Forklift operators maneuver four ton (or more) machines through aisles, over dock boards, into trailers, between racks, near pedestrians, on ramps and sometimes in hazardous environments. They cover a lot of territory even if the forklift never leaves the confines of a warehouse.
Not only does OSHA have regulations for the forklifts themselves, they also have specific requirements for forklift operators. The Powered Industrial Truck Standard outlines the topics that must be included during training, as well as requirements for refresher trainings.