The NFPA Journal sounded the alarm in a February 2026 investigation: lithium-ion batteries, now the preferred UPS chemistry for new data center builds, bring fire hazards that are fundamentally different from traditional lead-acid systems. Thermal runaway in lithium-ion cells is not a slow process — temperatures can spike to over 1,000°C in seconds, producing intense heat, flammable gases, and self-sustaining chemical reactions that can propagate from cell to cell.
Perhaps most concerning, lithium-ion batteries can retain significant stored energy even after visible flames have been extinguished. Documented incidents have shown re-ignition occurring hours after an initial event appeared to be under control. Traditional fire suppression systems designed for electrical fires may not be effective against these failure modes.
New Standards Acknowledge the Problem
The safety standards community is catching up. ISO 3941:2026 introduced Class L, a new fire classification dedicated specifically to lithium-ion battery fires, formally recognizing that these failures behave differently from any previously categorized fire type. New system-level fire testing requirements mandate that no flames escape containment during maximum temperature events and that external temperatures remain below the ignition point of nearby materials.
Additionally, UL1973-listed batteries are now required to undergo UL9540A testing, which evaluates thermal runaway propagation at the cell, module, and system level. These standards represent significant progress, but compliance across the global supply chain remains inconsistent.
What Operators Should Be Doing Now
Lithium Iron Phosphate (LFP) chemistry offers a meaningfully higher thermal runaway threshold (195°C) compared to NMC/NCA chemistries (170°C), making it the preferred choice for safety-conscious operators. But chemistry selection alone is insufficient. Active Battery Management Systems with real-time thermal monitoring, appropriate fire suppression rated for lithium-ion events, and cell-level isolation architectures are all essential components of a responsible deployment.
For facility operators who have not yet audited their UPS battery infrastructure against these evolving standards, the risk exposure is significant — and growing as battery densities increase alongside the AI workloads they support.