Five people received medical attention after the incident at the GM Technical Center in Warren, Michigan and one person was taken to a local hospital, GM said.
Warren Mayor Jim Fouts said he was told by Warren Fire Department officials that fumes from hydrogen sulfide caused an explosion inside a battery laboratory.
GM said the battery being tested was not for the Chevrolet Volt plug-in electric hybrid. GM said the explosion was related to "extreme testing on a prototype battery." People familiar with the matter said the battery was being developed for future electric vehicles.
Wednesday morning’s incident remains under investigation by GM and Warren officials, a GM statement said.
"Our efforts are focused on the well-being of our employees and we’re happy that they are all accounted for," said GM spokesman Greg Martin. "One required treatment. We are working closely with on-scene authorities to investigate the incident.
"It’s entirely premature to speculate on the cause or characterize the nature of the incident," said Martin.
GM was quick to point out that the Volt and its battery packs were not involved in Wednesday’s incident. The Volt has been highlighted as a centerpiece in GM’s push for more fuel-efficient cars and trucks.
The explosion follows another high-profile battery failure last month when Fisker Automotive’s luxury sedan, the Karma, failed during testing by Consumer Reports. The Karma’s battery, which was produced by A123 Systems, failed due to a manufacturing defect and A123 said it would send replacements.
An A123 spokesman declined to comment on whether the company’s battery was involved in the explosion. He referred questions to a GM spokesman, who also declined to comment.
A123 makes the battery for the upcoming Chevrolet Spark all-electric car, which will debut in 2013.
American consumers have been slow to embrace electric and rechargeable vehicles, in part because of their additional cost. Battery safety concerns could slow their adoption further, although industry analysts said problems are not unusual when trying to develop new technologies.
Last year, U.S. federal regulators opened an investigation into the safety of the Volt’s battery pack after its own tests uncovered fire risks. By January, NHTSA closed its probe without finding any defects and said it was satisfied with GM’s fix to better protect its lithium-ion battery pack.
"Some critics will use this story to bring back to life the investigation into Chevy Volt fires from earlier this year," said Michelle Krebs, auto analyst with Edmunds.com.
"While this incident deserves some scrutiny – especially since workers were hurt – the fact is that this is the reason why new car technology undergoes rigorous testing, to try to ensure that episodes like this don’t happen on the road."
GM suspended Volt and Opel Ampera production, due to weaker demand than anticipated, for five weeks ending April 23. The Opel Ampera, which is basically the same car as the Volt, is sold in Europe.
The company continues to work to adjust Volt production to market demand, GM has said, and its production suspension is not related to quality issues on the Volt or Ampera.
Two years ago, GM said it was nearly doubling the size of its battery labs at the GM Tech Center, to 63,000 square feet. The GM Tech Center is a sprawling campus of office and research buildings and grounds in suburban Detroit.