Bag valve mask The face mask size may be independent of the bag size for example, a single pediatricsized bag might be used with different masks for multiple face sizes, or a pediatric mask might be used with an adult bag for patients with small faces. Most types of the device are disposable and therefore single use,.Nonrebreather mask The nonrebreather mask covers both the nose and mouth of the patient and attaches with the use of an elastic cord around the patients head. The NRB has an attached reservoir bag, typically one liter, that connects to an external oxygen tank or bulk oxygen supply system.Dust mask A dust mask is a flexible paper pad held over the nose and mouth by elastic or rubber straps for personal comfort against nontoxic nuisance dusts. They are not intended to provide protection from toxic airborne hazards.Full face diving mask A fullface diving mask is a type of diving mask that seals the whole of the divers face from the water and contains a mouthpiece, demand valve or constant flow gas supply that provides the diver with breathing gas. The full face mask has several functions: it lets the diver see clearly underwater, it provides the divers face with some protection from cold and polluted water and from stings .Pocket mask Design. The pocket mask is a small device that can be carried on ones person. Air is administered to the patient when the emergency responder exhales through a oneway filter valve. Modern pocket masks have either a built in oneway valve or an attachable, disposable filter to protect the emergency responder from the patients potentially.Nonrebreather mask However, as almost all nonrebreathing masks are disposable, and manufactured in one adult size, most from decades of clinical observation do not provide a good seal with an individual patients face, thus permitting the inflow of large amounts of ambient air air follows the path of least resistance , and diluting the oxygen provided.Theatre of ancient Greece Thus, it is believed that the ears were covered by substantial amounts of hair and not the helmetmask itself. The mouth opening was relatively small, preventing the mouth being seen during performances. Vervain and Wiles posit that this small size discourages the idea that the mask functioned as a megaphone, as originally presented in the 1960s.