The UK Marine Accident Investigation Branch (MAIB) has published its interim report into a serious explosion and fire on-board the chemical tanker Stolt Groenland on 28 September 2019 at Ulsan in South Korea. The incident occurred during the ship-to-ship transfer of a highly flammable styrene monomer, one of 20 different chemical cargoes the vessel was carrying in 37 of its 39 cargo tanks.
At 1043, vapor started to release from a pressure vacuum valve for the tank which contained a styrene monomer. About two minutes later, a high-level alarm indicated that the level in the tank had reached 95%, soon followed by a ‘high-high’ level alarm indicating that the level had increased to 98%. By now, Stolt Groenland’s on-watch deck officer and the chief officer had made their way to the cargo control room.
At 1050, two explosions were seen and heard in rapid succession in way of the tanker’s cargo manifold. The resulting fireball passed very close to a road bridge above the quay.
The fire was fought from the shore and from the water and lasted until the early hours of the following morning. There was extensive damage to the vessel and a number of crew and firefighters were injured.
DAMAGE AND INJURIES
The fire was fought from the shore and from the water and lasted until early the following morning. The damage in way of Stolt Groenland’s cargo manifold and accommodation block was extensive. The following persons were injured: Stolt Groenland’s gangway watchkeeper, who was blown over the guardrails by the force of the explosion; a deck rating on board Bow Dalian; and, a number of shore workers, including firefighters and police during the emergency response.
Styrene monomer is used to make plastics, paints, and synthetic rubber. It is a colorless to yellowish oily liquid with an aromatic odor and is highly flammable. It has a flashpoint of 32°C (90°F). It is also toxic and reactive and is generally stable at ambient temperature. Polymerization1 of the monomer is initiated by heat or contact with peroxides. The polymerization process is exothermic and the monomer’s temperature may rise to the point where the reaction becomes very rapid and self-sustaining (runaway polymerization). Normally, temperatures above 65°C (149°F) are needed to initiate runaway polymerizations. To reduce the possibility of polymerization in storage and during transportation, Tert Butylcatechol (TBC) inhibitor is added to styrene monomer, typically at a concentration of between 10-15ppm, but higher levels might be needed depending on storage conditions and expected voyage duration. The depletion of TBC over time and its effectiveness as an inhibitor is affected by temperature, oxygen levels, and water.
What went wrong?
The MAIB’s initial findings were that the explosions were probably caused by the rupture of the deck above the cargo tank, followed immediately by the ignition of the styrene monomer vapor that was then released. The rupture was due to over-pressurization and the likely sources of the ignition were static electricity, sparks, or elevated steel deck plate temperatures resulting from the tank rupture.
The full interim report can be found Below
Source and download
|Published:||28 December 2019|
|Download:||Incident Report (566.7kB)|
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