Battery energy storage is the special hazard where conventional fire protection assumptions break down most completely. A lithium-ion cell driven into thermal runaway undergoes exothermic decomposition of its cathode and electrolyte that generates both heat and oxidizing species internally. It does not require ambient oxygen, which means it cannot be extinguished by displacing, diluting, or chemically inhibiting the surrounding atmosphere. Every agent-based suppression strategy is built on doing exactly that.
What can be accomplished is heat removal. A cell in runaway will consume itself regardless, and the question that determines whether the event is a module loss or a facility loss is whether adjacent cells stay below their runaway onset temperature. That is a cooling problem requiring substantial water volume applied for a long duration, which is why NFPA 855 discussions favor water-based approaches despite the electronics present, and why cell spacing, module barriers, and thermal management carry so much of the protective load.
The second and frequently underestimated hazard is the off-gas. Cells in runaway vent electrolyte decomposition products that are flammable, and in an enclosed room those gases accumulate toward an explosible concentration. Ignition then produces a deflagration, a pressure event the room was never built to contain, and one that has caused the most serious injuries in documented energy storage incidents. NFPA 855 requires explosion control for this reason, and its absence is the most common serious deficiency in installations across South Florida.