First, the number of people injured has climbed to five, with one taken to the hospital and four treated at the scene. The local deputy fire chief said none of the injuries were life-threatening. The fire department also told the local mayor that it was fumes from hydrogen sulfide that caused the explosion, but GM declined to comment on that aspect. We learned yesterday that a battery under "extreme testing" caused the explosion.
According to The Detroit News' David Shepardson on Twitter, "Chemical gases from the battery cells were released and ignited in the enclosed chamber. The battery itself was intact" and, "All areas of the Alternative Energy Center except for the battery lab and adjacent offices will operate normally on Thursday."
Unnamed sources have told the media that it was a prototype battery pack made by A123 that caused the fire. Fox News says that pack was being tested for use in the Chevy Spark EV and other all-electric vehicles. Batteries made by A123 were recently involved in a $55 million replacement effort in the Fisker Karma.