If an internal ladder is used, the access opening of the landing platform for the ladder shall be at least 675 mm (27") (3 planks) wide and not less than 900 mm (36") deep. Guardrail access openings to working platforms shall be protected system with a drop bar at top rail height. Access opening in work platforms shall be provided with hinged covers (hatch / trap door) which must be kept closed at all times, except during access by personnel.