A respirator assembly e.g. for NBC protection is formed from two separate sub-assemblies. The first sub-assembly comprises a flexible hood (or other suitable headgear), a rigid mounting ring and a peripheral face seal. The second sub-assembly comprise a face plate with lens, oronasal mask and inlet and outlet valves, and is demountably attachable to the ring. The first sub-assembly can be worn on its own with the user breathing ambient air through the front end, the second sub-assembly being added if and when a hazard is encountered. The positioning of the face seal in the first sub-assembly means that a comfortable and reliable fit can be ensured when the sub-assembly is donned prior to a mission, but the user is relieved of the physiological burden of wearing the complete respirator unless and until protection is required.