Code LGBF:

L = Type of tank:

Tank for substances in the liquid state (liquids or solids handed over for carriage in the molten state).
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G = Calculation pressure:

Minimum calculation pressure according to the general requirements of 6.8.2.1.14.
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B = Openings (see 6.8.2.2.2):

Tank with bottom-filling or bottom-discharge openings with 3 closures.
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F = Safety valves/devices:

Tank with a breather device, according to 6.8.2.2.6, fitted with a device protecting against the propagation of a flame; or explosion pressure shock resistant tank.