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Accident Report Detail

Preliminary Report: Pipeline: Gas Explosion Destroyed Minnehaha Academy

Executive Summary

The information in this report is preliminary and will be either supplemented or corrected during the course of the investigation.

On August 2, 2017, at 10:22 a.m., a building at the Minnehaha Academy (North Campus) in Minneapolis, Minnesota, was destroyed by a natural gas explosion. (See figure 1.) As a result of the explosion, two individuals were killed and nine were injured. At the time of the explosion, two workers were installing new piping to support the relocation of gas meters from the basement of the building to the outside. Two new meters mounted on a wall were ready for the new 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 mitigate the release of the gas, so they evacuated the area.

 Aerial view of Minnehaha Academy that shows the campus. 
Figure 1. Aerial view of Minnehaha Academy; yellow arrow indicates area of explosion.
(Photo courtesy of


A school maintenance worker heard and smelled the natural gas release and went to its source in the basement meter room where the workers had been. As he exited the basement, he made an announcement over his hand-held radio that there was gas in the building and to evacuate immediately. As he made his radio announcement, he ran up the stairs and searched for occupants. Less than 1 minute later, the building exploded. (See figure 2.)

Picture shows the destroyed building with debris scattered over the grass. 
Figure 2. View of damage. (Photo courtesy of the Minnesota Deputy Fire Marshal's office)

Minnehaha Academy, established in 1913, is a private school that includes preschool through 12th grade. The academy has two campuses: (1) the South Campus for preschool through 8th graders, and (2) the North Campus for 9th through 12th graders. The academy has about ninety faculty and an enrollment of over 800 students. At the time of the explosion, the academy was in recess for summer vacation; however, activities were ongoing with a small number of individuals.

Parties to the investigation include the Minnesota Emergency Management Services, the Minneapolis Fire Department, the Minneapolis Police Department, CenterPoint Energy, the Minnesota Office of Pipeline Safety, the Pipeline and Hazardous Materials Safety Administration, and Master Mechanical.

Probable Cause

The information in this report is preliminary and will be either supplemented or corrected during the course of the investigation.

Accident Location: Minneapolis , MN USA  
Accident Date: 8/2/2017
Accident ID: DCA17MP007

Date Adopted: 8/21/2017
NTSB Number:  
NTIS Number:  

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