Thermal Runaway Likely Caused Explosion at Ariz. Battery Facility

Eight firefighters were injured in the blast.

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PHOENIX (AP) — A “thermal runaway” likely caused the April 2019 explosion at a battery storage facility west of Phoenix that injured eight Peoria firefighters, according to a new report.

Authorities responded to a report of smoke at the McMicken Energy Storage facility in Surprise and called for more resources after realizing hazardous materials may have been involved.

The facility owned by Arizona Public Service Co. contains a utility-scaled battery to store and distribute solar energy.

The firefighters were evaluating the lithium battery when an explosion hospitalized them with chemical and chemical-inhalation burns.

A report commissioned by APS but conducted by outside experts concludes that the explosion “was actually an extensive cascading thermal runaway event, initiated by an internal cell failure ... caused by an internal cell defect.”

The report said the fire suppression system kicked on like it was supposed to, but it was only designed to handle an ordinary fire.

Experts who investigated the incident said new safety standards better address hazard assessment and training for first responders.