i wouldnt say it is a minimum requirement, it is more of a general requirement though.
Due to the wide variety of capacities of lifts out there they leave it up to the manufacturer to set the impact standards on each class of lift they make and require them to set impact ratings on each OHG based on the capacity of the lift. The mfg's will set a minimum rating based on said capacity based on what OSHA requires them to. They are required by law to label these capacity ratings and apply them to the component in the form of a capacity tag or plate located generally on the OHG usually around the top structure of the OHG.
If you look on the outermost rail on the OHG along the topside either right or left side there should be a dataplate with the capacity and test ratings stamped on it. If this tag is missing someone either removed it or it came off.