Vacuum & Hypoxia (What happens if you are exposed to the vacuum of space?)

· by · in Medical science, Science, Space exploration. ·

http://www.youtube.com/watch?v=zIDgfs7AlOY&feature=player_embedded

http://www.youtube.com/watch?v=lK8U8RZyzsM&feature=related

In scores of science fiction stories, hapless adventurers find themselves unwittingly introduced to the vacuum of space without proper protection. There is often an alarming cacophony of screams and gasps as the increasingly bloated humans writhe and spasm. Their exposed veins and eyeballs soon bulge in what is clearly a disagreeable manner.

The ill-fated adventurers rapidly swell like over-inflated balloons, ultimately bursting in a gruesome spray of blood.

As is true with many subjects, this representation in popular culture does not reflect the reality of exposure to outer space.

Ever since humanity first began to probe outside of our protective atmosphere, a number of live organisms have been exposed to vacuum, both deliberately and otherwise. By combining these experiences with our knowledge of outer space, scientists have a pretty clear idea of what would happen if an unprotected human slipped into the cold, airless void.

In the 1960s, as technology was bringing the prospect of manned spaceflight into reality, engineers recognized the importance of determining the amount of time astronauts would have to react to integrity breaches such as a damaged spacecraft or punctured space-suits.

To that end, NASA constructed an assortment of large altitude chambers to mimic the hostile environments found at varying distances above the Earth, accounting for factors such as air pressure, temperature, and radiation. Adventurous volunteers were subjected to simulations of the conditions found several miles up, and a handful of animal tests were conducted with even lower pressures.

Using the data from these experiments and their knowledge of outer space, scientists were able to make some reasonable conclusions about how the human body would respond to sudden depressurization.

A series of accidents over the years proved most of their extrapolations to be accurate. In 1965, in a space-suit test gone awry, a technician in an altitude chamber was exposed to a hard vacuum.

The defective suit was unable to hold pressure, and the man collapsed after fourteen seconds. He regained consciousness shortly after the chamber was repressurized, and he was uninjured. In a later incident, another technician spent four minutes trapped at low pressure by a malfunctioning altitude chamber.

He lost consciousness and began to turn blue, but escaped death when one of the managers kicked in one of the machine’s glass gauges, allowing air to seep into the chamber.

A Soviet Soyuz spacecraft
Artist’s rendering of a Soviet Soyuz spacecraft

In 1971, three Russian cosmonauts aboard an early Soyuz spacecraft tragically experienced the vacuum of space first-hand, as described in the Almanac of Soviet Manned Space Flight:

“…the orbital module was normally separated by 12 pyrotechnic devices which were supposed to fire sequentially, but they incorrectly fired simultaneously, and this caused a ball joint in the capsule’s pressure equalization valve to unseat, allowing air to escape. The valve normally opens at low altitude to equalize cabin air pressure to the outside air pressure.

This caused the cabin to lose all its atmosphere in about 30 seconds while still at a height of 168 km. In seconds, Patsayev realized the problem and unstrapped from his seat to try and cover the valve inlet and shut off the valve but there was little time left.

It would take 60 seconds to shut off the valve manually and Patsayev managed to half close it before passing out.

Dobrovolsky and Volkov were virtually powerless to help since they were strapped in their seats, with little room to move in the small capsule and no real way to assist Patsayev.

The men died shortly after passing out. […] The rest of the descent was normal and the capsule landed at 2:17 AM.

The recovery forces located the capsule and opened the hatch only to find the cosmonauts motionless in their seats.

On first glance they appeared to be asleep, but closer examination showed why there was no normal communication from the capsule during descent.”

When the human body is suddenly exposed to the vacuum of space, a number of injuries begin to occur immediately.

Though they are relatively minor at first, they accumulate rapidly into a life-threatening combination.

The first effect is the expansion of gases within the lungs and digestive tract due to the reduction of external pressure.

A victim of explosive decompression greatly increases their chances of survival simply by exhaling within the first few seconds, otherwise death is likely to occur once the lungs rupture and spill bubbles of air into the circulatory system. Such a life-saving exhalation might be due to a shout of surprise, though it would naturally go unheard where there is no air to carry it.

In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim’s mouth and eyes to quickly boil away.

The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin.

A NASA vacuum chamber
A NASA altitude chamber

Within seconds the reduced pressure would cause the nitrogen which is dissolved in the blood to form gaseous bubbles, a painful condition known to divers as “the bends.” Direct exposure to the sun’s ultraviolet radiation would also cause a severe sunburn to any unprotected skin. Heat does not transfer out of the body very rapidly in the absence of a medium such as air or water, so freezing to death is not an immediate risk in outer space despite the extreme cold.

For about ten full seconds– a long time to be loitering in space without protection– an average human would be rather uncomfortable, but they would still have their wits about them.

Depending on the nature of the decompression, this may give a victim sufficient time to take measures to save their own life. But this period of “useful consciousness” would wane as the effects of brain asphyxiation begin to set in.

In the absence of air pressure the gas exchange of the lungs works in reverse, dumping oxygen out of the blood and accelerating the oxygen-starved state known as hypoxia. After about ten seconds a victim will experience loss of vision and impaired judgement, and the cooling effect of evaporation will lower the temperature in the victim’s mouth and nose to near-freezing.

Unconsciousness and convulsions would follow several seconds later, and a blue discoloration of the skin called cyanosiswould become evident.

At this point the victim would be floating in a blue, bloated, unresponsive stupor, but their brain would remain undamaged and their heart would continue to beat.

