Japan Transport Safety Board issued an accident investigation concerning a chemical tanker that was conducting cleaning work in a cargo oil tank. Yet, the cleaning work resulted to an explosion leading to the injury of two seamen and damages to the cargo.
The Incident
On April 8, 2018, at approximately 1005 hours, an explosion occurred in the cargo oil tank of the chemical tanker ‘Golden Sunny Hana’, as it was sailing southeast off to the southeast of Kunisaki Port, Oita Prefecture, and the crewmembers were conducting cleaning work in a cargo oil tank.
Specifically, the tanker had onboard the master along with 14 crew members.
From the explosion, two seamen were injured, while her cargo oil tanks had holes and damages.
Probable Cause
According to Japan Transport Safety Board
- The accident occurred when the Vessel was conducting the Circulation Work in the No. 2 port cargo oil tank and the No. 2 starboard cargo oil tank during cargo oil tank cleaning work while off to the southeast of Kunisaki Port, Oita Prefecture, an explosion occurred in the No. 2 port cargo oil tank because steam was injected into the No. 2 port cargo oil tank under conditions in which a combustible gas mixture of vaporized pyrolysis gasoline and air in the explosive range was present.
- It is probable that the presence of the combustible gas mixture of vaporized pyrolysis gasoline and air in the No. 2 port cargo oil tank was not noticed because the gas concentration in the No. 2 port cargo oil tank was not measured prior to cleaning of the cargo oil tanks.
- It is somewhat likely that the combustible gas mixture was within the explosive range because flushing of the cargo lines and cargo oil tank bottoms was conducted under conditions in which ventilation and other measures were not implemented even though the gas concentration measurement taken after unloading was within the explosive range and approximately 30 liters of pyrolysis gasoline subsequently remained in both the No. 2 port cargo oil tank and the No. 2 starboard cargo oil tank, and the vaporized pyrolysis gasoline was not expelled outside, its gas concentration increased further with the passage of time, and it became mixed with air
- It is probable that steam was injected into the No. 2 port cargo oil tank with the intention of raising the temperature of the seawater used in the work of repeatedly pumping up liquid collected on the cargo oil tank’s bottom with a pump installed in the cargo oil tank and then spraying the liquid with the Cleaning Machine
Safety Recommendations
- Sufficiently provide ventilation with ventilation equipment after the flushing of cargo lines and cargo oil tank bottoms.
- Measure gas concentration before cleaning work and during cleaning work, cease work immediately when a measurement is in the explosive range, and continue work after providing ventilation with ventilation equipment or introducing inert gas and then confirming safety.
- Consider the danger of static electricity present in cargo oil tanks and do not inject steam if safety cannot be confirmed.
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