I purchased a USB to serial converter today. From the safety recommendations section of the manual:
When installing your USB to Serial Converter, do the following to avoid possible electric shock and damage to your system:
1. Turn off all power to your computer.
2. Unplug all cables connected to your computer, including the power cord.
3. Ground yourself by touching a metallic object before handling the USB to Serial Adapter and before installing the USB to Serial Adapter.
It doesn't end there, two pages later from the Hardware Installation section:
Follow the instructions below to install your USB to Serial Converter.
1. Power on your computer ...