Our chemistry teacher caused an explosion at school, by putting a piece of yellow phosphorous into red fuming nitric acid. He should have used red phosphorous, which just produces clouds of nitric oxide and is perfectly safe. Lots of the kids in the two front rows of the class got splashed with the acid and had to go to the hospital next door with acid burns, and had holes burnt in their clothing. Luckily, no one got it in their eyes. The school had to pay for new clothes.