The role of ESD lab coats and Smocks in the ESD Protected Areas

Most people tend to believe that if a person is wearing a wrist strap, an ESD Lab Coat or smock is redundant. This is due to the belief that any charge on the person or their clothes would find its way to ground via the wrist strap. This is a very common misconception so in today’s blog post we will explain in more detail why you should be considering the use of ESD lab coats or smocks in your ESD Protected Area (EPA).

What is the Purpose of ESD Lab Coats?

Put simply, it is to shield or replace standard high charging insulative clothing.

Clothing, particularly when made from synthetic fibres, is a significant charge generator. Worse still, the fabrics are insulative so the charge cannot be taken away to ground. As we have learned previously, all process essential insulators should be kept at a minimum distance of 30 cm from ESD Sensitive (ESDS) items. Is this feasible for operator’s clothing?

By wearing groundable static control garments such as an ESD Smock or Lab Coat you can shield the insulative clothing and minimise the electric fields generated from their clothing.

Some believe that Static Control Garments represent the single most important step to demonstrate commitment to an ESD Control Programme.

IEC TR 61340-5-2:2018: Protection of electronic devices from electrostatic phenomena – User guide, 5.3.3.4.7.1 Introductory remarks

The ESD risks associated with everyday clothing and workwear cannot always be easily assessed. The current general view of experts is that the main source of ESD risk may occur where ESDS can reach high induced voltage due to external fields from the clothing, and subsequently experience a field induced CDM type discharge. So ESD control garments may be of particular benefit where larger ESDS having low CDM withstand voltage are handled, and operators habitually wear everyday clothing or workwear that could generate significant electrostatic fields.

Properties

Most lab coats are constructed of a dissipative material that incorporates texturised 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 Lab Coats are an ESD protective product that should possess the following ESD control characteristics:

• Antistatic low-charging so they minimise 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 lab coat and
• Groundable so the user can easily and reliably connect them to ground.

Installation and Grounding of ESD Lab Coats and Smocks

Follow the directions below for proper installation and grounding:

• Put on the lab coat and fasten all of the snaps on the front of the lab coat, making sure that clothing is not exposed outside of the lab coat.

• Throughout use, the conductive cuff must be in intimate contact with the wrist skin. The conductive cuff should never be allowed to be pulled up and over the shirt sleeve.

• Ground the ESD lab coat. A popular way to ground an ESD lab coat is with a coiled cord either attached to a snap on the waist area of the lab coat or via a wrist strap snapped to the inside cuff of an ESD lab coat. If none of these methods are suitable, the lab coat should be grounded via the person’s wrist, removing charges via ESD footwear to ESD protected flooring.

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

IEC TR 61340-5-2:2018: Protection of electronic devices from electrostatic phenomena – User guide, 5.3.3.4.7.3 Proper use

ESD control garments should be properly fastened to avoid exposure of possible charges on personal clothing worn under the ESD control garments.
Groundable static control garments and groundable static control garment systems should be connected to ground before ESDS are handled and should remain grounded whilst handling ESDS.

Testing of ESD Lab Coats and Smocks

Panel-to-panel conductivity is essential to ensure portions of the lab coat are not left as isolated charged conductors. A Surface Resistance Test Kit can quickly measure the 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 lab coat. Being shielded the measured charge should be greatly reduced.

Cleaning of ESD Lab Coats and Smocks

The proper method to clean a lab coat is to wash the garment in cool or warm water, tumble dry with low heat or hang dry. Do not bleach your ESD lab coats! Make sure you only use non-ionic softeners and detergents when laundering.

Please also note that lab coats should not be altered in any way. The lab coat’s effectiveness is in fully covering the human body and their clothes – especially at the wrists and front of the body. Altering the lab coat in any way will nullify its effectiveness.

The typical useful and effective life of a lab coat under normal wearing and recommended washing conditions is a minimum of 75 washes.

Questions for you: Do you use lab coats? If so, what’s the reason you started using them?