The ESD ground should be <1 Ohm. Normally with a rack shorted to ground there can never be a build up and there is no risk to the operator since the charge would go to the path of least resistance, the ground not to an operator wearing ESD heel straps which has the 1 meg Ohm  resistor.
Secondly if the equipment is grounded and all product  is moved in ESD bags, racks or ESD trays then there will never be a realistic safety issue for the safety officer. 
In your case with the eurathane coating you'd have to consider the  insulating property. Does it wear down from sliding the boxes or product  to where there are thin areas where the product will discharge to the  shelf? The risk is higher is the winter when the moisture that bleeds off the charge in the air is less. You are at a bigger risk of a small charge walking across your carpet at home. 
MFG Engineer, ESD & Safety 

-------------- Original message -------------- 
From: Dave Dixon <[log in to unmask]> 

> Thanks for all of the great input. The powers that be have decided to 
> directly ground the shelves, because "that is what company X does". I 
> guess I am not to be concerned with any issues that might arise with the 
> (urethane?) coating. It sounds like it isn't enough of an insulator to 
> be a problem and is actually dissipative. 
> In truth, I feel this is not an issue either way. My thinking is, the 
> shelves could be made of rubber and lambskin, as everything on the 
> shelves is sealed within an ESD safe bag and then placed in an ESD safe 
> container! I appreciate all of the great advice, 
> Dave 
> 
> 
> -----Original Message----- 
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Gene Felder 
> Sent: Tuesday, November 18, 2008 6:18 PM 
> To: [log in to unmask] 
> Subject: Re: ESD Shelving Question 
> 
> I think you make all good points. 
> 
> The 1st problem Dave should address is "our supposed ESD shelving has a 
> clear thin insulative coating on it." That is never a good thing. 
> 
> Regarding a current limiting resistor in a shelf or worksurface ground 
> cord, it is not recommended for ESD control. Per Table 1 Grounding / 
> Equipotential Bonding Requirements of ANSI/ESD S20.20-2007, the Required 
> Limit for Equipment Grounding Conductor is < 1 ohm impedance. However, 
> if a Safety Officer believes it would be helpful, personnel safety is 
> more important than ESD control. 
> 
> The presence of the 1 megohm resistor can aggravate troubleshooting. If 
> a groundable point snap, say is loose, one might measure 2 or 3 ohms and 
> detect the problem. If the ground cord includes a 1,000,000 ohm current 
> limiting resistor, the problem will not likely be detected. 
> 
> Gene Felder 
> [log in to unmask] 
> 
> -----Original Message----- 
> From: Stadem, Richard D. [mailto:[log in to unmask]] 
> Sent: 2008-11-18 11:59 AM 
> To: [log in to unmask]; [log in to unmask] 
> Subject: RE: [TN] ESD Shelving Question 
> 
> Correct. However for shelving without any dissipative coating, as I 
> stated, it may not be "required", but it is certainly recommended if the 
> shelving does not have dissipative characteristics. Ask Roger Pierce. 
> 
> [Note: Added resistance is acceptable for the purposes of controlling 
> ESD provided electrostatic accumulation does not exceed specific EPA 
> requirements. The typical added resistance in grounding conductors is 1 
> megohm, although other values may be specified."] 
> 
> 
> -----Original Message----- 
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Gene Felder 
> Sent: Tuesday, November 18, 2008 1:27 PM 
> To: [log in to unmask] 
> Subject: Re: [TN] ESD Shelving Question 
> 
> Per ESD Handbook ESD TR20.20-2008 section 5.3.7.1 Workstation Shelving 
> "Shelving systems are frequently included as part of an ESD protective 
> workstation. The shelves in these systems can be used to store ESD 
> sensitive products (both packaged and unpackaged), documentation, 
> manufacturing tools, computer/printing equipment and test equipment such 
> as oscilloscopes. If the shelving system is designed to store unpackaged 
> ESD sensitive products, then it should be treated as an ESD worksurface. 
> This means that the surface must be properly grounded, possess a surface 
> conducive to charge dissipation and be free of unnecessary static 
> generators. However, if the surface is not intended to be used for 
> storing unprotected ESD sensitive products, then the shelf can be 
> constructed from non-ESD protective materials." 
> 
> Is the coating dissipative 1 x10E4 to < 1 x 10E11 ohms or above that and 
> insulative. 
