4 months later, investigators still looking for cause in APS battery facility explosion

PHOENIX (FOX 10) - It's been nearly four months since four Peoria firefighters were seriously hurt in an explosion at a solar batter facility in Surprise.

In April, members of Peoria's HAZMAT team responded to a fire at the APS battery facility that is known as the McMicken Site. Believing it was safe to enter, they opened the door, and an explosion blew them nearly 50 feet (ca. 15 m) away.

Since then, all four are out of the hospital and going through rehabilitation, but the cause of the explosion is still unknown.

The concept of a battery facility to store solar power for electricity is fairly new, and there isn't a precedent for this type of incident. What APS engineers and investigators are doing is discharging the energy out of all the lithium-ion modules, and then take apart each of them to inspect the insides of the units, looking for what caused the explosion.

APS officials have released video that shows the process of the disassembly. One by one, each battery module is disassembled, brought to a discharge station, and then moved to a location where they will be inspected. Lithium batteries are made of hazardous liquids, and in a lab, they're handled in airless glove boxes.

Engineering researchers at Arizona State University (ASU) are trying to come up with a lithium battery that uses solids, instead of liquids. When a lithium-ion battery overheats or is damaged, several reactions happen. The battery melts, then the liquid electrolytes in one side decompose, releasing a flammable gas.

"The gas is hydrocarbon gas like we use for the burner," said Hanqing Jiang, a battery expert at ASU's Engineering Research Center.

When the other side of the battery breaks down...

"It generates oxygen, and the flammable gas mixed together causes an explosion," said Jiang.

APS officials say there was a total of 378 battery modules in the McMicken Site, and each had its own fire suppression system.

APS is posting periodic updates on the investigation on its website, as they want to share what they're learning with the industry and first responders.

As for the injured firefighters, it is not known when, or even if, they will return to work.