If pressurized oxygen is administered within about one and a half minutes, a person in such a state is likely make a complete recovery with only minor injuries, though the hypoxia-induced blindness may not pass for some time.

Without intervention in those first ninety seconds, the blood pressure would fall sufficiently that the blood itself would begin to boil, and the heart would stop beating. There are no recorded instances of successful resuscitation beyond that threshold.

Though an unprotected human would not long survive in the clutches of outer space, it is remarkable that survival times can be measured in minutes rather than seconds, and that one could endure such an inhospitable environment for almost two minutes without suffering any irreversible damage.

The human body is indeed a resilient machine.

Another article:

EBULLISM AT 1 MILLION FEET:

Surviving Rapid/Explosive Decompression

Tamarack R. Czarnik, MD

WSU
Residency in Aerospace Medicine
Hypobaric Medicine

Abstract

Expected outcome of a space-equivalent decompression has improved dramatically in the past 40 years, from an a priori assumption of non-survivability to the possibility of survival and rehabilitation. This paper outlines the history of Man’s struggle with altitude, examines the known pathophysiology of Ebullism, explores the measures taken to improve survival in the Shuttle era, and investigates the state-of-the-art in treatment of rapid/explosive decompression.

I) HISTORICAL PERSPECTIVE

Since the earliest days of America’s Manned Spaceflight program, one of the foremost concerns has been that of decompressions beyond Earth’s atmosphere. Early experiments in the 1800s (1) on laboratory animals revealed the catastrophic consequences of decompression to near-vacuum: hypoxia, decompression sickness (DCS), arterial gas embolism (AGE) and ebullism, a ‘boiling away’ of water vapor from the body, generally considered (at the time) to be almost immediately fatal. While the conditions necessary for ebullism are present at an altitude of roughly 63,000 feet (referred to as the Armstrong Line), variations in the body’s temperature and pressure can allow this to occur as low as 55,000 feet (2); thus, the ‘line’ is perhaps better thought of as a band (3).

For as long as we’ve known the consequences of altitude, we’ve made plans to improve our survival. Croce-Spinelli and Sivel first used supplemental oxygen in their 1874 balloon flight (4). Paul Bert developed the first altitude chamber (with supplemental oxygen) in 1878, and in 1934 Wiley Post developed and demonstrated the first pressure suit for high-altitude flights (4). As human flight neared the 40,000 foot level (at which the partial pressure of oxygen in air equals the combined pressures of carbon dioxide and water in the body), positive-pressure breathing (PPB) was instituted to provide sufficient oxygen despite falling pressure. Counterpressure garments, designed to facilitate high levels of PPB, evolved into the more extensive partial-pressure suit (5), capable of protecting the wearer from ebullism down to 15 mm Hg (6), but ineffective against the concomitant DCS and AGE.

Full-pressure suits, like the ILC Dover used in the Apollo program, incorporated a helmet, surrounding the body with a pressurized gas envelope. Since a full-pressure suit for extravehicular activity (EVA) presents an enormous pressure differential with the surrounding environment, they are inflated to only about one-third of normal (sea level) pressure, about 4.3 psi, with 100% oxygen. Since this level of oxygen imposes a high risk of fire, the ‘shirt-sleeve’ environment of the Space Shuttle utilizes a 20% oxygen content at 14.7 psi.. This ‘Earth-normal’ atmosphere will also be used on the International Space Station (ISS), necessitating extensive prebeathing with 100% oxygen before EVA and increasing the risk and morbidity of an unplanned loss of pressurization (7).

If and when such a loss in pressure occurs, what can we expect?

II) PATHOPHYSIOLOGY OF EBULLISM

What does happen to a human exposed to vacuum? Can we successfully plan for a rapid decompression at 1,000,000 feet?

Hypobaria (low pressure) has life-threatening effects primarily on 3 systems: the Lungs, the Heart and the Brain. We examine each of these in turn.

Pulmonary Damage to the lungs in rapid or explosive decompression occurs primarily due to pulmonary overpressure, the tremendous pressure differential inside versus outside the lungs. 80 mm Hg is enough to cause pulmonary tears and alveolar rupture (8); pulmonary hemorrhaging, ranging from petechiae to free blood (depending on the magnitude and rate of decompression) is also seen (9). Emphysematous changes are seen especially in the upper lungs, while atelectasis and edema predominate in the lower lungs (10). When we get to the patient, the lungs will be a bloody, ruptured mess.

Cardiovascular Myocardial damage associated with ebullism is caused by stretching of the myocardium and anoxia (11). Heart rate rises the first 20 seconds (12), then drops to 40% of baseline at sixty seconds (12). By 2 minutes the arterial pressure wave is lost (13), but the cardiac contractility is maintained at least 5-7 minutes (14). Apneic animals resumed spontaneous respirations within 30 seconds of recompression as long as the heart continued to beat, but could not be resuscitated once asystole occurred (15). If our patient has a pulse, we might get him back.

Central Nervous System In rapid or explosive decompression above 60,000 feet, CNS damage is due to decreased cerebral blood flow and global cerebral anoxia (16). Little evidence of herniation is noted (16), though some damage to cerebral white matter and myelinated spinal cord is seen (13). Cases of accidental rapid and explosive decompression to date have not shown any lasting neurological damage (17, 18), though this includes only 2 cases. Our astronaut-patient may be rehabilitatable.

Though these are the most life-threatening changes seen in ebullism, subcutaneous swelling is also seen, due to creation of water vapor under the skin (19). This can rapidly distend the body to twice its normal volume (20). Our patient will look no better than he feels, though this means little in terms of survival.

