In its latest Safety Digest, UK MAIB references a case in which a barge crew member narrowly escaped injury when a bank of four lead-acid batteries exploded during generator start-up.
A barge crew member escaped injury when a bank of four lead-acid batteries exploded while starting a generator engine after completing the start-up checks. The batteries exploded simultaneously as the start solenoid closed to power up the starter motor. Fortunately, the battery bank was housed in a secure steel battery locker, which contained the explosion and limited the damage.
An investigation found that the batteries, in service for over five years, were low-maintenance, valve-regulated lead-acid (VRLA) types that were unsuitable for their intended purpose due to the battery circuit being maintained by a continuous float charge. The battery charging system was functioning correctly, maintaining the required trickle charge rate.
Given the wet cell nature of the batteries and their extended service time, the electrolyte level had likely dropped due to continuous float charging. This exposed the top of the cell plates, leading to corrosion. The cells shorted out when subjected to a high discharge load, causing the explosion (Figure 2).
Lessons Learned
Equipment → Selecting the right type of lead-acid battery is crucial:
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Flooded or wet cell batteries contain sulphuric acid/distilled water electrolyte and require regular maintenance to retain correct electrolyte levels. They must be stored upright to prevent leakage and are best suited for installations using float charging. Service lifespan: 5 to 7 years.
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Low-maintenance wet cell VRLA batteries have sealed cells with a valve arrangement to release gases during charging. They cannot be topped up and are best for intermittent use without float charging. Service lifespan: 5 to 7 years, but when used with continuous float charging, they should be replaced after 2 years due to an increased explosion risk under high discharge loads.
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Maintenance-free gel-type VRLA batteries share similar properties with wet cell VRLA batteries and are best for intermittent use. If used with continuous float charging, they should be replaced after 2 years.
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Absorbent glass mat (AGM) batteries, a type of VRLA battery, suspend electrolyte between plates for extended life and durability. Designed for intermittent charging, they should be replaced after 2 years if used with continuous float charging.
Maintain → Batteries are machinery and require a documented service and maintenance log. This record should include the battery type, onboard location, service entry date, inspection/maintenance details, corrective actions taken (if any), and the replacement due date.
Hazard → Safe stowage of battery installations is crucial to minimize impact in the event of a fire or explosion. To prevent gas buildup from the charging process, batteries should be stored in a purpose-built, well-ventilated locker in a cool, dry location. Light fittings in battery compartments should be corrosion-resistant and flame/explosion-proof.
