How CLOU’s battery system burned for 59 hours without spreading fire
Iain Hoey
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CLOU reports fire test for Aqua C2.5 battery system in North America
CLOU has announced the results of a 59-hour fire test on its Aqua C2.5 battery energy storage system, carried out at a CSA-accredited test site in April 2025.
According to CLOU, the test simulated a large-scale fire in a 20MWh deployment to assess thermal runaway containment and explosion prevention mechanisms.
The company said the evaluation was performed using four 5MWh containers configured side by side to mimic actual high-density energy storage layouts.
The ignition container burned for over 59 hours with temperatures exceeding 1300°C.
No fire suppression systems were triggered during the test, enabling analysis of how CLOU’s Active Ventilation & Explosion-Proof System prevented the spread of fire to adjacent units.
System withstood prolonged high temperatures without thermal propagation
CLOU stated that the test configuration placed the Aqua C2.5 containers in back-to-back and side-by-side arrangements.
The ignition unit, labelled Container A, was exposed to extreme conditions while the other three units were monitored for signs of thermal propagation.
The manufacturer said the internal temperature of Container A exceeded 1300°C and sustained combustion for 59 hours and 10 minutes.
It reported that adjacent containers did not experience thermal deformation or battery damage.
According to CLOU, this result demonstrated the ability of the ventilation system to direct flames vertically, preventing lateral heat spread.
Thermal sensors in the adjacent containers recorded no temperatures high enough to trigger runaway events.
Design features based on NFPA and CSA standards
CLOU said the safety system design is based on North American energy storage standards, including NFPA 69, NFPA 68, NFPA 855, and CSA/ANSI C800.
According to the company, explosion prevention is handled by active ventilation triggered at 10 percent of the lower explosive limit (LEL), reducing gas levels below 25 percent LEL.
It said the Aqua C2.5 is also equipped with pressure relief structures and fixed-angle louvers, which direct gas and flame discharge vertically during a blast.
This design is intended to prevent the ignition of adjacent containers, even in high-density deployment.
The test also aligned with CSA/ANSI C800 criteria, which call for full-scale validation of thermal runaway and containment effectiveness.
Multi-layered detection and suppression system
The company explained that the fire safety architecture begins with the battery management system monitoring real-time voltage and temperature.
It said the BMS triggers early-stage alarms and disconnects charge-discharge circuits to prevent thermal propagation.
If temperatures continue to rise, gas detectors activate forced ventilation to lower explosive gas levels.
At a secondary threshold, a water-based suppression system is deployed to cool overheated components and reduce reignition risk.
According to CLOU, this coordination between ventilation and suppression supports continuous removal of flammable gases during incidents.
Fire test included deflagration and explosion venting validation
CLOU reported that the fire test also evaluated the performance of structural venting under extreme conditions.
It said the five natural exhaust louvers served as flame outlets and pressure relief mechanisms.
According to the test data, flames were vented at a fixed upward angle, limiting the heat exposure to other units in the layout.
The louvers functioned independently of external power supply, activating through thermal pressure when necessary.
CLOU stated that the design ensures explosion prevention even during power loss scenarios.
The test confirmed the louvers’ effectiveness in avoiding flame spread during deflagration.
CLOU completes 59-hour fire test on Aqua C2.5 battery system: Summary
CLOU has published results from a 59-hour fire test on its Aqua C2.5 containerised energy storage system.
The test involved four 5MWh units in a 20MWh layout and was witnessed by CSA Group.
Container A was ignited and burned at over 1300°C for more than 59 hours.
No suppression systems were used during the test.
The fire did not spread to adjacent containers.
Temperatures in other units remained below thermal runaway thresholds.
Flames were vented upwards through fixed louvers to avoid cross-container ignition.
The ventilation system maintained flammable gas concentrations below explosive limits.
The safety system was designed in line with NFPA and CSA/ANSI C800 standards.
The system includes real-time thermal monitoring and automated ventilation and suppression triggers.
Louvers activated passively using thermal pressure in power loss conditions.
Explosion pressure was relieved by structural venting.
The fire test confirmed the system’s containment and venting performance.