This, then, is what we can expect to face. What measures have been taken to date to avoid ebullism in the space environment?

III) SHUTTLE-ERA COUNTERMEASURES TO EBULLISM

Shuttle Design The outcome of rapid decompression depends on multiple factors: rate of pressure change, absolute change in pressure, absolute pressure before decompression, ratio of initial pressure to final pressure, ratio of lung volume at the time of decompression to maximal lung capacity, and ratio of the cabin wall orifice (hull rupture) over the total cabin volume compared to the ratio of airway orifice over lung volume (21). The Shuttle, for example, is designed to sustain a pressure of 414 mm Hg for 165 minutes (long enough for an emergency return to Earth) in the presence of an 11 mm (0.45 inch) diameter hole (22). Data from the Long-Duration Exposure Facility indicates a flux in low-Earth orbit of 0.00001 meteoroids (and 0.0001 pieces of orbital debris) this size or larger per square meter per year (23). Thus, a good measure of protection from explosive decompression is provided by the ship itself.

Crew Altitude Protection Suit (CAPS) During launch and reentry, crewmembers are required to wear a fitted elastic garment, capable of preventing ebullism at pressures as low as 15 mm Hg (an altitude-equivalent of 70,000 feet) (5). In fact, these would be likely to reduce the risk of ebullism; unfortunately, this partial-pressure garment provides no protection from DCS or AGE.

Personal Rescue Sphere (‘Space Ball’) Should the shuttle become compromised and unable to return to Earth, a unique emergency system is in place. Each crew member has a Personal Rescue Sphere (PRS), a 34-inch diameter fabric garment into which they can be zipped (Plate 1) (22). The sphere is then inflated with oxygen, and can be carried through space to a rescue vehicle. Each PRS has its own supply of oxygen, a window, and a small telephone. In addition to emergency decompression, the ‘Space Ball’ might also be used if the cabin air became contaminated, allowing a suited crewmember to vent the entire atmosphere and replace it. Simple and rapidly donned, the Personal Rescue Sphere is the final refuge in the event of a decompressive emergency.

These are our current countermeasures for an emergency decompression. What technology is currently available to improve survival, which could be implemented in the near future?

IV) TREATMENT OF EBULLISM

There is currently no treatment protocol for ebullism; until recently, exposure to vacuum was generally accepted as nonsurvivable, based in part on 1960s animal research (24). But much research has been done in the intervening 30 years, and viable treatment options are beginning to emerge. Loosely characterized and in order of occurrence, these treatment phases are Return to Pressure (with hyperbaric oxygen), Basic Life Support (with high frequency ventilation), and Drug Therapy.

Return to Pressure Foremost in treatment considerations is rapid return to a pressure consistent with adequate oxygenation. Recompression reverses the massive bubbling and tissue swelling of ebullism (25), and allows for further treatment of the patient. On EVA or during planetary exploration, only on-site patching of the suit and repressurization would likely repressurize the patient adequately before asystole ensued.

On board the ISS, a depressurized crewmember would be brought to the combination airlock/compression chamber for recompression. Hyperbaric oxygen therapy would likely be used, due to its proven efficacy in treatment of DCS and AGE (both conditions associated with ebullism), although not all reports show it improves survival (26). Previous ISS design calls for a multiplace chamber rated to 3 ATA, sufficient for a Table 6 protocol (which does not increase body nitrogen; a Table 6A recompression to 6 ATA would, as 100% oxygen could not be used due to toxicity) (27). I am unable to ascertain at this time the proposed rating for the current design crew lock.

Basic Life Support Ebullism necessitates rigorous attention to basic life support (BLS) principles. Pulmonary hemorrhage and respiratory embarrassment will make vigorous endotracheal suctioning and intubation necessary. High Frequency Ventilation (HFV), a small-bore catheter ventilating at or above the resonance frequency of the lungs (600-2000 breaths per minute!), will avoid the pulmonary barotrauma and cardiac compromise associated with positive end-expiratory pressure (28).

Internal bleeding and plasma loss immediately following exposure (29) will require placement of 2 large-bore IV’s and use of fluid expanders (e.g. Dextran).

Due to water phase change and evaporative cooling, body temperature drops and facial and extremity tissues can freeze. However, numerous investigators report improved survival from decompression with hypothermia (30, 31), and thus it is felt this decreased temperature should be maintained for at least 2 hours before rewarming (32).

In addition, although asystole ensues after about 2 minutes, cardiac contractility continues for at least 5 minutes; advanced cardiac life support may be called for (current ISS design includes a defibrillator with data telemetry to the Flight Surgeon).

Drug Therapy A number of drugs have been tested for the prevention and treatment of Ebullism and the attendant conditions of DCS and AGE, with varying degrees of success.

Pentoxifylline (Trental) This drug, commonly prescribed for peripheral vascular insufficiency, increases red cell deformability and decreases blood viscosity. Cerebral blood flow, decreased by slow experimental decompression, has been shown to increase significantly with pre-exposure treatment (33). Its mild side effect profile and potential for increasing cerebral oxygenation following recompression recommend it as a possible EVA pretreatment.

NMDA Antagonists Hypoxia causes influx of calcium to the hippocampus and dorsal thalamic nucleus, causing hyperexcitability and seizure activity, mediated by the N-methyl-D-aspartate (NMDA) receptor (34). Blockade of this receptor protects the CNS (35). Two agents worthy of further research are MK-801, which protects when given as late as 75 minutes after exposure (35), and HWA 285 (Propentofylline) (36).

