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Batteries: A high hazard in facility

We make use of batteries as they provide an uninterruptable power source for various systems and critical processes. In utilities, batteries are used in Fire Protection system (FPS), Data Centers, Generators, Circuit breaker controls etc. Battery contains electrochemical cells that convert stored chemical energy into electrical energy. Broadly, batteries are classified as primary battery and secondary battery. The only difference is that secondary batteries can be recharged while primary batteries cannot be recharged. Most common form of secondary battery is lead-acid battery which can be of flooded or sealed type.

Flooded batteries are also known as Vented Cell battery. Lead Plates, Plate separators along with the Electrolyte (Sulphuric acid) are placed inside the plastic jar in flooded batteries. Sealed batteries are valve regulated lead acid (VRLA) batteries. It encompasses a pressure relief valve to vent the internal pressure built up inside the batteries.

Operation

When the battery is put on a discharging mode, a chemical reaction takes place between the Lead Oxide (PbO) on positive plate and Lead (Pb) on the negative plate along with the electrolyte to form Lead Sulphate and water. This chemical reaction results in generation of voltage across the battery terminals. The chemical reaction is reversed when the batteries are charged. In case if a battery is left alone, it will discharge. In order to maintain a battery in fully charged position, it has to be charged at a rate equal to self-discharging rate. This charging is known as “Trickle / Float Charging”. In case, more current is available than required, water in the battery will get dissociated in to Hydrogen and Oxygen gasses which are vented to the atmosphere. This creates water scarcity and this is the reason why water is added into Flooded Lead Acid Battery.

But it is not so in case of VRLA Batteries. VRLA Batteries are recombinant batteries, which mean Oxygen evolved will recombine with Hydrogen creating water and preventing water loss. A valve is provided as a safety feature in case the evolution of Hydrogen is in excess.

Ventilation of battery rooms

During the charging of batteries, Hydrogen gas is evolved. Hydrogen is a flammable gas with broad flammable range, making it a severe Fire Hazard. In the absence of proper ventilation, Hydrogen gas will form an ignitable mixture with the air, which may explode by a low energy Ignition source due to confinement and dispersion of hydrogen fuel in air. Ventilation requirement will vary with locations depending upon the size of the room, number of batterie and type of batteries. Hydrogen detectors can be installed in the battery room in case the hazard is high. Special precautions should be taken with regard to the inlet and outlet of air.

Heat is continuously generated from batteries and life of a battery reduces if it is operated at higher temperatures. Test results have proved that optimum results are obtained if battery room temperatures are maintained within 22-25OC. Operating batteries at elevated temperatures also can lead to thermal runaway. More Current is required to maintain float voltage if battery temperature is high.

Precautions

  • Always keep batteries in cool, clean and dry place
  • Avoid short circuiting of battery terminals
  • Do not store the battery in direct sunlight
  • Avoid exposure of battery to rain water
  • Always store batteries in upright position
  • Do not store batteries close to fire and heat generating equipment
  • Batteries should be placed in vibration free area
  • Battery racks should be stable and anchored
  • Ensure proper grounding
  • Ensure Interlinking cables are of uniform size and length
  • Keep the terminals clean.

Conditions of use

  • Do not incinerate a used lead acid battery
  • Do not attempt to dismantle the battery
  • Do not add de-mineralized water in a sealed battery
  • Do not add electrolyte to a sealed battery
  • Always use insulated tools while working on batteries
  • Never place any metallic object on battery terminals
  • Never make or break any live circuit
  • Tight the terminals within recommended torque values
  • Observe the polarities of the battery
  • Use personal protection equipments while working on batteries
  • Inspect regularly for any cracks or leaks.

Battery Hazards

  1. Chemical Hazard:
    1. Electrolyte is harmful for skin and eyes
    2. Electrolyte is corrosive in nature and electrically conductive
    3. Medical aid is required, if acid fumes are inhaled.
    4. Flush plenty of water in eyes in case acidic electrolyte contacts with eye.
    5. In case of acid contact with skin, affected part should be cleaned thoroughly with plenty of fresh water.
  2. Fire and Explosion Hazard:
    1. Ensure gap (minimum of 10mm) between adjacent batteries for adequate air flow.
    2. Never charge a battery in a sealed container.
    3. Avoid spark or smoke near a battery.
    4. Provide proper ventilation to prevent accumulation of Hydrogen gas in battery room
Sunny Verma
Consultant Engineer

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