Canned air isn't air, though it is canned. It's not even filled with a gas you normally find in air. Canned air or gas duster is a product that uses compressed gas to clean surfaces. It's nice for blasting out keyboard chow and dust bunnies in the cooling vents of computers and other electronic devices.

You may have heard about people dying from purposely inhaling canned air, presumably trying to get high off of it. There are two ways you can die from this practice. One is from anoxia or simply not getting enough oxygen. The other is from the toxicity of the gases used in the product. The usual gases found in canned air are difluoroethane, trifluoroethane, tetrafluoroethane, or butane. Butane is an interesting choice because it's flammable, so using canned air to cool hot electronics may not be a wise decision (see my burning bubbles project if you need convincing about potential flammability). Incidentally, burning the fluorocarbons tends to produce extra-nasty chemicals such as hydrofluoric acid and carbonyl fluoride.

My laptop would suffocate and overheat without a little help from canned air every now and then. It's a useful product to have around. Just don't go thinking it's a harmless household chemical, because it's not.