Why is 13,000 m the highest humans can survive breathing pure oxygen?
958382
Hi,\n\nWell for one thing, humans can go way higher than that WITHOUT supplimentary oxygen.  Quite a few people have climbed Mount Everest with no extra oxygen and it's altitude it over 29,000 feet!\n\nThis 13,000 foot limit is probably for pilots.  With time, the human body adapts to altitude (over days it makes more and more red blood cells), that's why climbers can go that high without extra oxygen.  But pilots, go up to that altitude very rapidly so they must have oxygen and even then there is a limit (13,000 feet.)\n\nAbove that altitude, as the person above said, you must pressurize the cabin so that the air is under a similar pressure to that on the ground.  This is needed because the pressure helps the lungs absorb oxygen.  At the low pressure at 13,000 feet, the rate of absorption is too slow for the rate your body uses it up, and you would begin to suffocate.\n\nGood question by the way!
1118805
the average person can hold their breath for about a minute and a half in desperation.    i believe the world record is well above 8 minutes now, but those people have lungs 4 times the capacity.   The brain is starved of oxygen at 4 minutes and brain cells begin dying rapidly.
646745
The maximum length of the tube is around fifty centimetres (twenty inches). A longer tube would place the lungs in deeper water where the surrounding water pressure is higher and the lungs would be unable to inflate when the diver inhales, because the muscles that expand the lungs are not strong enough to operate against the higher pressure.
18517
Define Survive.\n\nIf you are a real down to earth person, then the answer is simply that we needs the resources provided from those activites to live for a prolonged period, say 5 mins.\n\n\nWithout air, your brain will begin to die within minutes.   Oxygen is absolutely required by our cells to operate.
130673
13.1 miles or 21.1 Kilometers
496016
depends upon the environment.  Under normal conditions, a few hundred pounds will suffice to keep the diaphram from inflating the lungs.  In deep water, there are experimental blends that allow oxygen levels to be maintained.
253499
you will need first to know something about lung capacity.\n\nA person cannot completely exhale all the air contents in the lungs, because it would cause their collapse: Then,  some air remains inside, which can be denominated as minimum air. \nThe maximum amount of air that can be exhaled is denominated vital capacity (about an average of four liters) and the residual capacity (the one that is left in the lungs) is about one liter of average. \nThe total pulmonary capacity, therefore, is of about five liters of air (average). \nThe current volume of air inhaled and exhaled in the normal breathing is near half liter (at rest). Following the normal expiration, the amount of air that is taken with the possible deepest inhalation is known like complementary volume, and it is somewhere around three liters. \nFollowing the normal inspiration, the amount of air expelled in the greater possible exhalation is known as additional volume, or reserves, and it is approximately, a liter of air.\n\nIf we take as a media about 12 air intakes per minute (at rest), we might as well speak of about six liters per minute.\n\nNow you have all the guidelines. Under the stress of exercise, the intake frequency will increase, and also the quantities of air inhaled or exhaled, which can be even about five times the air intake at rest. Quantity of intakes can be brought up from 12 per minute to 50 per minute. There are variables, and all depends on how you demand your body, for how long, if you smoke or have smoked, age, etc. but just go ahead and do some math.\n\nFor your guidance, one cubic feet has 28.32 liters.\n\nPS: No yawning considered.
372603
Its got nothing to do with oxygen, that theories been scientifically disproven. But i dont have another answer, sorry
299063
Please.  Your lungs can not be down as much as 3 feet I believe, or the air would be forced out of your lungs.  Now if you snorkel at normal depth, you can hold your breath and go down as far as you can make it.  But you can't breath continuously unless the air is being pumped.  Your head will not collapse, it's filled with liquid which doesn't compress.
958887
Lavender gave you the key information you need, i.e., too much oxygen damages the body. Probably the best-known example of this is blindness in prematurely born infants due to breathing pure oxygen for extended periods (which is sometimes necessary to keep them alive). There are probably medical techniques available today to minimize this problem, but it has been a serious issue in past years (20 years ago in one example I am familiar with).\n\nHere is a bit more information about breathing pure oxygen, and some clarification of the comments from others.\n\nYou can breathe pure oxygen for short periods in order to recover from lack of oxygen (athletes do it, as do firemen who have inhaled smoke, for example).\n\nThe air we breathe at sea level is at a pressure of 14.7 psi, and 21% of it is oxygen. (78% is nitrogen, and most of the other 1% is argon.) If you take 21% of 14.7psi, you'll see that we are breathing oxygen at a pressure of about 3 psi.\n\nPilots and astronauts can breathe pure oxygen, but as Lavender points out, they breathe oxygen at a pressure lower than sea level air pressure. If their oxygen is delivered to them at 3 psi, then it is equivalent to the oxygen in our air at sea level. (And incidentally, the air we breathe is not much changed at elevations up to 5,000 or 10,000 feet. As a rule of thumb, you can notice the difference in air pressure (the difference in the availability of oxygen) when you get close to 10,000 feet of elevation. At 18,000 feet, the air pressure is about 50% of that at sea level. And after another 18,000 feet, the pressure at 36,000 feet is cut in half again, so it is about 25% of the sea level pressure.)
