Michigan fire services say their initial damage assessment of last week’s explosion at General Motors’ alternative energy test chamber could see the bill top US$3m.

Chemical gases from battery cells at the Warren plant reached an unknown ignition source, combusting gases and causing an explosion with several staff hurt, one of whom remains in hospital with head injuries.

“Our initial report is US$3m in total – US$2m to equipment and US$1m to buildings,” fire commissioner, Wilburt ‘Skip’ McAdams told just-auto from his Warren headquarters.

“General Motors is self-insured – they are working to determine content cost now. After the structural engineers have completed their reports and make their estimates for repairs, we will have a better knowledge. That is being done by GM officials themselves.”

Around 80 staff were hurriedly forced to evacuate GM’s energy facility with the remaining injured allowed to leave hospital with “bumping and bruising” caused by rapidly exiting the plant, which was subjecting an experimental battery to extreme testing.

The fire commissioner said the remaining hurt employee in hospital had a laceration to the back of his head, as well as several other injuries and he would be talked to this week to understand what happened in the accident.

“We need to find out exactly what he knows,” said McAdams. “Where he was found was not in direct proximity to the blast site itself. We don’t know if he walked away and we would like to find that out.

“We continue to work with GM officials to try and determine what was the ignition source and how this facility will be improved so this does not happen again.”

McAdams noted the US$3m figure could be revised downwards.

GM insists the explosion was not linked to the Chevrolet Volt or any other vehicle.