(This text file has no hard returns. Save it to your local disk and open it in your word processor or WordPad. Save by choosing "File > Save as..." Note the location.) AVIATION OXYGEN Information on the use of supplemental oxygen in general aviation aircraft. by: Jerry Nelson (Edited and updated by Brad D Huguet of Precise Flight) The following information is presented to give the reader an informal overview on the use of oxygen in general aviation aircraft. The use of flow meters in factory supplied built in oxygen systems and the use of portable oxygen systems are the major topics discussed. If the reader still has questions about the use of oxygen in general aviation, please give us a call. We will be glad to answer any of your questions and provide you with assistance as necessary. ABOUT OXYGEN Composition of Oxygen Oxygen includes 21% of the atmosphere at all altitudes. The remaining atmosphere consists of 78% nitrogen and 1% traces of other gases. Oxygen under normal conditions is an odorless, colorless, tasteless, non-combustible gas. It is the most important single element on earth. At each breath we fill our lungs with air. Millions of tiny air sacs (known as "alveoli") in our lungs inflate like tiny balloons. In the minutely thin walls enclosing each sac are microscopic capillaries through which blood is constantly transported, from the lungs to every cell in the body. The blood carries the oxygen extracted from the air in the lungs to every part of the body. Because the body has no way to store oxygen over a long period of time, it leads a breath-to-breath existence. The human body must have oxygen to convert fuel (the carbohydrates, fats, and proteins in our diet) into heat, energy, and life. The conversion of body fuels into life is similar to the process of combustion fuel. Oxygen is consumed, while heat and energy is generated. This process is known as "metabolism". The rate of metabolism, which determines the need for and consumption of oxygen, depends on the degree of physical activity or mental stress of the individual. Not all people require the same amount of oxygen. A man walking at a brisk pace will consume about four times as much oxygen as he will while sitting quietly. Under severe exertion or stress, he could possibly be consuming eight times as much oxygen as resting. There are three kinds of oxygen that are merchandised or sold to users; Aviation, Medical, and Welding. There is an ongoing controversy whether or not there is any difference between the different types. Oxygen gas is produced from the boiling off of liquid oxygen. It would appear that the oxygen is therefore the same. Where we obtain oxygen, all the different types of oxygen are supplied from the same manifold system. Then someone says that medical oxygen has more moisture in it. That is partly true. The oxygen going to a hospital bed is plain oxygen that comes from liquid oxygen. At the bed location, there is a unit on the wall that adds moisture. At this moment we now have medical oxygen. If the oxygen is in a pressure vessel or in a manifold system (like inside a hospital) then it is regular oxygen. The cost of medical or welding oxygen is normally much less than the oxygen you get at an airport. Also of interest, the suppliers of welding oxygen have told us, the purity level required for welding and cutting purposes is more critical than for breathing. The bottom line about the different types of oxygen is in the insurance liability of the oxygen supplier. The gas is the same but the insurance liability is different. The welding gas company may or may not supply you with oxygen for your aircraft. Likewise the medical oxygen supplier may or may not supply you with oxygen for your aircraft. Some of our customers have told us that they can only get medical oxygen for aircraft use if they have a prescription from their family doctor. We ask you to determine if the welding or medical oxygen is suitable for your use. We do not and cannot make any recommendation on the use of oxygen other than aviation oxygen. 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. 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, 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. 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 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 bu compression generated by compression. The more rapidly the cylinder is filled the higher the cylinder temperature beecomes. Excessive heat may result in ignition of any combustible material that is present. Filling Containers must be refilled by a gas manufacturer, gas distributor, or someone qualified in the refilling of aircraft oxygen cylinders. The markings stamped into cylinders shall not be removed or changed. The user shall not deface or remove any markings, labels, decals, tags, or stencil marks applied by the supplier and used for identification of content. The user shall not change, modify, tamper with, obstruct, or repair the pressure-relief devices. The user shall not repair or alter containers or container valves. Any other damage noted that might impair the safety of the container shall be called to the attention of the gas supplier refilling the container. Transporting Containers should not be used as rollers, supports, or for any purpose other than to contain the appropriate contents. The user should keep container valves closed at all times (charged or empty) except when the container is in use. Storing Compressed gas containers should not be subjected to atmospheric temperatures above 130 degrees F. A flame shall never