30 CFR §77.400

1. (a)Gears; sprockets; chains; drive, head, tail, and takeup pulleys; flywheels; couplings; shafts; sawblades; fan inlets; and similar exposed moving machine parts which may be contacted by persons, and which may cause injury to persons shall be guarded.
2. (b)Overhead belts shall be guarded if the whipping action from a broken line would be hazardous to persons below.
3. (c)Guards at conveyor-drive, conveyor-head, and conveyor-tail pulleys shall extend a distance sufficient to prevent a person from reaching behind the guard and becoming caught between the belt and the pulley.
4. (d)Except when testing the machinery, guards shall be securely in place while machinery is being operated.