HiTHIUM Completes World's First Open-Door Large-Scale Fire Test of a 6.25MWh BESS with kAh Battery Cells

HiTHIUM recently completed the world’s first open-door, large-scale fire test of its ∞Power 6.25MWh four-hour long-duration energy storage (LDES) system equipped with kiloampere-hour (kAh) battery cells. The test was conducted under the full supervision of UL Solutions, U.S. Authorities Having Jurisdiction, and fire protection engineers, and complied with the latest UL 9540A (2025) and NFPA 855 (2026) requirements.

The results showed that the high-energy-density 6.25MWh system, incorporating ultra-large-capacity battery cells, delivered stable and controllable safety performance under extreme conditions. The milestone represents a major step forward in safety validation at higher energy levels and strengthens the foundation for large-scale LDES deployment.

Extreme real-world scenario testing

Building on its previous open-door fire test of a 5MWh system, HiTHIUM carried out an upgraded validation focused on the ∞Power 6.25MWh LDES system and its core ∞Cell 1175Ah, verifying system-level safety at significantly higher energy levels.

The test was performed under highly stringent conditions:

• Container doors remained fully open throughout the test, creating an “open-door combustion” scenario to maximise 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.

• All active fire suppression systems were disabled, relying solely on intrinsic safety design.

Validating three core safety challenges

To address the compounded risks associated with ultra-large cells and high-energy-density systems, HiTHIUM implemented a multi-layer safety architecture spanning cell, module, and system levels, based on the technical approach of “release, protection and resistance.”

Release without explosion

To manage the energy release during thermal runaway of 1175Ah cells, the system incorporates a three-dimensional airflow channel with directional venting and a dual pressure-relief valve module design. This enabled rapid and controlled gas release, preventing explosive pressure build-up. No explosions or debris ejection were observed during testing.

Combustion without propagation

Despite open-door combustion and minimal spacing, fire-resistant module covers, reinforced steel enclosures and insulated multi-layer container structures confined the fire to a single battery system. No thermal propagation occurred between containers, and cell temperatures in adjacent containers remained below safety thresholds.

Resistance without structural failure

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

Advancing safety standards for LDES

The test marks a milestone in global energy storage safety validation, systematically confirming the safety performance of a 6.25MWh LDES system equipped with kAh battery cells.

As system capacity scales from 5MWh to 6.25MWh and beyond, HiTHIUM says it will continue advancing safety and reliability through rigorous design and extreme-condition testing. The company aims to support the development of higher global safety standards and accelerate the safe, reliable deployment of large-scale LDES systems to support the global energy transition.