be permitted to come in contact with any part of a compressed gas container. Containers shall not be stored near readily ignitable substances such as gasoline, waste papers, or combustibles of any kind. Containers shall not be exposed to continuous dampness, or sunlight. Handling Only properly trained persons shall handle compressed gases. The user responsible for the handling and connection of the container shall check the identity of the gas inside by reading the label or other markings on the container before use. If marking does not identify container content, the container shall be returned to the supplier without using it. Container color shall not be relied upon for content identification. Connections that do not fit should not be forced. Threads on regulator connections or other auxiliary equipment should match those on container valve outlets. Regulators, gauges, hoses and other appliances provided for use with a particular gas or group of gases should not be used on containers containing gases having different chemical properties. You may interchange parts only if information is obtained from the supplier indicating that it can be done safely. As an example; only pressure-regulating devices approved for use with oxygen should be used in oxygen service. Putting in Service Container valve should be opened slowly for safety. Valve outlets should be pointed away from you and other persons. Valve wheels or levers should not be hammered in attempting to open or close the valve. For valves that are hard to open or frozen because of corrosion, the supplier should be contacted for instructions. Before a regulator is removed from a container, the container valve should be closed and the regulator drained of gas pressure. Oxygen containers, valves, regulators, hose, and other oxygen apparatus should be kept free from oil or grease. They shall not be handled with oily hands, oily gloves, or with greasy equipment. Transfilling Transfilling of compressed gas from one tank to another is not recommended. If done, it must be carried out by a properly trained professional in a controled enviroment using proper equipment. FAA and Oxygen (From FAA Publications) Oxygen Requirements at Altitude The FAA requires that all pilots flying their aircraft above 12,500 feet for 30 minutes or longer, or upwards of 14,000 feet during the entire flight, must use supplemental oxygen. The amount required is 1 liter of oxygen per minute for every 10,000 feet. For example, at 18,000 feet there should be a flow of 1.8 liters per minute of oxygen available via a standard breathing device. The FAA requires there should be a device so attached to each breathing device that visually shows the flow of oxygen (Nelson flow meters meet this FAA requirement). The FAA also regulates that passengers must have supplemental oxygen available over 15,000 feet. It is recommended that supplemental oxygen be used at night at altitudes over 5,000 feet. Effective Performance Time This is the amount of time during which a pilot is able to effectively or adequately fly his aircraft with an insufficient supply of oxygen. At altitudes below 30,000 feet this time may differ considerably from the time of total consciousness (the time it takes to pass out). Above 35,000 feet the times become shorter and eventually coincides with the time it takes for blood to circulate from the lungs to the head. Cannulas The cannula type breathing devices can be used up to 18,000 feet. If a cannula is used, there must be a standby facemask available for each cannula in case of a head cold or congestion. Pilots should refer to FAR 23.1447 to see if any restrictions apply for their use of cannula type breathing devices in operating their aircraft. Average Effective Performance Time for flying personnel without supplemental oxygen: 15,000 to 18,000 feet ..........30 minutes or more 22,000 feet ...............................5 to 10 minutes 25,000 feet .................................3 to 5 minutes 28,000 feet............................2 1/2 to 3 minutes 30,000 feet .................................1 to 2 minutes 35,000 feet ............................30 to 60 seconds 40,000 feet ............................15 to 20 seconds 45,000 feet ..............................9 to 15 seconds Factors which will determine the Effective Performance Time Altitude. EPT decreases at high altitudes. Rate of ascent. In general, the faster the rate, the shorter the EPT. Physical Activity. Exercise decreases EPT considerably. Day-to-Day Factors. Physical fitness and other factors (smoking, health, stress) may change your ability to tolerate hypoxia from day to day, thereby changing your EPT. Cylinders Oxygen cylinders should be hydrostatically tested every 5 years. Steel Cylinders are usually tested every 10 years. Specially constructed oxygen cylinders could have a shorter period for hydrostatic testing. There could also be a limit on how long the cylinder may be used when it was supplied originally as a factory installed, built in oxygen system. Most cylinders can be used indefinitely, however some aircraft may be required to replace the cylinders after 25 years. Factory supplied built in oxygen systems will have the necessary maintenance information in the aircraft manual. Around the neck of the cylinder are letters and numbers stamped into the cylinder. Of importance to the pilot are three items. At the beginning of the numbers are the letters, DOT. This indicates that the cylinder has been approved by the Department of Transportation, which means they can be commercially filled. European cylinders may not have the DOT stamped on the cylinder. This could prevent the cylinder from being refilled in the USA. Owners of imported aircraft from Europe should be aware of this problem. After the DOT label, there will be 4 numbers. These indicate the rate cylinder pressure. 