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14 Jul

Monitors & Meters: Which One Do You Need?

ESD Monitors and Meters

Monitors and meters may seem like merely a question of semantics. And in most of the world it is, monitors are analogous with meters and vice versa.

But when you’re dealing with electrostatic discharge (ESD) prevention, both have specific purposes and uses that set them apart from one another. And it’s important you know which is which before you start or continue your work with items that can be harmed by ESD.

Monitor: What’s Happening in the Room?

In plain language, in an ESD Prevention situation, the Monitor (noun) keeps known sources of ESD in systematic reviews. It monitors (verb), the ‘progress’ or quality of ESD buildup over a period of time.

So we have monitors for people, that connect to their personal wrist straps, or connect between them and the ESD matting that they are using – in effect, monitoring both.

The key to a good ESD monitor is make sure they provide constant monitoring of the potential ESD in the room.  If the monitor fails, a single spark of static electricity can cost hundreds of dollars in damage before it’s quelled.

Meter: Where Is It?

Meters, in an ESD prevention situation, operate more as the means to locate the sources of ESD build up.

Much like the meters used for testing in construction situations, meters will show the relative ESD levels, allowing the user to pinpoint the exact spot where ESD is being generated or not dispersed properly.

This can be on ESD mats, clothing, people and flooring.

Specialty meters can detect and pinpoint ESD specifically in a cleanroom or ionized area.

There are meters that look at a wide variety of potential ESD buildups and smaller units that check select areas only. And meters that check the humidity, temperature, electrical resistance, and any or all of these at once.

There is a secondary subset of meters that you should also be aware of – Testers.

Testers check the grounding of electrical receptacles to ensure they are actually grounded. Imagine the problems and expense of not realizing your electrical plugs were not grounded and subsequently having to discard or repair any sensitive electronics that had been worked on or assembled during the time the ground was inactive.

There are also testers for personal wrist straps and grounding cords.

Are You ESD Aware?

So, the answer to our question above is YES.

It’s not an either/or situation. It’s both. Each tool has its purpose within your ESD control situation, and both are effective in their job – which is generating awareness of ESD.

We would love to be your full service, seamless ESD solution provider; contact us today for more information.

29 Jun

Custom Matting: A Ground Zero Specialty

Custom Matting-A Ground Zero Specialty

If you’ve ever worked with an X-Acto Knife or a box cutter, you know there are some dangers, just as there are with any knife. Remember, pay attention to what you’re doing! Never use a dull blade! Cut away from your body!

And of course, wear cut resistant gloves. Yes, we know you’re a man, and men don’t need certain protections… Okay, so both genders have their issues, but this one rule is the one we most often neglect – and that neglect leads to injuries.

You’re being careful, cutting along, everything’s going smoothly and SLICE!

Yes, that’s right, you’ve just sliced open your finger, there’s blood everywhere – you have to go to the emergency room and get stitches.

It kind of ruins your day.

OSHA reports that nearly 40 percent of all injuries attributed to manual workshop tools in the US involve knives with retractable blades.

And according to the Bureau of Labor Statistics, around 250,000 serious hand, finger and wrist laceration occur annually in the private industry.

So that scenario we described above?  It’s far more common than you might think. And, in the interest of your safety and our bottom line, we took action.

A Cut Above

So what did Ground Zero do to help insure your workplace safety?

In an earlier post, we talked about ESD mats – what they are and how they work, but today we’d like to get… a little personal, if that’s okay with you.

Most table and bench mats are built with either two or three layers. The top layer is resistant to chemicals, solder and flux, making it usable and easy to clean. The bottom layer is either a durable anti-skid surface and/or an adhesive backing, both to ensure safety on the work area.

Three-layer mats have the added bonus of a conductive scrim layered in the center that can coordinate with your personal wrist-strap constant monitors.

As you can imagine, all of these layers make the mats a little thicker than cardboard or just a vinyl mat. And, as you know, when cutting with an X-Acto knife or box cutter, the thicker the material you’re trying to cut is, the more prone the blade is to slipping, leading to that ER visit.

