Ammonium nitrate based fertilizer (UN 2071) must only be loaded in clean cargo space which can be opened up in an emergency.
When bagged or containerized cargo is loaded the cargo shall be accessible through hatch entries and mechanical ventilation must enable the vessel to exhaust any gasses of fumes generated from decomposition
Prior loading consideration must be taken about the need to open cargo hatches in case of a fire to provide ventilation and to apply water in emergency also we must take in to consideration about the risk of stability of the ship through flooding of the cargo space.
The residue left after decomposition may have only half the mass of the original cargo; this loss of mass may also affect the stability of the ship and shall be considered before loading.
For long international voyages it is a mandatory requirement to stow ammonium nitrate based fertilizer our of direct contact with a metal engine-room bulkhead which can be done by using wooden board to provide an air space between the bulkhead and the cargo.
IMDG Code Compliance Centre 