2015 and 2216 are common. After the end of all the numbers will be two numbers followed by a letter that looks like an inverted capital A, then two more numbers. This is the date of manufacture of the cylinder. The first numbers are the month (03 for example would be March) and the last two being the year of manufacture (96 would be for 1996). The date testing is required is based on this date, not when the cylinder was purchased. It is quite common to have an unused cylinder that could be one or two years old. Perhaps not fair for the buyer, but who said life was always fair. Outlets in Built-In Systems We understand that some systems require the O-Ring seals in the manifold outlets to be replaced on a scheduled basis. Consult your aircraft manual for more information. FAA Altitude Test Chamber We strongly recommend that anyone who uses or plans to use oxygen in aircraft attend one of the physiological training programs sponsored by the FAA and the military. Courses include information on hypoxia and hyperventilation, as well as offering altitude-chamber rides where you can safely experience your own reaction to oxygen deprivation. There is a waiting list for the courses. The cost for the courses is minimal. Courses are offered at many military bases around the country. You can get an application form by writing or calling the FAA Civil Aeromedical Institute, Airman Education Section AAM-420, P.O. Box 25082, Oklahoma City, Okla. 73125, (405) 686-4837. Better yet, contact your local FAA Accident Prevention Specialist and ask for AC Form 3150-7. One of our customers who recently attended one of these courses said that the instructor warned against the excessive use of lipstick and Chapstick type material on lips when using oxygen. He also said that you should not eat peanuts during the use of oxygen. In both cases, the excess oil along with ignition by a static electricity charge could cause a potential reaction with oxygen. Hyperventilation The symptoms of hyperventilation and hypoxia are somewhat related and often are misunderstood. The FAA defines hyperventilation as follows: "Hyperventilation (or over breathing) is a disturbance of respiration that may occur in individuals as a result of emotional stress, fright, or pain." The respiratory center of the brain reacts to the amount of carbon dioxide found in the blood stream. When you are in a physically relaxed state, the amount of carbon dioxide in your blood stimulates the respiratory center and your breathing rate is stabilized at about 12 to 20 breaths per minute. When physical activity occurs, the body cells use more oxygen and more carbon dioxide is produced. As a result, excessive carbon dioxide enters the blood and the respiratory center responds to this increasing breathing in depth and rate to remove the over supply of carbon dioxide. Once the excess carbon dioxide is removed, the respiratory center causes the breathing rate to change back to normal. To check for hypoxia or hyperventilation: -Check your oxygen equipment immediately. See if there is oxygen and the flow is at the proper rate for the altitude you are. The use of Nelson flow meters will verify if your system is working properly. -After three or four deep breaths of oxygen, the symptoms should improve markedly if the condition experienced was hypoxia. (Recovery from hypoxia is extremely rapid). -If the symptoms persist, you should consciously slow your breathing rate until symptoms clear and then resume your normal breathing. You can also breath into a bag, or talk aloud to overcome symptoms of hyperventilation. Under conditions of emotional stress, fright, or pain, the pilot's lung ventilation may increase although the carbon dioxide output of the body cells remains at a resting level. As a result, he "washes out" carbon dioxide from his blood. The most common symptoms are dizziness, rapid heart rate, blurring of vision, muscle spasms, sleepiness, and finally unconsciousness. After becoming unconscious, the breathing rate will be exceedingly low until enough carbon dioxide is produced to stimulate the respiratory center. Hyperventilation occurs as a result of the body's normal compensatory response to hypoxia. Excessive breathing does little good in overcoming hypoxia. Several aircraft accidents have been traced to probable hyperventilation. It is recommended that you induce hyperventilation by voluntarily breathing several deeps breaths at an accelerated rate (not while flying). You will begin to get some of the symptoms mentioned. Once you experience several of these symptoms, return to your normal rate of breathing. After you become familiar with the early warnings your body gives you, the likelihood of an accident caused by hyperventilation will be reduced. Caution: Do not hyperventilate while alone or in a standing position. You may fall and injure yourself. FAA Publications Strangely enough, the FAA does not have any publications available that cover the use of oxygen in general aviation. There is an excellent manual that is only given out when you go for an FAA Altitude Chamber ride. Nitrogen Considerations There is a new breathing problem with the advent of the high rate of climb 250+ horsepower homebuilts. Sustained rates of climb in excess of 2,000 feet per minute are possible with the