As global BESS deployment accelerates, Fike outlines why layered safety systems must evolve to meet the growing risk of thermal runaway.
It’s no secret that battery energy storage systems (BESS) are becoming a cornerstone of today’s power generation, as they are often required to capture renewable energy from wind and solar, manage peak demand on the grid, and power sustainable microgrids.
The adoption of BESS shows no signs of slowing down; in fact, in 2025 global deployed BESS capacity grew by around 700GWh.
As BESS adoption surges, especially in or near populated areas, the ever-present potential hazard of a lithium battery experiencing thermal runaway must be understood, and appropriate safety systems must be integrated to protect nearby people, first responders and the environment.
Thermal runaway and real world events
By now most people in the industry know the potential dangers of thermal runaway, when a damaged or malfunctioning lithium battery undergoes a chemical reaction that results in uncontrollable exothermic heat generation. ‘Propagating’ or ‘cascading’ thermal runaway then refers to the heat from one battery causing adjacent batteries within the BESS to also experience thermal runaway, which is ultimately where the real danger occurs.
Tom Farrell, principal engineer of test and validation engineering at Fike Corporation, spoke more on these hazards.
“Obviously, these batteries burn. We know they burn. They catch fire when they’ve been abused or when a defective cell begins thermal runaway inside of a module,” Farrell said.
“Early on when we had these fires, the first thought was to treat it like a fire by using Class B sizing and protective methodologies and prove the results with small-scale testing. A lot of organisations offered testing advice based on this kind of approach; however, it hasn’t worked out terribly well because a number of notable events have occurred.”
While the occurrence of thermal runaway is still relatively unlikely, the vast number of deployed BESS makes the threat of these incidents very real, such as the BESS fire at the Moss Landing Power Plant in January 2025, which led to the evacuation of more than 1,000 Californians.
This incident and many others that have occurred recently or in the past (such as the multiple BESS fires in Thuringia, Germany where an employee was injured and toxic fumes and heavy smoke created an environmental hazard) serve as important reminders of why education on these hazards is so important and why appropriate safety systems must not be overlooked.
The Swiss Cheese Model of Safety
To manage these risks, BESS designs should use multiple layers of protection. Instead of relying on a single safeguard, they combine many, so that if one fails, others stand ready. This concept is well illustrated by the Swiss Cheese Model of Safety (Fig 1).
During the process of designing a BESS, the following layers of safeguard should be taken into account:
Prevention
Monitoring of conditions that may cause a short circuit or other external influence to the battery or electronics that may initiate a fire:
- Water or humidity
- External temperature
- Switchgear and inverters
- Dust
- Atmospheric corrosion
- Coolant leakage which is typical for batteries.
Early warning
To prevent further damages, it is important to detect a malfunction that may result in a fire as fast as possible. A BMS (Battery Management System) should be combined with additional detection.
This ensures redundancy, like for instance cell overheat detection which can be carried out with Fibre Optic Linear Heat detection such as Fike DTS. Adding smoke detectors (preferably aspiration) will make it even more robust as we are looking for a different sign of fire.
For early detection of thermal runaway, a hydrogen detector is best used. Based on these alarms, a decision can be made to start early suppression and minimise off-gassing by managing the thermal propagation in the battery.
Thermal propagation management
The only proven method of suppressing BESS fires and cascading thermal runaway is ‘thermal propagation management’. Thermal propagation management systems control the heat of a thermal runaway event and control or even stop cascading thermal runaway.
This can be achieved by a variety of methods:
- Physically through materials used to separate the cells
- Separation
- Fluid injection
The latest development on fluid injection is Fike Blue, an agent that has demonstrated promising results in not only suppressing a fire like a typical fire protection system but also that has the added benefit of stopping cascading thermal runaway by filling the battery module and submerging the affected battery cells and absorbing the heat without breaking down.
The tests with Fike Blue were carried out with both new and second life batteries, with similar results:
- Stopping the progression of thermal runaway by reducing off-gas emissions, but leaving cells energised, making battery disposal more complex and potentially hazardous
- Controlling the cascading which will result in a burn-out battery which is safer to dispose of
Explosion control
NFPA 855 references ‘explosion control’ as an essential element to the overall safety of a BESS. Additionally, UL 9540A requires that any off-gassing resulting from malfunctioning batteries is maintained under 25% of LFL (lower flammability limit) to eliminate the risk of ignition.
To achieve reliable explosion control, the following may be recommended:
- Exhaust ventilation: Ventilation systems are required to periodically purge the environment of any potential off-gassing and ensure LFL is maintained below 25%
- Gas detection: Gas detectors are often used to identify off-gassing between the activation of exhaust vents or a malfunctioning battery in its early stages
- Explosion venting: In scenarios where reliable exhaust ventilation isn’t possible or when an additional layer of safety is preferred, explosion vents may be used to relieve a deflagration’s pressure and flames to a safe location.
Only 11% of BESS fires start at the battery. The majority of them start in adjacent control rooms with high voltage switch gears, HVAC and other electronics.
These fires may reach battery modules and begin the thermal runaway process. While ineffective for thermal runaway, gaseous agents such as SF-1230 (FK-5-1-12), aerosols, and inert gas systems are effective in these applications.
Recommendations
The threat of thermal runaway is real, and BESS deployment is continuously increasing and has shown no signs of slowing down. Therefore, Fike strongly recommends that decision-makers, manufacturers, regulators and buyers take this threat seriously, especially when BESS are installed within or nearby populated locations.
So, try to fully understand the risk, incorporate different protective layers (Swiss cheese) and test the solution.
Fike is just one of several industrial safety solutions providers who can help, and the company is urging everyone in this industry to take the thermal runaway hazard seriously.
