Some municipalities require that new gangways meet the 4" sphere rule. This means that you cannot pass a 4" ball through any location on the sides of the gangway. One option is 2" x 2" wire mesh infill panels that can be attached to any gangway. Other options are also available.
Wire mesh infill

 

Maine State Pier passenger boarding gangway system with wire mesh infill.
Wire mesh infill

 

Mystic Seaport Museum used four rows of security rail as infill on their gangway.
4 rows securty rail

 

These temporary gangways, with five rows of security rails, were used on Liberty Island while repairs were being done to the infrastructure after Hurricane Sandi.
5 rows of securty rail

 

This gangway is destine for the Independence Seaport Museum in Philadelphia.
gangway for Independence Seaport

 

This wooden picket infill was attached to the aluminum pier sections by the marine contractor who installed it. Another great solution.
wooden picket infill

 
wooden picket infill