In my second year of chemistry at uni we suddenly had to fill in health and safety paperwork before every lab - they explained that during the finals at the end of the previous year an older student had absent mindedly dropped a lump of sodium in the aqueous waste container, which exploded, causing all the different waste containers to break open and start mixing. Thankfully it only destroyed the fume hood, the immediately surrounding benches, and a few thousand pounds worth of glassware, and didn’t get as far as the really expensive equipment.