707055
We're taught to never hold our breath on ascent, no matter if it's an out of air emergency ascent situation or a normal ascent to the surface. The last breath we take in, at depth , grows in volume as we ascend. If we didn't constantly breathe with that all important exhalation, air in the aveoli (air sacs) of our lungs would grow in volume to the point they popped. You now get to drown in your own blood. \n By never holding out breath, we keep the pressure differential down to a minimum between ambient and internal.\n As for taking a deep breath before going down, it doesn't matter. We breathe at a normal rate, just like you are now and as long as we're not over exerting ourselves, that really doesn't change.\n\n Lol, diver dude, some really far out answers in there,eh?
201341
the reason is because at sea level, air pressure is measured to be one atmosphere or atm (there are other units of measure, such as mm of Hg, pascals, torrs, but the atm is easiest to remember) our bodies deal with that pressure every day (more if you are below sea level and less if you are above sea level)  when you go under water, you not only have the pressure of the water above you, but also the pressure of the atmosphere as well (every 33 ft of water deep is equal to 1 atmosphere)\n\nso, in short, you can be crushed by atmospheric pressure, it's just that our bodies can withstand that of the earth's.\n\nhope that helps!!
320348
Deep ocean travel requires two things:\nProtection from the enormous pressure\nAdequate supply of oxygen and breathing gas for the safe return to the surface.\n\nAs we dive deeper, our bodies are subjected to the increasing water pressure.  This is especially so if we dive only to depths of less than 100 meters.  As we dive deeper, our bodies are subjected to greater pressure.  Our blood absorbs MORE gas (namely nitrogen gas); as we return to the surface, the increased amount of nitrogen gas in the bloodstream begins to leave the bloodstream.\n\nIf divers return to the surface too fast, the nitrogen gas will bubble out too fast causing a painful and possibly fatal condition called "The Bends".  So, divers must "acclimate" to sea level pressure slowly.\n\nDivers who dive very deep must remain inside pressure chambers in which the air pressure is slowly reduced to sea level pressure, gently allowing the (bloodstream's) absorbed nitrogen gas to escape safely.
566593
100 m above sea level
37068
The air gets less dense, not lighter as elevation increases because there is less air on top to push down on the air beneath it you as you go up.  It would be like diving to the bottom of a swimming pool.  Whenever you go so deep, your ears start to hurt because the pressure of the water on you.  It's like that, but we're used to the pressure of the air.  \n\nTall people don't breathe easier, there isn't that much of a difference in pressure.  But actually, the higher you go, the harder it is to breathe.  There is less oxygen as you go up (that's why mountain climbers have to wear oxygen masks when climbing tall mountains like Everest!)
808043
Mount Everest\n\nIt is one of the seven wonders of the natural world. Not surprisingly the highest point on the earth's surface is located there on the border of Nepal and China. Although the exact height of the mountain have been disputed by surveyors for many years the most recent measurement revealed the mountain to stand at 8850 meters, nearly 5.5 miles. The adventure that led to this result took place in May 1999. Bill Crouse and his crew set an expedition to find the height of this point. Six months later they returned and claimed to have found the exact measurement of the highest point on earth's surface.\nMount Everest is the highest peak in the Himalayan mountain range. People were unaware that it was the tallest mountain in the world until 1856. George Everest of India made the discovery. Plate tectonics show that the height of Everest is still increasing at a steady rate of approximately one centimeter (0.394 inch) per year.\n\nMount Everest is over 8000 m above sea level. Winds travel at 161 kilometers per hour; the windchill is often 96 degrees Celsius below zero. At such high altitudes as Everest, less oxygen is able to enter the lungs, making it difficult to breathe. The amount of oxygen usable for breathing is determined by pressure in the atmosphere. The greater the atmospheric pressure the closer the oxygen molecules. At high altitudes, atmospheric pressure decreases, and air molecules are further separated. Therefore there is less oxygen that is able to enter the lungs.\n\nThough most people have recognized the highest point at Mount Everest, Mount Chimborazo located in the city of Rimobamba, Ecuador may also be considered as the highest point on earth. Although it is not as well known as Mount Everest, standing at 6310 meters it is also quite remarkable. Mount Chimborazo can be regarded as the highest point on earth because the planet is widest at the equator. The summit of Mount Chimborazo is then 3219 m further from the center of the earth than Mount Everest, making it what some consider the highest point. On the summit of Mount Chimborazo people will weigh less than any other location on earth.