The Correct Usage of Oxygen

This article came as an e-mail from Steele Lipe and is published with his friendly agreement.
The first photo comes from the “Segelfluggruppe Winterthur”.
The second photo is made by Ruud Rozendaal in the southern French Alps.

“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.”

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.  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 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 interest to glider pilots.
Essentially, the FAA in its FARs require:

Oxygen must be used by a pilot (not speaking of passengers) any time above 14,000 feet and above 12,500 feet in excess of 30 minutes.

The use of cannulas has 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 pouch on each side that allows the cannula to accumulate 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 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 and delivers it in 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..  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.
Oxygen Mask - not belonging to this article!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%.
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) my personal 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.  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.
Photo made by Ruud Rozendaal in the French AlpsTherefore in the USA, to be legal, either system will provide the pilot adequate oxygenation up to positive control.  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).  Next, at 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 6/2002 –

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.

A Note from the Editor:

We had an interesting question lately:

Why does a human not simply breath at a higher frequency if he or she suffers from a lack of oxygen?

The answer lies in the way of the oxygen measurement within the human body. The body does not measure the O2 concentration. Instead it measures the CO2 concentration within the blood and automatically regulates the breathing frequency. It works flawless on the ground. A high CO2 level relates to a high use of O2 and therefore results in accelerated breathing. When flying we remain quiet within our airplane. The CO2 concentration in our blood does not rise. Only the O2 concentration drops down significantly. Unfortunately a manually controlled increase in the breathing frequency does not help us either. We have only half the amount of O2 in the air at 16,000 ft and the transformation of oxygen into the blood is done under pressure. That pressure – you all know that – is not as high as at MSL. Therefore it is not possible to enrich the O2 concentration within the blood to a normal level even if on breathes twice as fast. One will suffer from a lack of oxygen. This is visible from high’s of 9.000 ft and upwards.

  • A nice story relating to that:
    My Partner and I myself were on a trip to Slovenia in a little aircraft. We were cruising along at 12.000 ft. The pilot was already breathing oxygen. We thought – naa… we won’t need it.
    I handed my partner a notepad and asked him to do a simple calculation and write down the result of 13 * 17 and sign the paper at the bottom. Well, he did that.
    After touchdown in Ljubljana he (being a accountant) noted with disbelieve that he actually messed the calculation up completely and to make matters worse – his signature was totally off the normal pattern – totally unreadable.
    He had regarded himself to be totally fit at 12.000 ft… Isn’t that scary?

Another warning:

If you are flying at high’s above 18.000 ft you have to have an emergency system (a secondary oxygen system) on board that can keep you alive and breathing for at least 10 minutes.
You are gone forever in case of a malfunction of your O2-System at those high’s without a backup.

A simple calculation:
You’ll only notice the malfunction at high’s of 12.000 ft once you already suffer from a lack of oxygen. If you extend the spoilers and speed brakes and descend with 190 km/h you can manage 30 m/sec. (You’d need a clear head and extreme concentration for that by the way). Well, if you have all that you’d need 100 sec until you reach 9.000 ft.
And those 100 sec. are probably not available. You are likely to pass out before.

You might have heard of the well known alpine glider pilot Jochen v. Kalkreuth and his book: “Segeln ueber den Alpen” – (Soaring above the Alps) He has written a standard piece of literature which is still of great interest. Well, he intended to gain experience for a second book on the influences of great high’s without oxygen. He trained intensively in the Alps.

His last comment via radio was: “I’m currently at 18.000 ft – without oxygen.” Friends listened to that message.

Sadly those word were his last ones for all times.

– friedel weber –
translated by Thiemo Gorath –

      Gliding Aviation Medicine,
      High Altitude Aspects and
       Mountain Wave Project 1999,
      St. Martin de los Andes, Argentina

Juergen K. Knueppel, Flight Surgeon; German Aero Club (DAeC), DGLRM, DFV, ASMA  / 9.2000


Mountain Wave Project 99 in Argentina was a scientific, Hi-Tec first time high altitude wave glider-flying excursion. Next to overall mission planning and management tasks was the human factors part, with its life- and human performance related aeromedical concerns, an extraordinarily demanding business. These experience are summarized as follows:

