US safety investigators began a weeklong inquiry on Friday into a fatal explosion at a Christian private school in Minneapolis, including examining whether workers moving a gas meter could have caused the blast.
School receptionist Ruth Berg and janitor John Carlson were killed.
The local medical examiner says the two people who were killed during an explosion at a Minneapolis school died from blunt force injuries sustained when part of a building collapsed.
Minnehaha Academy is a private Christian school in south Minneapolis with about 825 students from preschool through to 12th grade, local newspaper the Star-Tribune reported. The NTSB is investigating because it has jurisdiction over gas pipelines.
Jenny O'Brien, spokeswoman for the state agency, said such violations were considered routine.
The blast pushed part of the building's wall outwards, causing the roof to collapse and pancaking two floors into rubble, according to fire chief John Fruetel. Windows in other areas were blown out and shattered.
A team from the National Transportation Safety Board is on scene to determine what caused the natural gas explosion.
Minneapolis fire department officials told reporters on Wednesday there were early indications that a gas line was ruptured by contractors working on the campus. "We pray for his healing and for the wisdom of the doctors and nurses caring for him at this time", the school said in a statement.
He said another question is whether the contractors should have isolated the natural gas source before proceeding.
"The question is going to be, was it isolated in a way that they were confident they could do the work without the risk of a leak", he said. NTSB member Christopher Hart says investigators are looking into whether the explosion occurred while a gas meter was being moved. In 2014, the company had two paperwork violations related to letting employees know about job hazards.
It was not damaged in Wednesday's blast. Three remained in the hospital Thursday, one in critical condition, according to the Hennepin County Medical Center.
The explosion affected Minnehaha Academy's "upper school", which houses the high school.
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