> 
> Shelving per Table 3 of ANSI/ESD S20.20-2007 required limit is < 1 x 
> 10E9 ohms. 
> 
> This should be the surface resistance of the material, not resistance in 
> a current limiting resistor in the ground cord. 
> 
> A lower limit is recommended for worksurfaces and shelving if Charged 
> Device Model (CDM) failures are a concern. Per ESD Handbook ESD 
> TR20.20-2008 section 
> 5.3.1.7 Electrical Considerations "The most important functional 
> consideration for worksurfaces is the resistance from the top of the 
> surface to the groundable point. This establishes the resistance of the 
> primary path to ground for items placed on the surface. When worksurface 
> materials are being selected, consideration should be given to possible 
> CDM damage to ESD sensitive products. 
> If CDM damage is a concern, then setting a lower resistance limit for 
> the worksurface should be considered. Typically, the lower limit for 
> these types of worksurfaces is 1 x 106 ohms." 
> 
> Per Grounding standard ANSI/ESD S6.1 section 5.3.3 ESD Technical Element 
> Conductors "The grounding conductors (wires) from wrist straps, 
> worksurfaces, flooring or floor mats, tools, fixtures, storage units, 
> carts, chairs, garments and other ESD technical elements may or may not 
> contain added resistance. Where added resistance is not present, a 
> direct connection from the ESD technical element to the common point 
> ground or common connection point is acceptable and recommended. 
> Note: Manufacturers may add resistance to the grounding conductors for 
> purposes other than ESD (e.g. current limiting). Added resistance is 
> acceptable for the purposes of controlling ESD provided electrostatic 
> accumulation does not exceed specific EPA requirements. The typical 
> added resistance in grounding conductors is 1 megohm, although other 
> values may be specified." 
> 
> So, for ESD control, for a mat or shelf, a current limiting resistor is 
> not required in the ground cord. 
> 
> Note: the ESD Handbook ESD TR20.20 has just been updated 2008 version, 
> and is available for purchase from www.ESDA.org; see 
> http://www.esda.org/esdhandbook.html 
> $200.00 LIST/$150.00 if ESD Association member Provides guidance that 
> can be used for developing, implementing and monitoring an electrostatic 
> discharge control program in accordance with ANSI/ESD S20.20. 
> It also includes Glossary of Terms (ESD ADV1.0-2004). 
> 139 pages 
> 
> Gene Felder 
> [log in to unmask] 
> 
> 
> -----Original Message----- 
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Dixon 
> Sent: 2008-11-18 10:39 AM 
> To: [log in to unmask] 
> Subject: Re: [TN] ESD Shelving Question 
> 
> Thanks Richard, 
> I was aware that a direct ground isn't acceptable, and assumed 
> that the lead had the resistance built in. Guess I need to go back over 
> and check for myself! I appreciate you taking the time to help explain 
> about the dissipative coating, Dave 
> 
> 
> -----Original Message----- 
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. 
> Sent: Tuesday, November 18, 2008 12:05 PM 
> To: [log in to unmask] 
> Subject: Re: ESD Shelving Question 
> 
> True ESD shelving has a dissipative coating on it. Purely metal shelving 
> can be construed to be ESD shelving, provided that the only product 
> stored on it is in Faraday cages that will dissipate any charge to the 
> shelving. Having unprotected ESD assemblies sitting directly on a metal 
> shelf that is connected directly to ground does not constitute 
> protection. Metal shelves without benefit of dissipative coating should 
> be connected to ground through a 1 meg resistor. This prevents a direct 
> charge from going through the assembly, whether from ground to a 
> positively charged person or object, or vice-versa. 
> 
> -----Original Message----- 
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Dixon 
> Sent: Tuesday, November 18, 2008 11:10 AM 
> To: [log in to unmask] 
> Subject: [TN] ESD Shelving Question 
> 
> Hi Gurus, 
> We just noticed that our supposed ESD shelving has a clear thin 
> insulative coating on it. The grounding clamps bite into this coating, 
> and if you poke a probe through the coating, you can see that the 
> shelves are connected to ground. This runs against all my beliefs about 
> shelving materials. Shouldn't they be conductive on the shelves' 
> surface area as well? 
> Thanks in advance for any input! 
> 
> Dave Dixon 
> Engineering Technician 
> Aero-Mach Labs Inc. 
> 
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