So to help promote the safety of our customers’ workplaces, we decided to offer custom cut matting.

That’s right, any of the mats we sell can be custom cut to your specifications (with a small margin of +/-1/8th of an inch). Plus, each and every custom cut mat comes with an ISO certification showing it has been tested and met the latest professional standards.

So which would you prefer, a trip to the emergency room, or the ability to get to work on with your new ESD mat right out of the box – with all of your fingers intact?

Oh, and finally: a little safety advice, whether you want it or not. When using a knife or blade of any sort, stay sharp! Follow all of those rules we mentioned above, ‘cause we all know a lot of us do ignore them and they were created for our safety.

We would love to be your full service, seamless ESD solution provider; contact us today for more information

25 May

What Are the Standards for Electrostatic Protection?

Standards for Electrostatic Protection

So, you’ve just been tasked with building or designing your first Electrostatic Protection Area (EPA). You’ve started doing your research, but there are so many choices, from so many different companies. Suppliers, manufacturers, third party providers… If only there was some established standard for judging the efficacy and reliability of all those pieces and parts.

Well, you’re in luck! In 2007, the American National Standards Institute (ANSI) in cooperation with ElectroStatic Discharge Association (ESDA) released a unified set of standards for the design, implementation and maintenance of ElectroStatic Discharge control programs.

In the midst of World War I, five engineering organizations recognized the need to develop standards that could eliminate confusion and could be adhered to across all disciplines, without regard to politics, profits or personal preferences. These groups reached out to the U.S. Departments of War, Navy, and Commerce to form an impartial third party non-profit organization, then known as the American Engineering Standards Committee.

Following the war, the organization spent the next 20 years establishing several safety protocols still observed today, like eye protection, hard hat standards and in-house electrical safety while at the same time reaching out to other similarly tasked international organizations.

When the United States entered World War II, the organization, which would eventually come to be known as ANSI, helped to accelerate the war effort and productivity, created more effective quality control measures, as well as helping to advance photography, radio, and even the development of Velcro.

In 1970’s, ANSI established a public review process and began the herculean effort of moving the United States to the metric system. While the general public never really connected with the metric system, the effort did bring ANSI to the forefront of private sector companies who discovered standardization was a way to stay more competitive in an increasingly global economy.

With the advancement of personal computers in the late 70’s and early 80’s, engineers at several companies recognized a need for more understanding of electrostatic discharge and its prevention. They formed the ESD Association, a non-profit, voluntary professional organization that for almost 35 years has sponsored educational programs and developed standards to help eliminate losses due to electrostatic discharges.

Together, leaning on the historical experience of both military and several commercial organizations, ANSI and ESDA developed the definitive standard for ESD protection, the very cleverly named ANSI/ESD S20.20-2007.

Covering about every conceivable area of ElectroStatic Discharge, the ANSI/ESD S20.20-2007 utilizes both the human body model and the machine model to provide a broad set of guidelines for ESD protection.

The Human Body Model is the military standard that defines and rates the vulnerability of an electronic device to the ESD generated by a human being touching it. The Machine Model works similarly, except it rates the vulnerability of a device receiving a machine discharge into ground. It was originally developed by car manufacturers as their plants moved to more mechanized production technology.  The Human Body Model is about 10 times more sensitive than the Machine Model.

There is a lot to explore in the ANSI/ESD S20.20-2007 guidelines, but for the purpose of this primer, the document highlights 3 fundamental ESD control principles:

  1. All conductors should be grounded. This includes the personnel and the surfaces they are working on.  We recommend, at a minimum, personal grounding wrist straps, ESD table or bench mats, and a common ground cord.
  2. Necessary non-conductors – certain circuit board materials, device packaging, etc. – cannot lose their electrostatic charge by being grounded and appropriate precautions must be implemented.
  3. Static protective materials, such as ESD shielding bags or ESD totes and boxes must be utilized when transporting sensitive electronics outside a properly prepared EPA.

