Code S4AH:

S = Type of tank:

Tank for substances in the solid state (powdery or granular).
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4 = Calculation pressure:

Minimum calculation pressure: 4 bar (see 6.8.2.1.14)
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A = Openings (see 6.8.2.2.2):

Tank with bottom-filling or bottom-discharge openings with 2 closures.
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H = Safety valves/devices:

Hermetically closed tank (see 1.2.1).