A look at safety for energy storage systems

Safety issues associated with energy storages systems (ESS) have always been a concern. When accidents occur, in addition to damages caused by fires and explosions, ESS could release toxic substances and chemical hazards consequentially. Personnel could be exposed to electoral hazards and physical dangers during maintenance and emergency repairs.
 

Why fires break out?

ESS fires can be attributed to various reasons that range from climatic factors to maloperation, faulty integration process, and battery management system failure. Battery degradation and thermal runaway are the most discussed. Thermal runaway is the process where energy excessively releases, pushing up temperature, further resulting in short circuit currents. There are four major reasons behind this: battery overcharging and recharging, high external environment temperature, internal-short circuit (ISC), and machine deformation due to material penetration, squeeze, and bending.

Fire accidents are divided into class A, B, C, and D. Class A refers to general fires that can be extinguished with water or by cooling down temperatures. Class B is oil and gas conflagration that should be put out by removing oxygen. Class C means electrical fires that usually happen on connected appliances. Class D fires are those occur from reactive metals and can only be controlled with unique extinguishing agents.

Generally, energy storage fires are classified as Class C fires. However, as the burning of battery case and electrode (Class A), and that of flammable liquid electrolyte (Class B) are also involved, energy storage fires include multiple types . We can also assess risks for fires by looking into fuels, oxidizing agents, the amount of energy that incites the accident.
 

Fire extinguishment

During thermal runaway in an ESS, flammable gases are released from battery systems. These gases are very likely to have chemical reactions when cumulate certain amount and exposed to air, resulting in faster spread of fire and even explosion. For Li-ion batteries, specifically, backdrafts are common during thermal runaway. In that case, water only cools down temperature, rather than effectively douses fires, which can only be put out when chemical reactions end. Firefighters can use thermographic cameras to monitor fires, keeping temperatures checked. Even though the ESS has been disconnected, personnel shall watch out for remaining voltage, in case of electrical shock.  
 

Case study

In April 2019, a fire broke out at McMicken battery energy storage plant in Arizona, U.S. The plant came into operation in 2017, with batteries provided by LG Chem and installed by Fluence Energy. Investigation by DNV-GL attributed the incident to lithium dendrite that induced thermal runaway in the cell of one Li-ion battery. The fire spread to other cells, despite the activation of Novec 1230 clean agent fire suppressant. Massive amount of flammable gases gathered, resulting in the explosion.

The fire was not promptly stopped, for firefighters were never informed of any instant dealing measure in the emergency procedures back then. In light of this, Firefighter Safety Research Institute (FSRI), affiliated with Underwriters Laboratory (UL), suggested the inclusion of “Standard for the Installation of Stationary Energy Storage Systems, NFPA 855” in the firefighter training, in order to prevent another tragedy.
 

Conclusion

To prevent energy storage accidents, it is imperial not only to have comprehensive safety guidelines, but also to train relevant personnel for quick, accurate decision-making and basic protecting measures.

The graph below shows numbers of energy storage accidents around the globe that took place between 2019 and 2021. The amount of accidents has dropped over recent years, thanks to renovating cell technology and system suppliers introducing patented measures for fire prevention, hoping to increase safety factor for their products. When purchasing ESS, those certified by international standards shall be the most preferred, as safety is the first priority.

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