There are slightly less stringent standards that apply to floors and bench mats, but ANSI/ESD S20.20-2007 is the highest and most comprehensive guideline so far. So when you’re shopping for the parts needed to establish your EPA area, always look for companies that maintain that standard in their products and services.

We would love to be your full service, seamless ESD solution provider; contact us today for more information.

04 May

Finding ESD Storage Solutions

Finding ESD Storage Solutions

There’s a classic scene that appears, with some variation, in every James Bond film.  Bond gets assigned a new mission and he goes to see MI-6’s Quartermaster, or “Q.” Q gives Bond everything he needs to complete the mission, including a few items that seem unusual or out of place.

Of course, as Bond fans know, these elements will at some point be combined to facilitate a distraction so Bond can escape. And usually that distraction is a rather large explosion.

One wonders how he was transporting the items before so that they didn’t explode in his Armani suit.

Of course, in real life, when items combine, the result isn’t usually an explosion.  Or is it?

As we’ve mentioned before, the amount of Electrostatic Discharge (ESD) required to cause significant damage to sensitive electronics is far below the threshold where a human being can feel it.

By the time our bodies create a static charge that we can feel, it’s somewhere between 3 & 17 times stronger than what most electronics can handle without suffering damage.

Even just the controlled blowing of air, like the old canned air computer dust removal techniques can cause static ESD build-up that can be transferred to your sensitive electronics.  And that tiny electrostatic discharge can cause latent or catastrophic failure, costing you time and money.

We’ve discussed selecting the proper shielding bags in a previous post. Another important weapon in your Electrostatic Discharge defense arsenal is anti-static ESD storage containers.

ESD Storage Containers

ESD storage containers are typically made of a conductive material, such as polypropylene or high density polyethylene and provide an added layer of protection, shielding your work areas and personnel from the harmful effects of ESD.

The conductive material provides a barrier which these fields cannot penetrate and prevents the build-up of electrostatic charge. The bins, totes and miscellaneous storage containers come in both static dissipative and conductive. Both control a potential electrostatic discharge, one by resisting it, the other by neutralizing it.

Additionally, be on the lookout for non-ESD protected items that may stray into the Electrostatic Protected Area – transparent tape, plastic sandwich bags, water bottles, Styrofoam coffee cups, even just pieces of paper – can be the source of an uncontrolled electrostatic discharge.

Of course, all of these storage solutions should be used within the minimum guidelines of an Electrostatic Protection Area, that is, wrist straps, ESD mats and a common ground.

We would love to be your full service, seamless ESD solution provider; contact us today for more information.

12 Apr

What Are ESD Mats & How Do They Work?

Static Electricity and ESD Matting

Have you ever been working in your garage and accidentally made contact with a metal part of an ungrounded electrical appliance, like a box fan or a badly wired junction box? The jolt you receive wakes you up faster than a cup of coffee or one of those 5-hour energy drinks. Now imagine what that could do to sensitive electronics—devices and circuit boards with a much lower resistance than your skin.

Considering just the physical activity of moving your arms and legs can build up relatively large electrostatic discharges (ESD) that we may never notice, there’s very little activity that isn’t dangerous to electronic components – even their assembly. But there are steps you can take and tools that have been developed to protect your sensitive electronics. One simple, popular tool is an antistatic or ESD mat.

How Does an ESD Mat Work?

Antistatic or ESD Mats have a high electrical resistance, which allows the electrostatic discharge to “flow” across the surface of the mat at a slow rate – enough to get the ESD away from your electronics, while at the same time neutralizing what little charge inevitably does build up.

The simplest form of an ESD mat is simply that – a tabletop mat, about the size of a placemat, that you use on a desk, table or any flat surface. They typically connect with a personal grounding wrist strap – adding additional protection by drawing any ESD charge away from the person working on the device.

