Whenever the casing of a computer is opened and its internal workings are exposed (to change a hard drive or add memory chips, for example), there is a danger of damaging the computer with the buildup of static electricity that is held by the human body.

The internal workings of a computer, and especially the hard drive, are extremely susceptible to static electricity, which can cause considerable damage to the hard drive if it is zapped with even a small amount. Microchip damage can occur if it is exposed to static electricity as low as 10 volts, and humans are not able to perceive static electricity until it has reached about 1,500 volts. (Walking across a rug can produce a static electricity voltage of up to 12,000 volts, but static voltage is not life threatening.)

So it is possible to damage a hard drive with static electricity that is not even felt by the person because it is at such a low voltage. Also, computers become increasingly susceptible to static electricity damage as more and more circuitry is built into them.

To avoid zapping your components with static electricity, take precautions to ground the static electricity before touching any of the internal components of the computer. Wearing an ESD wrist strap or working on an anti-static mat will prevent any static electricity from damaging your computer. Another way to ground the static electricity is to touch the internal metal frame of the computer's case while the computer is plugged into an electrical socket. The static electricity will be discharged and grounded as the electrical circuit is grounded via the AC outlet.

And to be on the safe side, always handle the electronic circuitry on the motherboard, video card, modem, sound card, hard drive and other internal components by any insulated, non-circuitry areas if they have them to insure that you do not send a bolt of static electricity coursing through it.