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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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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 who 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.
Silicone and rubber oxygen masks designed to provide a tight fit 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.
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 tight fitting 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.
Three main kinds of oxygen masks are used by pilots and crews who fly at high altitudes.
Continuous flow masks supply 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).
Diluter demand oxygen masks supply oxygen on demand. As the user inhales a demand oxygen regulator opens a valve and supplies the amount of oxygen required for the altitude. As the altitude increases the amount of oxygen delivered by the regulator also increases to 100 percent oxygen. Duliter demand oxygen mask systems are used up to 32 thousand feet altitude.
With a pressure demand system, 100 percent oxygen can be forced by a pressure demand regulator into the lungs of aviators using these masks above 32 thousand feet altitude, as continuous flow or diluter demand oxygen regulators cannot provide enough oxygen at this altitude even though they may supply 100 percent oxygen. Inhalation of oxygen from a mask fitted to a pressure demand regulator is easy but exhalation requires more effort. Aviators are trained on the pressure demand breathing method in an altitude chamber. Because of their tight fit, pressure demand type aviator oxygen masks are often used in hyperbaric oxygen chambers and for oxygen breathing research projects with standard oxygen regulators.
Most commercial aircraft are fitted with oxygen masks for use in emergencies where the cabin pressurisation system is faulty, or where a problem has resulted in sudden decompression. In general, commercial aircraft are pressurized at a maximum cabin altitude equivalent to about 8,000 feet, where it is possible to breathe normally without an oxygen mask. If the oxygen pressure in the cabin drops below a safe level, risking hypoxia, compartments containing the oxygen masks will open automatically, either above or in front of the passenger and crew seats, and in the lavatories.
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 than oxygen.
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.
Medical oxygen masks are held in place by medical personnel or the user by hand, or they may be fitted with a light weight elastic headband so the mask can be removed quickly. Full face masks are secured by head strap harnesses with several straps that create a web around the head.. Tight fitting oxygen masks are secured upon the face by the 4 point head strap system with two head straps securing the mask at 4 places upon the mask to the face. Aviators pressure breathing oxygen masks are often equipped with "quick don" head harnesses that allow pilots and crews flying in pressurized aircraft to rapidly don their oxygen masks in an emergency. Military aviators oxygen masks are secured to flight helments by quick release retention methods.