The UK government’s Marine Accident Investigation Branch (MAIB) has released its final report on the explosion on a Cayman Islands-registered ship in South Korea. The massive explosion of the chemical tanker in the cargo port of Ulsan was caused by the rupture of a cargo tank.
Incident
On 28 September 2019, a cargo tank containing styrene monomer on board the Cayman Islands-registered chemical tanker ruptured due to runaway polymerisation. The catastrophic rupture released a large quantity of vapour into the atmosphere, and it subsequently ignited. 
Fire-fighting efforts by the emergency services took over six hours and involved more than 700 personnel and 117 units of fire trucks, pumps and fire tugs.
Investigation
During investigation, it was found that
- The explosions on board tanker were probably caused by the rupture of the deck cargo tank, followed immediately by the ignition of the styrene monomer vapour that was then released.
- The rupture was due to over-pressurisation and the likely sources of the ignition were static electricity, sparks or elevated steel deck plate temperatures resulting from the tank rupture.
- VDR data showed that the temperature of the styrene monomer had reached 100ºC at the time of the explosion. Such an elevated temperature indicates that the cargo was polymerizing.
Lesson learnt
- Adhere to the carriage and storage instructions details on the safety data sheet, the certifcate of inhibitor, and those provided by the charterer.
- Witness the addition of inhibitor into each cargo tank.
- Closely monitor cargo temperature for unexplained increases.
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Source: maib report
