ESD Shoe Blog

Can ESD shoes create risk of electricution in certain circumstances?

by admin on Jun.20, 2011, under ESD Shoes

Q: Can a facility technician wearing an ESD safety shoe pose a risk of electrocution?

The manufacturing area is grounded with a dissipative mat with a resistance of 10^7 ~ 10^8.

~R. Dran

A: You would be more prone to electrocution with ESD footwear on than not.  This is because ESD Static Dissipative and ESD Conductive footwear are designed to protect static sensitive devices and prevent the initiation of ordinance/munitions/explosive powders, gases, liquids etc. respectively… but with a lower threshold resistor to prevent defibrillation.

When wearing such footwear, you do not want to expose yourself to open line voltages… just as the case when wearing insulated footwear.  Be particularly careful of line voltages of 110 and above.

DoD 4145 26 M deals with explosive environments and the control of ESD in such environments, as well as NFPA 77.  For protection of ESD sensitive devices, consult ANSI/ESD S20.20-2007.  The former has requirements for a lower threshold of ESD work surfaces to be above 40,000 ohms for 110 systems and 75,000 ohms for 220 systems, but no such lower threshold for footwear, that I’m aware of.  They do have a combined resistance requirement of less than 1E6 ohms or a meg ohm for body, footwear, and flooring to ground in the case of ESD Conductive footwear.

For ESD Static Dissipative footwear, the  upper limit is 3.5E7 ohms or 35 megahoms, and the lower limit is at some fraction of a meg ohm… I guess that would be set by your ESD footwear/wrist strap tester.

Thanks for your question.

Best Regards,

Patrick McGowan, EET
Director of Engineering/ESD Auditor
Ground Zero ElectroStatics, Inc.
www.gndzero.com

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Should ESD shoes or heel grounders be worn outside?

by admin on Mar.11, 2011, under ESD Shoes

Q: Is it ok to wear ESD shoes or heel, toe, or sole grounders outside?

~ Anonymous

A: No.  MIL-HDBK-263B Appendix 1 page 101 40.1.2 states, “Conductive shoes, shoe covers, or heel grounders should be used to discharge personnel on conductive floors. These items should only be worn in the ESD protected areas and should be kept clean so that contaminants do not inhibit their conductive interface with the floor.

To be certain that you are not compromising the effectiveness of your ESD personal equipment you should not wear them outside the EPA (ESD Protected Environment). Simply don them before going into the EPA and take them off when you leave. This also serves to protect your investment and to maintain its longevity.

It is also very important to keep them clean (vacuum inside of shoes weekly and maybe clean out-soles and grounders with soapy water once a week) and you’ll get more wear out of them in addition to maintaining their effectiveness.

Best Regards,

Patrick McGowan, EET
Director of Engineering/ESD Auditor
Ground Zero ElectroStatics, Inc.
www.gndzero.com

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Proper Heel/Sole Grounder Placement

by admin on Feb.23, 2011, under ESD Shoes

Q: Where do the heel strap cords need to be placed?

  • INSIDE THE SOCK – Between the sock and skin
  • OUTSIE THE SOCK - Between sock and shoe?

Is this specified in any ESD documentation? If so, which standard?

A: I like this question because I used to always put the strap between my foot (skin) and the sock, aka stuff it into my sock and under my heel.  I later came to find that this wasn’t necessary.

I don’t believe it’s mentioned in any ESDA standards, perhaps in ESD SP9.2-2003 Footwear-Foot Grounders Resistive.  Foot Grounders are checked on a combo tester hopefully before you enter the EPA and if you pass and get a green light, you’re good to go. 

However, I’m seeing  some instructions say the strap is to go “inside the shoe or sock”, so…

MIL-HDBK-263B Section 40.1.1 Personnel ground strap  on page 100 says, “Personnel handling ESDS items should wear a skin-contact wrist, leg or ankle ground strap.”  So this would imply skin contact, but I found it’s not necessary.  If personnel wears cotton socks, the sweat and salt in our body makes ESD shoes work, so thusly, the strap can go outside the sock and on the shoe’s conductive insole.  Be sure to lay the strap across the heel though and not just across the arch if you do it this way.

So just put the strap between your sock and shoe insole and use your combo tester or test yourself from palm to earth ground and see that you’re reading less than 3.5E7 Ω per ANSI/ESD STM97.1-2006 Floor Materials and Footwear.  If you feel more comfortable putting it between the sock and skin, that’s fine too. 

I find it to be more comfortable, convenient, and hygenetically sound to place it between the sock and insole as well.  If there’s any mention of this to this detail elsewhere, it’s unbeknownst to me.

 - Patrick

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ESD and Body Resistance

by admin on Jan.18, 2011, under ESD Shoes

Q: We are making some highly explosive materials for Military use and need to test the operators body resistance before walking into our work areas to ensure there P.P.E. (Personal Protective Equipment) is right.

