should not be used to clean the nylon polyester grounding tab. Foot Grounders can be safely hand or machine washed on gentle cycle. Mild detergents, such as Woolite® or a liquid dish washing product used with warm water are recommended for cleaning, however care must be taken to ensure that these detergents are silicone free.

Conclusion

  1. It is recommended that ESD foot grounders are worn on both feet to ensure that a continuous path to ground is maintained at all times (even when lifting one foot).
  2. Contact strips should be tucked inside the shoe with as much contact area as possible to the bottom of the stockinged foot. ESD foot grounders rely upon the perspiration layer inside of the shoe to make contact through the stocking.
  3. Foot grounders must be used with an ESD protected floor system (such as properly grounded ESD floor finish, carpet tiles or floor mats) to provide a continuous electrical path from the user directly to the ESD ground.
  4. A current limiting of one or two megohm resistor in series with the contact strip is recommended but not required.
  5. ESD foot grounders should be tested independently at least daily while being worn to periodically test for proper grounding.