The British Marine Accident Investigation Branch (MAIB) has completed its investigation into the explosion on board the chemical tanker Stolt Greenland in 2019, finding that heated cargo tanks in neighboring compartments likely caused dangerous heating of temperature sensitive cargo.
On September 28, 2019, a cargo tank containing styrene monomer on board the chemical tanker registered in the Cayman Islands Stolt Greenland ruptured while docked at the port of Ulsan, South Korea. A spontaneous and uncontrolled polymerization reaction – the reaction of styrene molecules with each other to form polystyrene – caused the temperature and pressure in the tank to rise exponentially, shattering the tank across the main deck and bulkhead with a adjacent empty cargo tank.
The monomer vapor ignited almost immediately, causing two explosions in rapid succession. The second explosion detonated the O / S of the gangway above the starboard guardrail; he hung on for a moment, but decided to let go because of the heat of the fire. He fell into the water between the ship and the wharf, and climbed on a fender back to dry land.
The first mate sounded the fire alarm to reassemble the crew, then turned on the deck foam monitoring system and (along with the third mate) directed the monitors to the cargo manifold. Shortly thereafter, the captain ordered the abandonment of the vessel and the crew boarded the vessel’s free-falling lifeboat and managed to escape.
The neighbor’s crew product tank Dalian Arch also abandoned the ship when drops of scorching styrofoam rained down on their main deck. the Dalian and his crew were otherwise unharmed.
Images courtesy of MAIB
Local firefighters spent more than six hours putting out the blaze. The intervention involved more than 700 people and 117 fire trucks, pumps and fire towers.
Styrene polymers (dimers) and an inhibitor compound were found in the residues obtained from the combinations carried by a Dalian Arch crew member during the incident. This (and the presence of drops and drops of polystyrene all over the area) confirmed that the styrene had reacted with itself in an uncontrolled polymerization reaction. The presence of the inhibitor – and probably in sufficient quantity – indicated that improper storage practices were the cause of the reaction, according to the lab report.
An analysis of the temperature recordings of the Stolt Greenland found that the temperature in tank 9S (the tank containing styrene) began to rise several days after the crew began heating the cargo in tanks 8P, 9P, 10P, 11P and 7S. Although none of these tanks were directly adjacent to the 9S, the crew felt that it would be acceptable to heat the tanks nearby as long as they were separated by a compartment. Once the styrene has reached around 60-65 degrees Celsius, it is likely to enter a thermal runaway polymerization reaction, and the cargo documents provided for keeping the tank temperature below 30 ° vs. The tank reached 50 ° C three days before the accident, then 65 ° C during the day. before, then exceeded 90 ° C shortly before the explosion.
“This Stolt Greenland the crew were unaware of the high temperatures and polymerization of the styrene monomer in 9S, until they were warned by the activation of the high level alarm on the front of the deck, says that the temperatures of the unheated cargoes were not monitored at all, and that no temperature alarms were set, ”MAIB concluded. “If the temperatures of the styrene monomer had been closely monitored and the maximum temperature of [30 C] indicated on the prohibition certificate had been complied with, this accident would have been avoided. “
A similar (but less dramatic) self-heating incident affected a cargo of styrene aboard the tanker operated by Stolt Stolt Focus in August 2019, just one month before the incident on board Stolt Greenland. In the To concentrate incident, the crew controlled the heating problem by adding seawater to the cargo, then diluting it with benzene and adding an inhibitor. The cargo came from the same supplier, the same loading port, the same onshore tank and was traveling on a similar trade route, so MAIB asked Stolt to provide further information on the circumstances. “Stolt refused to do this because he did not consider the heating and subsequent disposal of the styrene monomer cargo to be a maritime accident or a maritime incident,” MAIB said.
On the recommendation of the MAIB, Stolt has launched a campaign across its tanker fleet to ensure its crews are made aware of the special handling requirements for heat-sensitive cargoes, including new reporting requirements to keep the head office informed of tank temperatures.