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Aeromedical Forum

Carbon Monoxide; the Quiet Killer

The weather is cooling down and you probably are cranking up the cockpit heater more often now. That’s fine. It’s hard to keep her straight and level when your teeth are chattering. But with the comfort of cockpit heat comes the possible discomfort of doing yourself in. Do I have your attention? Most general aviation aircraft use a time honored heating system where intake air is passed over the exhaust manifold of the engine. If you’ve ever bumped against a tailpipe you know that it’s red hot and has plenty of heat to spare. Using that heat to keep you warm and toasty while in the clouds is both elegant and efficient. There’s just one drawback. The exhaust from the internal combustion engine that’s making your propeller spin round contains large amounts of carbon monoxide.

Carbon monoxide is a colorless, odorless gas that is a byproduct of combustion. It spews out of any gas or diesel burning motor. As long as it travels through the exhaust manifold or tail pipe out into the atmosphere, it’s not a problem. However, if your aircraft’s exhaust manifold has a crack in it, that carbon monoxide will be sucked into the heating air and start building up in the cockpit. This is a big-time problem.

Carbon monoxide competes with oxygen for the binding site on hemoglobin. You’ll remember from your high school biology that hemoglobin is the molecule in red blood cells that carries oxygen from your lungs to all the cells of your body. Your body’s cells need oxygen to metabolize stuff. If the carrier sites in hemoglobin are occupied by carbon monoxide, the oxygen can’t bind and misses the boat. If your cells don’t get oxygen they and eventually you, die!

So how do you know if you’re taking on carbon monoxide? As I said, it’s odorless and colorless so you can’t smell or see it. Admittedly some of the other stuff from the exhaust might come through and give off a funky odor but don’t count on it. Sometimes your first hint is a headache. You might feel a little drowsy, have trouble concentrating, or experience blurring of vision. Sometimes these symptoms are minor and you just gradually slip into unconsciousness. Needless to say this complicates your flying.

Reaction to carbon monoxide varies from person to person.

If you are a smoker you are going to be much more susceptible to carbon monoxide poisoning.

What do you do if something smells funny or you are feeling a headache or drowsiness coming on and you think you are sucking up carbon monoxide?

• First, turn the cabin heat fully off.

• Crank up the fresh air ventilation to maximum.

• If you have it, use supplemental oxygen.

• Land as soon as possible. Let ATC know and ask for vectors

to the nearest suitable airport.

• After landing seek medical attention. Get to an ER. If you or a passenger is found to be severely exposed, talk with the ER doc about evacuation to a hyperbaric chamber. This is the treatment of choice for severe carbon monoxide poisoning. They have a chamber at Hennepin County Hospital in Minneapolis.

Obviously, prevention is the best medicine. There are several devices that can monitor for carbon monoxide. The cheapest is a stick-on colorimetric card that changes color when carbon monoxide is around. They are useful but not foolproof.

So make sure that a certified A & P mechanic inspects your heating system with each annual. You might have him take a look sooner if you suspect something, especially on an older general aviation airplane.


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