Written by the author, Yasmina Platt.
Reprint from September 12, 2012, from AOPA's Views From the Region (VFR) blog (https://blog.aopa.org/aopa/author/yplatt/page/5/) but updated multiple times since.
Yasmina Platt, AOPA’s Central Southwest Regional Manager, takes NASA’s Physiological Training, including the high altitude chamber and rapid decompression exercises, and shares her experience and highlights.
I have been trying to take NASA’s Physiological Training (a.k.a. high altitude chamber training) for several years now, but it wasn’t until High Performance Aviation, LLC scheduled it as an FAA Wings safety seminar that I was able to sign up.
For those who might be unaware, NASA’s *free* Physiological Training covers the physiological stresses of flight. More specifically, it teaches attendees about gas laws, hypoxia, hyperventilation, trapped gas, decompression sickness, spatial disorientation, cabin pressurization, and oxygen equipment in addition to exposing participants to high altitude chamber and rapid decompression exercises.
Early this morning, on September 11, 2012, my husband (also a pilot) and I arrived at NASA’s Sonny Carter Training Facility at the Johnson Space Center in Houston.
From 7:45 am until about 2 pm, all nine of us in the class received ground school from NASA experts. While we covered a lot of different physiological subjects, this blog will focus on hypoxia as it was the main topic of the seminar. Below I share some of the highlights I learned from the class (or refreshed in class but think are important points):
– Air is composed of 78% nitrogen, 21% oxygen, 0.03% carbon dioxide and 0.97% trace gases.
– Hypoxia is a state of oxygen deficiency (not lack of oxygen) in the blood, tissues, and cells sufficient to cause an impairment of mental and physical functions.
– Hypoxic signs are objective and, therefore, they can be seen by others. They include: increased rate and depth of breathing, cyanosis, slurring of speech, poor coordination, mental confusion, euphoria, belligerence, lethargic, and unconsciousness.
– Hypoxic symptoms are subjective sensations that only the person who is hypoxic can detect. These include: blurred vision, euphoria, nausea, tunnel vision, numbness, dizziness, air hunger, tingling, fatigue, hot and cold flashes, apprehension, headache, and belligerence.
– Although the percentage of oxygen contained in the air at 18,000 feet is identical to that at sea level (a little over 20%), the amount of air our lungs take in with each breath contains half the oxygen found at sea level.
– Respiration determines how well we function in flight. At 5,000 feet, we start to suffer hypoxia. Above 10,000 feet, the pO2 is too low to support life. This is different from the FAA’s 12,500 feet supplemental oxygen rule. Refer to 14 CFR Part 91.211 if you want to refresh your memory.
– The most dangerous feature of hypoxia is its insidious onset, a situation that comes on slowly, without obvious symptoms at first so the person is not aware of its development.
– If you ever experience any of the flight physiological sicknesses, it is recommended that you visit a flight medicine doctor (or diving doctor).
After lunch, we were assigned oxygen equipment composed of a helmet, a pressure demand mask and a few connectors. Then it was time for the NASA hypobaric (high altitude) chamber, the same one used for astronaut training. Cool!! We are going to play astronaut for a day! =) The high altitude chamber and rapid decompression exercises we participated in are designed to enable people to identify their own symptoms to hypoxia while inflight 1) in an unpressurized aircraft without oxygen or 2) in a pressurized aircraft and cabin pressurization is lost.
Let’s talk about the first exercise first… the high altitude chamber (see picture below). Once we were all assigned a seat, we breathed 100% aviator oxygen for 30 minutes to eliminate about 30% of the nitrogen out of our systems (remember the air composition explained above). At that point, the air inside the chamber was released, taking all of nine of us plus two instructors (several others, including a flight surgeon, monitored us from outside) to 25,000 feet at a fast 5,000 foot a minute rate. Once stabilized at 25,000 feet, we all removed our oxygen masks (in two different groups). At 25,000 feet, there is only about 1/3 of the amount of oxygen found at sea level. Needless is to say that it only took us a few minutes before we started to notice hypoxic symptoms/signs. It only took a couple of minutes for some and others were able to stay off the oxygen for about 4 minutes or longer. We were told to last as long as we could but to don our masks when we felt we needed to, knowing that everybody had to have oxygen back on at minute 5 to avoid unconsciousness. It was interesting to see how different people reacted to hypoxia in different ways, which is what makes this training so important. Most of us pilots know the “typical” symptoms of hypoxia; however, none of us know how our body reacts to hypoxia until we are exposed to it. It is also important to note that most people will experience hypoxic signs and symptoms in different orders. While some might start by feeling dizzy, others might start with a blurred vision, for example.
