SURPRISE, Arizona (NBC) - Eight firefighters are in the hospital after an explosion in Arizona.
It happened at an energy storage facility in a Phoenix suburb Friday night.
Crews were investigating a battery fire at the power substation when the explosion occurred.
Three of the eight injured firefighters were flown to a local burn center while the rest were taken to nearby hospitals.
The condition of the injured firefighters is unknown but their injuries do not appear to be life-threatening.
Right now -- the cause of the explosion is still under investigation.