MINNEAPOLIS (WCCO) — The National Transportation Safety Board says it is unsafe to get near the basement of Minnehaha Academy where gas work was being done.

The Hennepin County Medical Examiner’s office said Friday receptionist Ruth Berg and custodian John Carlson died from blunt force trauma in Wednesday morning’s explosion.

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Nine other people were injured in the blast. Bryan Duffey, an assistant soccer coach at the school, is still in critical condition at Hennepin County Medical Center.

On-site investigators treaded carefully around the rubble Friday, using caution in the hunt for clues.

Library shelves are visible through a gaping hole, and mangled brick walls are unpredictable.

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The investigation’s initial focus is on the school’s gas meter. It is unclear if or where the gas line would have been shut off.

“We understand that the gas company wants meters to be outside the building for access so that they can read the meters,” said Christopher Hart of the NTSB. “This meter was inside the building.”

A gas meter that was blown onto the pavement outside of the school (credit: CBS)

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Investigators are also interviewing employees of Master Mechanical, the Eagan contractor on site that morning.

“They want to know about the fatigue of the two workers involved, the father and the son involved,” Hart said.

Gov. Mark Dayton asked for patience Friday to allow the experts to do a thorough inquiry.

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“They’re extremely careful as they should be, and they’re extremely thorough as they should be and their, you know, timetable to come to a conclusion on this is entirely their prerogative,” Dayton said.

The NTSB also could not yet explain the significance of the gas meter blown about 50 feet from the rubble.

Because of the difficulty of getting safely into the heart of the school, the on-site team will likely be here longer than the planned five to seven days.

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