In every ship bulwarks or guard rails shall be provided on every exposed deck to which any passenger or vehicles may have access. Such bulwarks or guard rails, together with stanchions supporting the guard rails shall be so placed, designed and constructed, and in particular shall be of such a height above deck as to prevent any passenger who may have access to that deck or any vehicle from accidentally falling therefrom. Any freeing ports fitted in such a bulwark shall be covered by a grid or bars which will prevent any person from falling through the port.