ESD Standards

As a result of global co-operation, a suite of standards covering all aspects of electrostatic measurement and control is under continuous development.

The umbrella reference for these standards is IEC-61340. Many of the documents have now been adopted as European (EN) and British (BS) standards.

The key standards relevant to the electronics industry are:

• BS EN 61340-5-1:2007 Electrostatics: Protection of electronic devices from electrostatic phenomena – General Requirements.
• IEC/TR 61340-5-2:Ed.1 2007/8 Electrostatics – Protection of electronic devices from electrostatic phenomena – User Guide.

These standards can be purchased from the BSI website.

Performance Requirements (BS EN 61340-5-1:2007) static dissipative floor coverings

Implementation of BS EN 61340-5-1 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 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

Safety of personnel is the first consideration when selecting items for an EPA.

BS EN 61340-5-1:2007 contains 2 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 recommends that flooring within an EPA is chosen to maintain safe working conditions at all times. This means any type of ESD footwear and seating can be utilised; without suitable flooring, the range is substantially reduced. (SSE supplies a range of ESD footwear and seating.) 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.