"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. Because of the generic name "canned
air", it was mistakenly believed that the can only contains normal air or contains a less harmful substance such as
nitrous oxide. However, the
gases actually used are denser than air, and
inhaling these toxins can lead to
paralysis, serious injury or death. The usual gases found in canned air are difluoroethane, trifluoroethane, tetrafluoroethane, or butane."
from a chemistry site plus wikipedia