Crash and Breathe

Has this ever happened to you?

The interior of the plane began to fill with intense, heavy black smoke, which was extraordinarily painful to breathe and very toxic...It quickly became pitch black in the cabin from the heavy smoke, in spite of the bright light from the fire on the left side of the plane...I was feeling very faint and I later guessed I only had about 15 to 30 seconds of consciousness left.  Every breath caused me to convulse and was extremely painful...."

Thus begins the article entitled "Get Out NOW!" by Patrick R. Veillette, Ph.D. in the April 2007 issue of Business and Commercial Aviation.

Chances are that it hasn't happened to you; few people have such an experience, and fewer still survive it.  Your choices often come down to either being lucky or singing "It's a girl, Mrs. Walker, it's a girl."  But I had long held a theory about this precise scenario.  The theory was that there is, indeed, something one can do to increase his chance of survival.  Although one reads of airplane crashes involving fire and smoke, Veillette's article is the first I recall seeing in a journal targeted to aviation professionals.  I was eager to read it to find confirmation of my theory, which was this:

Hyperventilation Isn't Necessarily Bad

Hyperventilation—excessively rapid and deep breathing—is uniformly described as something to be avoided in aviation.  It can be triggered by decreased partial pressure of oxygen at high altitudes, or psychological factors such as panic.  It can cause faintness, tingling of the extremities, and eventual loss of consciousness.  (Which is bad, by the way.  Consciousness is a good thing when you're flying.)  But one consequence of hyperventilation is decreased carbon dioxide in the lungs and blood.  And, in my theory, this can be a good thing.

When you hold your breath, you know that the urge to begin breathing again builds up quickly, eventually making it impossible to not draw in that lungful of air.  You might reasonably consider this urge to be your body telling you that you need oxygen.  Not so!  It's actually your body telling you that you have too much carbon dioxide.  Under normal circumstances, your blood is almost completely saturated with oxygen, if it weren't for the CO2 buildup, you could hold your breath and remain conscious longer.  Which brings me to the consequence of my theory, which is a suggestion to hyperventilate before crashing.

An airplane crash, while it may be over in seconds, is often a drawn out affair.  Something goes wrong in the aircraft, and you need to get on the ground quickly.  Depending on what went wrong, "ground" and "airport" may not be synonymous.  Airplane "crashes" are frequently survivable.  If the aircraft is under any control at all, it is usually possible to "land" somewhere without instant destruction.  What happens after that depends on skill and a lot of luck.  You may walk away, you may die in the crash, and finally, there may or may not be a fire and smoke, from which you may or may not emerge among the living.

If you have managed, or so my theory goes, to hyperventilate by the right amount before the smoke and fire, you may have an extra edge when they're yelling "This way to the egress."  Although there are many ways to improve ones chances, e.g., smoke hoods or small SCUBA systems a la James Bond, they all require preparation.  Presumably, people who have been breathing earlier have what they need to hyperventilate with them at all times and need no accessories.

Hyperventilation Experiment

No RIKL Blog entry would be complete without mentioning the "no research" policy.  I don't consider the table below to be such, since I was the experimental subject and all the numbers were gathered in the ordinary course of doing whatever it is that I do.  I tried to determine the benefit of hyperventilation under real or mock conditions of not being able to breathe.

As you can see, hyperventilation confers a modest but significant benefit in permitting physical activity while being, for example, in a smoke-filled cabin.  It could conceivably be the difference between being trapped or being able to jump off the wing, hopefully without damaging too many limbs.

Conceivably.  It seems to be a sensible theory, and yet I saw nothing about it in the cited article.  This being the proverbial "matter of life and death," I took advantage of the opportunity to correspond about my theory with people who are actually expert in the subject, which correspondence follows:

From:  Dr. Quay Snyder
Gentlemen,

Thank you for the opportunity to comment on the suggestion to voluntarily hyperventilate to aid in the emergency egress of a smoke filled cabin.

The suggestion seems intuitively to make sense. However, I believe the human physiology of this action would actually be counterproductive. Without being too technical, I offer the following explanation.

Hyperventilation by voluntarily increasing the depth and rate of breathing does little, if any, to raise the oxygen saturation in the blood of an individual. Any increase in oxygen would be depleted by the body in 4-8 seconds, rather than giving "many seconds or perhaps a minute" of useful consciousness. The individual is better served by holding his/her breathe until away from the smoke/toxin filled environment. In a somewhat analogous situation, hyperventilating in a rapid decompression actually reduces the time of useful consciousness by almost 50%.

Instead, hyperventilation reduces the carbon dioxide saturation in the blood. This is a double edged sword. Reduced blood levels of carbon dioxide may reduce the body's drive to inhale allowing breath holding for 5-10 seconds longer at best. Hyperventilation may also cause decreased blood flow to the head making someone more likely to lose consciousness, particularly in a physically demanding or emotionally charged situation. This is why we teach pilots to control any hyperventilation in the cockpit.

The other downside of hyperventilating is that by the time smoke is noticed, toxic substances released from off-gassing aircraft cabin components are probably present in significant concentration. Hyperventilating will increase the exposure to these substances, thus increasing the risk of hazardous physiological consequences and reducing the ability to egress the aircraft.

The ideal situation is to have oxygen available and reduce/eliminate exposure to off-gassing toxins. A walk-around oxygen bottle with a tight face seal is ideal. Deploying the cabin oxygen masks to allow breathing until an egress can be attempted is an alternative. Using a commercial smoke hood to filter out toxic gases is a less desirable alternative. Finally, breath holding until egress is possible is what may be the only alternative. Air near the floor will tend to be less contaminated in most cases.

I hope this helps address the reader's concerns and well-intended suggestions.

Fly safely,
Quay
Quay Snyder, MD, MSPH

Response from me
Dear Dr. Snyder:

I'm the reader who posed the hyperventilation question, and I appreciate your comprehensive answer. I based my "intuition" on the fact that I do this almost every day. My chosen gym activity is normally lap swimming, and I always do my first length underwater, largely to prove to myself that I still can. I take a few deep breaths first, and inevitably make it to the far end with little difficulty. I had always assumed that it was the CO2 purging that did the job, since the O2 saturation was in the high 90s to begin with.

I accept your answer and hope never to have to prove it's correct! But just in the interest of science I'm going to experiment at the gym and see how much of a difference is made by an immediate underwater plunge.

Thanks again!
Richard Factor

Response from Dr. Snyder
Richard,

How did the experiment today go? I am curious.
Mine: Hyperventilate = 25 yds,
Single deep breath = 18 yds

Quay

From me:

It didn't. I'm in New Jersey, and the section of State Hwy 23 on which the gym is located was flooded out due to the worst single-day rainfall since the 1800's.

I'll try today and let you know. Assuming, of course, that the gym is still there!

Richard

And that was the last Dr. Snyder heard from me until I sent him an email pointing to this blog item.  The gym, fortunately was not washed away, and I have mentioned previously the irony of a big flood having prevented me from swimming!

Clearly my theory isn't as airtight as I had hoped.  I bow to Dr. Snyder's expert opinion, and have therefore written this blogitem to tell you:

Be sure you don't do what you had almost certainly never thought of doing under circumstances that will almost certainly never occur.

NP:  "Night Comes In" - Richard Thompson

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