  1. Flying at altitudes above 3.000 m / 10.000 ft in gliders requires general medical considerations, e.g. hypoxia.
  2. Wave Flying at altitudes above 6.000 m / 20.000 ft requires special high altitude preparations.
  3. High altitude scientific literature studies, basic instruction and hypobaric chamber training were performed.
  4. Technical planning, O2 requirement calculation and emergency training had to be done.
  5. If both oxygen systems (EDS & Bendix) are used properly as required, O2 supply is provided in a safe manner.
  6. At lower altitudes EDS provided sufficient O2 support, but battery function had to be watched closely.
  7. O2 -systems must work reliably; they need professional maintenance.
  8. Most used O2 -systems are not state of the art. Also EDS systems have to be technically improved.
  9. Technical support and manpower for servicing O2 -equipment in the gliders must be provided at local airfield.
  10. Available oxygen stores are not sufficient for long duration flights of more than 3 hours and performed at altitudes above 20.000 ft / 6.000 m. – All compromises in flight are disabling and dangerous for flight safety.
  11. Hypothermia, Hypoxia, Hyperventilation and DCS are the physiological threats.
  12. Timely sufficient O2 – pre-breathing during ascent prevented all but one flight up to 27.000 ft / 8.000 m from DCS symptoms, probably for the reason that the duration of stay at this altitude would only be a few minutes.
  13. Flight safety and altitude physiology rules were known due to prior intensive basic training.
  14. All flight safety related concepts were key elements for the success of MWP-99.

I. Introduction to Mountain Wave Project 99

    1. OSTIV and some other highly committed glider pilots, some of them scientists and meteorologists, traveled in Nov 1999 to Argentina to study the rule of the “Wave in the Andes”. They also anticipated the opportunity to head for new Long Distance World records in gliders of their class.
    2. In the wave a glider can be climbed at a rate of 1 to 10 m/s / 200 to 2.000 ft/min or even more. In this type of forceful lift, which is usually associated with high velocities of wind and often signaled by a formation of lenticular clouds, it is possible to easily gain several thousand meters of altitude up to 50.000 ft /15 Km.
    3. Such life threatening high altitude flights require aviation and space medicine considerations, flight-physiology training and technical support by aviation medicine trained specialists! The author, also a glider pilot and military trained flight surgeon took part in the preparation phase of this project and accompanied the excursion to San Martin de Los Andes.
    4. The Andes extend 7.000 Km in a nearly true north-south direction. The prevailing wind direction is primarily from the west. This wind creates large powerful mountain waves, which was the reason for exploring this remote area. Two groups of about 15 experienced pilots were accompanied by three powered high performance gliders, a double seated Stemme SV 10, an ASH 25 M and a single seat Nimbus 4 M.
    5. Supported by local Argentinean pilots, they flew more than 100 flights totaling several hundred flying hours and at times covered long distances of more than 1.800 Km / 1.000 NM with some world records.

II. History of High Altitude Glider Flying and its Medical Aspects

Wave Flying has become increasingly important in recent times, as equipment and knowledge have improved over the last ten to fifteen years. Long Distance Wave Flights in the European Alps now happen regularly. In New Zealand and France during the last world championships the competitors had to prepare for wave flights at altitudes of up to 23.000 ft / 7.000 m.

      1. At altitudes of more than 20.000 ft / 6.000 m, flying is lethal without oxygen. Decompression Sickness (DCS) with Types I and II (minor symptoms up to CNS and cardiovascular collapse) can readily occur and may destroy the health of a pilot.
      2. Adequate oxygen equipment and hypobaric chamber-training should be mandatory for this type of rigorous and demanding glider flying. It is imperative for flight safety. In the USA altitude records of about 50.000 ft / 15.000 m and recent speed records (Jim Payne) were all done with aid of the wave!

In the USA, Poland, and the former GDR, hypobaric chamber training along with hyperbaric chamber facilities were widely supported by the authorities, even demanded in some places, prior to wave flying.

  • For a long time in Germany there has been a general lack of knowledge about oxygen needs when flying above 10.000 ft / 3.000 m, with obvious detrimental influences on flight safety. This was the case for many years and no action was taken to improve this situation, even though expert opinion and knowledge in this field was available. One famous “Alpensegelflieger”, Jochen von Kalkreuth, died at high altitude several years ago of hypoxia in his glider, apparently due to confusion about high altitude limits.

