The Liberian-registered vessel was built by Mitsubishi Heavy Industries of Japan in 1964 and was a steam turbine-driven tanker of 64,081 tons deadweight.
One of the items for repair was the replacement of the missing cover for the drip tray of the vent pipe leading from the aft starboard fuel oil tank.
The explosion occurred as about 150 workers returned to the engine and boiler rooms of the vessel after their lunch break for repair and cleaning work.
The blast flung debris from the 35,600-tonne vessel as far as 100 metres (328 ft) away and started a flash fire that prevented dockside workers from rescuing those trapped inside the ship.
Sparks from the cutting torch used during repairs caused a fire, which ignited an explosive vapour mixture within the aft starboard bunker (fuel) tank of the vessel.