There have been numerous incidents of so-called “maintenance free” batteries catching fire and exploding on board ships.
Fortunately no-one has been injured from these incidents.
However such explosions have the potential to inflict serious injuries, such as permanent blindness and permanent skin damage, and can be the cause of fires.
In each instance, the batteries involved were the larger automotive ‘maintenance free’ type with no provisions for periodic topping up with water of the electrolyte (internal acid fluid). The exploded battery was under warranty.
The explosions have typically occurred several months after the battery was installed.
An unsafe condition may be created when a battery cell has a high concentration of hydrogen and gas due to a plugged or defective vent cap.
Also, overcharging the battery can result in electrolysis in the electrolyte (water and acid) – creating hydrogen and oxygen.
If enough hydrogen and oxygen accumulates in the battery, then vents out from the internal pressure, when it comes into contact with a spark, it will explode.
“Maintenance free” is a carefree description for starter batteries. Even where batteries do not require periodic water additions, maintenance requirements still extend to charging, cleaning battery tops, periodic re-tightening of battery connections, testing to confirm the working condition of the battery.
The “maintenance free” battery also loses water due to evaporation. Wherever there is an opening provided to top up the battery with water, topping up must be carried out.
During inspections
One explosion took place while a vetting inspector was onboard an oil tanker and witnessed during his presence.
The ship staff had been carrying out safety checks onboard ship, including trying out the emergency generators.
The panic situation coupled with blame games made all the ship staff demotivated.
In most cases of the observed explosions, the emergency generator would not start at the first attempt, leading to checks on terminals and battery circuits.
But the repeated attempted starts will increase the sparks and waiting hydrogen for explosion.
If this happens while a Port State Control or vetting inspection is in progress, you should request the inspector carry on with other inspections and in meantime investigate the issues.
Suggested control measures
These control measures are suggested for starter batteries.
On board ships the battery can be placed in an enclosed box with sufficient ventilation provided for the gases to liberate out freely.
Eye protection can be used whenever handling battery maintenance activities.
The capacity of the battery should be carefully selected at design stage. In no case it must be of insufficient capacity.
The battery charging circuit should provide constant voltage. When operated at the recommended charging voltage, they maintain the battery at or near full capacity and provide automatic replenishment of charge following a discharge.
Use a battery that has provisions for periodic top-ups with water, and provision for monitoring of liquid levels in all cells.
Any bulging of the battery within the warranty period should be reported and battery discarded immediately.
Sparks are mostly generated from slip on type connections. The wasted terminal is normally wound with copper strips to tighten again and the dangerous situation arises. Nut bolt tightening is better.
Operating starting batteries at temperatures above 25ºC will lead to higher water loss and shorter service life.
It would be prudent to place an instruction regarding periodic battery level check and top up of distilled water if required near Emergency and GMDSS Batteries.
Investigation
One investigation by an equipment manufacturer said there was less electrolyte in the battery. The plates inside the battery collapsed and touched one another causing short circuit.
The underlying cause was that the periodic check for electrolyte was not done in the last several months due to the battery being termed as “maintenance free.”