There is NO air at all in there, there is only the gas, which is self-propelling in most cans. Its highly dangerous as it is a bit like Monoxide, if you inhale enough, it will replace your oxygen and you can't oxygenate your blood, so *bump*...
Usually its an ethane, like Difluoroethane
Haha, I just read that Diflouro can actually catch fire... FROM STATIC! How muppety is that, apparently they use Triflouro mostly these days, especially if it says "static safe" on the can. Most have bittering agents added, and are Triflo so they are safe for use on electrical equipment, but both are still asphyxiants, and while its unlikely you'll die in a large volume of air (its heavier than air), you could possibly die (several reported cases in the states where muppets have used it to get a high from oxygen starvation) if you inhaled it directly from the can.
Also, apparently, don't shake, as its compressed at a LOW PSI, so it will mix the air and gas and defeat the purpose of it, and therefore spray more liquid than gas, wasting it. Store below 25 degrees C and it'll last longer too.