Calcium Channel Blockers This hypoxia-calcium-hyperexcitability cascade can also be interrupted at the calcium level, with calcium channel blockers that penetrate the CNS and prevent calcium loading without causing hypotension. Several that have been investigated are, in order of potency, vinpocetine, l-eburnamonine, vinconate and vincamine (37). All have been shown to increase survival following hypoxic injury.

Prostaglandins Several prostaglandins present a dose-dependent protection against cerebral hypoxia, including PGE, PGI2 and PGD2. All 3 inhibit platelet aggregation and vasodilation, which occur during ebullism (38).

EVA Modification Currently-used Extravehicular Mobility Units (EMU’s) operate at 4.3 psi; Russian Orlan-M suits are pressurized to 5.7 psi. As mentioned earlier, one determinant of the severity of ebullism is absolute change in pressure. A space suit pressurized to a lower pressure would impose a lower pressure differential on its occupant, and thus a lower severity of decompression. Research is currently underway to produce a suit pressurized to 3.5 psi, using ARGOX (62% argon — 38% oxygen) gas (39).

V) HUMAN EXPOSURES TO VACCUM

Attitudes towards survivability of humans in vacuum began to change as humans underwent accidentally decompressions and survived. In 1960, Joe Kittinger was ascending to 102,800 feet when he lost pressurization to his right hand. Instead of descending, he decided to continue the ascent, and his hand became painful and useless in the near-vacuum. On descending (by way of his record-breaking parachute jump), however, the hand returned to normal (40).

In a videotaped case in 1966, a technician in Houston was altitude-testing a space suit when he lost suit pressure and was instantaneously exposed to an altitude of 120,000 feet (18). He recalled the saliva boiling off his tongue as he passed out, and regained consciousness as the chamber monitor called 14,000 feet. He suffered no neurological sequelae and was not hospitalized.

In 1982 a technician was decompressed over 3 minutes to an altitude greater than 74,000 feet, and held at maximum altitude for another 60 seconds A manager had to kick in a glass ionization gauge atop the chamber to allow air to leak in (due to cycle stopped in mid-process), and by the time the chamber was opened the victim had been above 63 millibar for 1 to 3 minutes. The patient was cyanotic, frothing at the lips, bleeding from his lungs and had grade 4 barotrauma of both eardrums. He was given IV Decadron and recompressed to 6 ATA using NITROX (50% nitrogen — 50% oxygen) 5 _ hours after exposure. By 24 hours after exposure he was awake and alert; he was extubated at day 5, and at 1 year follow-up had neurological performance superior to testing before the accident (14).

Could an astronaut ever suffer direct contact with space, bleed out into the vacuum, and survive? In fact, one already has. Posting to sci.space, Gregory Bennett wrote:

“Incidentally, we have had one experience with a suit puncture on the Shuttle flights. On STS-37, during one of my flight experiments, the palm restraint in one of the astronaut’s gloves came loose and migrated until it punched a hole in the pressure bladder between his thumb and forefinger. It was not an explosive decompression, just a little 1/8 inch hole, but it was exciting down here in the swamp because it was the first injury we’ve ever had from a suit incident. Amazingly, the astronaut in question didn’t even know the puncture had occurred; he was so hopped on adrenaline it wasn’t until after he got back in that he even noticed there was a painful red mark on his hand. He figured his glove was chafing and didn’t worry about it…. What happened: when the metal bar punctured the glove, the skin of the astronaut’s hand partially sealed the opening. He bled into space, and at the same time his coagulating blood sealed the opening enough that the bar was retained inside the hole.” (41)

VI) CONCLUSION

Despite the losses of gravity, oxygen, warmth, pressure and every other life-sustaining characteristic of Earth, we have learned to adapt our surroundings to carry us higher and farther than the mass of humanity once thought possible. From Croce-Spinelli’s first use of oxygen to the union of the first 2 pieces of the next millenium’s space station, we have not allowed any environment to hold us out; nor, if we can judge by history, should we.

Advances in medicine have given us the tools to start treating this latest problem, the boiling away of our own flesh, and accidents at altitude have allowed us to begin to test them, with some success. We have only begun to crawl out of the protective envelope of our birth planet, and we will not stop here.

“The Earth is the Cradle of mankind, but one does not live in the cradle forever.”