ESD mats also use a common ground to draw the electrostatic discharge away from offending areas. Without that ground, the mat could, in theory, protect the item being worked on at first, but would then transfer the ESD to the very next thing it comes into contact with – the next item, the person holding it (and then to the item), or even right back onto the item it was originally meant to protect.

For larger workspaces, or dedicated ESD workstations, you can invest in rolls of ESD matting or custom-sized mats. You can even get ESD matting with built-in static control monitors and self-adhesive backing.  Just make sure, regardless of the size or quantity used, that all of the mats are grounded.

You can also increase protection as well as worker safety by investing in ESD flooring mats, which not only act as further neutralization of potential electrostatic discharge but also can provide cushioning, easing the fatigue of the person standing while working on the electronic devices. The hazard of slippery floors is also alleviated by an ESD flooring mat.

Bear in mind that not all ESD matting is tested to the same level.  We recommend checking to make sure the mats you are buying are properly assessed to ensure you are getting the protection you need, and ideally, include ISO certification for your company’s protection.

We would love to be your full service, seamless ESD solution provider.  Contact us today for more information.

29 Mar

The Truth About 11 Myths of Electrostatic Discharge

11 Myths of Electrostatic Discharge

Would it surprise you to know that a good portion of our modern world would be unable to function without the help of electrostatic discharges (ESD’s)?

No one seems to know quite how it happened, but in 1984, Scott M. Kunen applied for a patent for a “touch controlled switch” – a device he had developed to allow lamps to be turned on or off with the touch of a human hand.

Little did he know that less than a decade later, computer companies would begin adapting his technology, covering it with a variety of static controlling sheaths, creating the capacitive-touch screen, the basis for all modern smart phones, tablets and touch screen laptops.

So, here’s the truth about the myths of electrostatic discharge.

Myths About Electrostatic Discharge

Myth #1 – All ESD is bad.

The truth is, most people use ESD everyday to make phone calls, send text messages, and create emails. The touch controlled switch and the capacitive-touch screen both operate by transmitting small ESD charges from your body into the devices to signal turning a light on, or the letters or numbers desired.

Myth #2 – Electrostatic Discharge is a modern day problem.

Believe it or not, ESD and necessary precautions to prevent it are older than the United States. In the 1400’s, forts and places that stored or produced explosives, gun powder, and even sawdust could fall prey to horrible accidents, so early forms of ESD control were developed and implemented.

Except, of course, when the good guys needed to blow up the bad guys’ stash in a Hollywood movie.

Myth #3 – ESD problems are really quite rare.

In truth, because of the extremely low levels of ESD required to damage small electronics and the fact that damage isn’t always visible or catastrophic, we may never know just how prevalent ESD events are.

Visible static sparks generated by our bodies have to build up between 500-1000 volts, and it takes twice that charge to be felt.  Most sensitive electronics can be damaged by 100 volts or less.

And even if the device continues to function as expected, its life expectancy may be severely diminished and in some cases, latent failure can occur, causing even more damage.

Since we cannot fully prevent or even detect an ESD event, all precautions should be taken to avoid an accidental discharge.

Myth #4 – Discharging fingers and tools before using them is sufficient precaution against ESD mishaps.

Unless you are able to hold your body AND tool perfectly still, you can (and often do) build up a replacement charge that can be discharged into your electronics.

As mentioned above, because of the negligible amount of charge necessary to potentially damage the sensitive parts, you have no way of knowing you are not transmitting a dangerous ESD. It’s better to be safe than sorry.

We recommend that you always use personal wrist straps, dissipative mats and grounding cords for the best chance of circumventing ESD problems.

Myth #5 – You have to touch an item to transmit an ESD to it.

As mentioned above, it takes very little for the human body to build up an electrostatic discharge. Just the movement of lifting your foot off the ground can generate up to 1,500 volts.

And that generated charge can easily leap from your hand to your unprotected device inches away.

Stay tuned next week for Part 2 of The Truth About 11 Myths of Electrostatic Discharge…

We would love to be your full service, seamless ESD solution provider, no matter what your size or budget.  Contact us today for more information.

