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Effects Due to Altitude

As the total atmospheric pressure decreases with altitude, the available oxygen pressure decreases in proportion. This necessitates 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 or to the same extent in all individuals.

An FAA flight surgeon gave me an excellent definition on the term, Hypoxia. He called it "STUPIDITY". What typically happens when experiencing serious hypoxia symptoms, it that your ability to make quick, rational decisions becomes more difficult because of this "stupidity".

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 this is an altitude that requires the use of oxygen. A person's age will drastically effect 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 30 minutes prior to going above that altitude. The time on oxygen lets the oxygen and nitrogen levels stabilize properly. It is suggested 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

Normal healthy people who live at higher altitudes have somewhat adapted to the effects of high altitude. However these people 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 elevation you live at.

Requirement of More Oxygen for Passengers

We have many pilots tell us women need oxygen much sooner than men do. Typically the problem seems to occur around 9,000 to 10,000 feet. The symptoms for the women 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 the hemoglobin content of the 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) for use at these low oxygen altitudes. A good rule of thumb is that women normally need oxygen about 2,000 feet sooner than men do. Of course there are exceptions.

Another more obvious reason for more oxygen for passengers is due to nervousness of passengers who have had little or no 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. There are however, 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. 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. We had 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 manufactureres 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 higher temperatures 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. This may include oil from the operator's hands, contaminated tools, lubricants, etc.

Oxygen under pressure presents a hazard in the form of stored energy. Rapid release of high-pressure oxygen (through orifices or needle valves) in the presence of foreign particles can cause friction or impact. This can result in temperatures which may be sufficient to ignite combustible materials and rapidly oxidize metals.

A cylinder will become warm as it is filled from a high-pressure source. This is due to the heat generated by compression. The more rapidly the cylinder is filled the higher the cylinder temperature becomes. Excessive heat may result in ignition of any combustible material that is present.