Mass. Gen. Laws ch. 149, § 127

The belting, shafting, gearing, drums and all machinery having movable parts in all factories, workshops, mechanical and mercantile establishments, if so placed as to be dangerous to employees while engaged in their ordinary duties, shall be securely guarded so far as practicable. Guards, dogs or other safety devices installed on belting, shafting, gearing, drums and all machinery having movable parts shall not be disconnected or removed, except when such belting, shafting, gearing, drums and all machinery having movable parts has been shut down for repairs. No machinery except steam engines in a factory, workshop, mechanical or mercantile establishment shall be cleaned while running.