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
Clearing a jam, cleaning or adjusting a part is when hands get closest to the danger zone. During production, servicing that requires you to remove or bypass a guard, or put any part of your body into the point of operation, generally falls under the lockout/tagout rule. Stop the machine, lock it out and check that it cannot start before you reach in. If you are not trained to lock out that machine, get someone who is. (29 CFR 1910.147(a)(2)(ii))
ASK THE CREW
Where are the nip points and rotating parts on the equipment you run today?
From the talk: Machine guarding. Read it in full, free, with the questions and the sign-in sheet.