The common situation was that expensive oxygen equipment was rarely bought or used.

  • With intensive support by the German Armed Forces, namely by Rainer Wienzek from Bueckeburg, the Military Flying Club and the knowledge and training by the Institute of Aviation Medicine, this situation in Germany has improved during the last ten years. It has focused on the following main subjects:


  • Inexpensive, newly developed, Oxygen Demand Systems, like “EDS” from Mountain High/USA and “FLOWTIMER” from Spiegelberg in Hamburg have helped to resolve the problems of the limited stores of oxygen that can be carried aboard a glider. Now it is possible to fly for more than 11 hours with a 5 ltr bottle up to 18.000 ft / 5.500 m.
  • At altitude new “PULSE OXYMETRY” devices can measure the amount of oxygen available in the pilot’s body, more commonly known as the oxygen saturation of hemoglobin, using a sensor clip on the finger. This measurement shows the pilot that he is either in a “safe” range or that he is becoming hypoxic.

III. High Altitude Physiology Training and Preparation for MWP 99

A team of flight surgeons discussed and proposed the following detailed plan to prepare for this expedition in the Argentinean Andes. In fact, not all of the preparation could be completed in time before the expedition started.

      1. Flight medical exams prior to travel with emphasis on heart, lung and hematological functions.

– Focusing on health problems that could be exacerbated at high altitudes. Those were addressed in advance to provide a margin of safety for the participants.

  • Review of the basic literature to understand altitude physiology concerning gas, pressure, and diffusion laws.

– This is mandatory to understand high altitude dangers including the planned hypobaric chamber training.

  • Calculate oxygen requirements for the planned flight duration at different altitudes to be flown.

– As a rule at altitude O2 consumption is 1 ltr oxygen at 200 bar / ATA, per hour, per person.

  • Prepare life support equipment for each glider to meet oxygen needs, including possible emergency situations.

– This had to be done a long time in advance in order to design systems and organize the equipment. One unsolved problem exists for altitudes above 20.000 ft / 6.000 m, as a “rule of thumb” there is not enough space in the glider to store sufficient oxygen for this altitude.

  • Lectures in Altitude Physiology: (+ Pressure changes in the body + oxygen deficiency at altitude + type of oxygen deficiencies + time reserve (TUC) + decompression sickness (DCS) + thermophysiology and others) and a practical hypobaric chamber ride, version No.1. – This is the first chance to experience hypoxic symptoms at 25.000 ft / 7.500 m during a routine chamber run. The pilots had to get used to the chamber routine, to gain basic experience and learn O2 -discipline, like PRICE-Check (Pressure, Regulator, Indicator, Connections, Emergency Equipment) etc.
  • Hypobaric chamber ride, version No. 2. Introduction and training-practice of the O2 -equipment used in the glider, redundant additional systems and review in-flight emergency procedures. It was important to learn, plan and discuss different emergency options during flight, like O2 -system failure.
  • Documentation of all flights. Logger, paper, standardized questionnaire.
  • Pre- and post-flight briefings conducted by a flight surgeon. This exchange of experience helps to establish safe flying criteria.
  • Plan Search and Rescue Emergency Procedures (SAR), find local support, like a hyperbaric chamber, qualified hospitals, rescue systems, emergency phone numbers.
  • Technical equipment needed for Oxygen refills and additional technical supplies and support available at local airport.


IV. Practical Experience during MWP 99

1. Oxygen Equipment

EDS (Electronic Oxygen Delivery System), nasal cannula, System No. I

      1. All gliders carried EDS from Mountain High as the primary oxygen system. These systems had their own O2 -bottle, independent of a second system.
      2. Stemme had two EDS Systems attached to one 5 ltr bottle. It seemed to work correctly, but it had to be routinely checked for proper operation. It consisted of two systems connected to one valve.
      3. All bottles used were German Standard with 200-bar / 200 ATA pressure carrying a 3 or 5 ltr bottle.
      4. EDS worked excellently in most of the flights excellently.
      5. In a few cases EDS was likely to run low on battery power, without the pilot noticing and without realizing the audio-warning, if not monitored closely! This was dangerous and a point of concern!
      6. If more than one pilot is flying in an aircraft, some additional cross checking has to be done to insure adequate battery power. Alternate options should be discussed, like regular battery change or another permanent power resource such as solar panels.
      7. There has to be some technical test capability on the site available to be able to check such an apparatus, especially when it ages and more malfunctions occur. These systems have no regular “Quality Test Regimen”, as other aircraft equipment and technical maintenance rules require.

