First rule of fixing things that can kill you: power it off. Before you do anything, power it off. Then, check again to make sure it’s powered off. Maybe check a third time just to be ABSOLUTELY sure. Put a physical blockage on whatever you need to so it can’t be powered on while you’re working on it - zip tie the breaker open, throw the power cord over a pipe or under the machine, hit the knife-switch on the side of the machine in addition to throwing the breaker, whatever you need to.
Hell, if you need to, get your coworker to stand there and yell at anyone trying to turn the thing back on. That’s how we did it when anyone had to fix the cardboard baler at my old grocery store - power off at wall, power off at baler, and at least one, preferably two people watching to make sure nobody did anything stupid.