Due to the special construction of combination carriers,
the vent line from the cargo hatchway coaming is situated very close
to the level of the cargo surface. In many cases, the inert gas main
line passing along the main deck may be below the oil level in the
hold. During rough weather oil or water may enter these lines and
completely block the opening and thus prevent an adequate supply of
inert gas during either tank cleaning or discharge. Vent lines should
therefore have drains fitted at their lowest point and these should
always be checked before any operation takes place within the cargo
hold.