California Code, Labor Code - LAB § 7604

Adequate and substantial bull rails, stringer rails or curbs shall be installed at the waterside of all flush aprons on such wharves, docks or piers as are in active service for movement of cargo therefrom to vessels. This section shall not apply to any pier designed with depressed spur tracks on at least one side, on which cargo is worked between rail cars and ships but not in the narrow wharf area between depressed tracks and pier edge.