MSHA - Code of Federal Regulations - 30 CFR 56.14111
30 CFR § 56.14111
Slusher, backlash guards and securing.
(a) When persons are exposed to slushing operations, the slushers
shall be equipped with rollers and drum covers and anchored securely before
slushing operations are started.
(b) Slushers rated over 10 horsepower shall be equipped with backlash
guards, unless the equipment operator is otherwise protected.
(c) This standard does not apply to air tuggers of 10 horsepower or
less that have only one cable and one drum.