The metered dose inhaler (MDI) was developed in the 1950’s,when the propellant is CFCs (Chlorofluorocarbons). CFCs were found to deplete the ozone layer high above the earth. The Montreal Protocol was enacted worldwide to reduce the amount of CFCs used, to decrease the ozone depletion. CFC’s have been used in many products, including MDIs. Alternative devices have been developed to replace the CFC propellant in MDIs. Dry powder devices .The Hydrofluoroalkane Propellant, short for HFA propellant, also called Hydrofluoroalkane 134a, are replacements for the CFC propellant.