— Konstantin Tsiolkovsky, 1895

REFERENCES

  1. Boyle as quoted in Wilson, CL, Production of Gas in Human Tissues at Low Pressures, AF-SAM-61-105, USAF SAM, Brooks Air force Base, Texas, Aug 1961.
  2. Sears WJ. “Vaporization of Tissue Fluids at Extreme Altitudes — A Review” (Abstract) SAFE Symposium, San Antonio, TX. 1989.
  3. Pilmanis AA. “Decompression Hazards at Very High Altitudes,” Armstrong Lab Publication Number AL/CF-SR1995-0021, pg. 58. Dec 1995.
  4. DeHart RL. “The Historical Perspective”, pg. 11. In: Fundamentals of Aerospace Medicine (RL DeHart, ed.) 2nd edition. Baltimore; Williams & Wilkins. 1996.
  5. Webb P. “The Space Activity Suit: An Elastic Leotard for Extravehicular Activity”, Aerospace Medicine. 1968; 39: 376-383.
  6. Sheffield PJ and RL Stork. “Protection in the Pressure Environment: Cabin Pressurization and Oxygen Equipment”, pg. 127 In: Fundamentals of Aerospace Medicine (RL DeHart, ed.) 2nd edition. Baltimore; Williams & Wilkins. 1996.
  7. Hitchcock, FA. “Tolerance of Normal Men to Explosive Decompression,” Journal of Applied Physiology, 1948, 1:153.
  8. Hall, WM and EL Cory. “Anoxia in Explosive Decompression Injury,” American Journal of Physiology, 1950, 160:361-365.
  9. Edelmann A, WV Whitehorn, A Lein, FA Hitchcock, Pathological Lesions Produced by Explosive Decompression, WADC-TR-51-191.
  10. Dunn JE, RW Bancroft, W Haymaker, DW Foft, “Experimental Animal Decompressions to Less Than 2 mmHg Abs. (Pathological Effects),” Aerospace Medicine, 1965, 36:725-732.
  11. Burch BH, JP Kemp, EG Vail, SA Frye, FA Hitchcock, “Some Effects of Explosive Decompression and Subsequent Exposure to 30 mmHg Upon the Hearts of Dogs,” Journal of Aviation Medicine, 1952,23:159-167.
  12. Cooke JP, RW Bancroft, “Some Cardiovascular Responses in Anesthetized Dogs During Repeated Decompressions to a Near-Vacuum,” Aerospace Medicine, Nov. 1966, 37:1148-1152.
  13. Casey HW, RW Bancroft, JP Cooke, “Residual Pathological Changes in the Central Nervous System of Dogs Following Rapid Decompression to 1 mmHg,” Aerospace Medicine, 1966, 37:713-718.
  14. Kolesari GL, EP Kindwall, “Survival Following Accidental Decompression to an Altitude Greater Than 74,000 Feet (22,555 m),” Aviation, Space and Environmental Medicine, Dec. 1982, 53(12):1211-1214.
  15. Edelmann A, FA Hitchcock, Observations on Dogs Exposed to an Ambient Pressure of 30 mmHg, WADC-TR-53-191.
  16. Boyce J, (Moderator), Ad Hoc Space Station Hyperbaric Treatment Facility Design Safety Committee, Nov 30, 1987, NASA Johnson Space Center, Houston TX.
  17. Kolesari et. al., pg. 1214
  18. Roth EM, “Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects,” NASA CR-1223, 1968.
  19. Ivanov PN, AG Kuznetsov, VB Malkin, YO Popova, “Decompression Phenomena in the Human Body in Conditions of Extremely Low Atmospheric Pressure,” Biophysics (USSR), 1960, 5:797-803.
  20. Parker JF and VR West (editors), Bioastronautics Data Book, 2nd edition, NASA SP-3006, 1973, pg. 5.
  21. Waligora JM, MR Powell, RL Sauer, “Spacecraft Life-Support Systems”, pg. 111. In: Space Physiology and Medicine (Nicogossian, Huntoon, Pool ed.), 3rd Edition. Pennsylvania: Lea & Febiger. 1993.
  22. Harding, R. Survival in Space, pg. 59. New York: Routledge. 1989.
  23. Nicogossian AE, DE Robbins, “Characteristics of the Space Environment,” pg. 54. In: Space Physiology and Medicine (Nicogossian, Huntoon, Pool ed.), 3rd Edition. Pennsylvania: Lea & Febiger. 1993.
  24. Pilmanis, pg. 60.
  25. Stegmann BJ, “Considerations for the Survival of Ebullism,” (Master’s Thesis), Dept. of Community Medicine, Wright State University, 1989. Pg. 36.
  26. Stegmann BJ, AA Pilmanis, EG Wolf, T Derion, JW Fanton, H Davis, GB Kemper, T Scoggins, “Evaluation of Medical Treatments to Increase Survival of Ebullism in Guinea Pigs,” (Abstract) Sixth Annual Workshop on Space Operations, Applications, and Research (SOAR ’92). NASA Conference Publication 3187, 1993; II:569.
  27. Stegmann BJ, “Considerations for the Survival of Ebullism,” (Master’s Thesis), Dept. of Community Medicine, Wright State University, 1989. Pg. 39.
  28. Calkins JM, “Physiologic Consequences of High Frequency Jet Ventilation,” Medical Instrumentation, Sept-Oct 1985, 19(5): 203-206.
  29. Kemph JP, FA Hitchcock, “Changes in Blood and Circulation of Dogs Following Explosive Decompression to Low Barometric Pressures,” American Journal of Physiology, 1952, 168:592.
  30. Erde A, “Experience with Moderate Hypothermia in the Treatment of Nervous System Symptoms of Decompression Sickness,” Proceedings of the 2nd Underwater Physiologic Symposium, National Research Council, National Academy of Sciences, WA, :66-74.
  31. Koestler AG, Replication and Extension of Rapid Decompression of Chimpanzees to a Near Vacuum. ARL-TR-67-2, Aeromedical Research Lab, Holloman Air Force Base, 1967.
  32. Stegmann, pg. 38.
  33. Koppenhagen K, “Cerebral Blood Flow Under Hypobaric Conditions: Effects of Pentoxifylline (‘Trental’ 400),” Pharmatherapeutica, 1984, 4(1): 1-5.
  34. Chen CH, Chen AC, Liu HJ, “Involvement of Nitric Oxide and N-methyl-D-aspartate in Acute Hypoxic Altitude Convulsion in Mice,” Aviation, Space and Environmental Medicine, 1997 Apt; 68(4): 296-9.
  35. Gill R, AC Foster, GN Woodruff, “Systemic Administration of MK-801 Protects Against Ischemia-Induced Hippocampal Neurodegeneration in the Gerbil,” Journal of Neuroscience, Oct 1987, 7(10):3343-3349.
  36. DeLeo J, L Toth, P Schubert, K Rudolphi, GW Kreutzberg, “Ischemia-Induced Neuronal Cell Death, Calcium Accumulation and Glial Response in the Hippocampus of the Mongolian Gerbil and Protection by Propentofylline (HWA 285),” Journal of Cerebral Blood Flow Metabolism, Dec 1987, 7(6): 745-751.
  37. King GA, “Protective Effects of Vinpocetine and Structurally Related Drugs on the Lethal Consequences of Hypoxia in Mice,” Archives of Internal Pharmacodynamics, 1987, 286(2): 299-307.
  38. Stegmann, pg. 49.
  39. Pilmanis AA, KM Krause, JT Webb, LJ Petropoulos, N Kannan, “Staged Decompression to a 3.5 PSI EVA Suit Using an Argon-Oxygen (ARGOX) Breathing Mixture,” First Biennial Space Biomedical Investigators’ Workshop, pp. 9-11. AF Research Laboratory/HEPR, Brooks AFB, TX. 1998.
  40. Gordon L, Aviation Week and Space Technology, 13 Feb 1996.
  41. Landis, G.A. Personal communication, 1999.

