People tend to believe that if a person is wearing a wrist strap, an ESD lab coat (also known as smocks) 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 and this blog post will explain in more detail why you should be considering the use of ESD lab coats in your ESD Protected Area (EPA).
Purpose of ESD lab coats
While the ESD Standard does not require ESD lab coats, they are a very practical. Some even believe, ESD lab coats represent the single most important step to demonstrate commitment to an ESD control programme. Clothing, particularly when made from synthetic fibres, are significant charge generators. Worse for ESD control, the fabric is an insulator so the result can be very hostile: an isolated charged insulator which cannot be grounded.
An insulator will not let charges flow and will therefore hold the charge until either neutralised over time (naturally over hours or days) or with an air ioniser (artificially under a few seconds).
In the meantime, your sleeves, waist, etc. may have several thousand volts (a very significant electric field to expose nearby conductors) that may induce charges on nearby isolated conductors. This is the main reason people wear ESD lab coats: so they can shield the insulative clothing and minimise the electric fields generated from their clothing.
Examples of lab coats – for more details click here
“The ESD risk provided by everyday clothing cannot be easily assessed. The current general view of experts is that the main source of ESD risk may occur where ESDS [ESD sensitive items] can reach high induced voltage due to external fields from the clothing, and subsequently experience a field induced CDM [Charged Device Model] 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 that could generate electrostatic high fields.” [CLC TR 61340-5-2 2008 User guide Garments clause 22.214.171.124 Introductory remarks]
ESD lab coat properties
Most lab coats are constructed of a dissipative material which 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 decrease 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
Below are directions for correct installation and grounding of ESD lab coats:
- Place the lab coat on 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, it is essential that the conductive cuff is 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 common 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 appropriate, the lab coat should be grounded via the person’s wrist removing charges via ESD footwear to ESD protected flooring.
Wearing your ESD lab coat correctly
“Garments on which high levels of static electricity can be generated are one of the causes of ESD damage. It is important that such charged garments do not come into contact with ESDS. The covering garments need to be grounded, either through direct contact with the wearer’s skin, or by alternative means such as being electrically connected to a wrist strap. It is important that the ESD protective garment sleeves cover the end of the inner garment sleeves.” [EN 61340-5-2 paragraph 5.2.5.]
Grounding a lab coat using the snap at the waist
ESD lab coats are a conductor and therefore should be grounded. If not grounded, the ESD garment can be a potentially hostile 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.
Testing of ESD lab coats
Panel-to-panel conductivity is vital to ensure portions of the lab coat 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 2.5kg electrodes on different fabric panels.
Surface ESD Tester
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 significantly reduced.
Cleaning of ESD lab coats
The correct 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! Please insure 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 coats effectiveness is in fully covering the human body and street clothes – particularly 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 washings.
Questions for you: Do you use lab coats? If so, what’s the reason you started using them?