A small ferry’s battery fire deserves global attention

A seawater fire extinguishing system that had been installed as an additional safety precaution on the Norwegian battery-hybrid ferry Ytterøyningen may have “contributed to escalating” events that led to an explosion that struck the vessel on 11 October. It followed an onboard fire the previous evening, according to a preliminary report into the incidents published last week by battery supplier Corvus, but what caused the blast is not yet known.

Although the vessel was a small local ferry operating on a short route in western Norway and the fire had been detected when the vessel was just 200m from its berth at which it docked safely, I believe this incident merits worldwide attention. With battery hybrid power systems becoming more common and an expectation that they will take an important place in the path towards zero-carbon shipping, a fire and explosion involving batteries should alert system designers and operators that this is not a risk-free option.

However, this was the first fire in a battery ferry in Norway and we should be grateful that this wake-up call has been sounded on such a vessel as this, rather than on a large passenger ship far out to sea.

In fact, Ytterøyningen was not using its batteries at the time, because they had been disconnected for some service work on their cooling system. A Corvus spokeswoman told me that its service staff were pressure-testing the cooling system with air and filling it with coolant prior to the incident.

The report does not say why this service work was needed: the batteries and their cooling system had been installed by the nearby Westcon yard in Ølen just four months beforehand. It had redelivered the ship after conversion to its battery-hybrid arrangement in June this year and the ferry was towed back there the same day as the explosion for investigations to begin.

Instead of its batteries, the ferry’s diesel engines were maintaining its regular service when, in the early evening of 10 October, a fire broke out in the battery compartment. It was close to its berth at Sydnes on the island of Halsnøy at the time and the vessel was able to moor safely and all 15 people on board “disembarked as scheduled”, Corvus’ report notes. There had been “a small fire and it was extinguished”, it says.

According to a local news report at the time, the fire was reported to the police at 1840 and was under control soon after 2100, with firefighters staying on site through the night. At about 0700 the next day, there was a large explosion in the adjacent switchboard room, the news service added.

In its statement last week, Corvus said that the explosion’s cause “must still be concluded as a result of further investigation.” That investigation involves the police among others and, although both class society DNV GL and the Norwegian Maritime Authority (NMA) have endorsed Corvus’ account, the NMA said in a statement last week that it would like to “consider the report from Norwegian National Criminal Investigation Service before drawing our conclusion.”

Asked about the police’s role in the investigation, Corvus’ chief executive Geir Bjørkeli told me that, because this accident is the first of its kind, “they want to use this incident to generate valuable knowledge that is of interest to the general public.”

The sprinkler system that Corvus believes may have played a role had been fitted to supplement the vessel’s Novec 1230 inert gas firefighting, which had also been activated during the fire. Corvus’ theory is that the saltwater may have caused short circuits in the electrical system. Whether a freshwater sprinkler would have avoided the short circuits is not known. Mr Bjørkeli told me that although saltwater is more damaging than freshwater, “the extent of the damage from seawater compared to freshwater is not determined yet.”

Although the explosion’s cause remains uncertain, the fire is better understood. “The investigation and findings so far show that the fire was most likely due to a coolant leak from a gasket in the Corvus liquid-cooled energy storage system and that it was a one-off event,” the report says.

This gasket should have sealed the cooling plate outside a battery module but it was found to be twisted, although whether that was a result of “recent service work on the cooling system or if it was caused by other reasons” cannot yet be confirmed, it adds.

That leak “created arcing between electrical components, at pack voltages of 10,00VDC, igniting a fire [which] was fuelled by ethylene glycol components from the coolant and caused external heating of battery modules,” the report says. It was the arcing that caused the initial fire, it stressed, and the batteries did not short-circuit.

Unfortunately, because of the service work, the batteries were not connected to the ship’s systems so no signals were sent through the ship’s alarm system. But the report does offer one positive finding, however: the Corvus Passive Single Cell Thermal Runaway Isolation safety system “worked as designed and intended, most likely limiting the damage from the fire,” it says.

Follow-up action

Although only preliminary findings have been issued so far, “we are so confident about the current findings that we have chosen to make them public,” the footnotes to Corvus’ report explain. Those notes also mention what the company describes as “the most important learning from this”, which is that even if batteries are not in use, “alarms need to be forwarded to the ship’s system.”

Mr Bjørkeli told me that Corvus is already taking action in response to its findings. Most of the battery systems it delivers are air-cooled and it has temporarily stopped selling liquid-cooled systems, he said. The company has also offered to rebuild existing installations that have liquid cooling arrangements, replacing them with air-cooled alternatives.

Long-term decisions on possible design changes to its liquid-cooling systems “are awaiting the final report,” but “this incident have given everyone new knowledge that we need to take into a design review. … We need to make sure this cannot happen again,” he said.

NMA also found encouraging details in the report. Its own response, issued on behalf of its acting director general of shipping and navigation Lars Alvestad, notes that “if you disregard the incident with the explosion, investigations have also shown that extinguishing in the first phase went according to plan and that the ferry was evacuated in a safe and secure manner.”

And Mr Alvestad remains confident that “batteries do not pose a greater risk than more conventional energy sources on ferries.” However, he said, this incident “demonstrates the importance of continuously working on making improvements with regards to routines and safety measures” and he predicted that the final report’s findings “will be important contributions to the continued work on the phasing in of new technology.”

His remarks echo my view. Industry-wide improvements in safety usually stem from large high profile incidents. This one is neither of those, but its impact should be no less significant.

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