Assumed Operation of a device:

  • Operator stands on a metal pad that is on the floor.
  • Push a metal button that is on the wall with there finger.
  • The unit gives a Green light to indicate pass (0 to 1M ohm).
  • Or if a fail a Red light, above 1M ohm.
  • It would also be good to have the resistance valve display as well, either via a digital meter or an analog meter.

The resistance values have to be 0 to 1M ohm.

Do you have any products that will do this or can you modify one of your existing products to do this?

Thank you,

Dave L.

.

A. Before answering your question I must point out that I disagree with your lower limit.  To be less than 1e6 ohms is right, but to be less than about 5e5 or 500,000 ohms is incorrect.

It’s not safe for the personnel due to electrocution risk and heart defib, not to mention that it is outside of the realm of providing a soft-ground to charge dissipation.  We want to neutralize charges to a safe level, but not too quickly.  The energy being dissipated to earth that quickly would defeat the purpose of eliminating the spark that you are trying to avoid.

According to DoD 4145.26-M C6.4.7.5.1 on page 92, (Test criteria for Testing Conductive Footwear, Floors, and Tabletops), the maximum resistance of a body, plus the resistance of the conductive shoes, plus the resistance of the floor to the ground system shall not exceed 1,000,000 ohms total.  That is, if 500,000 ohms is the maximum resistance allowed from the floor to the ground system, then 500,000 ohms is the maximum combined resistance allowed for the person’s body plus the resistance of the conductive shoes.  The contractor can set the maximum resistance limits for the floor to the ground system and for the combined resistance of the person’s body plus the shoes, as long as the total resistance does not exceed 1,000,000 ohms.

In other words, if you use ESD Conductive shoes (see the HK-4327-TN) on an ESD conductive floor, you will meet this requirement.  You might even meet this with SD shoes, but I would not risk it.  I would use the conductive shoes and you should pass the tester without getting a fail for high or a fail for being too low.

Best Regards,

Patrick McGowan

patrick@gndzero.com

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ESD Footwear on SD vs SC Floors

by admin on Nov.02, 2010, under ESD Shoes

Q: Can we convert a insulated floor surface by just putting ESD wax over it and installing some ground points that have contact with the wax?

Do you think that this is possible?

- Javier G.

A: That is a good question.

I know It’s possible.  A company that I used to work for in Denver as an electronics manufacturer for medical equipment did this back in the 70′s, 80′s, 90′s and has the same VCT Static Dissipative flooring with an ESD Sealer today.  I don’t think it’s the best solution long term, but it does pass ANSI/ESD S7.1-2005 per ANSI/ESD S20.20-2007.  It passed the standards because the PTP (Point to Point) and RTG (Resistance to Ground) readings were below 1E09 Ohms (1 Gig ohms or 1000 Meg ohms).  I worked at this company as an installer, tech support repair technician, final test tech, bio-med trainer, Tech Services customer service rep, and ultimately, R&D Engineer.  To this day, the electronics manufacturing dept. still has maintenance coat the floor on a monthly basis, even though they’ve gone to SMT.  I’d like to see them install our ESD Conductive DuroStat Vinyl Tile.  They’d probably spend less money and get maximum performance in the long run.

We like to see it at 1E08 and below.  We have chemical products that will get you there.  They may need to be applied as often as monthly or every few months depending on your traffic and usage within your ESDA (ElectroStatic Discharge Area).  Your static conductive (2.5E04 to 1.0E6 ohms RTG and/or PTP) or static dissipative (1.0E6 to 1.0E9) flooring system will have to be accompanied with ESD footwear.

We have a product tailor made for such a flooring system that will get your ESDA to pass the standards and perform as it should for static dissipation.  It is called ZeroStat Coat and can be used on non-porous flooring applications.  Shock Stop can be used on carpet systems and upholstery.  The Coat and similar products can be used on flooring that already meets ESD compliance and is done so for ease of cleaning and maintenance.  For ESD footwear, I’ll show you my personal favorite, a sporty ESD Static Dissipative shoe.

Now, when It comes to grounding of such a flooring system it would be non-practical to dig up a non-esd floor just to install the copper grid and terminate it to earth or electrical ground (which wouldn’t work because you can’t ground an insulator-which would be the case for the backside of your flooring system and the non-conductive adhesive), yet these floors work.  The large capacitance and relation to ground work with the common laws of physics to provide the charges with a path to ground, so long as the surface is properly coated and maintained.  Thus, you CAN ground a conductor.

