The Correct Usage of Oxygen from DG Flugzeugbau GmbH

Also read the Talk on Oxygen given before the Soaring Society of America. a PDF version may be downloaded.

The Correct Usage of Oxygen from DG Flugzeugbau GmbH
This article is a copy of an article I wrote for (DG Flugzeugbau GmbH) and is used with their permission.

Question: "I've been using an A14A system for a long time, and am tempted to change to the EDS set-up. I have contacted Mountain High, and spoken to suppliers; what I would like is feedback from actual users of the system. What is it's ceiling (I think MH says 30,000 feet), and how do you find consumption compared to a good demand system. The ceiling seems a long way below an A14A, and I wonder is the claimed consumption saving only relative to a constant flow system.” Answer: Mountain High, Co. states that the ceiling is 25,000 feet. The rest of the question will be answered in the following discussion. Qualifications: First of all I am an Physician Anesthesiologist and have studied oxygen, its absorption, uptake, distribution, and utilization in our bodies extensively. In addition, I have flown gliders (DG-100 and now a DG-600M) innumerable times over 18,000 feet with my highest level 37,400 feet. For safety and study my ship is equipped with 4 different regulators and delivery systems (A14 {USAF military surplus}, EDS, low flow for Conserve cannulas, and high flow for a Sierra mask) and two different sources with automatic crossover in case of freeze up, exhaustion, or loss of pressure. I have personally studied		E D S System as supplied by Mountain High
oxygenation of the human body while in flight using newer methods of investigation than those used by the U. S. Air Force during W.W. II upon which FAA decisions and regulations are based. I have also spoken at the San Diego and the Reno SSA Conventions on the use of oxygen at altitude by pilots with particular emphassis onglider. The FAA in its FARs (FAR 91.211C) require: Oxygen must be used by a pilot (not speaking of passengers) any time above 12,500 feet in excess of 30 minutes and above 14,000 feet. The use of nasal cannulae have been approved by the FAA for use up to but not including 18,000 feet, but to be legal (FAR 25) the pilot must also carry a full face fitting mask when a cannula is used. The mandated flow to the cannula must be 1.0 liter/minute/10,000 feet or more. A waiver (in so many words) of these restrictions was given by the FAA to Ted Nelson and the oxygen system he popularized using lower flows and the oxygen conservation cannula. The "Conserve cannula" was initially developed for the breathing impaired but has been used also in aviation. The trick with these cannulas is the presence of a pouch on each side that allows the cannula to accumulate during exhalation the constantly flowing oxygen until it is needed during inhalation. Therefore, the gas flow during exhalation (breathing out) and the normal pause before the next inhalation is not wasted. Using the conserve cannula, the flow may be reduced to between 300 and 400 cc’s per minute (about 1/3 of the FAA requirement for non conservation cannulas). I ran the experiments and was also the guinea pig for Ted Nelson when he tested the low flow version of his flow meter system. I have measured oxygen saturation (% of oxygen carried by the red blood cells compared to the amount of oxygen the blood is capable of carrying) on myself during numerous flights at altitudes in the approved FAA altitude envelope and above. According to Mountain High, whose information is to my knowledge anecdotal, their initial aim was to provide oxygenation for hang glider pilots using an apparatus with minimal weight. Instead of using a pouch reservoir to accumulate oxygen, Mountain High’s EDS regulator, calculates the amount of oxygen that should be delivered at the alltitude and delivers it via a high flow at the beginning of the following breath. Thus, theoretically, the same amount of oxygen is delivered from the EDS as from the conservation cannula. There may possibly be a slight loss of gas from the conserve cannula that is probably not lost when using the EDS system especially at altitudes above 18,000 ft (not permitted by the FAA). Therefore, the EDS system may be slightly more efficient. I have used both systems extensively and have realized no great savings of oxygen when using the EDS unit.
There are two disadvantages with the EDS system. First, it is more expensive and secondly it requires a battery. I believe others have discovered, as have I, that the battery may fail at the wrong time. I have had to cancel or abort flights because of battery failure and thus the failure of the EDS system. Its advantage is it is automatic and within the confines of the FAA regulations user friendly. The Nelson regulator (now sold by AirOx) requires operator attention to keep the flow at least at the recommended level. When climbing in wave conditions or flying above 10,000 feet (I suggest using oxygen at 10,000 feet) I have usually set the flow regulator to a level above my present level so that I do not need to adjust it too often. The waste of oxygen is no more than 5 to 10%. There are two disadvantages with the EDS system. First, it is more expensive and secondly it requires a battery. I believe others have discovered, as have I, that the battery may fail at the wrong time. I have had to cancel or abort flights because of battery failure and thus the failure of the EDS system. Its advantage is that it is automatic and within the confines of the FAA regulations user		Segelfluggruppe Winterthur using a oxygen regulator similar to an A-12.
friendly. The Nelson regulator (now sold by AirOx) requires operator attention to keep the flow at least at the recommended level. When climbing in wave conditions or flying above 10,000 feet (I suggest using oxygen at 10,000 feet) I have usually set the flow regulator to a level above my present level so that I do not need to adjust it too often. The waste of oxygen is no more than 5 to 10%.
Above 18,000 feet the FAA requires a full fitting face mask such as the Sierra mask with a reservoir bag and a flow of 1.0 liter/min/10,000 feet. In theory, and in my observations, this system is sufficient for our needs up to about 39,000 feet at which time better control of the oxygen concentration requires an A14 type system or similar. The A14 system adjusts the inspired concentration of oxygen by barometric means and at about 43,000 feet 100% oxygen is delivered. It is not automatic. At higher altitudes adequate oxygenation may only be provided with pressure breathing or an external pressurization system such as a pressurized cockpit or pressure suit. Pressure breathing is very fatiguing and unless practiced it should not be attempted. For those outside of the USA (FAA) in my personal experience the use of both the EDS and conserve cannula systems has provided me with adequate oxygenation at altitudes of 24,000 to 25,000 feet. (I have not been higher than 25,000 feet with either because of FAA wave window control, so I can not attest to the altitude where each system has reached its maximum effectiveness.) The pouches on the conserve cannula, in actuality, will hold the amount of gas that is needed at about 18,000 feet without wastage. Above that altitude, in theory, the resultant higher flow will be lost to overflow. At levels above 18,000 the EDS may be beneficial but not legal in FAA controled airspace. I should not hazard a guess as to the maximum effective altitude of the EDS unit but I would surmise that it might be usable up to the very low 30,000s. To my knowledge, this has not been measured at this time.

