(a) Cargo tanks may have sighting ports as a secondary means of liquid level gauging in addition to the gauges under § 154.1305, if:
- (1) The tank has a MARVS that is less than 69 kPa gauge (10 psig);
- (2) The port has a protective cover and an internal scale; and
- (3) The port is above the liquid level.
- (b) Tubular gauge glasses must not be liquid level gauges for cargo tanks.
- (c) Plate type gauge glasses must not be liquid level gauges for cargo tanks, except deck tanks if the gauge connections have excess flow valves.