Diluter Demand Systems , with face mask; system No. II

      1. Stemme S10 VT,115 hp, had a certified Bendix diluter demand system, the standard system GAF F4F/ Alpha Jet.
      2. The Bendix system met all legal technical and maintenance requirements.
      3. It was equipped with masks, which were attached with Velcro tape on German military textile caps. This seems to be an excellent solution and fits tightly.
      4. There were long elongated hoses for convenience.
      5. The system is built into the panel (one for each crew member), so it can be operated individually.
      6. The 5-ltr bottle was the primary O2 resource.
      7. For higher or longer flights there was a battery of six individual 1 ltr bottles, which fitted behind one seat with specially constructed attachments and pressure valves.
      8. Some pilots stated that they put the mask on in case of use at high altitude above 20.000 ft / 6.000 m sometimes over the “nasal-cannula” of the EDS. They considered this a “Backup-System”, in case the diluter demand system ran out of oxygen.
      9. ASH25 M, 54 hp, had two EDS Systems attached to the one EDS valve on two connected 3-ltr bottles.
      10. A big 5 ltr bottle was positioned parallel to the front of the aft seat. It served two Draeger diluter demand systems, similar to the Stemme System.
      11. Nimbus 4 M, 40 hp, single seat, was equipped with EDS and a small independent diluter demand system, two independent 5 and 2 ltr O2 -bottles.

2. O2 -Resources

      • O2 -resources for flights up to 20.000 ft / 6.000 m were sufficient, and in the case of higher altitudes there were time limits for its use.
      • Officially recognized standards for oxygen supplies that can provide up to 15 hours flying time at higher altitudes were not met! (Klaus Ohlmann’s single seat, 15-hour flight on S 10 was double seat equipped!)
      • Draeger Company states: Calculate altitude 6 to 11 Km: 1 ltr (bottle pressurized 200 bar) per hour, per person)!
      • To carry more oxygen bottles is nearly impossible, as there is also an engine and fuel tanks which take up space.
      • There has to be some invention to increase the oxygen stores in these gliders. In technical terms, a bottle should be light weight, and small in size or the fuselage has to be adapted for O2 -tanks. – This is also a concern for regular sport gliders.
      • Oxygen equipment/material is of military origin and often old and outdated. Technical testing cannot be done easily. This is a stringent safety concern!
      • As long as this equipment is the only one primarily used, trained personnel and test equipment have to be available at the site by some means to keep the life support systems in first rate condition.

3. DCS Prevention

    • “Preventive Decompression Sickness (DCS) Oxygen Breathing” before and during flight cannot be done sufficiently at the moment, due to lack of oxygen stores in the glider.
    • In case of a preplanned, rapid climb to more than 20.000 ft / 6.000 m (e.g. to 8.500 m) altitude, this cannot be done without danger. 100% oxygen is already needed before take off and right from the start during the climb. This is mandatory to prevent Type II DCS Illness of a neurological nature, like severe headache, stroke, hearing loss, or partial blindness.
    • The ground calculation is 15 ltr 100% O2 per min (1 breath 750 ml times 20 per minute), which results in about 600 ltr O2 in 40 min, which amounts to a 3 ltr container. See also Annex 1: Practical Preventive Measures and Treatment of DCS in High Altitude Glider Flying above 22.000 ft / 6.000 m , J. Knueppel, 11/1999.
    • Some team members did three flights on three consecutive days up to: No 1= 8.000 m, No 2=5.500 m, No 3= 8.500 m. The flights lasted from 9 to eleven 11 hours, higher altitudes climbed in about three hours. Even though the pilots flew several times at this high altitude, in these specific cases on three consecutive days, they experienced no signs of DCS-symptoms at all. This was not the expected finding, but probably due to the fact that pilots stayed at high altitude only a short time to exchange higher glider velocities in favor of longer flight distances.
    • Additional O2 was provided through EDS above 10.000 ft / 3.000 m and through Bendix Diluter Mask above 20.000 ft / 6.000 m. This regimen was used in most flights.
    • Logger data have to be analyzed exactly! But the conclusion was with the empirical experience up to this point, from O2 / time schedules of oxygen-use during the performed flights in 1999, that DCS seems to be sufficiently preventable!
    • In contrast, one experienced Argentinean pilot suffered in and after flight with severe headache and bends, which cleared over night. He used only the EDS-system in a rapid ascent to about 8.000 m / 27.000 ft. -This really gives some evidence of the dangers of DCS.
    • Further data will be needed to prove all these experience.
    • In case of a DCS emergency it would have been necessary to fly the pilot in 1ATA cabin pressure to La Plata to the Navy hospital, because the hyperbaric chamber at ALICURA was not available to the pilots.

