(KMSP) - The Minnehaha Academy incident is not the first major gas explosion in Minnesota, and it likely won't be the last.
More than 177 million Americans use natural gas in their homes, according to the American Gas Association.
In Minnesota, in the last 20 years, most natural gas explosions have been caused by some kind of human error, but several high profile cases also remain unsolved.
Natural gas explosions occur roughly every other day in the U.S. and Minnesota has had some memorable ones.
Twenty-four years ago in St. Paul, a corner grocery store was destroyed and three people killed, when a crew struck a gas line at 3rd Street East and Maria Ave.
It was a similar story in St. Cloud 19 years ago, when a utility crew struck a gas line, killing four people.
Sometimes the cause is aging infrastructure, like it was six years ago when a fireball erupted in front of a Cub Foods at W 60th Street and Nicollet Avenue. A leaking water pipe caused the ground underneath a gas pipeline to washout, the pipeline bent and the couplings failed.
But some cases remain a mystery. Three years ago, a New Year's explosion in a Cedar-Riverside apartment killed three people. Investigators still don't know the source of the gas leak, much less the ignition that set off the explosion.
Once a crime has been ruled out, and investigators can't find the cause, it's often left to insurance companies and years of litigation.
In Minnesota there have been 66 gas pipeline incidents in the last 20 years, with seven fatalities, 13 injuries, and $16,048,851 in damages, according to the Minnesota Office of Pipeline Safety.
Natural gas is mostly methane, which is 30 times more potent than carbon dioxide. Odorless and colorless, it becomes potentially explosive at a concentration between five and 15 percent.
The rotten egg smell was added to natural gas 80 years ago after a school explosion in New London, Texas killed 295 people. It remains the deadliest school disaster in U.S. history, serving yet another reminder of how much worse the disaster at Minnehaha Academy could have been.