25 Feb

Building an Electrostatic Protected Area (EPA)

How to Build an Electrostatic Protected Area

Almost everyone’s familiar with the image of a white “cleanroom” or “bunny suit.” They show up in just about every depiction of people working in computer facilities in popular entertainment, and it’s a highly sought after specialty ‘armor’ in the video game Fallout 4.

What most people may not know is that the suits are designed not to protect the person inside, but the delicate circuitry they’re working on.  But not everyone who works with small, sensitive electronics needs to spend money for a full-on, disposable suit.

If you work with a lot of small electronics, a more affordable solution is to put together an electrostatic protected area (or EPA).  This doesn’t have to take up a lot of space and can actually be quite portable.  It just needs to be done properly.

Let’s start with the basics and work our way up to the safest and most expensive options.

Simple EPA

At a bare minimum, all personnel working within an EPA should have a personal grounding wrist strap.  These make sure any excess energy is grounded – forced away – from the electronic devices and circuit boards being handled.

Connected to that grounding strap is a dissipative mat. Dissipative means quite simply to disperse or disappear.  A properly designed and implemented dissipative mat does for the surface what the grounding wrist strap does for the person – protects sensitive electronics from electrical discharges.

Mats can be purchased pre-cut or in rolls, depending on what your needs are.

Attached to both of these is a common point cord, also referred to as a grounding cord.  These cords are fully insulated and take any electrostatic charges away from the person and the ESD mat to be grounded safely.

Often these simple options are packaged together as a field service or workstation kit that can be purchased as one unit to avoid forgetting any key elements.

Now that we’ve established the minimum requirements for an EPA, let’s look at additional options that can be easily implemented within your system to further insure the safety of the components and reduce the risk and excess cost of replacement.

From the Ground Up

For more permanent EPA installations, there are a variety of flooring options that can be integrated.  Everything from conductive and dissipative vinyl tiles to anti-static carpeting that can be utilized in the work area or just in the area surrounding your EPA system.  You can even add flooring with a high-end moisture barrier as well as anti-static protection.

Sole Protection

One of the most obvious ways we build up a potentially dangerous electrostatic discharge is just by walking.  Static charges build up naturally.  While a personal grounding wrist strap will help dissipate the charge, there are additional options for your feet.

Shoe covers with conductive strips are a quick, low cost addition to an existing EPA system and great for alleviating the risk of allowing visitors into the EPA area.

For employees whose duties mean they spend substantial time in the EPA area, you can add foot and heel grounders, toe grounders and sole grounders.

For even more protection, grounders can be upgraded to ESD shoes.  These come in a variety of styles for your business setting – even weatherproof boots and hiking models.

Additional Considerations

Adding isolation protocols and ESD protective containers can also complement your EPA system and reduce the chance of any accidental charges building up or discharging into your electronic components.

Of course grounding should be a consideration with any additions to your EPA system.  Whether it’s flooring or matting, grounding cords with a built in resistor add that much more protection to your area.  And the more working parts you have, the more grounding capability you require.

There are simple options to increase the grounding ability of any size EPA system, as well as monitors that can be added to the system – at the personal or system-wide level.

And if you really feel the need to cover yourself top to bottom, there are more workable clothing options as well.

Contact us today for more information; we would love to be your full service, seamless ESD solution provider.

12 Feb

ESD: Grounding, Isolation & Prevention

The Pilllars of ESD Protection

We’ve all had it happen. We’re opening our car door on a cold day, or we’ve just shuffled in our socks to the door and the moment we reach out, pop! A small snap of static electricity reminds us that we’re alive.

Think back to when you were a kid – your dad or uncle perhaps, showed you the power of static electricity by rubbing a balloon on your head and sticking it to the wall or causing your hair to rise up of its own accord. These tricks with static electricity are great for a chuckle or two. When you’re rubbing the balloon or your socks on the floor, it creates an imbalance of electrons, and that potential energy rests on your body or the surface of the balloon, waiting to discharge. Eventually it does and this sudden restoring of the electrons to their neutral state is called an electrostatic discharge or ESD.

