Eos Energy Enterprises (NASDAQ: EOSE) said independent testing of its Z3 battery modules showed no thermal runaway, no sustained fire, and no propagation to adjacent modules under direct flame impingement and overcharge conditions.

Energy Safety Response Group (ESRG), an independent fire testing organization, conducted the tests using methods equivalent to large-scale fire testing as referenced in the 2026 edition of NFPA 855, the standard governing stationary energy storage system installations. The standard now requires large-scale fire testing to confirm that a system failure does not spread between units at specified spacing. Testing also showed no ignition of off-gas.

"The inherent fire safety of our zinc aqueous chemistry has been foundational to Eos from the beginning," said Francis Richey, Eos Chief Technology Officer. "Under direct flame and overcharge, the Z3 modules did not experience thermal runaway, sustain fire, or propagate failure."

Matthew Brown, Chief of the Allegheny County Department of Emergency Services, noted that his department responded to an incident involving overcharged battery modules at Eos' Turtle Creek facility in November 2025. "Even under that real-world stress, the system did not enter thermal runaway or escalate into a fire event," Brown said.

Separately, Eos announced it received ISO 14001 certification, the internationally recognized standard for environmental management systems, following a third-party evaluation. The certification covers Eos' operations and manufacturing facilities.

The Pittsburgh-based company said it is targeting 4 GWh of annual production capacity across its Turtle Creek and Thorn Hill manufacturing facilities.