The Circulation System — Page 31, Lesson 48

I want to walk you through a critical safety topic within the circulation system: carbon monoxide poisoning. This is a serious hazard in aviation, and I need you to understand exactly why it's so dangerous, how it affects your body, and what you must do about it. Let's start with where carbon monoxide comes from. It's produced by incomplete combustion of carbon. Now, the source matters a lot in aviation. Jet exhausts contain less than 1% carbon monoxide, which is relatively low. But exhaust gases from reciprocating engines—the piston engines found in many light aircraft—can consist of as much as 9% carbon monoxide. That's a huge difference. The danger is that this gas can be introduced into the cabin air from leaking exhaust systems and heater fumes. The book states that the dangers of a presence of carbon monoxide cannot be emphasized too strongly, and I want you to take that seriously. So why is carbon monoxide so dangerous? It comes down to how it interacts with your blood. Your red blood cells contain a protein called haemoglobin, which normally carries oxygen from your lungs to your tissues. But haemoglobin has a much greater affinity for carbon monoxide molecules than for oxygen—up to 210 to 250 times greater. That means haemoglobin will preferentially grab carbon monoxide instead of oxygen. When carbon monoxide combines with haemoglobin, it forms a compound called carboxyhaemoglobin. This gives the blood a bright pink colour, which is a visible sign if you know what to look for. And critically, carbon monoxide is odourless—you cannot smell it—which adds significantly to its dangers because you won't know it's there until symptoms appear. Now, let's talk about the symptoms of carbon monoxide poisoning, because recognising them early could save your life. The first symptom is a headache, or a tightness across the forehead, along with nausea and dizziness. The peril here is that these symptoms might not be immediately recognised as carbon monoxide poisoning by the individual, thereby increasing the danger. As a precaution, fresh air should always be used in conjunction with cabin heat to minimise the effects of possible carbon monoxide poisoning. There's another important factor: the mild hypoxia associated with flying at cabin altitudes of 8 to 10 thousand feet accentuates the effects of carbon monoxide. So if you're already at altitude with reduced oxygen pressure, carbon monoxide hits you even harder. Finally, and this is crucial, the effects of carbon monoxide are cumulative. That means a pilot who flies several times in the same day or on successive days in an aircraft with carbon monoxide concentrations can eventually suffer serious effects. It builds up in your system over time. Let me run through the full list of symptoms so you know what to watch for. They include: headache, tightness across the forehead, dizziness and nausea; impaired vision; a general feeling of lethargy or weakness; impaired judgement; personality change; impaired memory; slower breathing rate and weakening pulse rate; loss of muscular power; flushed cheeks and cherry-red lips; convulsions; and ultimately, death. Notice that impaired judgement and personality change are on that list—that means you might not even realise you're being affected, which is why it's so insidious. Now, if you suspect carbon monoxide poisoning, here is the treatment sequence you must follow. First, turn off cabin heat. Second, stop all smoking—smoking introduces more carbon monoxide. Third, if oxygen is available, it should be inhaled by those affected. Fourth, increase the supply of fresh air through vents and windows. And fifth, land as soon as possible. That's your priority—get the aircraft on the ground. Finally, there are factors that increase your susceptibility to carbon monoxide poisoning. These include altitude, smoking, age, obesity, and your general state of health. So if you're a smoker flying at altitude in an older aircraft, you are at significantly higher risk. That covers the key points on carbon monoxide from the circulation system chapter. Let me know if you have any questions, or if you're ready to move on.