5.3.5(b) Emergency bilge suction. In addition to the direct bilge suction required by 4-6-4/5.3.5(a), an emergency bilge suction is to be fitted for main propulsion machinery spaces on all oceangoing vessels 55 m (180 ft) in length and over. The emergency bilge suction is to be directly connected to the largest independently driven pump in the propulsion machinery space, other than the required bilge pumps. Where this pump is not suitable, the second largest suitable pump in the propulsion machinery space may be used for this service, provided that the selected pump is not one of the required bilge pumps and its capacity is not less than that of the required bilge pump.