ESD is caused by static electricity. In order for an ESD event to occur there must be a buildup of static charge. Very high charge levels are actually quite rare. In a normal factory environment, taking basic ESD precautions (grounding-straps, anti-static smocks, ionizers, humidity control, etc.) static levels can be kept below a few tens of volts. In an uncontrolled environment, like an office, static levels rarely get above 2000 volts. Under some worstcase conditions (wearing synthetic fabrics, rubbing against synthetic upholstered furniture, extremely low humidity)
levels can go as high as 12 to 15 thousand volts. Actually to get to 15000 volts or higher you would need to be in an uncomfortably dry environment (humidity below 10%) otherwise static charge will naturally dissipate through corona discharge. It would definitely be considered a “bad hair day.” Humans can generally feel a static shock only above 3000 volts. A discharge greater than 4000 volts can cause an audible “pop.” But repeated lower level discharges can be imperceptible and still may have a cumulative damaging effect on sensitive ICs. All ICs, even those with robust protection, can be damaged if they are hit hard enough or often enough.