AVIATION Oxygen -- page 2 of 6

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Effects Due to Altitude.

As the total atmospheric pressure decreases with altitude, the available oxygen pressure decreases in proportion, thus necessitating supplemental oxygen. A lack of sufficient oxygen will bring on hypoxia. Symptoms of hypoxia may begin as low as 5,000 feet with decreased night vision. The retina of the eye is affected by even extremely mild hypoxia. At 8,000 feet, forced concentration, fatigue and headache may occur. At 14,000 feet, forgetfulness, incompetence and indifference makes flying without the proper supplemental oxygen quite hazardous. At 17,000 feet, serious handicap and collapse may occur. These effects do not necessarily occur in the same sequence nor to the same extent in all individuals.

A FAA flight surgeon gave me an excellent definition on the term, Hypoxia. He called it "STUPIDITY". What typically happens when experiencing serious hypoxia symptoms, you get too stupid to realize that something is wrong.

For the regular smoker (especially with older people), these effects all occur at much lower altitudes. A person at sea level who regularly smokes a pack of cigarettes a day, may theoretically be at 7,000 feet. If that person were flying at 12,000 feet, the actual altitude experienced could be as much as 19,000 feet. Obviously an altitude requiring the use of oxygen. A person's age drastically effects night vision. A 60 year old has only 1/3 of the night vision of a 20 year old. Of importance, there is very little peripheral vision at night. The see and be seen concept of aircraft collision avoidance is obviously limited during night flying.

It is recommended that if one were to go above 18,000 feet, that person should be on oxygen for at least for 30 minutes prior to going above 18,000 feet. The time on oxygen lets the oxygen and nitrogen levels stabilize properly. Suggest that if you know you are going above 18,000 feet from sea level at the maximum climb rate, then put on the oxygen before takeoff. By the time you get to 18,000 it probably will have taken about 30 minutes.

People Living at High Altitudes.

A normal healthy person who lives at higher altitudes has somewhat adapted to the effects of high altitude. However that person still must have supplemental oxygen above 12,500 feet. The effects of hypoxia may be lesser for that person at 12,500 feet, but the problems are still there. Above 15,000 feet it doesn't make any difference what altitude you live at.

Requirement of More Oxygen for Passengers.

We have many pilots tell us women passengers need oxygen much sooner than they do. We are not talking high altitude either. Typically the problem seems to occur around 9,000 to 10,000 feet. The symptoms for the women passengers are sleepiness and headaches. Several doctors have told us the reason for women to be effected by the beginning symptoms of Hypoxia is caused by a difference in their hemoglobin content in their blood. Of interest, women also experience different conditions in breathing requirements while scuba diving. We have received several orders for oxygen equipment mainly for women passenger use at these low oxygen altitudes. A good rule of thumb is that women normally need oxygen about 2,000 feet sooner than men. Of course there are exceptions.

Another more obvious reason for more oxygen for passengers is due to nervousness of passengers who have had no or little experience flying in light aircraft. When one is nervous, the body is working harder, thus needing more oxygen.

Use of Oxygen in Pressurized Cabins.

Under normal conditions there is no need for supplemental oxygen in an aircraft equipped with a pressurized cockpit. However, there are conditions that can require additional oxygen. Many pressurized aircraft only bring the cabin altitude down to 10,000 feet. We have found that many people have trouble at 10,000 foot altitudes, in this case the equivalent altitude of 10,000 feet. There is a strong possibility that a heavy smoker could have problems with a lack of oxygen when in a pressurized cabin. We have a few customers who have purchased portable systems to provide the additional need for oxygen. Recently we have a customer with a Cessna 340 (pressurized cabin twin) that has been complaining about fatigue while flying at 25,000 feet. To solve his problem he is using the built in emergency constant flow system. The normal duration is not sufficient, but with the Nelson A-3 flow meter and oxygen conserving Oxymizer breathing device, he now has several hours of supplemental oxygen available to assist with his breathing needs.

Safety Considerations Dealing With High Pressure Cylinders.

The use of oxygen in general aviation is quite safe. The use of it is done on a regular basis throughout the world. Reading the manufactures instructions and going by them, as well as the use of common sense, make oxygen use practical. The use of oxygen, no different than the use of the aircraft itself, does have some potential problems. In that light, the following information is important and should be remembered when dealing with oxygen.

Although oxygen is non flammable, materials which burn in air will burn much more vigorously, and at a higher temperature, in oxygen. If ignited some combustibles such as oil, burn in oxygen with explosive violence. Some other materials which do not burn in air will burn vigorously in oxygen-enriched atmospheres.

A hazardous condition does exist if high pressure oxygen equipment becomes contaminated with hydrocarbons such as oil, grease, or other combustible materials which may include oil from the operator's hands or contaminated tools.

Oxygen under pressure presents a hazard in the form of stored energy.

Rapid release of high pressure oxygen through orifices, needle valves etc. in the presence of foreign particles can cause friction or impact resulting in temperatures which may be sufficient to ignite combustible materials and rapidly oxidize metals.

A cylinder will heat as it is filled from a high pressure source, due to the heat of compression generated as gas is forced into the cylinder. The more rapidly the cylinder is filled, the higher temperature rise in the cylinder. Excessive temperature may result in ignition of any combustible materials that are present.

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