The greatest safety line ever contantly drilled into me, and which is in the front page of virtually every machinery service manual, is.... "Never attempt to adjust, repair, or lubricate any machine or engine, that is in motion".
With all due respect, in this industry the greatest safety line is:-- be ever vigilante and aware of your surroundings.
We have no option than to adjust engines, track and balance propellers and rotors all whilst the thing is running and making large amounts of noise.
It is so fkcuing easy to have a lapse and the consequences are fatal.
RIP