29 CFR 1910.30
This OSHA standard regulates "Other Working Surfaces", which includes dockboards (bridge plates). The standard requires that the dockboards be strong enough to carry the loads imposed upon them. The boards must be capable of being secured or must be designed so they will not slip while being used. Additionally, the dockboards must be designed to allow their safe handling, i.e., hand holds.
The standard also requires a safety device to be used (positive protection) to prevent railroad cars from moving while dockboards are in use. If a railroad car moves while a forklift is either inside or crossing the dockboard, and the dockboard slips, the driver of the forklift could be seriously injured.
The standard references a Commercial Standard CS202-56 (1961) "Industrial Lifts and Hinged Loading Ramps" which is published by U.S. Department of Commerce.