Another important thing we learned in class is that a typical person has a blood oxygen saturation (the blood’s ability to carry oxygen) of 98% at sea level while that percentage goes down to 87% at 10,000 feet. This was verified by one of the class participants by using an oxygen sensor in one of his fingers. As soon as we leveled off at 25,000 feet and he took his mask off, his percentage went down to 86-87%. Then it continued decreasing to about 81% before he had to put his oxygen mask back on.
I am going to quote one of the instructors in describing how people feel or look when they are experiencing hypoxia: “Lights are on, but no one is home” and “the pistons were not firing well.” My personal feelings/signs/symptoms during the exercise were the following: (and, yes, we wrote them down during the exercise and answered a few basic questions – not so basic when you are oxygen deprived though)
– Minute one: Feeling ok.
– Minute two: Feeling ok but started getting a little dizzy.
– Minute three: Feeling ok but started getting really hot and my dizziness continued.
– Minute four: Still really hot and my legs started to tingle.
– My vision was pretty clear the entire time and so was my thinking/brain from what I could tell. I was able to complete the exercises without too much trouble; however, it does take more effort to concentrate (and this might prevent you from doing other tasks at the same time).
Remember “insidious onset”? Yes, it is very difficult to know when you are getting hypoxic and, worse yet, when you are really “losing it.” Hypoxia doesn’t give much warning.
The last exercise of the day was the rapid (1 to 10 seconds) cabin decompression. In groups of two or three, we each experienced what all flight attendants demonstrate on commercial airliners when they simulate the oxygen masks dropping from the overhead. I never questioned the fact that they want us to “wear our masks first before assisting others;” however, I learned exactly why during this exercise. If you don’t have enough oxygen yourself, you can’t function and, therefore, you can’t help anybody, causing you and the other person to quickly become hypoxic. Some of the indications of a rapid decompression include explosive noise, windblast/flying debris, fogging (we certainly saw that!), temperature drop and pressure.
I am very glad I now know the hypoxia symptoms I (again, different from what others might experience) could experience inflight, how to recognize them and when to take action before it’s too late. Should I have experienced hypoxia in an aircraft (rather than in a chamber) for the first time, there is no doubt in my mind I would have passed out, become unconsciousness and potentially passed away. My main two symptoms were hot flashes and leg tingling. How many times do we feel hot (and sweat) in an non-air conditioned aircraft? Many times… so I would have just opened or turned the air vent towards me a bit more. And the leg tingling… well, this happens to me sometimes so I wouldn’t have thought too much about it. Pilots (and passengers) have seconds (in the case of the rapid decompression) or just a few minutes to recognize their symptoms before putting their masks on or risking becoming unconscious. After going through this training, my personal altitude limitation without appropriate oxygen will be 10,000 feet regardless of the FAA’s conservative supplemental oxygen regulation.
We all found the training to be invaluable for pilots and I wish more pilots got a chance to take it. I want to thank B.R. with High Performance Aviation, LLC for his initiative and work in scheduling several different classes to accommodate a total of 75 pilots who registered to undergo this training. I also want to thank the wonderful staff at NASA’s Human Test Support Group for their dedication and for sharing their knowledge with us. Some of the instructors involved included S.C., J.R., S.S., R.W., B.G., B.B. I am protecting their identity by only sharing their initials. The instructors were even nice enough to show us NASA’s Neutral Buoyancy Lab (NBL), a majestic 202’ long x 102’ wide x 40’ deep pool with 6.2 million gallons of water where astronauts train their spacewalks in the closest environment to weightlessness. The pool had full scale replicas (although not entirely attached due to its large size) of parts of the International Space Station.
Just remember what one of the instructors told us “If you can breathe, you can think; if you can breathe, you can perform; and if you can perform, you can survive” and keep that in mind as you fly along… and, if you ever have a chance to take this training, DO IT! You’ll be happy you did…
BLOGS ON THIS PAGE
- NASA's Physiological Training
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- Helicopter Add-On: Transition Training From Fixed-Wing to Rotary-Wing
- Flying to National Parks
- Aviation Vocabulary and Phrases in Spanish
- Friendly Airports and Helipads in the Central Southwest Region
- What to Do with Your Pilot Certificate