Tankerman · Inert Gas — Deck Water Seal
The deck water seal in an inert-gas system serves to:
- ACool the cargo
- BMeasure ullage
- CPrevent hydrocarbon gas/cargo from flowing back from the tanks toward the machinery space✓ Correct
- DStrip the tanks
Explanation
The water seal is a one-way barrier: it lets inert gas flow to the tanks but blocks back-flow of flammable cargo vapor toward the IG plant and engine room. Combined with the non-return valve, it isolates the deck from the machinery space.
Authority: SOLAS II-2; ISGOTT
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