Most people do not start feeling the effect of an ESD event until the discharge is at least 2000 volts. It typically takes a ESD discharge of greater than 2,000 or 3,000 volts for a person to feel the “zap”. The number varies because the sensitivity of people is different and measuring the voltage is imprecise, so neither 2,000 nor 3,000 is an exact number. However, because an operator does not feel a charge, does not mean that they are not putting an component at risk. Common components used in modern electronic devices are susceptible to 100 volts or less.
The ESDA Handbook ESD TR20.20 provides guidance that can be used for developing, implementing, and monitoring an electrostatic discharge control program in accordance with ANSI/ESD S20.20. It also mentions ESD that a person can fill a few different places.
Wrist Strap section 5.3.2.1
“Static electricity is a natural phenomenon that occurs in all climates and at all levels of relative humidity year round. Most people cannot feel an electrostatic discharge unless the static voltage is greater than 2000 volts.”
Nature of Static Electricity Section 2.3
“The quantity, charge, is difficult for most people to visualize without some reference. As an example, an average person has a capacitance of about 100 picofarads (pF) and can feel a static discharge at their fingertips when the potential difference between their body and a grounded conductive object is about 3,000 volts (3 kV).”
ionizer Discharge Time and Product Sensitivity Section 5.3.6.5.3.3
“Most personnel will not notice static discharges from the human body until they exceed 3,000 volts.”