Fortress Power Passes Large-Scale Fire Test – Highest Standard in the Industry

Fortress Power eFlex 5.4 has passed the most stringent fire safety test-large scale fire test – UL 9540(A)

We’re very excited to announce that Fortress Power is now one of a very few Lithium battery manufacturers that passed the UL 9540(A) large-scale fire test. The UL 9540A large fire test is the new test method for evaluating thermal runaway fire propagation in a battery energy storage system (BESS). This test was developed to address safety concerns identified by the building codes and the fire service in the United States.

The current ICC International Fire Code (2018 IFC) allows an individual BESS unit not exceeding 50 kWh and having a maximum quantity of systems totaling 600 kWh of energy per indoor fire area (battery room). The 2018 IFC and the draft NFPA 855 standard for the installation of energy storage systems currently limit the individual BESS unit size for  batteries tested to UL 9540 standards to 250 kWh.

A critical component of the UL 9540A test method is that the abuse of systems continues until system failure.  Typically, heating single or multiple cells at 5C/minute results in thermal runaway. By abusing the smallest repeat unit of the system, the test is understanding the extent to which that failure propagates. While in operation, a battery management system (BMS) would likely detect temperature or voltage anomalies.  UL 9540A test methods assume these systems are non-functional and that cells in the battery pack have reached thermal runaway.  In doing so, it judges the systems’ capability at responding to thermal runaway.  In fact, the battery pack level test is designed around figuring out how to repeatedly force the battery to fail.

If one or multiple Fortress Power battery cells run into thermal runaway, it won’t cause the whole battery pack to catch fire. Fortress Power eFlex 5.4 unit only generates smoke after 4 hours of heating with the cell temperate reaching over 250F (120C). The battery pack stabilizes and the temperate drops back to 95F (35C) in 5 hrs.

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During the whole 14hrs of testing, there was no visible flame/fire observed.   This is all thanks to Fortress Power’s high-quality extruded aluminum battery body design and the tier 1 prismatic lithium iron phosphate module design.   The battery pack design not only gives the product a sleek look but also makes the battery much safer.  Many other battery manufacturers have failed the test due to cobalt-based lithium-ion battery cells and/or poor battery pack architecture design.

Eric Wang, the CTO of Fortress Power comments: “Safety and reliability are our No 1. Priorities in the residential energy storage system. We select best-in-class Lithium iron phosphate battery cells and power electronic components in all our battery systems.  Our digital processor based battery management system (BMS) has an optimized control algorithm to protect the battery cell and prolong its lifespan. In addition, our patented enclosure design achieves 4 times better thermal performance than our competitors.

Our eFlex 5.4 has been tested by nationally recognized testing labs to the full range of UL tests (UL 1973, UL 9540, and UL 9540(A)), which enable a faster and easier permitting process with the local authorities having jurisdiction (AHJ). Our dealers can now install eFlex 5.4 units worry-free, while the end-users can enjoy their lifestyle knowing they are safe during power outages.


Click Here For Testing Video!

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