Glasair and Lancair type of aircraft. Total time to climb to 20,000 feet can be less than 10 minutes. The problem here is that the average person's body cannot adapt to that change of altitude in that time period. It takes at least 20 minutes for the body to adjust to that change. The problem is nitrogen gas bubbles in the body. This is called "the Bends"; the same problem that can occur in deep sea diving. Extreme pain can occur and if a nitrogen gas bubble develops in the brain, death can occur. The ability of these new aircraft to gaib altitude at such a quick rate makes the likely hood of developing "The Bends" more probable. Some people may make it to 20,000 feet OK, but many more will not make it to 25,000 feet in these short time periods. To make things worse, there are no FAA requirements or recommendations about the effects of high rates of climb. Hopefully the FAA and the manufacturer's of these aircraft will advise pilots about these problems. There are two ways of solving the problem for most situations. One is to limit the climb to 20,000 feet to less than 1,000 feet per minute. The other suggestion is to put on the oxygen as soon as you start the engine and let your body adapt more rapidly. More technical information is needed on this matter. As we find out more information, we will pass it on. Flow Meters A device visually indicating the flow of oxygen must be used with each breathing device. Typically what is supplied is an indicator in-line between the breathing device and the hose connector. This in-line type of indicator is operated by the flow of oxygen. As soon as there is a flow of oxygen, the red indication is replaced with a green reading. The change from red to green only shows that there is a flow of oxygen (which is the only thing the FAA requires). The green indication does not tell you that the system is working properly. As a matter of fact, the green indication on some of the red/green indicators will operate with a flow of oxygen required for less than 5,000 feet. You could actually be flying at 25,000 feet with the flow indicator showing green, but only have enough oxygen for 5,000 feet. In our opinion the typical red/green indicator is practically worthless and potentially very dangerous. The Nelson flow meters replace the red/green indicator. To reduce the possibilities of hypoxia, the Nelson flow meters provide a fail safe means of visually observing the actual oxygen flow to the breathing device, while providing a means to adjust the flow of oxygen as required. The Nelson flow meters are basically a tapered 3-inch tube with the large end at the top. A round ball is placed inside the tube. The flow of oxygen enters at the bottom portion of the tube. When the scale is about vertical, the ball will move upward and is supported at a point where the area around the ball is just large enough to pass the volume of oxygen flowing through the system. A flow control needle valve is designed into the flow meter to allow the user to adjust the flow of oxygen to the breathing device. By adjusting the position of the floating ball with the flow control needle valve to coincide with the altitude scale, the user can provide the correct supplemental oxygen for that altitude. A special chart is not required to determine the correct amount of oxygen since the correct flow rate is calibrated in thousands of feet of altitude. Types of Oxygen Systems There are several types of oxygen systems commonly found in general aviation aircraft: 1. Constant flow 2. Altitude adjustable 3. Altitude compensating. Each type has advantages and disadvantages. Constant Flow Systems The most common and lowest cost system found in general aviation is the constant flow type. The basic system includes three parts: the cylinder(s), regulator, and manifold system. The cylinder is common to all systems. It can be made from steel, aluminum, or composites. The tank pressure is usually less than 2,200 pounds per square inch (psi). The regulators, which step down the pressure from 2200 psi to 20-75 psi can be attached separately from the cylinder(s) or directly screwed onto the cylinder. Most regulators are of the diaphragm type. They typically hold a constant output pressure between 20 and 75 pounds, depending on the manufacturer. The cylinder doesn't have to be completely full, the pressure will remain the same. A manifold system is built into the regulator for portable systems. For built-in systems there is a manifold system installed in the aircraft. The manifold system operates at the 20-75 pound pressure range, and not the 2,000+ pound cylinder pressure. The constant flow type provides the same output pressure or flow regardless of altitude. There is virtually no maintenance required. It is low in cost and low in weight. The regulator output is typically 2.5 to 3.0 liters per minute at a regulated line pressure of 25 to 75 pounds. The output is controlled by a small orifice in the regulator itself, done by the connector going into the manifold system. The connector orifice can be a hole as small as .012 inches in diameter. Cessna aircraft with factory supplied built in oxygen systems use a constant flow type of system manufactured by Puritan. Most portable systems are also of the constant flow type. We strongly recommend the manifold output pressure of all constant flow systems (Cessna built in systems in particular) be checked for factory recommended output pressure at least during the annual. This may or may not be a required check during the annual, but it should be. We found one customer's Cessna 210 that