What is the importance of using ESD Footwear on ESD Floor?

Q. What is the importance of having the personnel within an EPA to wear ESD footwear on an ESD Flooring system?

A. Thanks for the inquiry. It was good speaking with you earlier. You had stated that you had concerns about the grounding of your flooring system and my first question to you was about the use of ESD footwear. I believe that you had stated that not everyone was using esd footwear.

You pose a situation here that needs to be addressed as a top priority at all levels of ESD Awareness for every client that we come into contact with. I don’t mean to over-simplify this but I am seeing a common trend in the ESD industry; your ESD system is only as strong as the weakest link in the chain. Another way to say this is; If you buy a Plasma TV, it needs to come with a power cord and you need to plug that in.

It appears that some people in the electronics industry are unaware of the importance of ALWAYS wearing ESD footwear on an ESD floor. I know of two instances where we went and installed the state-of-the-art ESD Conductive flooring and while we were wrapping up the installation, I’d asked the production managers what their plans were for ESD footwear.
· In one instance, they said that the company would flat-out refuse to go to that trouble. This was at an oil refinery and a very industrial environment.
· In another instance, I’d asked whether the techs and installers would start wearing ESD heel-grounders, sole-grounders, toe-grounders, shoe covers, disposable grounders, or ESD shoes. One of the techs asked me, “Do you have any that look cool?” or “are they comfortable?” I wear a pair of Static Dissipative sneakers that just so happen to be cool and comfortable. They are more expensive than heel or sole grounders, but maybe worth it. The production manager of that department told me, “If these things are uncomfortable and too time-consuming, they’re not gonna wear them and we can’t make them.” I disagree. You can make them wear them. My thought is, if you’re gonna spend all this money on compliance to ESD, it might as well work for you. These ESD floors really do work. They really do work and provide a safe and controlled path to earth for the charges that come from our bodies if we give them a path to ground. Having ESD footwear on an ESD flooring system gives the end-user the freedom to remain esd compliant while standing and walking about the ESDA as well as when they are seated at their workstation with a wrist strap on.

Now I’d like to conclude with a bit of theory of tribocharge and would like to stress that ESD compliance needs to be approached as a profit center and not just a means of obtaining compliance to some standard.

ESD control is one of the biggest profit generators in the industry. Granted, I’m not in sales. I’m technical. I’ve learned enough about the electronics industry to know that losses are budgeted. In other words, companies have built ESD losses into their budget;
· Material and Inventory
· Labor & Re-work Costs
· Facility Burden & Overhead
· Warranty Support
· Field and Customer Service
· Sales and Customer Relations

I guarantee that any floor that we’ve installed is properly grounded. We are very redundant when it comes to grounding. The copper tape we use, the conductive adhesive, the ground plates, the static conductive or dissipative flooring material, and the mere physics of the flooring system would ensure an adequate and balanced path to ground for static charge.

So why are people getting shocked now and perhaps not so much before? It typically takes 2500 to 3500 volts to discharge before we feel it as a shock. It takes sensitive electronics 100 volts and sometimes less to “feel it.” An ESD sensitive device may be destroyed (best case scenario, or hard failure-giving the test or field tech something to do), damaged (worse scenario as it will fail later, somewhere down the road-the dreaded and expensive service-call), or crippled (worst case scenario as the component is one of those nuisance intermittent failure that’s near impossible to find-always seems to fix itself whenever the tech comes to look at it).

So it drives me crazy when people in the industry start to become concerned with ESD when it gets “dry” outside. High humidity (35-65% rH) will knock the voltage of tribocharge off an ordinary residential grade carpet from 10’s of thousands of volts down to about 1500 volts. How convenient! That’s below our tactile threshold of 2500 to 3500 volts! But now the problem is well hidden and we are oblivious to the fact that we are destroying sensitive electronics on a regular basis. I don’t know. It seems like wetting your finger and using that to grade the scale of a hurricane.