We install a product with all of our ESD flooring installations that should be used with these chemical applications as well.  Our ESD ground plates are easy to install and are somewhat unique to our company.  I have the experience and equipment to see these plates improve the PTP and RTG readings and PTP stability on any ESD flooring system.  Although our presence in the industry is vast, this product is not commonplace as of yet.  The stainless steel plate is connected to earth or electrical (equipment) ground via a lead wire and a #10 eyelet which can fit onto the center screw of an AC receptacle faceplate and attaches to the ESD flooring system with double-sided conductive tape.

If you have any trouble navigating any of the hyperlinks that I’ve provided, please go to www.gndzero.com and go to grounding and then Floor Maintenance Products, Personnel, and Mechanisms for the previous links.

Feel free to contact our sales dept. via alan@gndzero.com for pricing and availability and feel free to contact me at patrick@gndzero.com for any further questions.

Best Regards,

Patrick McGowan, EET
Director of Engineering/ESD Auditor
Ground Zero ElectroStatics, Inc.
www.gndzero.com

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ESD Hazardous Material Boots / Shoes

by admin on Oct.19, 2010, under ESD Shoes

Q: My company requires the use of ESD or SD boots/shoes. This requirement is due to the flammable nature of propane vapor and the danger of mixing static electricity. Are anti static boots or boots with an anti static sole in this category? It is nearly impossible to find a quality outdoor type of boot with esd.

Thanks

Rocky B.

Company Amerigas Propane

A: Patrick McGowan [mailto:patrick.gndzero@gmail.com]
Subject: ESD shoes

Hello Rocky.  You are dealing with flammable gases, liquids, powders, explosives, ordinance, munitions, etc.  Your situation goes above and beyond ESD control for the purpose of protecting sensitive electronic devices and such.  You’re dealing with a serious safety issue and I hope you stay safe.  My cousin witnessed a serious accident when a propane company rep was seriously burned while filling a propane tank in her back yard.  He was evidently attacked by bees and he had caught fire and is recovering now.

As far as ESD control in your situation goes, I just cannot claim to be an expert here.  The ESDA and ANSI/ESD S20.20 will not touch this stuff with a 10-foot pole.  You have to go to documents such as NFPA 77 and DoD 4145.26-M for help with this.

In chapter C6 of the latter document, they will discuss “Electrical Safety Requirements for AE Facilities”.  So, we’re talking about a controlled environment.  Where is your place of work?  Are you dealing with the transport and filling of propane tanks/bottles?  Are you dealing with trenching, setting of tanks with a boom?  You are probably exposed to the outdoors and who knows what the ground exposure is under your feet.  So, even if you have ESD boots on, what is your RTG when you’re standing on dry grass or some weeds?  Is the ESD apparel including footwear sufficient?  Should some kind of bonding to a Common Point Ground for you, the nozzle, and the tank be done?  These are questions your company needs to address.

Now, when it comes to ESD boots, I have a nice pair of ESD Conductive (not SD, or Static Dissipative) boots myself, which would be sufficient per NFPA 77 and DoD 4145.26-M per C6.4.7.5.1, page 92, which states, “The maximum resistance of a body, plus the resistance of the conductive shoes, plus the resistance of the floor to the ground system shall not exceed 1,000,000 ohms total.  That is, if 500,000 ohms is the maximum resistance allowed from the floor to ground system, then 500,000 ohms is the maximum combined resistance allowed for the person’s body plus the resistance of the flooring system.”  Keep in mind that you want to remain “soft grounded”, or above about 40,000 ohms or 4.0E4 ohms to prevent being too close to ground for situations of getting crossed up with line voltage. (I once touched a propane tank and got shocked!  That’s right.  It felt like 120/240 AC too.  My dad worked for a propane company setting tanks with a boom truck.  He had to trench and install the line to the home.  We found that somebody put the house ground wire to the propane tank.  We let the Electric Company come take care of the situation before we would do anything with that tank.  Could you imagine what would have happened to me if I’d been bonded direct to earth?  Heard defib is the main issue here.  Had I had my SC ESD boots on, it would have probably been about the same as without due to the current limiting.  IDK.)

See, we can get your body and footwear to less than 5.0E5 ohms or 500,000 ohms.  But what about the ground you’re standing on?  The combination of you, through your cotton only socks and ESD Conductive shoes and across the ground you’re standing on.. to earth or a good groundable source, such as perhaps the vehicle you’re working on or the propane tank your working on, needs to be less than 1 meg ohm or 1.0E6 ohms, according to these standards.  (Your industry may fall in line to this here.  You need to find this out for sure.  We will not assume if this is right for your industry.  Propane may be totally different.)

I have the HK-4327-TN.  You can also see my verification of them as an ESD Conductive shoe vs a Static Dissipative shoe here at our ESD Pros site.

You’re in a situation where I would think bonding is paramount for your situation because an ESD failure in your case could ignite a flammable vapor or liquid (depending on the temperature in the case of 1075, right?) and the result is immediate.  You are in danger of harm, as well as are other sources around you.

