What is Thermal Runaway and How to Prevent Thermal Runaway?

Thermal runaway in VRLA lead acid batteries is not uncommon.

Typically, the most ‘at risk’ are batteries that are aged and near end of life.
Thermal runaway is a situation where the current flowing through the battery cell begins to overcharge causing the cell temperature to rise, which increases the current causing a further rise in temperature, and uncontrolled, this is repeated over and over.

VRLA ( valve regulated Lead Acid ) batteries work by exchanging oxygen molecules between positively charged lead plates and negatively charged plates, ultimately forming water and hydrogen gas, creating electricity.

Environment conditions can trigger Thermal Runaway in batteries.

What to investigate:-

• Lack of ventilation
• High ambient temperature
• Severe environment swings from exceptional LOW temperatures to very HIGH temperatures.
• Dirty, dusty environment.
• Flooding
• Over loaded batteries.
• Batteries that have not been replaced – very old,beyond end of life

Thermal runaway is a REAL phenomenon.
In basic terms, a faulty charging current failure without functional temperature control imbalances the functionality of the chemical structure within the battery. VRLA chemical reactions are accelerated as the excessive oxygen recombination depolarizes the negative charge causing a rapid rise of the internal temperatures of the battery.

As the internal battery temperature nears 120°C–130°C the separator finally melts allowing the anode and cathode electrodes to make contact and cause an internal short circuit and generating more heat, and so on and so on. This is Thermal Runaway .

The casing of the battery continues to retain the heat until it can’t contain it any longer. Then the cells rupture & vent the flammable hydrocarbon gases and hydrofluorocarbon electrolytes at this point add the introduction of a spark, or burnt live cable, which ignites the electrolyte and the gases burst into flame, Now you have a fire.

Unless this is controlled immediately, the fire will spread from Battery to Battery. Worst case potentially leading to an explosion.

The gases realised by Thermal Runaway are TOXIC.

Get professional help immediately – Call the Fire Service.

In extremely rare instances it can occur within NEW batteries, although this is exceptionally rare. Still it can happen.

These dangers are REAL.

• Acid leaking from batteries – harmful to the skin
• Toxic gases – harmful to breathe
• Fire – destructive to the building and life

Thermal runaway mostly occurs in old and badly maintained batteries. Although we advise that ALL batteries are regular checked for appearance and heat. Thermal Imaging is advised.

Effects of thermal runaway to a UPS System

How To Prevent Thermal Runaway

Basic environmental conditions will prevent 99.9% of the RISK

To be SAFE implementation of the following advice will eliminate risks :-

• Ensure Free Flowing ventilation
• Environment ambient temperature range between18-22C Max
• Eliminate the risk of exceptional LOW temperatures to very HIGH temperatures. Keep the space at no more than 22C consistently.
• NO Dust in the environment.
• NO Water intrusion in the environment.
• NEVER overload the manufacturers capacity of the batteries.
• NEVER repeatedly deplete the battery and re-charge to maximum
• ALWAYS Replace the batteries WITHIN the design life period.
• NEVER continue to use the batteries AFTER there design period
• REPLACE any faulty battery immediately.
• Failure to replace will cause the next battery to over-charge. Risk
• When you see a battery swollen, replace all the batteries.

Regular service and preventive maintenance is a necessity

Call POWERCONTINUITY on 0845 055 8455

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