Large explosion on board a medium sized container vessel due to non-declaration of DG cargo.

Narrative
Beginning of September 2012, a 4500 TEU Container Vessel under pilotage was in the process of reaching the open sea after leaving port when a large explosion shook the vessel. The explosion was immediately identified by the personnel on bridge in the area of cargo hold 3 as the hatch cover was thrown off position and large amounts of smoke developed immediately. The vessels master reacted by sounding the general alarm, informing the shore authorities by distress call and ordering the fire team to start fire fighting.
A major emergency response was triggered and upon arrival tugs started fighting the on board blaze, constantly spraying huge amounts of water into the cargo hold and its surroundings for nearly a full day until stability was at the limit.
In the wake of the explosion and consequent fire, no injuries or fatalities occurred. There was no need for a shore side evacuation.
Two containers in the central rows were identified to being of particular concern due to the severe damage they had suffered and the lack of remaining contents in them. The lack of contents suggested either that the cargo in this container had extensively burned or that it had reacted and decomposed. The commodity inside each container was described as 450 drums of water treatment compound (probably calcium hypochlorite), loaded as general cargo with no suggestion of a dangerous cargo property. It can be assumed that due to exterior factors (heat, improper stowage) the chemical decomposed and reacted violently.

Findings
The cargo in both containers was clearly identified as DG cargo but was not declared and manifested as such. This caused wrong stowage through non-segregation.

Recommendation
It is recommended that general rules and procedures are implemented allowing to track exporter and importer contract relationship on container shipments with particular emphasis on cargo specification. In case an importer receives cargo not properly specified, manifested or packed, stowed and segregated, notice should be given.
It is further recommended that carriers and their local agents provide a better service and advice to their customers once booking orders are received, based on vessel operation and the required diligence in preparation.

Lesson to Learn
This marine casualty reveals the need to extend the search for the root cause to remote sectors far beyond the occurrence site. Particularly in container shipping, the safety of seafarers is to a large extent dependant on the safety awareness of outside sectors within the shipping industry.