Self-Sustaining Decomposition of Fertilizers

Self-sustaining decomposition is the failure mode of ammonium nitrate based fertilizers, and it is not combustion. Once initiated, the reaction propagates through the cargo mass without needing atmospheric oxygen, which is why excluding air does not stop it and why the response inverts against every other self-heating cargo in the IMSBC Group B family.

The full article will cover the mechanism, the compositional variables that govern susceptibility, and the IMO trough test that the Code uses to determine whether a fertilizer is liable to self-sustaining decomposition. It will set out the emergency response the schedules require: open the cargo hatches to provide maximum ventilation, treat the fixed gas fire-extinguishing system as inadequate, apply copious amounts of water, and isolate any heat source, with flooding considered only with due regard to stability.

It will also cover the two investigated casualties that shaped current practice. The German Federal Bureau of Maritime Casualty Investigation reported on the Purple Beach in the German Bight in May 2015, and the Isle of Man Ship Registry reported on the MV Cheshire, which decomposed three days out of Norway in August 2017 with roughly 42,500 tonnes declared as non-hazardous and became a constructive total loss. The Cheshire recommendations named the warning signs as oxygen depletion, water accumulation, visible vapours, temperature rise and a smell of ammonia.