Section 56.50-90 - Sounding devices(a) Each tank must be provided with a suitable means of determining liquid level. Except for a main cargo tank on a tank vessel, each integral hull tank and compartment must be fitted with a sounding pipe or other level indicating device acceptable to the Marine Safety Center.(b) Where sounding pipes terminate below the freeboard deck on cargo vessels, they must be fitted with gate valves. On passenger vessels, where sounding pipes terminate below the bulkhead deck, they must be fitted with gate valves.(c) Except as allowed by this paragraph, on each vessel constructed on or after June 9, 1995, no sounding pipe used in a fuel-oil tank may terminate in any space where the risk of ignition of spillage from the pipe might arise. None may terminate in a space for passengers or crew. When the Commanding Officer, Marine Safety Center, determines it impracticable to avoid terminating a pipe in a machinery space, a sounding pipe may terminate in a machinery space if all the following requirements are met:(1) The fuel-oil tank has an oil-level gauge complying with paragraph (d) of this section.(2) Precautions are taken such as fitting an effective screen (shield) to prevent the fuel oil, in case of spillage through the end of the pipe, from coming into contact with a source of ignition.(3) The end of the pipe is fitted with a self-closing blanking device. (d) Other oil-level gauges may be used instead of sounding pipes if all the following requirements are met: (1) In a passenger vessel, no such gauge may require penetration below the top of the tank, and neither the failure of a gauge nor an overfilling of the tank may permit release of fuel into the space.(2) In a cargo vessel, neither the failure of such a gauge nor an overfilling of the tank may permit release of fuel into the space. The use of cylindrical gauge-glasses is prohibited. The use of oil-level gauges with flat glasses and self-closing valves between the gauges and fuel tanks is acceptable.(e) The upper ends of sounding pipes must be closed by a screw cap or plug.(f) On mobile offshore drilling units where installation of sounding pipes may not be practicable for some tanks, alternate means of determining liquid level may be used if approved by the Commandant.CGFR 68-82, 33 FR 18843, Dec. 18, 1968, as amended by CGD 73-251, 43 FR 56800, Dec. 4, 1978; CGD 83-043, 60 FR 24774, May 10, 1995; CGD 95-028, 62 FR 51201, Sept. 30, 1997