Section 108.160 - Vertical ladders(a) Each vertical ladder must have rungs that are-(1) At least 41 centimeters (16 inches) in length;(2) Not more than 30 centimeters (12 inches) apart, uniform for the length of the ladder; and(3) At least 18 centimeters (7 inches) from the nearest permanent object in back of the ladder.(b) Except when unavoidable obstructions are encountered, there must be at least 11.5 centimeters (41/2 inches) clearance above each rung.(c) Except as provided in § 108.540(h)(3)(ii) , each exterior vertical ladder more than 6 meters (20 ft.) in length must be fitted with a cage or ladder safety device meeting ANSI Standard 14.3 (1974) for fixed ladders.(d) No vertical fixed ladders may be made of wood.CGD 73-251, 43 FR 56808, Dec. 4, 1978, as amended by USCG-2002-13058, 67 FR 61279 , Sept. 30, 2002