had a line pressure in excess of 200 pounds. The correct pressure should be about 70 pounds for the Cessna's built in Puritan system. Excess manifold pressure from the oxygen regulator can cause the hose going to a flow control device to burst. The disadvantage of the constant flow system is that there is a waste of oxygen at lower altitudes. The system typically provides the pilot a flow of 2.5 liters per minute. This is the correct amount of oxygen at 25,000 feet. If the aircraft were at 15,000 feet however, only 1.5 liters per minute are required. There is a waste of 1 liter per minute of oxygen. The excess oxygen used has no serious medical effect other than drying out your nose quickly. Obviously there is an economic disadvantage. Using a Nelson flow meter with a constant flow oxygen system eliminates the non-required high flow rate of oxygen. The savings can be over 100%. By setting the flow to what you actually need, two things are accomplished. The saving of oxygen is accomplished thus extending the use of oxygen in your aircraft or lowering oxygen costs. You also have improved the safety at oxygen altitudes by knowing that the system is working properly. If the floating ball is at the correct altitude setting, then everything is working properly. With the Nelson flow meter used in a constant flow oxygen system you can have your cake and eat it too. The economical constant flow system with the addition of a low cost Nelson flow meter will provide you with a system that is reliable, safe, and economical. Altitude Adjustable Systems An altitude adjustable oxygen system is similar to the constant flow system except there is an adjustable control to set the necessary flow. This adjustment is accomplished by turning a control knob so a reading on a gauge calibrated in altitude is the same as the aircraft's altimeter setting. There is significant savings since you are not wasting the excess flow of oxygen. Not many built in systems use this type, however some portable systems have this feature. The military surplus A8A regulators of the altitude adjustable type are commonly used in many sailplanes. One disadvantage to this type of system other than it's higher cost, is that there is no positive indication of flow to the individual breathing devices. You cannot adjust individually the flow of oxygen to each of the breathing devices. Not all people require the same amount of oxygen (for example the smoker). The red/green indicator is commonly used to show flow. As previously mentioned, this doesn't tell you that the system is working properly. The Nelson flow meters can effectively be used with this type of system. The flow meter can be set wide open and the resulting flow from the altitude adjusting system can be observed in the flow meter. What is recommended is to have at least one Nelson flow meter installed so that the pilot can monitor the resulting flow from the altitude adjustments made on the flow adjustment control on the regulator. What most users do is turn the altitude adjustment to the service ceiling of the aircraft and leave it there all the time. Do the adjusting on each of the Nelson flow meters, this way you can individually adjust each breathing station as required. Altitude Compensating Systems The altitude compensating system is similar to the altitude adjustable systems except that the adjustment is done automatically instead of manually. Beechcraft and Mooney use this type of system. Also, some portable systems have this feature. The systems work quite well in the automatic mode. There are again disadvantages to this type of system. Some systems do not turn on or provide any oxygen until the system is at 8 to 10,000 feet. If you want oxygen at a lower altitude, you are out of luck. Like the altitude adjustable system, you cannot individually adjust the flow of oxygen since all of the outlets are controlled by the automatic system. If there is a person on board who requires extra oxygen, you cannot provide additional oxygen for that person. In addition, usually there is no actual flow meter available to indicate if the automatic flow control device is working properly. The use of a Nelson Flow Meter in the pilot's station will tell you if the automatic system is working properly. Demand and Pressure Demand Systems There is a fourth type of system that is not commonly used in general aviation aircraft: the demand type. This system is recommended for use from 30,000 to 40,000 feet. Since most general aviation aircraft (other than turbine aircraft) don't operate in these altitudes, we will not concern ourselves with these systems. Electronic Delivery Systems The Electronic Delivery System (EDS) by Mountain High Equipment is the most recent type of this system. In general terms this is the way the system works. When you inhale from the EDS system, a small pulse of oxygen is delivered to a standard nasal cannula. No oxygen is flowing unless you inhale. As you increase the altitude (to 18,000 feet max.), the duration of the pulse of oxygen is increased automatically. The increased duration of the oxygen cylinder will be very significant. The EDS system is about twice the cost of a similar constant flow system, but the weight of the system will be significantly less for the same duration. We highly recommend the EDS system and now currently offer the system for sale. The EDS system is an excellent choice where space and weight of the cylinder is important. The EDS system works particularly well for aircraft such as the Glassair, Lancair, Venture, and other aircraft where there is a premium