Vacuum Effect of spaceflight on the human body

this painting, experiment on bird in air pump depicts experiment performed robert boyle in 1660 test effect of vacuum on living system.

human physiology adapted living within atmosphere of earth, , amount of oxygen required in air breathe. minimum concentration, or partial pressure, of oxygen can tolerated 16 kpa (0.16 bar). below this, astronaut @ risk of becoming unconscious , dying hypoxia. in vacuum of space, gas exchange in lungs continues normal results in removal of gases, including oxygen, bloodstream. after 9 12 seconds, deoxygenated blood reaches brain, , results in loss of consciousness. death gradually follow after 2 minutes of exposure—though absolute limits uncertain.

humans , other animals exposed vacuum lose consciousness after few seconds , die of hypoxia within minutes. blood , other body fluids boil when pressure drops below 6.3 kpa (47 torr), vapor pressure of water @ body temperature. condition called ebullism. steam may bloat body twice normal size , slow circulation, tissues elastic , porous enough prevent rupture. ebullism slowed pressure containment of blood vessels, blood remains liquid. swelling , ebullism can reduced containment in flight suit. space shuttle astronauts wore fitted elastic garment called crew altitude protection suit (caps) prevented ebullism @ pressures low 2 kpa (15 torr). spacesuits necessary prevent ebullism above 19 km. spacesuits use 20 kpa (150 torr) of pure oxygen, enough sustain full consciousness. pressure high enough prevent ebullism, simple evaporation of blood, or of gases dissolved in blood, can still cause decompression sickness (the bends) , gas embolisms if not managed.

a short-term exposure vacuum of 30 seconds unlikely cause permanent physical damage. animal experiments show rapid , complete recovery normal exposures shorter 90 seconds, while longer full-body exposures fatal , resuscitation has never been successful. there limited amount of data available human accidents, consistent animal data. limbs may exposed longer if breathing not impaired. rapid decompression can more dangerous vacuum exposure itself. if victim not hold breath, venting through windpipe may slow prevent fatal rupture of delicate alveoli of lungs. eardrums , sinuses may ruptured rapid decompression, soft tissues may bruise , seep blood, , stress of shock accelerates oxygen consumption, leading hypoxia. injuries caused rapid decompression called barotrauma, , known scuba diving accidents. pressure drop small 100 torr (13 kpa), produces no symptoms if gradual, may fatal if occurs suddenly.

most of information known way human body reacts due accidental decompression, during experimental spaceflight projects. 1 such case discussed in nasa technical report: rapid (explosive) decompression emergencies in pressure-suited subjects:

@ nasa s manned spacecraft center (now renamed johnson space center) had test subject accidentally exposed near vacuum (less 1 psi) [7 kpa] in incident involving leaking space suit in vacuum chamber in 65. remained conscious 14 seconds, time takes o2 deprived blood go lungs brain. suit did not reach hard vacuum, , began repressurizing chamber within 15 seconds. subject regained consciousness @ around 15,000 feet [4600 m] equivalent altitude. subject later reported feel , hear air leaking out, , last conscious memory of water on tongue beginning boil.

there has been 1 recorded incident of death decompression in spaceflight, soyuz 11 decompression accident in 1971, resulted in death of 3 cosmonauts on board.