Effect of Human Activities and Environmental Conditions on Electrostatic Charging

The generation of electrostatic charge is considered for the cases of standing up from a chair and removing a garment at dew points with temperature and relative humidity (RH) of -13.1 °C (5 °C, RH 25%), -10 °C (27 °C, RH 8%), -8.9 °C (18 °C, RH 15%), -1.7 °C (38 °C, RH 8%), 5 °C (27 °C, RH 25%), 5.6 °C (18 °C, RH 45%), and 13.9 °C (27 °C, RH 45%). Using ESD mitigation shoes/floors rather than non-ESD can reduce the voltages by a factor of ~2 to 5 for garment removal and ~2 to 7 for standing up from a chair. For the garment removal, the charge voltage will drop to 100 V within ~0.5 to 6 s and within ~1 to 30 min when ESD and non-ESD mitigation shoes/floors are used, respectively. For the standing-up form a chair, the corresponding times are ~0.5 to 3 s and ~1 to 4 min, respectively. For the extreme case at 22 °C, RH 5%, the voltage can surpass +/- 20 kV. Finally, it is shown that the voltages a person will charge up to may vary by +/- 30% just because of different capacitances to ground. Residential home settings will lead to the highest voltages (60 pF test person to ground, U.S. wood frame house), while standing on a concrete floor only half of the voltage may be reached (120 pF)

Electrostatic Charging Caused by Standing up from a Chair and by Garment Removal

The generation of electrostatic charge is considered for the cases of standing up from a chair and for taking off a sweater. The charge voltages have been recorded at 27°C with relative humidity (RH) of 8%, 25% and 45% and at 38°C with 8% RH. Different footwear and flooring systems have been used to cover both ESD and non-ESD mitigating footwear and flooring combinations. The voltages caused by the activity (event voltage) and the decay times are discussed

Dependence of ESD Charge Voltage on Humidity in Data Centers: Part I - Test Methods

The effect of absolute and relative humidity on the charge generated in the human body during different human activities was investigated. Environmental conditions were varied between a relative humidity of 8% to 45% in a temperature range of 5°C to 38°C (41°F to 100.4°F); additionally, a wide range of footwear and flooring types were considered. The human activities studied included well-defined walking, random walking and scraping feet, taking off a sweater and dropping it, and standing up from a chair. The first part of this three-part paper mainly describes the test and data analysis methodology. One conclusion based on the voltages generated across different footwear and flooring combinations is that charge generation depends on the particular activity and associated materials. However, low relative humidity and a low, but not very low, dew point in general produce conditions favorable for high-voltage generation. Of all of the experiments performed, standing up from a chair yielded the highest body voltage. Two other parts of the three-part paper present a detailed analysis

Dependence of ESD Charge Voltage on Humidity in Data Centers: Part III - Estimation of ESD-Related Risk in Data Centers using Voltage Level Extrapolation and Chebyshev\u27s Inequality

This paper is the third in a series that investigates the electrostatic discharge (ESD)-related voltages and risks in data centers. This paper analyzes the risk of damage or upset under the following environmental conditions: 45% relative humidity (RH), 25% RH, and 8% RH at 27°C, and 8% RH at 38°C. The main purpose of this study is to evaluate the increase of ESD-related upsets or failures caused by reducing the RH from 25% to 8%. The pattern walking test, random walking test, and extrapolation method described by Moradian et al. (2014) are used in this paper. As the distribution function of the tribo-charging-induced voltage is not directly known, Chebyshev\u27s inequality is used to predict the upper bound for the probability of ESD-related failures

Determination of the Effect of Humidity on the Probability of ESD Failure or Upset in Data Centers

The relative rate of electrostatic discharge (ESD)-related failures or upsets is derived for various types of data centers based on different flooring systems and personal footwear. As the estimation of the actual number of ESD-related failures or upsets is impossible, hypothetical scenarios of data centers are considered with the assumption that the operator actions and IT equipment are constant in all these data centers. Then, using industry accepted ESD robustness thresholds, the probabilities of exceeding these thresholds are calculated and compared, which allows us to estimate the relative rate of ESD-related failures or upsets as a function of environmental conditions, flooring types, and footwear. The estimation is based on a welldefined walking pattern which has good repeatability. Due to limitations on performing the well-defined walking pattern for long periods of time and due to the small probability of observing very high voltages, an extrapolation approach is used to determine the probabilities of exceeding ESD robustness levels. Two approaches have been used to obtain the extrapolation functions used to predict higher voltage levels. (1) The extrapolation was performed based on the distribution functions measured in our test, and (2) the extrapolation was performed based on literature data. The literature data predicts higher risk levels, however, in many cases both extrapolations lead to the same conclusions with respect to risk level. Based on the calculated probabilities and different categories of data centers, recommendations regarding the flooring system and footwear control are provided