Code L15DH(+):

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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15 = Calculation pressure:

Minimum calculation pressure: 15 bar (see 6.8.2.1.14)
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D = Openings (see 6.8.2.2.2):

Tank with top-filling and discharge openings with no openings below the surface of the liquid.
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H = Safety valves/devices:

Hermetically closed tank (see 1.2.1).
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(+) = The indication of a "(+)" after the tank code means that the substance is subject to special provisions. In that case the alternate use of the tanks for other substances and groups of substances is permitted only where this is specified in the certificate of type approval. Higher value tanks according to the provisions at the end of the table in 4.3.4.1.2 may be used with due regard to the special provisions indicated in Column (13) of Table A in Chapter 3.2.