on space. A 14 cubic foot EDS system complete with case only weighs 8 1/2 pounds and will supply oxygen for one person at 18,000 feet for up to 18 hours. Two EDS systems can be installed to one cylinder for use with two people for maximum duration. Another alternative is to have the pilot equipped with the EDS unit and the passenger equipped with an A-3 flow meter/Oxymizer( that is connected directly to the regulator via a WYE fitting. Regulators There are two types of regulators that are used: diaphragm and piston. The purpose of the regulator is to take the 2,000 pounds of pressure in the cylinder and bring it down to a much lower level so the oxygen can be distributed easily. Typically, the regulated output pressure is between 25 to 75 pounds. Most manufactures use a diaphragm type regulator instead of a piston type. The advantage of the diaphragm type is that it holds about the same output pressure whether the tank is full or almost empty. The piston type regulator sometimes has the disadvantage of its output pressure being effected by the tank pressure. However, the latest type of piston regulators operating at 15-20 pounds of pressure do an excellent job in maintaining output pressure. Our lower cost oxygen systems use these new piston regulators. Portable Systems There are many advantages of the portable system; lower cost probably being the most obvious. When selecting a portable system several important considerations must be taken into account. An often-overlooked advantage of a portable system is availability of oxygen. Some airport FBO's do not have oxygen available. If you were based at such an airport, you would have to fly somewhere just to have the built-in oxygen system refilled. That can be very costly and waste a lot of time. With a portable system you can go to alternate sources of supply as previously mentioned. Even at FBO's who have oxygen, portable systems are usually cheaper to refill than built-in systems. Portable systems can be easily changed from one aircraft to another. This can be helpful if you have, use, or purchase different aircraft. Breathing Devices Face Masks There are two types of facemasks in general use: the partial rebreather and the sequential breather. The partial rebreather type is typified with a simple design and an external plastic bag. This type usually has a very flexible face mask construction that is somewhat fragile and easy to distort when subjected to excess heat. The mask design does work quite well below altitudes of 25,000 feet if in good condition and installed properly on the face. This type of mask should not be used above 25,000 feet because it doesn't have a positive seal against the face. Persons with beards should be aware of the possibility of oxygen leakage around the beard. Consequently, these people should not fly above 18,000 feet with this type of mask. One of the purposes of the bag is to collect unused oxygen that will be rebreathed into your lungs. It requires the standard 1-liter per minute of oxygen flow for every 10,000 feet. The use of a microphone with this type of mask can be simplified if a small boom type mike is used. Simply cut a small hole the diameter of the boom and slit the diameter of the microphone in the side of the mask. Then insert the unit into the mask. This works pretty well. When storing the simple type of facemask in the aircraft, make certain that the mask is properly stored in some kind of container that does not cause deformation of the mask. Either use a cloth pouch or a plastic box such as used for storing food in a refrigerator. With excess heat the mask can deform, this causes a poor seal on your face, which reduces its effectiveness. This is especially so when using the mask above 20,000 feet. The partial rebreather type with a molded facemask is a better type of mask for higher altitudes (20,000 to 30,000 feet). The facemask will not distort and will always seal against the face (except for persons with beards). However, there can be a problem with a built-in microphone. Sometimes an echo develops when talking with this type of mask. This distortion is transmitted along with your voice, which can sometimes make your voice unintelligible. The sequential rebreather mask has a check valve system that efficiently allows the induction of oxygen and outside air into the mask. It then allows your breath to be exhaled through ports to the outside of the mask. Under ideal conditions this type of mask can be used up to 40,000 feet. Standard Cannulas The medical cannula breathing device has been successfully adapted for use with aircraft. Doctors' Diamond and White of the Southern California area were instrumental in getting the FAA approval for its use. The cannulas are being used extensively with excellent results by thousands of pilots and their passengers. The cannula breathing device can be used satisfactorily up to 18,000 feet however, it should not be used above that altitude. One of the reasons for restricting its use above 18,000 feet is due to problems controlling the exhalation of carbon dioxide (CO2). Below 18,000 feet, the control or regulation of CO2 into the lungs is not too critical. At some point above 18,000 feet, it becomes critical. 