We see many companies with a conductive tile floors that measures mid-10^5 ohm resistance to ground and the operators are wearing foot grounders on each foot that passes the touch-testing, but what peak voltage on the body is generated?
Over the years, there have been independent studies conducted per ANSI/ESD STM97.2, Floor Materials and Footwear – Voltage Measurement in Combination with a Person showing that with conductive flooring measuring less than 1 x 10^6 ohm resistance and footwear measuring in the low 10^6 ohm resistance range, the following body voltage spikes were recorded:
- Using heel grounders, body voltage spikes to ±250 volts
- Using sole grounders, body voltage spikes were reduced to ±75 volts or less
- Using full coverage grounders, body voltage spikes were reduced to ±25 volts or less.
Basically, the greater the footwear contact surface, the higher the probability that while walking, bending, kneeling, reaching, etc. the operator will be in contact with the ESD floor.
“Procedures For The Design, Analysis And Auditing Of Static Control Flooring/Footwear Systems” by Stephen L. Fowler, William G. Klein, and Larry Fromm includes:
“With heel grounders his potential dropped to 250 in one installation and 450 in the other, these being the peaks when both heels left the floor, as they did with nearly every step. When care was taken not to allow simultaneous contact loss with both grounders the values were 40 and 170 volts respectively. When he used a sole grounder, which is essentially a combination of heel and toe grounders, the peak voltage in both cases dropped below 30 volts.”
Photos on Shoe of Full Coverage Grounders and Sole Grounder
Conductive flooring less than 1 megohm (1 x10^6 ohms) is often preferable for grounding operators wearing foot grounders. However, if the resistance upper limit is only less than 1 x 10^9 ohms, end users must add the ANSI/ESD STM97.2 test method for body voltage to the qualification of their footwear/flooring operator grounding system. It is no longer enough to know that a standing operator is grounded. ESD flooring requires maintenance to keep them clean and effective. All ESD flooring should be cleaned with a good quality ESD floor cleaner that will not leave behind an insulative residue that can raise floor resistance. Many companies also want their floors to have a nice appearance. A good quality dissipative floor finish can improve durability and gloss while also reducing the charge generation characteristic of the floor to less than <50 volts.
Application Photo of Statguard Floor Finish
From published article “Now is the Time for ESD Control Programs to be Improved” by Fred Tenzer and Gene Felder. See full article at InCompliance Magazine- September 2012