Friday, May 20, 2005

ESD garments and compliance with 61340-5-1

An enquirer asked today:

>> A supplier has said that they are not going to use ESD coats but use a
>> standard poly cotton coats and this was acceptable. I believe this is
>> not correct please can you confirm that they should be using esd type
>> coats

This is an interesting question and really subject to personal judgement of the facility ESD Coordinator.

61340-5-1 includes garments under "ESD Protective items" and says "Specific ESD protective items when used within an EPA shall have the characteristics described......measured in accordance with the test methods.... at the highest and lowest expected or rated humidity values".

In other words you don't have to use ESD protective garments, but if you do use them they must comply with the specifications given. The specifications include:
"Coats, jackets, smocks and overalls shall completely cover all clothing in the area of the arms and torso"
"There shall be electrical continuity between all parts of the garment."
Garments shall characteristics on the outward facing surface in accordance with table 1"
"Garments complying with ESD requirements shall be clearly marked" (with the appropriate ESD symbol recommended)

Table 1 merely says that the point-to-point resistance (Rp) must be less than 10^12 ohms. In addition, a charge decay test is mandatory where Rp > 10^10 ohms or the "material is of non-homogenous woven or other construction containing insulating areas"

So, providing any coat supplied for use in the EPA has Rp < 10^10 ohms over there range of expected or rated operating humidities, it is compliant with the standard. If it has 10^10 ohm < Rp < 10^12 ohm, it should probably also have to pass the charge decay test. In practice many perfectly good ESD coats will fail the charge decay test, and it is planned to be omitted from the next version of the standard! Pragmatically I normally advise users if necessary to waive this last requirement, making note of the technical reasons for doing so.

So in short, if your suppliers coats meet the Rp < 10^12 ohm criterion (especially at low humidities) I would probably accept this as compliance with 61340-5-1.


Anonymous said...

I work for a company that just recently implemented the wearing of ESD smocks. Granted, there are areas of the company that definitely should have ESD protection and areas where it is a must. However, I work in the storage/warehouse area of the company. All components are packaged in ESD bags or original supplier packaging. Most parts are never physically touched as either they are deposited into an ESD bag or an ESD container and then "poured" into the bag. A few choice items are more sensitive than others and these are dispensed with finger cots on, on a grounded surface and with an ionizer on. We all wear grounded footware.
The problem is that these smocks are extremely "warm" and uncomfortable. There are no ventilation perforations or pockets. We have worked to bring the room temperature down but there are no windows and no circulation. We have enquired about design changes or modifying existing smocks and have been turned down.
Further, we work in close quarters, and the trailing smocks pose a high risk of getting tangled up or caught in something.
In your opinion, do you find it necessary to wear smock in conditions such as I described?

Static Doctor said...

It's difficult for me to comment without seeing your situation - but the choice of whether an ESD garment is necessary is really for the ESD Coordinator on-site who must weigh up the aruments for and against the choice.

Anonymous said...

Why don´t you wear ESD T-shirt or poloshirt. It is more suitable for your working area.