Ruud Rozendaal in the
southern French Alps

Therefore, in the USA, to be legal, either system will provide the pilot adequate oxygenation up to the positive control altitude. The choice really depends upon the pilot's pocket and the trust in batteries vs. the necessity of paying attention to the flow regulator.

As far as efficiency is concerned, the EDS and the conserve cannula are the most efficient but are altitude limited (18,000 feet in the USA by FAA Regulation). Above 18,000 ft., a flow rate about 3 times higher, is the standard mask and reservoir systems (Sierra and others) which are good to about 39,000 for a well functioning unit without leaks. The A14 to my knowledge is the most wasteful but probably not much more than the high flow mask and bag, but it is not altitude limited unless you fly above 43,000 feet at which time pressure breathing needs to take place.

There is only one recommendation I would like to make. Whenever, you as a pilot use an oxygen system please keep it on and active until you have landed and stopped your aircraft. There seems to be (not substantiated) evidence that there may be a time of significantly lowered blood oxygen in a pilot following removal of the system. In any case, the approach and landing is the most stressful time in any glider flight and the pilot should be as oxygenated as possible. Because of this observed “hypoxia” I recommend VERY STRONGLY that a pilot not remove the oxygen mask of cannula until after landing.

The above express my philosophy and my investigations and in the case of oxygen my ongoing interest. Thank you for hearing me out. I welcome comments and arguments.

Just remember to be safe and to fly as safely as you can.
Oxygen is sure a lot cheaper than your glider or your Life!

- Steele Lipe - 11/1998 – Revised 6/2011 -

The copyrighted talk given before the Soaring Society of America in San Diego, California and again in Reno, Nevada
is available in PDF format by contacting the author, Steele Lipe. Please add "DG Oxygen Website" to subject line, thankyou.