V. Reference List

    1. Evolved Gas, Pain, the Power Law, and Probability of Hypobaric Decompression Sickness, John Conkin et al.: ASEM, Vol. 69, No. 4, April 1998.
    2. Paradigms for the Treatment of Hypobaric Decompression Sickness, Todd S. Dart et al.: ASEM, Vol. 69, No. 4, April 1998.
    3. Guidelines for Treatment of Decompression Illness, Richard M. Moon et al.: ASEM, Vol. 68, No. 3, March 1997.
    4. 1990 Hypobaric Decompression Sickness Workshop: Summary and Conclusions, Andrew Pilmanis: AL/CFTS, Brooks AFB, TX 78235, NATO AGARD Panel, April 1991.
    5. Towards New In-flight De-Nitrogenisation and Altitude Decompression Sickness Risk, Andrew Pilmanis: AL/CFTS, Brooks AFB, TX 78235, Feb. 1992.
    6. An Abrupt Zero-Pre-Oxygenation Altitude Threshold for Decompression Sickness Symptoms, James T. Webb et al.: ASEM, Vol. 69, No. 4, April 1998.

Practical Preventive Measures and Treatment of DCS in High Altitude Glider Flying above 22.000 ft / 6.000 m

Juergen K. Knueppel, Flight Surgeon; German Aeroclub (DaeC), DGLRM, DFV, ASMA
Glider pilots, who fly above 20.000 ft / 6.000 m must understand the basic principles of Henry’s Gas Law in order to be prepared to counter and treat DECOMPRESSION SICKNESS (DCS). – Reviewing the latest literature in ASMA Journal, Vol. 69, April 1998 (Aviation Space and Environmental Medicine), some new scientific articles were presented on DCS, also called “Divers Sickness”. They highlight some valuable points worth considering, as follows:

      1. Nitrogen bubble formation in the human body is generated through hypobaric pressure; as a rough rule above 1/2 of the original permanent pressure. This is e.g. if 1 Atmosphere at sea-level with 29,92 inch / 760 mm Hg is reduced to 14,96 inch / 380 mm Hg at an altitude of 18.000 ft / 5.500 m . (This is to compare with the generation of CO2 bubbles, when a bottle of carbonated water is opened.- “Hypobaric” pressure is below atmospheric pressure and allows air bubbles to be released from the blood serum.)
      2. The formation of gas bubbles is dependent of ascent rate, time at altitude and De-Nitrogenisation before the climb with 100% oxygen. (For example: One half atmosphere is reached in 18.000 ft / 5.500 m, or diving in water from 33 ft / 10 m to sea-level.)
      3. Scientifically there are great interpersonal differences and situational variations, which contribute, like age, weight, muscle activity, recurrence of ascent, time at altitude or other individual predispositions.
      4. Scientific knowledge is still under consideration, as many problems are still not completely understood and solved (space suits, space travel). Nevertheless, several empirical limits and insights have to be followed to prevent possible disastrous health consequences!
      5. It is possible to be killed through DCS!
      6. DCS in glider flying is a new subject. The professional aviation world knows how to deal with DCS, but it wasn’t considered to be a problem in the glider world. In 1994 LTC Bob Weien, MD, FS USARMY discussed the first time high altitude glider flight and DCS risk. Symptoms were reported regularly, but not identified as DCS. -Scientifically Glider Flying DCS is a new problem.
      7. The scientific barrier for DCS Symptoms without pre-breathing oxygen and with a climb of 5.000 ft per minute / 25 m per second is 21.000 ft / 6.300 m.
      8. Above this altitude about 5% of pilots without a pressurized cabin will experience DCS Symptoms (which are muscular, skeletal, pulmonary, and minor or major neurological symptoms). Most pilots below this won’t experience any symptoms at all.
      9. In case of pre-breathing 100% oxygen, depending also on the time flown at lower altitude, the barrier goes up. The longer 100% oxygen is administered on the ground, the higher you can go without DCS.
      10. The two main DCS symptoms must be differentiated as follows:

