Oxygen Masks
One of the most critical features in the oxygen supply system is the breathing mask. An oxygen mask is used for the purpose of delivering oxygen to the user's respiratory system. Oxygen masks are designed for either pressure breathing or continuous flow regulators. The features such as microphones, amplifiers, regulators, or connectors will be determined by the application. All masks include some kind of face seal and an arrangement of valves to direct the flow of inhaled and exhaled gases. The mask provides facial protection from fire and projectiles.

Pressure-Demand Oxygen Mask Assemblies
The pressure-demand oxygen mask is used by air crew members who wear fixed wing helmet assemblies and use oxygen routinely. The pressure-demand oxygen mask is based on the MBU-12/P (Figure 1-36)

 oxygen mask subassembly. The MBU-12/P subassembly features an integral hard shell (polysulphamate) face piece (silicone), flexible silicone hose, and combination inhalation and exhalation valve. Components must be added to or removed from the basic MBU-12/P subassembly to obtain the desired oxygen mask configuration (Figures 1-37 thru 1-43). The versatility of the pressure demand oxygen mask allows it to be worn with chest mounted regulators in tactical jets as well as panel mounted regulators and walkaround bottles. A properly fitted oxygen mask is essential to helmet retention in high speed ejections.

Quick-Don Oxygen Mask
The MBU-10/P Oxygen Mask Assembly (Figures 1-44, 1-45) consists of a hanging suspension holder, a suspension assembly, an oxygen mask assembly, a cable and plug assembly, and a dust cover. The MBU-12/P oxygen mask subassembly is used and is supplied in one size - regular. The Quick-Donning MBU-10/P oxygen mask assembly permits the air crew to breathe gaseous oxygen. The oxygen supply enters the face piece through the valve located at the bottom of the mask. 

Inhaled air passes out through the same valve. The exhalation portion of the valve is constructed so that a pressure of only one millimeter of mercury greater than the inlet pressure being supplied by the regulator will force open the valve and allow exhaled air to flow from the mask. The mask also provides automatic electrical switching from the headset microphone to the oxygen mask microphone. This feature permits the air crewman while wearing the mask to transmit the same as with the headset microphone, without the need to unplug the headset microphone and then plug in the oxygen mask microphone. Currently the MBU-10/P oxygen mask is used on selected C-130 Aircraft.

Sierra Quick-Don Oxygen Mask
The Sierra Quick-Don oxygen mask (Figure 1-46) is designed to provide the proper dilution of oxygen with cabin air to conserve oxygen at lower altitudes. The Sierra Quick-Don mask consists of a spring loaded head harness, face piece, microphone, and oxygen supply hose. The mask has two oxygen settings, NORMAL and 100% OXYGEN. The selector switch is located on the left side of the regulator attached to the mask. A white button located on the front of the regulator allows the crew member to receive additional oxygen under pressure. The Sierra Quick-Don Mask is carried on some C-9, C-12, CT-39 and T-44 aircraft.

Full Face Oxygen and Smoke Mask
The full face oxygen and smoke mask (Figure 1-47) is designed to dispense gaseous oxygen from a demand type regulator to the user. The smoke mask provides oxygen and face protection to air crew members who use oxygen equipment only in rare or emergency situations. The mask also provides protection from smoke, carbon monoxide, or other incapacitating gases. The full face oxygen and smoke mask has a single configuration of the face piece, delivery hose, and MC-3A connector. The mask consists of a molded rubber face piece with microphone cavity. It has five fitting straps, an acrylic plastic lens, and exhalation valve. The delivery hose (K-4 hard hose) is composed of non-stretch, non-kinking, smooth bore, flexible hose with an integral corrosion resistant wire. The hose cover is knitted or braided of tubular polyamide or polyester. The communication cable is molded into the hose with leads extending for attachment for a mask mounted microphone. It also has a connection for attaching to the aircraft communications system. The MC-3A connector is provided for access to the aircraft oxygen system. The full face oxygen and smoke mask is carried on P-3 and C-130 aircraft.