Developed jointly with industry and international authorities, a new report addresses proper ventilation, fire suppression and battery design
Class society DNV GL has released a new report on battery safety in ships, assessing the explosion and fire risks in maritime battery installations and the effectiveness of fire extinguishing systems in the event of a battery fire.
Launched two years ago, the report, Technical Reference for Li-ion Battery Explosion Risk and Fire Suppression, was developed through the Maritime Battery Joint Development Project, a collaboration between Norwegian, Danish and US maritime authorities, battery manufacturers, system integrators, fire extinguishing system suppliers, shipyards and shipowners.
“Batteries onboard ships are both environmentally friendly and cost-effective solutions that we wish to see more of in the future,” says Norwegian Maritime Authority (NMA) acting director Lars Alvestad. “This project has been important in learning the risks of these systems and using the new insight to improve safety requirements.”
Batteries are becoming increasingly popular in maritime applications to improve efficiency, fuel consumption and greenhouse gas emissions. More than 300 vessels with batteries are in operation, under construction or on order.
A battery fire can burn extremely hot, producing toxic and explosive gases. DNV GL’s new report presents the results of research on what happens during a fire in a battery compartment, the release of gases, and the usefulness of various extinguishing systems in combatting the fire and preventing explosions.
One of the most important findings concerns ventilation systems, which are critical to avoiding an accumulation of explosive gas. The report concludes that ventilation alone will not adequately mitigate gas accumulation if a significant portion of the battery system ignites.
"In addition to fire suppression and ventilation, the battery design must have preventative safety barriers so that the fire and gas emissions are limited to as small a part of the battery system as possible," says DNV GL project manager for the research project Henrik Helgesen.
The report provides new recommendations on ventilation systems, based on a newly created model which identifies the appropriate size and type of ventilation system based on a vessel’s battery installation. Early fire and gas detection are also essential, meaning that the gas sensor should be located as close to the battery as possible.
With maritime battery installations becoming increasingly popular, the report’s release follows in the wake of a small fire and subsequent explosion onboard a Norwegian battery-hybrid car ferry in October that had raised concerns about the safety of lithium-ion energy storage systems. Preliminary results from the ongoing investigation released by battery manufacturer Corvus Energy, in conjunction with authorities, indicate that the fire most likely started due to a coolant leak from a gasket in the liquid-cooled energy storage system.
Both the NMA and DNV GL supported the investigation’s preliminary findings.
In its findings, Corvus found the most probable cause of the fire was a leakage from a twisted gasket in the battery system’s liquid cooling circuit. The leakage created arcing between electrical components, at pack voltages of 1,000 v DC, igniting a fire. The fire was fueled by ethylene glycol components from the coolant and caused external heating of the battery modules.
Due to ongoing service work, no part of the battery system was connected to the shipside systems at the time of the incident. Consequently, no alarms from the battery system were sent through the ship’s alarm system.
Both the ferry’s inert gas system and saltwater fire sprinkler system were deployed during the incident. While the saltwater sprinkler system was installed as a secondary safety barrier, indications are that its activation contributed to escalating the incident.