Type I DCS: Symptoms are primarily bends; pain in the joints; considered minor!
Type II DCS: Symptoms are of neurological nature, brain and nerve-malfunction, considered severe!

  • Most important are the variables, like elapsed time, altitude, intensity, quality of onset etc., which determine outcome!

– Sudden incapacitation in flight, like hearing-loss or striking headache with vision-problems need immediate care and special medical treatment for survival! (Hyperbaric Pressure Chamber! ” Hyperbaric “pressure is above atmospheric pressure and forces air bubbles into the blood serum. See also No 1!)
Bends at altitude slowly developing with minor intensity, disappearing at descent requires 100% oxygen!

  • All DCS symptoms need to be surveyed as they can return in the next 24 h and might require hyperbaric pressure therapy to resolve.
  • Hyperbaric pressure chambers exist, -portable and fixed based-, with the Navy, Airforce and with Diving Companies. They can save life and provide routine therapy in diver / DCS accidents.
  • First Aid, if DCS symptoms appear, is:

a. always 100% OXYGEN,
b. HYDRATION by drinking isotone solutions (water with 1/3 apple-juice, 1/2-teaspoon saline).
c. transport to a HYPERBARIC CHAMBER, “dive” to 3 ATA for 2 to 5 hours, which hopefully will resolve the problem!

  • In-flight pre-breathing times of 100% oxygen, between 13-16.000 feet (not higher!) don’t prevent minor DCS symptoms, but prevent the most dangerous Type II DCS symptoms. The longer 100% O2 is inhaled, the more useful is it for the body!
  • High altitudes above 30.000 ft / 10 Km require as a rule 1 to 2 hours pre-breathing 100% O2 on the ground. One hour breathing 100% O2 flying at an altitude of 13.000 ft / 4.000 m seems to have a similar effect!
  • If glider pilots fly high above 20.000 ft / 6.000 m, it is important to go higher stepwise by ascending slowly, preferably for hours, than only in a few minutes. This reduces the DCS Risk!
  • Going up fast, staying up long at high altitude (i.g. 4 hours over 25.000 ft / 7.500 m) without pre-breathing will most probably cause DCS to develop.

75% of all U 2 Pilots who fly at cabin altitudes of 30.000 ft / 9.000 m experienced DCS at least once in their flying career, even with 100% oxygen breathing and with part time pre-breathing in advance!

  • DCS develops in general after one hour after ascent! If it is experienced, the pilot must descend immediately!
  • After DCS-symptoms have appeared, pilots have to descend and breath 100% oxygen, for 2 hours or even longer, after landing. This method should also be applied as a safety procedure, even when symptoms disappear during descent.
  • Rule is: No Flight the Next Day, after a high altitude flight and if DCS Symptoms occurred during flight!
  • For follow up of DCS mishaps it is essential to document all important data on a protocol. Debriefing after flight and a second protocol the next day is recommended.
  • If in doubt: Ask a doctor/diving doctor or flight surgeon over the phone for consultation, (Airforce, Navy) or over one of the 24 hours worldwide civilian DCS emergency numbers: like DAN Suisse 0041 32-3223823 or DAN Europe 0039 085 8930333 (all languages)!

Last, but not least!
(Quoted from: Clinical Aviation Medicine; Rayman,R  2000)
The Breakoff Phenomenon

Rayman and Gillingham and Previc describe a rare event experienced by Pilots at very high altitudes who feel they have indeed “slipped the surly bonds on earth”. The term break off covers a variety of high altitude flight experience, from simply feeling good through euphoria to psychological detachment. As noted by Rayman, it is important to advise pilots flying at high flying altitudes of the phenomenon and the need to report any such unusual experience. Psychiatric consultation should be requested if the event degrades flying performance or if the pilot is negatively influenced by the experience after return to earth.