Procedures For The Design, Analysis And Auditing Of Static Control Flooring/Footwear Systems
Conclusions and Recommendations
ESD Coordinators must be proactive.
It is too late to specify the floor after it is installed. This means working with Corporate Real Estate in addition to local facilities personnel. Being proactive is necessary to avoid ESD considerations being just an afterthought. It is much easier to get the job done right when involved from the very beginning. Remember: you will have to live with the floor and its ESD Audit performance for several years.
- Understand the floor preparation processes, the installation processes, and cleaning/maintenance processes. These are critical to having a successful project. Make sure the floor has a moisture emission test performed prior to the selection of the ESD floor. Follow the manufacturer's instructions carefully for floor preparation, installation and electrically grounding.
- Use only qualified installers. One of the most important aspects of the installation is the adhesive in regards to spreading, curing and coverage.
- Maintain records of measured resistance. No traffic should be allowed on vinyl or epoxy floors before curing is complete.
- After 48 hours evaluate the installed floor. Make a sketch of the area ahead of time showing the measurement points.
Today too many people still consider floors and footwear independently. Floors and Footwear must be chosen as a system. A good floor will not cover up bad footwear, nor will good footwear cover up a bad floor. Present 5 lb. weight electrodes are not adequate for judging floor performance. Floor resistance should be measured using the heel electrode methodology at 100 Volts. This method is more representative and reproducible. This due to the weight of the electrodes being more representative of those experienced in normal applications and due to the ease of use especially for large floor areas.
Present definitions and therefore test methodology for determining performance of footwear is inadequate. As a result shoe construction is often far from optimum. The shoe has been considered a monolithic device when in fact it must perform two nearly independent functions. First it should provide an electrical connection between the person and the floor without compromising electrical safety for the person. Second its shoe/floor interface must provide for a rapid recombination of generated charge.
The following shoe construction is recommended for optimum performance:
Outer sole surface resistance should ideally be less than 107 W. The more conductive the outer sole the better as more recombination of charge occurs (and thus lower personnel voltages). The only limiting factor should be the floor marking concerns of highly carbon loaded sole materials or other physical considerations.
The midsole construction of the shoe should be insulative enough to obviate any electrical safety concerns.
Users find it confusing that the resistance limits for defining conductive floors are very different from those for defining conductive packaging. Terms like "dissipative" and "conductive" are not necessary nor helpful. A continuous scale of resistance should used.
Present methodology for determining flooring resistance is inadequate.
- Floor resistance to ground should be less than 108 W as measured with the heel electrodes at 100 Volts for optimum performance.
- The construction of the floor and the grounding system should be insulative enough to obviate any electrical safety concerns
All audits must include an evaluation of static potential on the person appearing from all causes as well as an audit of contributing factors, such as shoe and floor resistances.
Appendix
Tips for ESD Flooring Installations
Because the electrical properties of floors depend so greatly on installation, the following comments are made:
It is likely that most ESD coordinators or consultants only get one or two opportunities to influence the choice of ESD Flooring and its installation process during their tenure. This is such an expensive, critical job that some key considerations must be addressed.
References
- Klein, William G., "Floor Generated Static-A Resistance Limited Phenomenon," Compliance Engineering, Fall 1991.
- Fowler, Stephen L. and William G. Klein, "Static Phenomena and Test Methods for Static Controlled Floors," EOS/ESD Symposium Proceedings, 1992.
- Klein, William G., "Performance Oriented Design and Test Procedures for Static Control Footwear," EOS/ESD Symposium Proceedings, 1993.
- Freeman, P.S. and R.Y. Moss, " Sources of Error in Resistance Measurements on Conductive Flooring," EOS/ESD Symposium Proceedings, 1991.
- Hewlett Packard Document A-5951-1589-1, "Workmanship Specifications for ESD Control," Revision F, Appendices M and O.
- ESD Association Standard 7.1, "Floor Resistance-Resistive Characterization of Materials".
- Janszen, Arthur, Unpublished Work, Brunswick Corporation, 1967.
- ESD Association Standard 9.1, "Footwear-Resistive Characterization".
- ANSI Z-41, Safety Footwear.
- NFPA 99, Health Care Facilities.
- ASTM F-150, Electrical Resistance of Conductive Resilient Flooring.
- AATCC 134, Static Propensity of Carpets.
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