A report into the explosion and fire on board the chemical tanker Stolt Groenland in Korea in 2019 has been released by the UK’s Marine Accident Investigation Branch (MAIB).
On 28 September 2019, a cargo tank containing styrene monomer on board the Cayman Islands registered chemical tanker Stolt Groenland ruptured causing an explosion and fire.
The tanker was moored alongside a general cargo berth in Ulsan, Republic of Korea and the Singapore registered chemical tanker Bow Dalian was moored outboard. The ignition of the styrene monomer vapour resulted in a fireball, which reached the road bridge above. Both vessels were damaged, and two crew suffered minor injuries. Fifteen emergency responders were injured during the fire-fighting, which lasted for over 6 hours.
The rupture of the styrene monomer tank resulted from a runaway polymerisation that was initiated by elevated temperatures caused by heat transfer from other chemical cargoes. The elevated temperatures caused the inhibitor, added to prevent the chemical’s polymerisation during the voyage, to deplete more rapidly than expected. Although the styrene monomer had not been stowed directly adjacent to heated cargo, the potential for heat transfer through intermediate tanks was not fully appreciated or assessed. Critical temperature limits had been reached before the vessel berthed under the road bridge in Ulsan. The tanker’s crew did not monitor the temperature of the styrene monomer during the voyage, and therefore were not aware of the increasingly dangerous situation.
A similar dangerous styrene monomer polymerisation incident had occurred a couple of weeks earlier on board another Stolt Tankers B.V. ship, Stolt Focus. The heat generated by the polymerisation process was noticed before the critical runaway temperature was reached. The styrene monomer cargoes on board both tankers was loaded at a similar time from the same tank in Houston and were exposed to similar environmental conditions. The incident on board Stolt Focus was not reported to the ship’s Flag State or other masters in the Stolt Tankers fleet.
Following the accident, the Ministry of Oceans and Fisheries, Republic of Korea, prohibited ship-to-ship transfer operations for dangerous cargo on general cargo berths in Ulsan. Stolt Tankers took immediate action to ensure that the temperatures of all cargoes carried on board its ships were monitored and reported to its shore management. It also took steps to enhance crew awareness on the hazards of inhibited and heat sensitive cargoes. The company is developing technological and administrative initiatives to assist with the safe stowage and monitoring of heat sensitive cargoes.
MAIB has made a recommendation to Stolt Tankers aimed at ensuring the wider marine chemical sector benefits from the lessons learned from the Stolt Focus incident and research initiatives that were carried out as a result of this accident. Recommendations have also been made to the Cayman Island Shipping Registry, the Chemical Distribution Institute and Plastics Europe (Styrene Producers Association). These are intended to assist in ensuring that the guidance provided in certificates of inhibitor and styrene monomer handling guides is consistent and achievable given the limitations of equipment and testing facilities on board ships.
Styrene monomer (also known as ethenylbenzene, phenylethylene, phenylethene, vinylbenzene, or cinnamene) is an aromatic hydrocarbon and a building block of the plastics industry. Over 30 million tonnes of styrene are produced annually, much of it transported by sea to plastics production plants.
Styrene monomer is a colourless, transparent liquid under ambient conditions and has a distinctly sweet odour. It is a volatile and flammable substance with a flashpoint of 32ºC. Its boiling point is 145ºC and its auto ignition temperature is 490ºC.
The harmful effects of styrene monomer include severe irritation to eyes and mucous membranes, as well as gastrointestinal effects. Chronic exposure to styrene monomer leads to central nervous system dysfunction, such as headache, fatigue, weakness, depression, hearing loss and nerve damage.