MINNEAPOLIS - Officials with the National Transportation Safety Board say the explosion at Minnehaha Academy occurred when contractors were moving a gas meter though the full scope of its investigation will likely take a year.

Chairman Christopher Hart said during a press conference Thursday that his crew will spend the next week or so at the school, assessing the damage.

However, he said the scene is very complex.

"The damage was extensive to the building," Hart said. "And we will await a determination from the proper authorities that it is safe because we'll have to go inside the building to really make a determination of what happened."

The NTSB is the agency that is in charge of pipeline accidents. They say they've investigated roughly 20 gas explosions involving commercial buildings in the last five years or so.

He said this investigation, like others, will be extremely exhaustive and detailed, which is why final determinations won't be made for months to come.

Hart said they are looking for witnesses to the explosion to come forward and help with the investigation.

Day one of the investigation included a quick drive-by tour of the scene. Hart said they will hold another press conference on Friday with updates.

An explosion at Minnehaha Academy Wednesday morning killed two people and injured nine others.

In an email from the district, Minnehaha Academy President Donna Harris said Upper School will likely start classes Tuesday, September 5, as "we need more time to effectively plan the school year." Lower and Middle School orientation days and the start day will not change, she added. There will be no change to the Upper School athletic schedule, so fall sports will begin Monday, August 14.

Minneapolis Schools Superintendent Ed Graff says he's reached out to Minnehaha Academy to offer assistance adding Lincoln Community School may a facility that could be used to help in this time of need.