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Rare Air: Why You Should Carry Supplemental Oxygen

by Paul Engstrom, Aviation Writer and IFA Member

At what altitude do you need supplemental oxygen so your brain continues to function normally, enabling safe flight?

Federal Aviation Regulations (FARs) suggest that the magic number is 12,500 feet. Between that level and up to 14,000 feet, according to the FARs, crew members must have supplemental oxygen if a flight lasts longer than 30 minutes.

But in practice, the highest safe altitude without extra oxygen may be much lower than that'as low as 8,000 feet, studies show. Even the Federal Aviation Administration encourages pilots to use supplemental oxygen above 10,000 feet during the day and above 5,000 feet at night, when thin air can compromise vision.

Somewhere around 10,000 feet, the percentage of oxygen-carrying hemoglobin in red blood cells may fall as low as 80 percent, compared to 97'99 percent at sea level, notes Dr. Fred Furgang, an anesthesiology professor at the Miami School of Medicine.

Hypoxia, or insufficient oxygen saturation of blood leading to a breakdown of mental and physical processes, isn't the only danger. Another threat, given that you probably haven't experienced this strange malady, is not even realizing you're hypoxic and, consequently, failing to take any countermeasures.

Symptoms you may not notice or associate with hypoxia include a deterioration of judgment and coordination, euphoria or a false sense of security, nausea, cold or hot flashes, blurred or tunnel vision, drowsiness, headache, dizziness, sweating, and a faster breathing rate. Beyond a certain point, oxygen starvation can quickly cause death.

Another not-so-obvious factor figuring into the supplemental-oxygen equation is your physical circumstances and condition at the time of the flight.

For example, the effects of hypoxia will occur at still-lower pressure altitudes if the cabin temperature is cold, you're flying under stressful IFR conditions, or if you're anemic or a smoker, have alcohol in your bloodstream, are aged, or are taking medication such as over-the-counter antihistamines.

As a practical matter, therefore, it's impossible to know at precisely what altitude you'll need supplemental oxygen on any given day. That's why Dr. Robert W. Carlson, an instrument-rated pilot and professor of medicine at Stanford University, offers this advice: 'Think ahead of your altitude.'

In other words, anticipate hypoxia instead of waiting until it grabs you. That means:

  • Carry supplemental oxygen in the aircraft even if you don't expect to need it.
  • Don an oxygen mask or cannula'at 8,000 feet during the day and 5,000 feet at night, Dr. Furgang recommends'before ascending to the danger zone and below FAA-mandated altitudes.
  • Carry, use, and routinely check a portable pulse oximeter. It measures the percentage of oxygen saturation in arterial blood so you know when supplemental oxygen is warranted.
  • Avoid stormy weather by flying around rather than over it.
  • Fly at a lower altitude, if it's safe and practical to do so.

When he isn't flying, Paul Engstrom writes and edits from Sebastopol, Calif.

The information contained herein is meant for informational purposes only. Neither IFA, nor Paul Engstrom assume any responsibility or liability for events that occur due to actions you or others on your behalf take based on the information given in this article. You are proceeding at your own risk. It is strongly advised that you seek the opinion and advice of a qualified aviation medical examiner and appropriate medical physician for any medical needs you may have.