—————————————————————————————————————————————

Human Exposure to Vacuum

Geoffrey A. Landis

A frequently asked question is: how realistic is the scene in 2001: A Space Odyssey where astronaut Bowman makes a space-walk without a helmet? How long could a human survive if exposed to vacuum? Would you explode? Would you survive? How long would you remain conscious?

The quick answers to these questions are: Clarke got it about right in 2001. You would survive about a ninety seconds, you wouldn’t explode, you would remain conscious for about ten seconds.

frame from the movie 2001: A Space Odyssey
Astronaut Bowman ejected into space without a helmet

 

Could You Survive?

The best data I have comes from the chapter on the effects of Barometric pressure in Bioastronautics Data Book, Second edition, NASA SP-3006. This chapter discusses animal studies of decompression to vacuum. It does not mention any human studies.

page 5, (following a general discussion of low pressures and ebullism), the author gives an account of what is to be the expected result of vacuum exposure: 
“Some degree of consciousness will probably be retained for 9 to 11 seconds (see chapter 2 under Hypoxia). In rapid sequence thereafter, paralysis will be followed by generalized convulsions and paralysis once again. During this time, water vapor will form rapidly in the soft tissues and somewhat less rapidly in the venous blood. This evolution of water vapor will cause marked swelling of the body to perhaps twice its normal volume unless it is restrained by a pressure suit. (It has been demonstrated that a properly fitted elastic garment can entirely prevent ebullism at pressures as low as 15 mm Hg absolute [Webb, 1969, 1970].) Heart rate may rise initially, but will fall rapidly thereafter. Arterial blood pressure will also fall over a period of 30 to 60 seconds, while venous pressure rises due to distention of the venous system by gas and vapor. Venous pressure will meet or exceed arterial pressure within one minute. There will be virtually no effective circulation of blood. After an initial rush of gas from the lungs during decompression, gas and water vapor will continue to flow outward through the airways. This continual evaporation of water will cool the mouth and nose to near-freezing temperatures; the remainder of the body will also become cooled, but more slowly.

“Cook and Bancroft (1966) reported occasional deaths of animals due to fibrillation of the heart during the first minute of exposure to near vacuum conditions. Ordinarily, however, survival was the rule if recompression occurred within about 90 seconds. … Once heart action ceased, death was inevitable, despite attempts at resuscitation….

[on recompression] “Breathing usually began spontaneously… Neurological problems, including blindness and other defects in vision, were common after exposures (see problems due to evolved gas), but usually disappeared fairly rapidly.

“It is very unlikely that a human suddenly exposed to a vacuum would have more than 5 to 10 seconds to help himself. If immediate help is at hand, although one’s appearance and condition will be grave, it is reasonable to assume that recompression to a tolerable pressure (200 mm Hg, 3.8 psia) within 60 to 90 seconds could result in survival, and possibly in rather rapid recovery.”

Note that this discussion covers the effect of vacuum exposure only. The decompression event itself can have disasterous effects if the person being decompressed makes the mistake of trying to hold his or her breath. This will result in rupturing of the lungs, with almost certainly fatal results. There is a good reason that it is called “explosive” decompression.

 

Will You Stay Conscious?

The Bioastronautics Data Book answers this question: “Some degree of consciousness will probably be retained for 9 to 11 seconds…. It is very unlikely that a human suddenly exposed to a vacuum would have more than 5 to 10 seconds to help himself.”

A larger body of information about how long you would remain conscious comes from aviation medicine. Aviation medicine defines the “time of useful consciousness”, that is, how long after a decompression incident pilots will be awake and be sufficiently aware to take active measures to save their lives. Above 50,000 feet (15 km), the time of useful consciousness is 9 to 12 seconds, as quoted by the FAA in table 1-1 in Advisory Circular 61-107(the shorter figure is for a person actively moving; the longer figure is for a person sitting quietly). The USAF Flight Surgeon’s Guide figure 2-3 shows 12 seconds of useful consciousness above 60,000 ft (18 km); presumably the longer time listed is based on the assumption that Air Force pilots are well-trained in high-altitude procedures, and will be able to use their time effectively even when partially disfunctional from hypoxia. Linda Pendleton adds to this: “An explosive or rapid decompression will cut this time in half due to the startle factor and the accelerated rate at which an adrenaline-soaked body burns oxygen.” Advisory Circular 61-107 says the time of useful consciousness above 50,000 ft will drop from 9 to 12 seconds down to 5 seconds in the case of rapid decompression (presumably due to the “startle” factor discussed by Pendleton).

