US Patent 7647927 Self-contained breathing system

A breathing apparatus is operable in self-contained and filtered modes of operation. In the self-contained mode of operation, a breathable gas is delivered to a user from a self-contained source of breathing gas. In a second, filtered mode of operation, a suction source draws ambient air through a filter removing contaminants and delivers filtered ambient air to the user. A method of delivering air to a subject is also provided.