HiTHIUM has successfully conducted the world’s first open-door large-scale fire test on its ∞Power 6.25MWh 4-hour long-duration energy storage (LDES) system, which utilizes kiloampere-hour (kAh) battery cells. The test was carried out under the full oversight of representatives from UL Solutions, U.S. Authorities Having Jurisdiction, and Fire Protection Engineers, in strict compliance with the latest UL 9540A 2025 and NFPA 855-2026 standards.

The results confirm that the high-energy-density 6.25MWh system, equipped with ultra-large-capacity cells, delivers stable and controllable safety performance under extreme conditions. This achievement marks a critical breakthrough in safety validation for LDES systems at higher energy levels, reinforcing the safety groundwork required for widespread industry deployment.

Extreme Real-World Scenarios: Testing Safety Limits at Elevated Energy Levels

Following its earlier open-door fire test on a 5MWh system, HiTHIUM progressed to validate the upgraded ∞Power 6.25MWh LDES system and its core ∞Cell 1175Ah, assessing system-level safety at substantially higher energy concentrations.

The test was designed under exceptionally severe conditions: container doors remained fully open throughout to simulate “open-door combustion,” maximizing oxygen supply and flame exposure; adjacent containers were placed back-to-back and side-by-side with only 15 cm spacing; the system was tested at 100% state of charge; and all active fire suppression systems were disabled, relying entirely on the system’s inherent safety design.

Three Core Safety Challenges: Validating a Multi-Layer Protection System

To mitigate risks associated with ultra-large-capacity cells and high-energy-density systems, HiTHIUM employs a multi-tier safety architecture spanning cell, module, and system levels. Guided by the principle of “release, protection, and resistance,” the test addressed three fundamental safety challenges:

● Release Without Explosion: Controlled Management of Ultra-High Energy Discharge

To manage the substantial energy release during thermal runaway of the 1175Ah cells, HiTHIUM implemented a three-dimensional airflow channel with directional venting, along with a dual pressure relief valve design at the module level. This allowed rapid yet controlled gas release, preventing explosive pressure buildup. No explosions or debris ejection occurred during the test.

● Combustion Without Propagation: Dual Physical Barriers Against Heat Transfer

Even under severe open-door combustion and minimal spacing, the system withstood direct flames and intense heat transfer. Fire-resistant module covers, reinforced steel enclosures, and insulated multi-layer container structures contained the fire within a single battery system. No thermal propagation was observed between containers, and temperatures in adjacent units stayed within safe limits.

● Resistance Without Structural Failure: Maintaining Integrity Under Extreme Heat

The ∞Power 6.25MWh system incorporates a high-strength steel frame, stiffeners, and dual-layer partitions to endure prolonged high-temperature exposure. Following continuous combustion, the affected container remained structurally intact, with no significant deformation or collapse.

A Milestone Achievement: Raising the Bar for LDES Safety Standards

This test comprehensively validates the overall safety of the ∞Power 6.25MWh LDES system with kAh cells, representing a milestone within the global energy storage safety framework.

As system capacities grow from 5MWh to 6.25MWh and beyond, HiTHIUM continues to prioritize safety and reliability through rigorous design standards and extreme-condition testing.

Moving forward, HiTHIUM will maintain its strategic focus on LDES, further advancing safety foundations and core technologies. By contributing to higher global safety standards and collaborating closely with industry partners, HiTHIUM aims to accelerate the deployment of LDES systems that are larger in scale, more reliable, and safer—supporting a steady and sustainable global energy transition.