The students were working close to an empty 55-gallon drum that contained oil residue. There was a vapour around the drum which ignited, causing the loud explosion.....SOMEONE IS IN BIG TROUBLE for leaving it there.
http://www.cp24.com/servlet/an/local/CTVNews/20110526/110526_school_explosion/20110526/?hub=CP24Home
http://www.cp24.com/servlet/an/local/CTVNews/20110526/110526_school_explosion/20110526/?hub=CP24Home