My personal experiences with hypoxia have varied greatly from one exposure to the next at similar altitudes. I've noticed the effects of hypoxia at altitude/duration as low as 10,000'/30 minutes when I was already tired or a bit sick. I've felt and performed reasonably well with no supplementary oxygen at 14-15,000'/60 minutes on other occasions. (don’t worry, not as flight crew)
I suspect if you were to ask these same passengers to perform some simple tasks requiring a bit of mental prowess or physical dexterity after an hour at 13,000', you would have a few laughs at the results.iflyforpie wrote:I fly all kinds of passengers (read unfit and elderly tourists) at those altitudes without O2 all of the time and I've never seen any display signs of hypoxia...
From http://www.avmed.in/2011/03/flying-into ... g-hypoxia/
It is important to remember that there are several factors which affect the onset and the severity of the effects of hypoxia. This includes:-
• Altitude. Higher the altitude, lower is the partial pressure of alveolar oxygen; hence shorter is the latent period and greater the severity of effects.
• Rate of ascent. The greater the rate of ascent the more rapid the onset of signs and symptoms of hypoxia
• Duration at Altitude. The effects of hypoxia are more severe if the duration at altitude is prolonged. This is due to the fact that the effects of hypoxia are cumulative.
• Ambient Temperature. High or low environmental temperature favours the development of hypoxia.
• Physical Activity. Physical effort at altitude raises the demand for Oxygen and hence the symptoms of hypoxia are more severe. This fact is to be remembered by aircrew other than pilots too.
• Individuals Susceptibility. Individuals differ considerably in their ability to withstand hypoxia.
• Physical Fitness. A high standard of physical fitness is conducive to a better tolerance of hypoxia. Regular physical training improves the tolerance levels.
• Smoking. Smoking makes an individual more liable to suffer from hypoxia due to binding of haemoglobin with Carbon monoxide present in the smoke. A smoker who smokes prior to sortie has already compromised him-/herself to hypoxic insult, where s-/he is at an apparent altitude of 7,000, 14000, 22000 ft as compared to a non-smoker pilot at sea level, 10000 and 20000 ft, respectively. Be informed that if one smokes three cigarettes before a sortie, it is as if s-/he is already at an equivalent altitude of 8000 feet, with its implications due to compromised vision.
• Organic Diseases. Effects of hypoxia are more severe in those with disease of the heart, lungs or blood, which interferes with the normal oxygenation and circulation, to restrict adequate physiological compensation.
• Emotional State. Apprehension and anxiety make an individual more susceptible to the effects of hypoxia.
• Acclimatisation. Acclimatisation while residing at high altitude raises the individual’s ability to withstand hypoxia.
• Equivalent Lung Altitude. Breathing air at a sea level is associated with a certain partial pressure of oxygen in the lungs (104 mm Hg). By breathing 100% Oxygen, the same partial pressure is brought about at a much greater altitude i.e. at 33,000 ft. The table below shows various equivalent lung altitudes while breathing 100% Oxygen. This concept is found useful in designing the Oxygen system for combat aircraft to ensure adequate oxygenation of the aircrew at different altitude.
