Section 143.110 - Guards and rails(a) Except for helicopter landing decks which are provided for in paragraph (b) of this section, and areas not normally occupied, the unprotected perimeter of all floor or deck areas and openings shall be rimmed with guards and rails or wire mesh fence. The guard rail or fence shall be at least 42 inches high. The two intermediate rails shall be so placed that the rails are approximately evenly spaced between the guard rail and the floor or deck area: Provided, That if a toe board is installed then one of the intermediate rails may be omitted and the other rail placed approximately half way between the top of the toe board and the top guard rail.(b) The unprotected perimeter of the helicopter landing deck shall be protected with a device of sufficient strength and size as to prevent any person from falling from such deck.(c) Each catwalk and each stairway shall be provided with a suitable guard rail or rails, as necessary.