How does ventilating a cargo tank blow-up a ship’s bowthruster compartment? According to Canada’s Transportation Safety Board recently released investigation of the explosion aboard AlgoCanada on 24 July 2009 it went like this:
The apparent wind across the vessel’s bow creatFFull reportull reported an area of lower pressure in the forecastle. This, coupled with the open PV valves, induced a flow of gasoline vapours from the cargo tank into the forecastle through the drying unit and the modified non-return valve. Once the heavier-than-air vapours passed through the tank-drying unit, they settled downward and into the bow thruster compartment.
This compartment contained a heater unit that was automatically controlled by a thermostat, along with electrical lighting fixtures and a ventilation fan, none of which were explosion-proof. Smoke and burn patterns on the electric heater indicated that it was likely the ignition source.