Oxygen mask
From Wikipedia, the free encyclopedia
An oxygen mask provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover the nose and mouth (oral nasal mask ) or the entire face (full face mask). They may be made of plastic , silicone , or rubber.
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[edit] Medical plastic masks
Plastic masks are used primarily by medical care providers for oxygen therapy as they are disposable and reduce cleaning costs. As they are light in weight they are accepted by many patients whom may feel uncomfortable wearing an oxygen mask. Plastic masks also allow medical care providers to see through the mask to the face of a patient and determine if they are in distress.
[edit] Silicon and rubber masks
Silicon and rubber oxygen masks designed to provide a tight seal without leakage are used by aviators, medical researchers, and hyperbaric chamber or other patients that require administration of 100% oxygen such as carbon monoxide poisoning victims.
[edit] Hoses and tubing / regulators
Hoses or tubing connect an oxygen mask to the oxygen supply. When hose is used it may have a ribbed or corrugated design to prevent twisting and cutting off the oxygen flow. The quantity of oxygen delivered from the storage tank to the oxygen mask is controlled by a valve called a regulator. Some types of oxygen masks have a breathing bag made of plastic or rubber attached to the mask or oxygen supply hose to store a supply of oxygen to allow deep breathing without waste of oxygen with use of simple fixed flow regulators. Valves inside tightly sealed oxygen masks control the flow of oxygen into the mask and exhalation from the mask so that rebreathing of exhalation gas is not possible thus insuring inhalation of 100% oxygen.
[edit] Aviators masks
Three main kinds of oxygen masks are used by pilots and crews who fly at high altitudes.
Continuous flow masks supply (obviously) a continuous flow of oxygen to the mask. The mask is usually equipped with a "rebreather bag" (recognizeable from airline demonstrations), which recycles part of the exhaled air and saves oxygen. This type of mask is used by general aviation aircraft flying above 12'500 feet MSL (up to about 25'000 MSL) and for airline passengers.
"Diluter demand" and "Pressure demand" masks supply oxygen only when the user inhales. They both require an airtight seal between the mask and the user's face (which is why airline pilots cannot wear beards).
With a pressure demand system oxygen can be forced by a pressure breathing regulator into the lungs of aviators using these masks above 32 thousand feet altitude, as standard oxygen regulators cannot provide enough oxygen at this altitude. Inhalation of oxygen from a mask fitted to a pressure breathing regulator is easy but exhalation requires more effort. Aviators are trained on the pressure breathing method in an altitude chamber. Because of their tight sealing, pressure breathing type aviator oxygen masks are often used in hyperbaric oxygen chambers and for oxygen breathing research projects with standard oxygen regulators.
[edit] Aviation passenger oxygen masks
Most commercial aircraft are pressurized at a maximum cabin altitude of 8,000 feet, where it is possible to breathe normally without an oxygen mask. If the cabin altitude reaches 14,000 feet or higher, or a decompression occurs and hypoxia is imminent, compartments containing the oxygen masks will open automatically, either above or in front of the passenger and crew seats, and in the lavatories.
Most oxygen masks have a yellow facial cup with elastic bands for securing the mask to the passenger's face. The mask may also have a concentrator bag that may or may not inflate depending on the cabin altitude. Passenger oxygen masks cannot deliver enough oxygen for sustained periods at high altitudes. This is why the flight crew needs to place the aircraft in a controlled emergency dive to a lower altitude where it is possible to breathe without emergency oxygen. If there is a fire on board the aircraft, masks are not deployed, as the production of oxygen may further fuel the fire.
There are two systems that are typically found on aircraft:
- A gaseous manifold system, which connects all oxygen masks to a central oxygen supply, usually in the cargo hold area. Pulling down on one oxygen mask starts the oxygen supply for that mask only. The entire system can be reset in the cockpit.
- A chemical oxygen generator system connected to all masks in the compartment. Pulling down on one oxygen mask removes the firing pin of the generator, opening the oxygen supply for all the masks in the compartment. Oxygen production cannot be shut off once a mask is pulled, and oxygen productions typically lasts for 12-15 minutes. During the production of oxygen, the generator becomes extremely hot and should not be touched. A burning smell may be noted and cause alarm among passengers, but is otherwise normal.
Aircraft safety cards and in-flight safety demonstrations explain their location and use of oxygen masks.
[edit] Self-contained breathing apparatus (SCBA)
Firefighters and emergency service workers use full face masks that provide breathing air and eye and face protection. These masks are typically attached to a tank carried upon the back of the wearer and are called self contained breathing apparatus (SCBA). Because oxygen breathing is hazardous in areas where fires may be burning, SCBA units are normally filled with compressed breathing air rather then oxygen.
[edit] Specialized masks
Specialized full face masks that supply oxygen or other breathing gases are used by divers and astronauts to remove nitrogen from their bloodstream prior to space walks (EVA) or underwater decompression.
Full face and other tightly sealed oxygen masks are secured upon the face by adjustable headstraps.
