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Contracted workers lacked crucial training and were unauthorized to carry out some of the tasks while moving a natural gas meter just before they set off the earthshaking blast at Minnehaha Academy in 2017 that killed two people and injured several others, according to newly released federal findings.

Along with its scrutiny of the work crew’s credentials to do the work, the agency also pointed out secondary shortcomings by CenterPoint Energy in connection with the explosion, which occurred as the natural gas supplier and Eagan-based Master Mechanical Inc. (MMI) collaborated in moving meters from inside to outside the Upper Campus building on Aug. 2. School was out of session but 36 staff members and six students were present.

Nine people were wounded, and part-time custodian John F. Carlson, 82, and receptionist Ruth Berg, 47, were killed.

Instruction at the private school’s 104-year-old building was relocated as demolition and rebuilding took place. Classes resumed at the campus in August.

The findings released Monday by the National Transportation Safety Board (NTSB) noted that the two-person crew’s foreman lacked the proper licensing and training “to work on the covered tasks” associated with moving the utility’s meters.

The “contract helper,” the foreman’s son, lacked any training for pipe fitter work, failed to complete the required CenterPoint Energy qualifications program and had just roughly eight months’ tenure with MMI at the time of the blast, the NTSB added.

“The probable cause of the natural gas explosion … occurred when a pipe fitting crew disassembled piping upstream of a gas service meter” that was off-limits to the workers, the agency concluded.

Specifically, the MMI workers were not qualified or authorized to demolish piping or work on an existing meter, the NTSB said. It was during that work that a valve was opened, leading to the uncontrolled release of gas and the subsequent explosion.

The NTSB said it could not determine how “a full-flow natural gas line at pressure was opened” while the piping was being removed. The flow continued for nearly an hour from the moment of the late-morning blast until CenterPoint personnel closed the valve, which was under debris.

The agency also pointed out that CenterPoint and MMI failed to have “detailed documentation that clearly established the scope of the work to be done,” and that the lack of such specificity contributed to the explosion.

That missing information included formal CenterPoint illustrations that “should have been provided to MMI and communicated in person prior to the start of the work,” according to an NTSB statement provided to the Star Tribune late Tuesday afternoon. “MMI proceeded without this formal exchange of information.”

The only CenterPoint employee in the vicinity at the time was a block away in a company vehicle and waiting for a construction vehicle heading to the work site, the NTSB found.

CenterPoint declined Tuesday to say whether it agreed with any or all of the NTSB’s findings. Instead, it released a statement that included changes to its procedures including that it now sends a letter each year to contractors “to remind them of the dividing line” that prevents them from working on CenterPoint’s equipment.

Other changes included reviewing procedures for relocating meters from inside to outside, project documentation, training and how it communicates with contractors. CenterPoint also said it no longer uses MMI as a contractor.

In a statement Tuesday, MMI stopped short of endorsing the NTSB’s conclusions: “We appreciate the thorough investigation conducted by the National Transportation Safety Board and respect the findings contained in the board’s final report.”

MMI spokesman Bob McNaney said company leadership would not answer any questions about the NTSB report, including whether it agreed with the agency’s conclusions and whether either member of the crew doing the gas meter work at the school are still employees.

In July, lawsuits alleging negligence were filed in Hennepin County District Court against the utility and the contractor by several victims of the explosion.

CenterPoint said Tuesday it reached a confidential agreement with assistant boys soccer coach Bryan Duffey, the most seriously injured among the survivors. The remaining cases against CenterPoint are pending.

MMI on Tuesday declined to address the status of any legal actions taken by the injured victims or families of those killed.

Last year, Berg’s survivors settled a lawsuit with MMI and CenterPoint. No lawsuits have been filed by Carlson’s family.

Paul Walsh • 612-673-4482