That little tiny jolt of static electricity seems small but is really 3,000 volts – for humans, it’s the amperage that gets you. Unfortunately, for small electronics: circuit boards, semiconductors or even simple devices around the home, much smaller static discharges – ones too light to ever be sensed by our skin – can cause minor errors, or even completely destroy a device’s usefulness. In this situation, ESD is no laughing matter.

In a business—especially one that manufactures or handles a lot of electronics, but even in a typical office environment—this kind of damage can get expensive quickly.

So today, we’re going to talk about the three pillars of controlling ESD: Grounding, Isolation and Prevention.

Grounding

If you’ve worked with small electronics much at all, you’re probably aware that there are certain things you should do to prevent damage to that circuitry. You’re probably familiar with the third prong on many electrical cords. Just like the grounding plug diminishes the risk of you being electrocuted, grounding yourself and your work area keeps your circuit boards and electrical components safe by discharging any built up static electricity.

At a bare minimum, utilizing a grounding wrist band is extremely helpful. Many sellers include disposable bands when they ship electronic components, but we highly recommend owning and utilizing your own personal metal ground wrist strap that connects directly to your work surface with a personal ground cord. Always make sure the wrist strap is snug and is touching the skin to allow the charge to dissipate.

Isolation

Static charges cannot penetrate containers that are made of conductive materials or have a conductive layer. That’s why electronic components usually arrive in metallized shielding bags or a conductive tote box. Don’t forget you must ground them before opening. And don’t set these components just anywhere. What many people fail to realize is that simple items that can be found on any normal work surface – even an ESD mat – can also cause unnecessary static buildup that could lead to a fatal discharge.

Transparent tape, plastic sandwich bags, water bottles, Styrofoam coffee cups, even paperwork or blueprints can hold a static charge just waiting to wreak havoc on unsuspecting components. And even if you are properly grounded, holding the components too close to your clothing can also result in an ESD.

Prevention

Always take proper precautions when working on electronic components. Follow all of the tips above, and if you’re going to be working on several components or multiple projects, we recommend investing in some ESD bench and table matting for your work surface. It integrates well with a personal ground cord and wrist band and is the best solution for ESD prevention. A few dollars spent here as well as on ESD protective containers can mean plenty of money saved on ruined components as well as lost time while waiting for replacements.

Following these simple suggestions can mean a much safer environment for both you and your electronic components – and you can leave the static charge at home for parlor tricks.

Contact us today for more information;  we would love to be your full service, seamless ESD solution provider.

31 Aug

Common Sources of ESD Damage You May Have Overlooked

Common Sources of ESD Damage

As we’ve talked about previously, often the sources of static electricity go completely unnoticed. This is because we humans can’t even detect a static charge until it gets up to about 3,000 volts. The problem is that sensitive electronics can be damaged by a charge down in the 100-volt range.

If you’re in the business of manufacturing printed circuit boards or other electronics, you already know how serious a problem electrostatic discharge in the work environment can be. But for the rest of us, we may not recognize just how big of a problem ESD can be, and how much it is affecting our critical devices.

Once you become aware, then you’ll want to start addressing the problem by setting up a static-free zone, or an ESD protected area (EPA).

One of the first and biggest areas that you’ll probably begin to address in more critical environments is the flooring itself. Putting in one of the many types of ESD floors will help carry static charges away to ground right through the floor, rather than allowing it to end up damaging your sensitive equipment.

Another method of controlling ESD involves using specially designed ESD shoes that will allow static charges to dissipate.

Using ESD flooring and ESD shoes addresses a major source of static discharge buildup.

But where else do static charges come from?

