The hazard
Machines do not know the difference between the material and your hand. Moving parts can crush, cut, pull in or throw things faster than anyone can react. Guards are there because nobody can stay perfectly careful every minute of every shift. A missing or bypassed guard can turn a normal day into a serious injury.
The action
Before you start a machine, look at the guards. They should be in place, secure, and not cracked, bent or loose. Guards must be attached to the machine where possible, and a guard must not create a hazard of its own, such as a sharp edge or a new pinch point. Know where the stop button is, and report any problem before the machine runs. (29 CFR 1910.212(a)(2))
ASK THE CREW
What is our procedure when a machine jams, and who is authorized to lock it out?
From the talk: Machine guarding. Read it in full, free, with the questions and the sign-in sheet.