Gates publishes a detailed Preventive Maintenance manual, with strong content regarding safety practices. Most of these are common sense - lock out the drive before touching the mechanical system, for example.
When working with any electrical power source, take extra care to make sure to avoid any hazardous situations. Many years ago, during a power survey, I had a near miss when hooking up a data logger in the power supply box. While I had many, many, experiences setting up the test equipment, this particular time I was shocked (literally) when clamping on an amperage probe. I was very lucky - just a few hours of a numb arm and no lasting effects.
What is the point? Never assume that the system is safe. Ask, ask again, and double check to make sure every appropriate safety precaution has been properly taken before working on a belt drive system. Accidents happen because people get in a hurry, or overlook the obvious, or make an improper assumption. Remember - you're talking about your health - act accordingly and be mindful of the proper safety measures when doing any installation or maintenance work.