1.6 Laboratory Safety and Tools
1.6.3 When should a wrist strap not be used for grounding?

There are some exceptions to wearing a wrist strap in order to provide a safe ground. Never wear a wrist strap when working on a monitor or when working on a computer power supply. As a general rule of thumb, most individuals should never even attempt to open a monitor case. However, if in a situation where a monitor case must be opened, do not ground the body.

Components inside a monitor can hold a charge for a long time, even after the monitor has been unplugged from its external power source. The amount of voltage that a monitor can contain, even when turned off and unplugged, is enough to kill. Wearing a wrist strap helps heighten the risk of contacting the monitor's dangerous electric current. The Cathode Ray Tube (CRT) in the monitor is charged to as much as 20,000 volts or more. This charge can last for weeks after the monitor is turned off.

Worksheet (PDF, 7 KB) 
  Lab Safety Checklist