Recently, HiTHIUM completed the world’s first open-door large-scale fire test of its ∞Power 6.25MWh 4h long-duration energy storage (LDES) system equipped with kiloampere-hour (kAh) battery cells. The test was conducted under the full supervision of representatives from UL Solutions, U.S. Authorities Having Jurisdiction, and Fire Protection Engineers. The test strictly complied with the latest requirements of UL 9540A 2025 and NFPA 855-2026. The test results demonstrate that the high-energy-density 6.25MWh energy storage system, incorporating ultra-large-capacity battery cells, exhibited stable and controllable safety performance under extreme conditions. This marks a critical breakthrough in safety validation at higher energy levels for LDES systems, further strengthening the safety foundation for large-scale industry deployment.
Open-door Large-scale Fire Test
Extreme Real-World Scenarios: Confronting Safety Limits at Higher Energy Levels
Building on its previous open-door fire test of a 5MWh system, HiTHIUM conducted an upgraded validation focusing on the ∞Power 6.25MWh LDES system and its core ∞Cell 1175Ah, verifying system-level safety at significantly higher energy levels. The test was conducted under the most stringent conditions: the container doors remained fully open throughout the test creating an “open-door combustion” condition to maximize oxygen supply and flame impact; adjacent containers were arranged back-to-back and side-by-side with only 15 cm spacing; the system operated at 100% state of charge; and all active fire suppression systems were disabled, relying solely on intrinsic safety design.
Fire test site
Three Core Safety Challenges: Comprehensive Validation of a Multi-Layer Protection System
To address the compounded risks introduced by ultra-large-capacity cells and high-energy-density systems, HiTHIUM implemented a multi-layer safety architecture spanning the cell, module, and system levels. Guided by the core technical approach of “release, protection, and resistance,” the test validated the three core safety challenges.
● Release Without Explosion: Precise Management of Ultra-High Energy Release
To manage the massive energy release during thermal runaway of 1175Ah cells, HiTHIUM designed a three-dimensional airflow channel with directional venting, and the module adopted a dual pressure relief valve safety design. This structure enabled rapid and controlled gas release at the cell and module levels, preventing explosive pressure buildup. No explosions or debris ejection were observed during the test.
● Combustion Without Propagation: Dual Physical Barriers Against Thermal Spread
Under the most severe conditions of open-door combustion and minimal spacing conditions, the system endured direct flame exposure and intense heat transfer. Fire-resistant module covers, reinforced steel enclosures, and insulated multi-layer container structures confined the fire to a single battery system with no thermal propagation across the containers, and temperatures of cells in adjacent containers remained below safety thresholds.
● Resistance Without Structural Failure: Structural Stability Under Extreme Thermal StressTo withstand prolonged high-temperature exposure, the ∞Power 6.25MWh system was structurally reinforced with a high-strength steel frame, stiffeners, and dual-layer partitions. After continuous combustion, the affected container remained structurally intact, with no significant deformation or collapse observed.
The main structure remained intact after fire test
A Milestone Achievement: Redefining Safety Standards for LDES
This test systematically verified the overall safety performance of the ∞Power 6.25MWh LDES system equipped with kAh battery cells, representing a milestone within the global energy storage safety validation framework. As system capacity continues to increase from 5MWh to 6.25MWh, HiTHIUM remains committed to advancing safety and reliability through rigorous design standards and extreme-condition testing. Looking ahead, HiTHIUM will remain focused on LDES as a strategic priority, further strengthening its safety foundation and core technologies. By participating in the development of global energy storage safety frameworks to higher standards, and working closely with industry partners, HiTHIUM aims to drive LDES toward larger scale, higher reliability, and safer, more efficient deployment —supporting a steady and sustainable global energy transition.
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