A slightly more general interest book, Survival in Space by Richard Harding, echoes this conclusion: 
“At altitudes greater than 45,000 feet (13,716 m), unconsciousness develops in fifteen to twenty seconds with death following four minutes or so later.” 
and later: 
“monkeys and dogs have successfully recovered from brief (up to two minutes) unprotected exposures…”

 

Would Your Blood Boil?

No.

Your blood is at a higher pressure than the outside environment. A typical blood pressure might be 75/120. The “75” part of this means that between heartbeats, the blood is at a pressure of 75 Torr (equal to about 100 mbar) above the external pressure. If the external pressure drops to zero, at a blood pressure of 75 Torr the boiling point of water is 46 degrees Celsius (115 F). This is well above body temperature of 37 C (98.6 F). Blood won’t boil, because the elastic pressure of the blood vessels keeps it it a pressure high enough that the body temperature is below the boiling point– at least, until the heart stops beating (at which point you have other things to worry about!). (To be more pedantic, blood pressure varies depending on where in the body it is measured, so the above statement should be understood as a generalization. However, the effect of small pockets of localized vapor is to increase the pressure. In places where the blood pressure is lowest, the vapor pressure will rise until equilibrium is reached. The net result is the same.)

 

Would You Freeze?

No.

A few recent Hollywood films showed people instantly freezing solid when exposed to vacuum. In one of these, the scientist character mentioned that the temperature was “minus 273”– that is, absolute zero.

But in a practical sense, space doesn’t really have a temperature– you can’t measure a temperature on a vacuum, something that isn’t there. The residual molecules that do exist aren’t enough to have much of any effect. Space isn’t “cold,” it isn’t “hot”, it really isn’t anything.

What space is, though, is a very good insulator. (In fact, vacuum is the secret behind thermos bottles.) Astronauts tend to have more problem with overheating than keeping warm.

If you were exposed to space without a spacesuit, your skin would most feel slightly cool, due to water evaporating off you skin, leading to a small amount of evaporative cooling. But you wouldn’t freeze solid!

 

Has Anybody Ever Survived Vacuum Exposure in Real Life?

Human experience is discussed by Roth, in the NASA technical report Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects. Its focus is on decompression, rather than vacuum exposure per se, but it still has a lot of good information, including the results of decompression events involving humans.

There are several cases of humans surviving exposure to vacuum worth noting. In 1966 a technician at NASA Houston was decompressed to vacuum in a space-suit test accident. This case is discussed by Roth in the reference above. He lost consciousness in 12-15 seconds. When pressure was restored after about 30 seconds of exposure, he regained consciousness, with no apparent injury sustained.
A few further details are given here.

Before jumping to the conclusion that space exposure is harmless, however, it is worth noting that in the same report, Roth includes a report of the autopsy of the victim of a slightly longer explosive decompression incident: 
“Immediately following rapid decompression, it was noted that he began to cough moderately. Very shortly after this he was seen to lose consciousness, and the picture described by the physicians on duty was that the patient remained deeply cyanotic, totally unresponsive and flaccid during the 2-3 minutes [to repressurise the altitude chamber] down to ground level.
… “Manual artificial respiration was begun immediately… The patient at no time breathed spontaneously; however, at the moment ground level was reached he was seen to give a few gasps. These were very irregular and only two or three in number.
…
“The conclusion of the [autopsy] report was as follows: “The major pathologic changes as outlined above are consistent with asphyxia. It is felt that the underlying cause of death in this case may be attributed to acute cardio-respiratory failure, secondary to bilateral pneumothorax…” “

Many other cases of death following decompression are noted in the aviation literature, including one spaceflight incident, the Soyuz-11 decompression accident, in 1971. A recent analysis of this accident can be found in D. J. Shayler, Disasters and Accidents in Manned Spaceflight.

On the subject of partial-body vacuum exposure, the results are not quite as serious. In 1960, during a high-altitude balloon parachute-jump, a partial-body vacuum exposure incident occurred when Joe Kittinger, Jr. lost pressurization in his right glove during an ascent to 103,000 ft (19.5 miles) in an unpressurized balloon gondola, Despite the depressurization, he continued the mission, and although the hand became painful and useless, after he returned to the ground, his hand returned to normal. Kittinger wrote in National Geographic (November 1960):
“At 43,000 feet I find out [what can go wrong]. My right hand does not feel normal. I examine the pressure glove; its air bladder is not inflating. The prospect of exposing the hand to the near-vacuum of peak altitude causes me some concern. From my previous experiences, I know that the hand will swell, lose most of its circulation, and cause extreme pain…. I decide to continue the ascent, without notifying ground control of my difficulty.” 
at 103,000 feet, he writes:
“Circulation has almost stopped in my unpressurized right hand, which feels stiff and painful.”
But at the landing:
“Dick looks at the swollen hand with concern. Three hours later the swelling will have disappeared with no ill effect.” 
The decompression incident on Kittinger’s balloon jump is discussed further in Shayler’s Disasters and Accidents in Manned Spaceflight:
[When Kittinger reached his peak altitude] “his right hand was twice the normal size… He tried to release some of his equipment prior to landing, but was not able to as his right hand was still in great pain. He hit the ground 13 min. 45 sec. after leaving Excelsior. Three hours after landing his swollen hand and his circulation were back to normal.” 
See also from Leonard Gordon, Aviation Week, February 13th 1996.