\n\nAs the highest point on the earth's surface, Everest has become the ultimate challenge for any determined high altitude climber. A group led by George Mallory first attempted it in 1921, however the summit was not reached until 1953 when Sir Edmand Hillary and Sherpa Tenzing Norgay of New Zealand survived the challenging task. Edward Whymper of Britain was the first man to successfully reach the summit of Mount Chimborazo in 1880.\n\nOne of the highest places you can take your car is to Ojos del Salado in Chile. This is the world's tallest volcano at about 22,560 feet. If you live in the U.S. and want some place closer to home, try Colorado. It's many tall moutain peaks make for good high altitude driving.\n\n"And then there’s the Volkswagen exec, who stands up and announces that his company now holds the world record for highest altitude attained by a stock vehicle. Rainer Zietlow, some guy who claims he’s attained fame by taking stock vehicles to extremely high altitudes, piloted a stock Toureg with the base 3.2L V6 to the peak of Chiles Ojos del Salado, the worlds tallest volcano. Guiness marks the record altitude at 19,950 feet. Perhaps VW should tag its Toureg with the title of “Best Luxury SUV above sea-level”."\n\nThe other claim to the highest road (therefore the highest place accesible by car) on Earth is the Manali-Leh route (300 miles) just north of Lahore in the Indian Himalayan mountains.\n\nIt crosses four high passes which range in height from 14,000 to 18,000 feet.\n\nAt Leh, the Khardung La, claims to be the highest point.\n\nThe link below is to a very old army map showing some of the route.\nhttp://www.myhimalayas.com
136486
Oxygen is the only gas we really need to breathe in order to stay alive. If we don't breathe oxygen (or if we don't breathe enough oxygen), we soon die. Interestingly enough, too much oxygen can be a bad thing also. At right is a diagram illustrating the range of oxygen concentrations that we can breathe safely. The green and red bar represents a scale of inspired oxygen partial pressures (PO2), ranging from zero oxygen on the left, to a PO2 of 2.0 ATA on the right. Through evolution, our bodies have become optimized to breathe oxygen at a partial pressure (PO2) of 0.21 ATA. If the inspired PO2 is much less than this, our bodies begin to shut down -- leading to unconsciousness when the PO2 drops below about 0.1 ATA (i.e., 10% oxygen at sea level). This is called hypoxia. Breathing more than 0.21 ATA oxygen is generally fine ... up to a point. If the inspired PO2 is maintained above about 0.5 ATA for prolonged periods of time (many hours to days), people begin to suffer what is usually referred to as "pulmonary" or "chronic" oxygen toxicity. The effects of this include a burning sensation or irritation in the lungs, and can affect breathing. Except for people who spend days under pressure at a time (e.g., commercial divers on oil rigs), this form of oxygen toxicity is not much of a problem for divers.\n\nHowever, as the inspired PO2 starts to climb above about 1.2 to 1.4 ATA, another kind of oxygen toxicity, called "CNS" (for "Central Nervous System") or "acute" oxygen toxicity, becomes a significant problem. Although a variety of subtle symptoms such as muscular twitching in the face and tunnel vision have been attributed to this kind of oxygen toxicity, the really important symptom is severe, uncontrolled convulsions. Although these convulsions do not appear to cause any sort of permanent damage by themselves, the problem of a diver experiencing such convulsions being able continue to hold a regulator in his or her mouth is obvious. More than a few divers have drowned underwater, apparently a result of oxygen-induced convulsions. This is perhaps the most serious and insidious of diving maladies, because it comes on unpredictably and without warning, and usually results in the death of the afflicted diver.\n\nThere is no clear understanding on the exact biochemical processes involved with CNS oxygen toxicity, nor is there a clear consensus on what the "safe" upper PO2 limit should be. Convulsions have occurred in divers breathing an inspired PO2 as low as 1.2 ATA, but such cases usually involve extenuating circumstances (such as medical conditions in the divers which pre-dispose them to convulsions). Conversely, commercial divers in Europe have routinely breathed oxygen partial pressures as high as 1.9 ATA in the water, and hyperbaric chamber facilities regularly expose patients to 2.8 ATA of oxygen (or more) without difficulty. Amid the ambiguities, two trends seem very consistent. The first is that high levels of exercise (perhaps more specifically, high levels of CO2 in the blood) appear to increase the probability of suffering from a convulsion. Secondly, divers immersed in water have a lower tolerance to elevated concentrations of inspired oxygen than do divers kept dry in a hyperbaric chamber or undersea habitat. (this over and above the fact that divers in a dry habitat are much more likely to survive a convulsion than are divers immersed in water). Another unavoidable reality regarding oxygen toxicity is the extreme range of variation both between individuals, and within a single individual.\n\nWhen immersed underwater, most divers regard a PO2 of 1.4 ATA as a safe upper limit during periods of physical exertion, and 1.6 ATA during periods of rest.