Not sure about air but pure oxygen can kill you.
Yup! Oxygen is a highly toxic and corrosive gas, in high concentrations and pressures. Just the amount of O2 in air can kill a diver who's gone past about 200 feet in depth. And while it's not in itself flamible, it is required for combustion, and will take a glowing ember to a roaring inferno in an instant. Also, oxygen can cause a "flash fire" when it comes in contact with certain petroleum products, or other flammable materials.
On the other hand, it really sucks when you don't have enough of it...