Abstract: An emergency portable oxygen supply unit for use in assisting a person to breath in an oxygen depleted environment such as that present within a structure during a structural fire. The unit has a face mask affixed to a housing which also supports an air filter and a source of pure oxygen. As the person wearing the air mask inhales, a flapper valve within the housing opens an oxygen valve and allows pure oxygen to be mixed with air which has passed through the air filter thereby providing breathable air.