The Marine Accident Investigation Branch (MAIB) examines and investigates all types of marine accidents to or on board UK vessels worldwide, and other vessels in UK territorial waters.
This Safety Digest draws the attention of the marine community to some of the lessons arising from investigations into recent accidents and incidents. It contains information that has been determined up to the time of issue.
The Incident
A specialist deep-sea vessel was using equipment capable of operating at extreme depths to conduct deepwater experiments, the on board power supply for which was provided by lithium-ion (Li-ion) batteries that were encased in several metal tubes attached to its framework.
Probable cause
An inspection of the equipment after a successful deployment identified a potential leak from one of the metal tubes. However, other work priorities meant that the technician in charge of the
equipment decided to leave it in its storage area and delay the removal and further examination of the battery.
Seven hours later, the vessel’s bridge team heard a loud bang followed by a fire detection system warning for the deepwater equipment storage area. The attending crew members discovered a scorched and damaged metal battery tube lying on the deck.
Examination of the battery tube indicated that sea water had leaked into the battery compartment and contaminated the Li-ion battery, which caused pressurised gasses to build up and self-combust and resulted in a brief explosion. The remaining battery tubes were removed to a secure storage area for further checks.
The Lessons
- Risk: Li-ion batteries are both common place and a popular choice; a 1kg Li-ion battery can store the same amount of energy as a 6kg nickel metal hydride or lead acid battery. However, Li-ion battery failures do occur and have often resulted in fires that are difficult to extinguish.
- Hazard: Lithium reacts intensely with water, which can corrode or damage the internal battery safety devices and cause it to overheat, ignite, rupture or leak. Salt water is far more conductive than fresh water, which means that the battery can discharge more quickly, and the electrical current will break down the salt by electrolysis, producing hydrogen and chlorine gas. Put simply, a Li-ion battery should not be exposed to water or moisture.
- Maintain: A Li-ion battery that is found to be damaged or affected by water should not be used or charged. Remove the battery to a secure place where it can be monitored and potential spontaneous combustion can occur safely. In the event of a fire, use an ABC1 or BC2 powder fire extinguisher to put it out. Other methods include misting the fire with chemically exfoliated vermiculite or dousing it with large quantities of fresh water.
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Source: MAIB
