General Guidance

ESD Control Flooring Systems Performance Requirement BS EN 61340-5-1:2007

Implementation of BS EN 61340-5-1:2007 will provide an ESD protection regime with control of personal body voltage to < 100V. The minimum requirement for floors with an EPA is that the Resistance to Ground (Rg) <1 x 10⁹Ω.

If a floor is used, in conjunction with ESD footwear, for the grounding of personnel, the following parameters apply:

• either: Rg of the person/footwear system < 3.5 x 10⁷Ω
• or: Rg of the person/footwear system < 1 x 10⁹Ω and body voltage is maintained at <100V.

SSE recommend that the first criteria is adopted because the test equipment is relatively inexpensive and simple to use, compared with instruments for body voltage measurements.

Safety Considerations for Flooring Installations

Personnel safety is the first consideration when selecting items for an EPA. BS EN 61340-5-1:2007 contains two clauses relating to safety. Clause 4.0 states ‘electrical hazard reduction practices should be exercised..’.

Clause 5.3 states: ‘Some of the elements listed in Tables 1-4 do not have a defined lower resistance limit. However, a minimum resistance value may be required for safety reasons’.

Personnel may be exposed to a situation where they are grounded, simultaneously, through several elements in the EPA. These could include footwear, wrist strap, seating and the floor. In the event of an electric shock at mains voltage, the combination of the parallel paths through all the elements may expose the person to significant risk of harm. Analysis of various scenarios indicated that selecting a floor material that provides Rg > 1 x 10⁶Ω is, by far, the lowest risk strategy. With a floor Rg at this level, even when low resistance footwear and seating are in use, electric shock current will be limited to a safe level.

SSE recommend that flooring within an EPA is chosen to maintain safe working conditions at all times, without having to rely on specially selected footwear and/or seating; the characteristics of these items can be highly variable. By adopting the safety criteria used for wrist straps, equivalent to the 1MΩ resistor in the cord, the floor system will be safe at all times.

ALL FLOORING SYSTEMS OFFERED BY SSE FOR ESD CONTROL IN THE ELECTRONICS INDUSTRY MEET THE SAFETY CRITERIA DETAILED ABOVE.

Why RG<35 MΩ for Person/Footwear/Floor?

The graph below illustrates the relationship between body voltage and Rg. At 35MΩ, body voltage will be maintained at <100V, which is the level consistent with the requirements of BS EN 61340-5-1:2007.

Future Proofing a Flooring Installation

ESD control flooring is a significant investment, with a potential useful life in excess of 10 years. Many electronic devices will become more sensitive to ESD as micro-circuit geometry shrinks further. There are already devices in use with ESD sensitivities of <50V HBM. Choosing a floor with this trend in mind makes sound technical and commercial sense.