A walking body-voltage result describes the tested footwear-flooring combination under the conditions tested. It does not establish the highest voltage a person could develop during other workplace activities. Standing up from a chair or removing a garment can generate charge through interactions that the prescribed walking test does not reproduce.
Does the defined walk capture the highest voltages?
What the defined walking pattern was created to do
Atieh Talebzadeh, Mahdi Moradian, Yunan Han, Abhishek Patnaik, David E. Swenson and David Pommerenke authored “Dependence of ESD Charge Voltage on Humidity in Data Centers (Part 1 – Test Methods),” published in ASHRAE Transactions, Volume 121, Part 1 (2015). The well-defined walking pattern was created to allow repeatable results when comparing floor and shoe combinations, and the study identifies it as the pattern described in the ANSI/ESD STM97.2 standard.
Where the defined pattern ranked among the study’s activities
| Activity in the study | Observed body voltage |
|---|---|
| Well-defined walking pattern | Lowest peak voltages of the activities studied |
| Random walking | Maximal voltages about 50% larger than in the defined pattern, and about 30% larger on average |
| Standing up from an office chair, or removing and dropping a sweater | Highest voltages in the study |
The study attributes the defined pattern’s low peaks to its design: a well-reproducible method for comparing conditions rather than a worst-case activity.
Why chair and sweater charging is different
During the sweater and chair experiments, high voltages can occur even with ESD floor combinations, because the charge separation does not occur at the shoe-floor interface. A walking-pattern result therefore does not describe the voltage a person develops when standing up from a chair or removing a garment.
How footwear and floor pairing changes walking voltage
ESD shoes on a conductive rubber floor
In the study’s walking experiments, ESD shoes on a conductive rubber floor reduced the maximal voltage by a factor of 10 or more compared with non-ESD-reducing floor and shoes. The reduction is reported for the study’s tested ESD material set averaged over environmental conditions.
ESD-mitigating versus non-ESD-mitigating materials in random walking
In the study’s random walking experiment, voltages were low for ESD-mitigating materials, while non-ESD-mitigating materials led to voltages in the kV range.
Does lower humidity always raise body voltage?
Conditions the study found favorable for high voltage
In the study, low relative humidity together with a low, but not very low, dew point generally produced conditions favorable for high body-voltage generation. The study states this as a general tendency across its experiments, not as a numeric humidity threshold.
A lower dew point does not necessarily mean a higher voltage
The study’s results indicated that a lower dew point will not necessarily lead to a higher charge voltage.
How the tested conditions limit what a result means
The foreword to ANSI/ESD STM97.2-2016 states that the test method provides data that is relevant in the user’s specific environment, application, and controlled laboratory conditions. A walking-voltage result therefore describes the tested footwear and floor system under the tested conditions. It is not a ceiling on the voltage a person can develop in other activities or under other conditions.
Frequently Asked Questions
In the cited study Dependence of ESD Charge Voltage on Humidity in Data Centers (Part 1 – Test Methods), the defined pattern produced the lowest peak voltages of the activities studied. The study identifies the pattern with STM97.2 and describes it as a repeatable comparison method; its results do not establish a worst-case voltage ceiling.
The cited study Dependence of ESD Charge Voltage on Humidity in Data Centers (Part 1 – Test Methods) found that chair and sweater activity could produce high voltages even with ESD floor combinations because charge separation occurred away from the shoe-floor interface. That finding concerns the study’s tested materials and conditions.
The reduction of tenfold or more was reported for the tested ESD-shoe and conductive-rubber set in the cited study Dependence of ESD Charge Voltage on Humidity in Data Centers (Part 1 – Test Methods), averaged over environmental conditions and compared with non-ESD-reducing floor and shoes. It is a study-specific finding, not a performance guarantee for other footwear or floors.
The cited study Dependence of ESD Charge Voltage on Humidity in Data Centers (Part 1 – Test Methods) concluded that a lower dew point did not necessarily lead to a higher charge voltage. Low relative humidity together with a low, but not very low, dew point generally favored high voltage in its experiments; this is a study-specific tendency, not a numeric humidity threshold.