MSHA - Code of Federal Regulations - 30 CFR 77.407
30 CFR § 77.407
(a) Belts, chains, and ropes shall not be guided onto power-driven
moving pulleys, sprockets, or drums with the hands except on slow moving
equipment especially designed for hand feeding.
(b) Pulleys of conveyors shall not be cleaned manually while the
conveyor is in motion.