(1) on deck stowage of a container packed with dangerous goods;
(2) stowage of a container packed with dangerous goods for which on deck only stowage is specified in the IMDG Code; and
(3) the interpretation of the words "not in the same vertical line unless segregated by a deck" for vertical segregation.
Considering these issues, we developed new requirements for stowage and segregation and examined the effect of the requirements on the stowage plan on such ships.
3 Additional stowage requirements on ships with partially weatherproof hatchway covers
3.1 Basic principles for limitation of on deck stowage
The risks of on deck stowage of a container packed with dangerous goods, due to a gap between hatchway covers, are caused by the possibility of ingress of dangerous goods into the cargo hold under the gap. When the dangerous goods packed in a container are gases or solids, the risks due to the gap between hatchway covers are insignificant. We assessed the risks of on deck stowage of a container packed with dangerous liquids as follows:
(1) The probability of ingress of a dangerous liquid into a cargo hold through a gap between hatchway covers is the product of the probability of spillage of the liquid and that of ingress of the spilled liquid into a cargo hold. Therefore, the probability of ingress of a dangerous liquid into a cargo hold is very small;
(2) Only a small part of spilled liquid may enter into a cargo hold. Therefore, the amount of liquid entered into a cargo hold is very small; and
(3) Spillage of a dangerous liquid from a container on deck can be found by ships personnel and the risk due to spillage can be managed by them.
Thus, we consider that a container packed with dangerous liquids can, also, be stowed on a hatchway cover provided that the effective means for managing the risks, e,g., removal of source of ignition and adequate ventilation, are provided in the cargo hold below the hatchway cover.
3.2 Containers stowed in vertical lines not on hatchway covers
It should be noted that at starboard and port ends of a deck, only a small part of a container is stowed on a hatchway cover and most of the container is not on the hatchway cover, in general. Therefore, it is rational to consider that a container in such vertical lines on deck is not a "container stowed on a hatchway cover". Strictly speaking, an interpretation is necessary, e.g., as follows:
"Where the projection of the centre of the container is not on a hatchway cover, such container is not on a hatchway cover."
