NTSB Pipeline Accident Brief: Natural Gas Explosion at Minnesota Educational Facility

Executive Summary
​On August 2, 2017, at 10:22 a.m., local time, a building on the north campus of the Minnehaha Academy, a private school in Minneapolis, Minnesota, was destroyed by a natural gas explosion. Figure 1 shows an aerial view of the north campus prior to the accident, with a yellow arrow pointing toward the explosion site. Figure 2 is a photograph of the accident site taken after the building explosion, with emergency responders and gas company personnel on scene. At the time of the explosion, two workers were installing piping to support the relocation of gas meters from the basement of the building to the outside. Two new meters mounted on an exterior wall were ready for the piping to be connected. While workers were removing the existing piping, a full-flow natural gas line at pressure was opened. The workers were unable to control the release of the gas; thus, they evacuated the building and warned others to evacuate. The explosion occurred during their evacuation. Two individuals were killed, and nine others were injured.

Probable Cause​
The National Transportation Safety Board determines that the probable cause of the natural gas explosion at the Minnehaha Academy occurred when a pipefitting crew disassembled piping upstream of a gas service meter. Contributing to the accident was the lack of detailed documentation that clearly established the scope of work to be performed.