An incorrectly fitted valve and an ineffective automated safety system caused one-metre flames to emerge on the deck of the Suiso Frontier — the world’s first liquefied hydrogen (LH2) carrier vessel — a day after loading its first ever hydrogen shipment in an Australian port, an investigation has concluded.
The experimental ship — built by Kawasaki Heavy Industries to prove it was commercially viable to ship LH2 over long distances — was docked at the Port of Hastings, southeast Australia, on the evening of 25 January 2022, ahead of a month-long journey to Japan, when the flames were spotted by a crew member.
According to a year-long investigation published today by the Australian Transport Safety Bureau, a government agency, the “serious incident” occurred during an attempt to burn excess boil-off gas from the 1,250-cubic-metre LH2 cargo tank.
Because hydrogen is only a liquid at temperatures of minus 253°C, when stored in an insulated tank, the H2 at the outermost edges is warmed by ambient air and reaches boiling point, turning the LH2 into gaseous hydrogen a gas. This “boil-off gas” then needs to be removed to reduce pressure inside the tank and ensure it does not expand and explode.
The ship’s gas combustion engine was switched on to burn the boil-off gas, but an apparently minor part — a pneumatic solenoid valve that opened and closed a metal plate called a “damper” that worked with a fan to ensure adequate air supply to the burner — had been incorrectly fitted with the wrong specifications.
This meant that the spring-loaded damper closed, cutting off the gas combustion engine’s air supply for cooling (as well as combustion and dilution). Due to hydrogen’s wide flammability range, combustion of the gas continued for several minutes after the damper closed, and temperatures inside the unit began to rise to 450°C.
The hydrogen flame gravitated towards the ambient air outside the vent, and it “probably reacted” with salt deposited by the sea air on the inner flue surfaces, resulting in a one-metre yellow flame seen by an able seaman.
Two flame scanners inside the gas combustion unit were supposed to spot any flames and immediately shut down the machine, but no abnormalities were detected. This was because a “low air pressure transmitter” was located between the fan and the damper, but did not activate because when the damper closed, the air pressure on the fan side of the damper did not drop, investigators found.
The 24-volt direct-current (DC) solenoid valve failed because it was incompatible with the 230-volt alternating current (AC) power supply from the gas combustion unit’s control system, the report concluded.
But thanks to the eagle-eyed able seaman radioing to the ship’s cargo control room, the gas combustion unit was quickly shut down, and a fire was prevented.
The report does not explain what might have happened if the flame — which only lasted five seconds — had not been spotted, but the 24 crew members were mustered to their emergency stations and began preparing fire houses, as per standard procedures.
The gas combustion unit’s manufacturer, German company Saacke, has since installed limit switches to monitor the position of the dampers, and the control system has been programmed to automatically shut down the unit if an “open” signal is not detected.
“This incident highlights the importance of ensuring automated shipboard operating systems are equipped with safety controls to prevent hazardous consequences in the event of a malfunction,” the report concluded.
“Since operators may be inherently removed from the control loop of automated systems, there is a heightened risk that they will not be able to identify abnormalities promptly and respond to them.
“Therefore, system safeguards should be appropriate for promptly alerting operators to any issues,or automatically stopping the operation to prevent damage or injury.”
It added: “The incident also shows the importance of stringent manufacturer quality controls to ensure correct system components are specified and fitted to equipment.”
The ship eventually sailed to Japan with its LH2 cargo a day later than planned, on 28 January, arriving in Kobe, Japan, on 25 February.
