OSHA is federal law requiring employers to provide safety and Workers' Comp. provides limited no-fault insurance.
BUT
Typically the employer purchases a machine from an OEM (Original Equipment Manufacturer)and, sometimes, purchases installation from a contractor. The employer, explicitly or implicitly, specifies that the machine will conform to all applicable laws including OSHA specifications. Typically the employer is not qualified to determine for himself whether the machine conforms and the OEM and contractor know that. Therefore the OEM and contractor assume responsibility of conformance and have product liability if the machine or installation do not conform and is responsible for an accident.
(There are, of course, situations in which buyer and seller assume other commitments.)