Hypoxia Most  people  are  not  aware  of  the  body’s enormous  increase  in  oxygen  requirements  caused by  an  increase  in  physical  activity.  Strenuous exercise like cross-country running results in a greatly  increased  need  for  oxygen,  which  is evidenced by deep and rapid breathing. Even mild exercise like getting up and walking around a room may double the air intake. In the case of the aviator, leaking of an oxygen mask, which may go completely unnoticed while the wearer is at rest, may lead to collapse and unconsciousness when  an  attempt  is  made  to  move  from  one station to another in the aircraft. A walkaround (portable) oxygen bottle sufficient for 24 minutes of quiet breathing maybe emptied by 17 minutes of use when the user is moving around inside the aircraft. Effects  of  Hypoxia People  differ  in  their  reactions  to  hunger, thirst,   and   other   sensations.   An   individual’s reactions vary from time to time under similar circumstances.  Illness,  pain,  fear,  excessive  heat or cold, and many other factors govern what the response will be in each particular case. The same thing is true of individual reactions to oxygen starvation.  The  effects  of  hypoxia  on  a  given person  cannot  be  accurately  predicted.  For example, a person may be relatively unaffected one day, but highly susceptible the next. It is difficult to detect hypoxia, because its victims are seldom able to judge how seriously they are affected, or if they are affected at all. The  unpleasant  sensations  experienced  in  suffoca- tion are absent in the case of hypoxia. Blurring of vision, slight shortness of breath, a vague, weak feeling,  and  a  little  dizziness  are  the  only warnings. Even these may be absent or. so slight as to go unnoticed. While still conscious, the aviator may lose all sense of time and spend his/her last moments of consciousness in some apparently meaningless activity. In such a condition, a person is a menace to the crew as well as to the himself. Since the aviator  understands  that  it  is  the  reduced  air pressure at higher altitudes that determines the effect on the body, dependence should be upon the altimeter rather than sensations or judgment to determine when oxygen is needed. The effects of hypoxia at various altitudes are discussed in the following paragraphs. BELOW 10,000 FEET.—  At or below 10,000 feet,  some  effects  of  hypoxia  may  be  present. Generally, the eye is the first part of the body to suffer effects of hypoxia. Even at a relatively low altitude of approximately 5,000 feet, where no other  effect  of  hypoxia  can  be  detected,  night vision is appreciable reduced. At 10,000 feet, night operations may be seriously handicapped by poor night   vision,   which   is   due   to   mild   oxygen starvation. Thus, the use of supplemental oxygen on  night  flights  above  5,000  feet  is  required. Although hypoxia affects the eyes in the daytime as well as at night, the results during the day are usually not as noticable below 10,000 feet. BETWEEN 10,000 AND 15,000 FEET.— Although efficiency may be considerably impaired at  10,000  to  15,000  feet,  death  from  oxygen starvation at these altitudes is virtually unknown. The greatest dangers are from errors in judgment or  performance  due  to  drowsiness  or  mental confusion. At these altitudes, long flights without oxygen   produce   persistent   drowsiness   and excessive  fatigue  for  many  hours  afterward. Frequently, persistent headaches develop soon after  completion  of  the  flight.  For  these  reasons, the use of oxygen on flights above 10,000 feet is required. Portable oxygen systems are available for aircraft that do not have oxygen equipment. BETWEEN 15,000 AND 20,000 FEET.— Flights at 15,000 to 20,000 feet, even for short periods, must not be attempted without the use of  oxygen.  Collapse  and  unconsciousness  are common. Failure to use oxygen could result in death, especially when the situation is complicated by loss of blood in combat or by shock due to pain  or  fear. BETWEEN 20,000 AND 25,000 FEET.— During World War II, most military flying was done  in  unpressurized  aircraft  at  altitudes  of between  20,000  and  25,000  feet.  Most  of  the resulting anoxia deaths occurred in this altitude range.  The  general  symptoms  of  drowsiness, mental  confusion,  dim  vision,  and  dizziness occur here, as at lower altitudes, but they come on much more quickly, allowing less opportunity for  corrective  action.  Consequently,  under  no circumstances  should  aircraft  ascend  to  these altitudes,  even  for  short  periods,  without  the  use of  oxygen  by  all  persons  aboard.  The  movement of personnel in the aircraft requires the constant use of walkaround equipment. Unusual actions or failure of a crew member to respond quickly 4-3