18,000 feet may not be an exact point where the CO2 regulation is critical, but it is an easily remembered altitude (you are in positive controlled airspace above 18,000 feet) to change over to a face mask. The oxygen required for the standard cannula is the same as a face mask (1 liter per minute for every 10,000 feet). There are no savings of oxygen with the standard cannula. The advantages of the standard cannula are freedom to talk, eat, and drink. The cannula is much more comfortable than a face mask, especially for long durations. There are restrictions on the use of the cannula devices. Pilots should refer to FAR 23.1447 to see if any restrictions may apply for their use of cannula type breathing devices in the operation of their aircraft. What is or is not allowed is subject to discussion and legal determination. The ultimate decision to use the cannula must be made by the pilot in command of the aircraft. The FAA requires that there be a standby face mask on board for each cannula device that is being used. Oxymizer( Cannula The oxygen conserving cannula breathing device was introduced into the aviation field in 1987. The purpose of the device is to reduce home health care oxygen cost or consumption for those requiring oxygen on a daily basis. Chad Therapeutics' Oxymizer( has been very successful for this purpose. Two versions are produced by Chad; one with a reservoir built into the face piece, the other with a separate reservoir apart from the face piece. Both units perform equally well with the same specifications. The standard cannulas waste oxygen. The Oxymizer( conserving device accumulates the continuous flow of oxygen that is normally wasted during exhalation. This accumulated oxygen is then available as a bonus at the very beginning of the next inhalation when it is taken deep into the lungs for maximum efficiency. This permits drastic reductions in the oxygen flow rates while maintaining proper oxygenation of the blood. As a result, the contents of a portable oxygen system lasts much longer. This increase oxygen availability as much as 75%. We tested the Oxymizer( ourselves to determine the application of its use in aircraft. This was done about 2 years after other suppliers to the aviation market first marketed the units. With the assistance of an anesthesiologist who is a several thousand hour Cessna 210 pilot and sailplane enthusiast, tests were made to measure the oxygenation of the blood at various altitudes. A portable medical device (an Oximeter), was used for these measurements. The aircraft used was a turbo Cessna 206. The subject for the testing was a male nonsmoker in average health (not an avid athlete) 50 years of age. With the test equipment in the aircraft and the aircraft at 12,000 feet, the oxygen saturation level in the subject's blood measured about 90%. This correlates with an accepted minimum level of 90% saturation level for the average person to perform non-athletic type activities. If the supplemental oxygen system could maintain at least 90% saturation levels up to 18,000 feet, the subject could safely be provided supplemental oxygen to perform the physical and mental activities required for piloting the aircraft. With the aircraft at 18,000 feet and the subject using the Oxymizer( with a flow rate of .6 liters per minute, saturation levels of 89-90% were obtained. Our consultant suggested that .6 liters per minute (which was the recommended amount at the time of testing) be deemed too close to an unsatisfactory level. By raising the oxygen flow rate slightly to .7 -.75 liters per minute, the user would be guaranteed to have a saturation level in excess of 90%. The Nelson flow meters intended for use with the Oxymizers( are set to provide a minimum of .7 liters per minute of oxygen at 18,000 feet. Our consultant also suggested that the Oxymizer( should not be used by smokers. It is possible that a smoker's lungs could be damaged enough that 90%+ blood saturation level would not be possible with the use of Oxymizers(. We now note on the Oxymizer( instructions, "For Use By Non Smokers Only". Perhaps this is too much of a generalization by our consultant and us. More correctly, we should say that the Oxymizer( should not be used by anyone with a serious lung disease. The problem here is that the determination of a "serious lung disease" must be determined by the pilot. Our testing was done with the Oxymizer( with the reservoir built into the face piece, however the type with the separate reservoir (pendent type) should work equally well. We recommend the use of the face piece reservoir type of Oxymizer( instead of the pendent type because the pendent type in our opinion, is difficult to store properly in an aircraft. The somewhat large diameter tubes going to the pendent are easily kinked and deformed while in storage. On the other hand, the face piece reservoir that we market is easily stored. The tubes can be coiled up around the unit and placed in a simple container or in the Oxypack carrying case with no damage. The test results confirmed the acceptability of using the Oxymizer( for supplemental oxygen use. Based on our testing and field reports from users of Oxymizers( for over two years, Ted Nelson Company endorses the use of Oxymizers( for supplemental oxygen use for aircraft at altitudes less than 18,000 feet. Oxymizer( is a registered trademark of Chad Therapeutics, Inc. The FAA restrictions that apply to the regular cannula devices also apply to the Oxymizer(. There must be a standby face mask on board for each Oxymizer( cannula that is in use. Use Of Cannulas During High Stress Situations I have been told by a leading military aero space doctor that while one is using a cannula during very high stress situations, there may be higher oxygen flow rates required for that individual. A likely situation for additional oxygen flow would occur during single pilot IFR conditions during actual IFR weather at