I would encourage you to browse our site and look here for ESD bonding, grounding, and clamping options and even consider the mobile static Hazmat kit as an option.  You can create your own ground with mobile grounding options if that’s acceptable to your situation.  I’d ask you to contact Alan Garst, who I will CC here, for further assistance on what we can offer you with regards to ESD peripherals.

I thank you for your questions here and would like any +/- feedback so I can know if we’re being helpful to your unique situations which are not unique to you of course.  ESD control is such a vast field and we want to stay on the cutting edge of service to this industry.


Best Regards,

Patrick McGowan

Technical Services Department
719-676-2548

Fax: 719-676-2549

patrick.gndzero@gmail.com
www.esdpros.com

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ESD shoe covers

by admin on Oct.04, 2010, under ESD Shoes

From: Pat M.

To: Chris H.

Subject: ESD shoe covers

Q: Hello, Chris. I’m an electrostatics engineer. I’d like to find the standards that are used to control clean room contamination. Can I obtain these standards and if so, which ones are pertinent to ESD products such as shoe covers?

For example,

  • What is P010 and IES-RP-CC-003.2 and what are its limits?
  • What are clean room limits for various clean rooms: for example 100,000 and 10,000 clean rooms?
  • Do you know anything about an ISO Class 8 clean room and its qualifications?

Thanks in advance for your time. If you can find these answers, great; otherwise, you may be able to steer me in the right direction.

A: Pat, You ask some good yet open ended questions. The IEST specification you referenced is a standard for testing clean-room materials (gloves, wipes, cots, etc). The new version is 3.3 which I have attached for your reference. I also have included a clean-room consumable guide we have published. It does speak to the different environment classifications and appropriate materials for each.

A class 10,000 environment means: there are less that 10,000 particles per square foot of size .5 micron or larger. For a class 100,000, there are less than 1,000,000 particles per cubic foot of size .5 micron and larger. These really refer to air quality (which is achieved by mass filtration) and not materials. However, different materials have different out gassing or shedding (of particles) characteristics, so they can be selected based on their cleanliness. For a class 100,000 or class 10,000 clean-room the standards are pretty minimal and a standard polypropylene shoe cover is acceptable. It is when you get to class 1,000 or 100 or 10 that it gets much more specific in acceptability.

Best Regards,

Chris H.

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Are ESD shoes and Conductive shoes the same thing?

by admin on Jul.21, 2010, under ESD Shoes

Q: Are ESD shoes and Conductive shoes the same thing?

A: There are two types of ESD shoes, Static Dissipative and Static Conductive.

The Static Conductive shoe will guarantee a combined resistance of personnel and footwear of less than 1.0E6 Ohms.  I have a pair of Static Conductive shoes that when I’m standing on a static conductive flooring system (2.5E4 Ω to 1.0E6 Ω), my combined resistance from my body through the ESD footwear and through the ESD conductive flooring system to electrical ground or earth is less than 1.0E6 ohms per DoD 4145.26-M, C6.4.7.5.1: “The maximum resistance of a body, plus the resistance of conductive shoes, plus the resistance of the floor to the ground system shall not exceed 1,000,000 ohms total”… “The contractor can set the maximum resistance limits for the floor to the ground system and for the combined resistance of a person’s body plus the shoes, as long as the total resistance does not exceed 1,000,000 ohms.”

This Static Conductive shoe is typically used for electrical safety requirements for facilities that deal with explosive environments such as ordinance, munitions, explosive powders, flammable liquids, etc.  This is outside of the realm of ANSI/ESD S20.20-2007 and MIL-HDBK-263B.

If you’re goal is the protection of static sensitive devices, then Static dissipative shoes on a static conductive flooring system or a static dissipative flooring system will suffice so long as the combined resistance of personnel, footwear, and flooring to electrical or earth ground is less than 3.5E7 Ω as per ANSI/ESD STM97.1-2006.  In that case, a good static dissipative shoe will be more than 1.0E6 or a meg ohm, but the resistance will probably be less than 35 Meg ohms.  The best way to measure the footwear is to have personnel wear them for at least 10 minutes prior to going to the tester and checking for pass/fail low/fail high, as that’s the most practical way to test them.  You can measure the resistance of the shoe from insole to outsole, but they aren’t used that way on the ESD flooring system.  The ESD shoe relies on sweat from the personnel that wears them.

My combined resistance from my body, through my Static Conductive HK-4327-TN (men’s) or Static Dissipative SH-4341-WH shoes and through a static conductive floor to electrical/earth ground is about 1.6E6 Ω.

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Welcome to ESDshoeblog.com

by admin on Jul.06, 2010, under ESD Shoes

Welcome to ESDshoeblog.com, a blog dedicated to improving the performance of you ESD and anti-static shoes.

Technorati claim token: 7UKU66PR79WX

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