8 of 13Attribution: Universal Studios
The New London School explosion in New London, Texas, on March 18 in 1937, killed 295 students and teachers.
Earlier that year, the school had cancelled their natural gas contract and instead hired plumbers to tap an oil company's gas pipeline, in a practice that was not explicitly organised but generally tolerated, as natural gas extracted with oil was considered waste product and flared off.
It's believed an instructor, Lemmie R Butler, turned on an electric sander, which caused a fatal spark on March 18.