reasonably high altitudes (15,000 to 18,000) while using either a standard cannula or the Oxymizer(. What happens typically is, your breathing rate will increase because of the high stress due to the increased work load of the pilot. The higher breathing rate will lower your inspired oxygen level, thus requiring a higher oxygen flow rate. We suggest that during actual IFR conditions above 15,000 feet a cannula device not be used. Change to a conventional face mask with its appropriate higher flow rate. Connectors All portable aircraft oxygen systems reduce the final oxygen flow rate to the breathing devices by restricting the oxygen flow after reducing the tank pressure with the regulator. Usually the connector going into the regulator does the restriction. If the restriction is not done in the connector, then it is designed into the manifold system in the regulator. This restriction is usually done with a small diameter hole; as little as .012 inches in diameter. The other method of restricting is done by compressing a fibrous material in the connector's oxygen passageway with a set screw type adjustment. Of concern to the pilot is the proper operation of the restriction in the connector. The small diameter holes may corrode in time, thus reducing the flow rate. In addition, the fibrous type of restriction can expand due to being exposed to high moisture and humidity conditions. This may also reduce flow. Various manufacturers make connectors that have different flow rates as determined by the various types of restrictions. The connectors are usually color coded and sometimes marked with the usable oxygen altitude range (example: 14 to 22,000 feet). The problem here is that the color codes can come off. The user can be using the wrong flow connector without knowing it. In most cases you cannot tell the difference between the various flow rate connectors made by the same manufacturer. All the Nelson manufactured connectors are designed to provide about 2.5 + liters of oxygen with a 45 PSI regulated pressure at 25,000 feet. The Nelson flow meters can also be used to determine if the oxygen system has the proper connectors. When at altitude with the Nelson flow meter fully opened and the indicating ball is positioned at a lower altitude reading, then there is probably something wrong with the connector. This is not too common with newer aircraft, but we do see the problem quite often with older aircraft. There is some confusion as to what kind of connectors are used in the various aircraft, especially with Cessna's. Cessna uses two different types depending on the year of the aircraft. Prior to 1979 the Puritan 566 type was used. After 1979 the Puritan 750 was used. During 1978 to 1980 there is a chance that either type could have been used. The aircraft manual does not indicate which type is used. We have a brochure available that shows the different types of connectors we manufacture or distribute. The 750 connector has an output prong diameter about 3/16 of an inch. The 566 connector has an output diameter about 3/16 of an inch. The 566-output prong is about 1/4 inch in diameter. Another way of determining what type of Puritan connector is used is to look at an outlet built into the Cessna aircraft. When looking at the outlet, one will see only one hole for the 750 connector. Two concentric rings will be seen if a 566 connector is used. If a customer needs connectors for a Cessna built during 1978 to 1980 and he isn't sure of the connector type, we supply both types (invoice for both types), and then the customer returns the unused connectors back to us. We will then credit the customer for the unused connectors when they are returned. The factory supplied built in oxygen equipment in Beech, Mooney, and Piper is almost always Scott equipment. An exception is the pressurized P Baron. I know of one aircraft that has Puritan 750 connectors for the emergency oxygen equipment. A customer might think he has a factory supplied built in system, but it can turn out to be a custom installation of a different manufacturer than Scott or Puritan. Sky-Ox built in systems are found in several older aircraft installations. The older Sky-Ox connectors may not work with a flow meter. The older type Sky-ox connector has a large internal O-Ring inside the base of the connector, where as the newer type Sky-Ox connector has a external O-Ring on the prong end of the connector. The new type connector has been in use since 1988 or so. Using the older type Sky-Ox connector a leak can occur at the internal O-Ring. When the flow meter is reducing the flow to the proper amount, some backpressure is generated between the connector and the flow meter. The O-Ring seal assembly in the older type connector acts like a piston with backpressure. The seal can actually be lifted off its seat causing a leak. The newer type of Sky-Ox connector with the external O-Ring does not have this problem. The newer type Sky-Ox connector can be used with the older type Sky-Ox system. We recommend purchasing the Nelson flow meter with a new type Sky-Ox connector. The information given herein is deemed accurate and reliable, but there is no guarantee given or expressed for its accuracy. All of the information given may be copied or reproduced with the exception of this material for use in commercial magazines. Please give Precise Flight, Inc. credit if this information is published. Thank you. PRECISE FLIGHT, INC. NELSON OXYGEN EQUIPMENT 63120 POWELL BUTTE ROAD BEND, OR 97701 541-382-8684 800- 547-2558 www.preciseflight.com 3 17 Revision B March 10, 1999