I had recently responded to a tech question about mere esd shocks regardless of the concerns to component level damage, ordinance, munitions, etc., but here I tried to relate the two:

The stuff that you are dealing with in your home and in your car is a lot higher voltage than what is acceptable to the electronics industry, but it works the same way.

We feel discharges of about 3000 volts and as high as 10’s of thousands of volts. Everything always charges. Tribocharge is basically the contact and separation of dissimilar materials. When I pet one of our cats in the drier winter months, I literally feel little shocks every time and if you do this in total darkness; you can see the little arcs!

The reason we get shocked usually is because we are the ones that charge up to a high voltage and we discharge rapidly or get shocked when we touch a metal door handle or the screw on a light switch plate.

We install static conductive (2.5e4 or 25,000 ohm to 1e06 or 1 Meg Ohm) and static dissipative (1e06 to 1e09 ohm) floors and provide esd footwear. It also works to treat a floor with an anti-stat chemical. If you’ve got carpet, you can take a spray bottle and put about 9 parts water to about 1 part anti-stat. In an industrial or commercial environment, you would go with Shock Stop or Ultra Spray. I go around the house barefoot or in my socks, so that’s better than the best ESD shoes on the market. Oh, and I have a pair of Converse SD ESD shoes that I wear on job sites for ESD testing.

The human body is more conductive than it needs to be to dissipate ESD charges, but you can’t usually go around without shoes. Besides that, in production and test areas or ESD Sensitive areas, they want to keep the personnel at at least 1 Meg ohm from ground. This protects them from high current if they should encounter AC line voltages. Besides that, you don’t want to discharge too quickly. It’s like a charge going down a slide. The slide can’t be too steep or you discharge too much energy too quickly or arc over. If the slide is not steep enough, well the charge has no fun! It sits there and causes an ESD event before the voltages get down to a safe level.

So the shoes you are wearing, the clothes on your body and the floor you are walking on all play a part. When you are walking on a sidewalk, you are probably on a porous concrete slab which has quite a bit of moisture in it and if you had esd shoes, sole grounders, etc. on, you would stay at a low charge. But once you go onto a highly insulative VCT, sealed wood floor, or residential carpet, you have no where to dissipate those charges to.

What’s practical in electronics environments is not so much in the residential or consumer environments. I’d like to find a solution for these other markets, but it would have to be affordable and practical enough to justify doing it.

We can install an ESD floor that has about 100,000 ohms from point to point (between two probes placed 3 feet apart or from Resistance to Ground (any point on the floor to electrical ground or earth (ANSI/ESD S6.1 and ANSI/ESD S7.1-2005 per ANSI/ESD S20.20-2007) I also have the equipment and have been providing our end-users with Body Voltage Generation tests that show exactly how much voltage I hold with respect to ground on our ESD installed floor through my ESD footwear. The voltage is typically less than +/- 10 volts.

The basic laws of ESD; you can dissipate the charges on a conductor, but not an insulator. Some insulators and isolated conductors cannot be removed from the ESDA (ESD Sensitive Area). If you discharge a conductor within the vicinity of an isolated conductor, a charge will be induced onto it. With an insulator, it will hold a charge until something interacts with it, thus an ESD event. The only way to deal with these two situations is typically with the use of an ionizer. These things pump a balance of + and – ions into the air and they really work.

For your house, they say plants help. Obviously, as was mentioned, humidity works too. If you could get the humidity up to between 35 to 65 %, it would knock the charge generation from your carpet from 10’s of thousands of volts to around 1500 volts. Remember, we can’t feel or sense much if anything below about 2500 volts. People vary. Some people are kind of dry compared to others. I’d like to learn more about this myself. Whenever I go into my office, I test my Converse shoes on this combo-tester of ours and this one time I had a really bad cold and I could not pass the test. I was too dry (no sweat layer on my skin).

So, in that long and windy dissertation, I hope that I adequately demonstrated the importance of ESD footwear in conjunction with an ESD flooring system.