Believe it or not, the typical work environment is loaded with sources of static electricity. Here are some examples you may not have thought about:

  • a typical “scotch tape” dispenser:  the tape itself builds up a static charge coming off the roll (which can be up to a few thousand volts!)and the dispenser is usually made up of insulating materials that can build up a charge
  • plastic baggies (for components) can have a few hundred to over 1,000 volts of static charge built up on them with simple handling.
  • plastic water bottles (or any plastic bottle containing liquid) can build up thousands of static volts of electricity
  • any other products made out of insulating, rather than conductive materials (plastic cups, bins, organizers, etc.)

As you can see, often the sources of static electricity are so close at hand, and so seemingly benign, that they’re very easy to miss.

What Can You Do About It?

Bringing static electricity under control at a given workstation can be accomplished using a few simple tools:

  • ESD work mats will carry the charge away from any conductive materials you set on them
  • ESD grounding straps or wrist straps allow the wearer to stay grounded at all times, preventing the buildup of a static charge on the human body
  • The use of monitors and meters will allow for quick and easy measurement of static buildup, which will help identify and eliminate sources of ESD before they become a problem

Need help setting up your ESD protected areas? Give us a call today, and one of our ESD control experts will be happy to provide all the help you may need!

18 Jun

We don't need no stinking wrist straps, do we?

Q: I have read the White Paper 1: A Case for Lowering Component Level HBM/MM ESD Specifications and Requirements and found the ESD Control Programs and Resulting Data (Chapter 1, Page 20-23) particularly interesting.

Assuming a production environment with ESD flooring, footwear (and clothing), by the time a person walks to a workstation and sits down, the voltage of this persons should not exceed 500V (or even 100V as seen in Figure 3). That would mean even a seated operator in this case would not need to wear wrist strap, that theory would be correct right? After sitting down and this person sits on a stool (feet off the floor) with resistance to floor < 1.0x10exp9ohms, any HBM risk would be further reduced wouldn’t it?

A: Hello ****.  Nice try.  Even if you have an ESD flooring system and even if you have ESD footwear and even if you have an ESD task chair with ESD casters or an ordinary task chair with an ESD chair cover (very effective as well), ESD smock on… you STILL have to wear the wrist strap when seated at an ESD workstation.

The only time, per ANSI/ESD S20.20-2007 page 4, 8.2 Personnel Grounding, that personnel in the EPA (ESD Protected Area) should be without a wrist strap is when doing standing or walking about operations, and then two conditions must be met;
·         “When the total resistance of the system (from the person, through the footwear and flooring to the grounding / Equipotential bonding system) is less than 3.5E7 Ω…”
·         “When the total resistance of the system (from the person, through the footwear and flooring to the grounding / Equipotential bonding system) is greater than 3.5E7 Ω and less than 1.0E9 Ω and the BVG is less than 100 v per 97.2…”

This is what is said about seated personnel:

“When personnel are seated at ESD protective workstations, they shall be connected to the grounding / Equipotential bonding system via a wrist strap system.”

Hope this helps.   I guess you could say redundancy is good in the realm of ESD.  It’s the weak link in the chain that will cause an ESD event.  If someone lifts their ESD footwear from the ESD flooring system while seated, they can tribocharge to above 100 volts.  It takes only 0.3 seconds of charge time to exceed 20.20 requirements.  If personnel is seated and getting up to go to break, it seems best to stand up, remove the wrist strap from the wrist, carefully set it down and walk away from the ESD workstation.  Worst case is to take the wrist strap off while still seated, set it down, put your hand on the ESD workstation and near ESDS devices, then stand up out of the task chair before leaving the work station.  Under proper conditions and with good bench mats, clean ESD floors, ESD task chairs, etc. in place, no ESD event.  The problem with ESD events is that we cannot see, hear, feel them.

The only alternative to not wearing a wrist strap while seated may be the used of a smock with a grounding coil cord attached to it.  You can see the footnotes on the 20.20 document at the bottom of page 4 for further details.

 We adhere to and meet or exceed requirements put forth in ANSI/ESD S20.20-2007 or IEC 61340-5-1, which assumes a target HBM of 100 volts and less.