As Battery Energy Storage System (BESS) adoption continues to increase, their deployment will expand more and more into populated areas. Therefore, understanding the potential hazards within a BESS, and the solutions that are proven to work, are more critical than ever before.
In the event of certain battery conditions like overcharging, overheating or puncturing, or other kinds of abuse factors, an internal short will occur and produce an exhothermic reaction known as “thermal runaway.” Once this process begins, it cannot be stopped, and therefore a chain reaction occurs as the fire spreads to adjacent batteries until the entire BESS is consumed.
Each affected battery cell suddenly generates a large amount of heat and offgas such as hydrogen, hydrogen fluoride and oxygen depending on the battery chemistry. The more batteries that go into thermal runaway, the more flammable offgas produced.
Because of the intense heat generated from these events and fire that may jet from a battery cell, this creates an extremely combustible environment within the enclosure and why NFPA 855 recommends “explosion control” as an essential element to the overall safety of a BESS – especially for installations near residential and commercial areas.
NFPA 855 states that flammable gas concentrations must not exceed 25% of the Lower Flammability Limit (LFL) where gas may accumulate. While traditional fire protection methods cannot ensure this outcome, recommended methods that do reduce the risk of combustion include:
- Exhaust Ventilation – Ventilation systems are often used to periodically purge the environment of any potential offgassing and provide an extra layer of protection to ensure LFL is maintained below 25%.
- Explosion Venting – In scenarios where reliable exhaust ventilation isn’t possible or when protection against the worst-case scenario is necessary, explosion vents may be used to relieve a deflagration’s pressure and flames to a safe location.
- Gas Detection – As an added precaution, gas detectors may be used to identify offgassing between the activation of exhaust vents or the signs of thermal runaway in its very early stages.
“Explosion control in the context of an ESS should include a vent because every battery that goes into thermal runaway generates explosive gas in that atmosphere and it has to go somewhere,” Tom Farrell, Fike Principal Engineer of Test & Validation, said.
“It may be possible to achieve enough ventilation to stay below 25% of the LFL, but in the case of an unpredictable factor such as an electrical failure that may take those systems down, passive explosion venting is still highly recommended in many applications.”
Finally, one other explosion control method is Fike Blue. Fike Blue flows through the BESS during the early stages of thermal runaway, fills the affected battery module and absorbs the heat to ensure the cascading event is stopped.
Numerous internal and third-party tests have proven that applying Fike Blue saves all of the battery cells within the module except for the initial malfunctioning battery and potentially a few of the adjacent cells. Because the spread of thermal runaway is suppressed, the remaining battery cells within the module will be unaffected and therefore will not produce offgas, resulting in a much safer outcome than other scenarios such as letting the module, and potentially the entire BESS, consume itself.
“If you have 1000 cells inside a battery, and you let all those burn, you generate 1000 cells worth of toxic gas that is going into occupied spaces and rendering them unoccupiable for some time,” Farrell said. “If you’re able to suppress it and stop propagating thermal runaway, instead of losing 1000 cells, you may only lose 50, which means that gas can be dispersed and get to levels which are not quite so toxic.”