Finally, posting to sci.space, Gregory Bennett discussed an actual space incident: 
“Incidentally, we have had one experience with a suit puncture on the Shuttle flights. On STS-37, during one of my flight experiments, the palm restraint in one of the astronaut’s gloves came loose and migrated until it punched a hole in the pressure bladder between his thumb and forefinger. It was not explosive decompression, just a little 1/8 inch hole, but it was exciting down here in the swamp because it was the first injury we’ve ever head from a suit incident. Amazingly, the astronaut in question didn’t even know the puncture had occured; he was so hopped on adrenalin it wasn’t until after he got back in that he even noticed there was a painful red mark on his hand. He figured his glove was chafing and didn’t worry about it…. What happened: when the metal bar punctured the glove, the skin of the astronaut’s hand partially sealed the opening. He bled into space, and at the same time his coagulating blood sealed the opening enough that the bar was retained inside the hole.”

 

Explosive Decompression

The discussion here has focussed only on exposure to vacuum. However, in general the action of being exposed to vacuum will also involve a rapid decompression. This event is generally known as “explosive decompression,” and apart from the simple effect of vacuum on the body, the explosive decompression event itself will be hazardous. As noted, explosive decompression will be particularly bad if the decompression subject attempts to hold his or her breath during decompression.

In The USAF Flight Surgeon’s Guide, Fischer lists the following effects due to mechanical expansion of gases during decompression.

  • Gastrointestinal Tract During Rapid Decompression.
    One of the potential dangers during a rapid decompression is the expansion of gases within body cavities. The abdominal distress during rapid decompression is usually no more severe than that which might occur during slower decompression. Nevertheless, abdominal distention, when it does occur, may have several important effects. The diaphragm is displaced upward by the expansion of trapped gas in the stomach, which can retard respiratory movements. Distention of these abdominal organs may also stimulate the abdominal branches of the vagus nerve, resulting in cardiovascular depression, and if severe enough, cause a reduction in blood pressure, unconsciousness, and shock. Usually, abdominal distress can be relieved after a rapid decompression by the passage of excess gas.
  • The Lungs During Rapid Decompression.
    Because of the relatively large volume of air normally contained in the lungs, the delicate nature of the pulmonary tissue, and the intricate system of alveolar airways for ventilation, it is recognized that the lungs are potentially the most vulnerable part of the body during a rapid decompression. Whenever a rapid decompression is faster than the inherent capability of the lungs to decompress (vent), a transient positive pressure will temporarily build up in the lungs. If the escape of air from the lungs is blocked or seriously impeded during a sudden drop in the cabin pressure, it is possible for a dangerously high pressure to build up and to overdistend the lungs and thorax. No serious injuries have resulted from rapid decompressions with open airways, even while wearing an oxygen mask, but disastrous, or fatal, consequences can result if the pulmonary passages are blocked, such as forceful breath-holding with the lungs full of air. Under this condition, when none of the air in the lungs can escape during a decompression, the lungs and thorax becomes over-expanded by the excessively high intrapulmonic pressure, causing actual tearing and rupture of the lung tissues and capillaries. The trapped air is forced through the lungs into the thoracic cage, and air can be injected directly into the general circulation by way of the ruptured blood vessels, with massive air bubbles moving throughout the body and lodging in vital organs such as the heart and brain.
    The movement of these air bubbles is similar to the air embolism that can occur in SCUBA diving and submarine escape when an individual ascends from underwater to the surface with breath-holding. Because of lung construction, momentary breath-holding, such as swallowing or yawning, will not cause sufficient pressure in the lungs to exceed their tensile strength.
  • Decompression Sickness.
    (also known as “Bends”)
    Because of the rapid ascent to relatively high altitudes, the risk of decompression sickness is increased. Recognition and treatment of this entity remain the same as discussed elsewhere in this publication.
  • Hypoxia.
    While the immediate mechanical effects of rapid decompression on occupants of a pressurized cabin will seldom be incapacitating, the menace of subsequent hypoxia becomes more formidable with increasing altitudes. The time of consciousness after loss of cabin pressure is reduced due to offgassing of oxygen from venous blood to the lungs. Hypoxia is the most immediate problem following a decompression.
  • Physical Indications of a Rapid Decompression.
    …
    (a) Explosive Noise. When two different air masses make contact, there is an explosive noise. It is because of this explosive noise that some people use the term explosive decompression to describe a rapid decompression.
    (b) Flying Debris. The rapid rush of air from an aircraft cabin on decompression has such force that items not secured to the aircraft structure will be extracted out of the ruptured hole in the pressurized compartment. Items such as maps, charts, flight logs, and magazines will be blow out. Dirt and dust will affect vision for several seconds.
    (c) Fogging. Air at any temperature and pressure has the capability of holding just so much water vapor. Sudden changes in temperature or pressure, or both, change the amount of water vapor the air can hold. In a rapid decompression, temperature and pressure are reduced with a subsequent reduction in water vapor holding capacity. The water vapor that cannot be held by the air appears in the compartment as fog. This fog may dissipate rapidly, as in most fighters, or not so rapidly, as in larger aircraft.
    (d) Temperature. Cabin temperature during flight is generally maintained at a comfortable level; however, the ambient temperature gets colder as the aircraft flies higher. If a decompression occurs, temperature will be reduced rapidly. Chilling and frostbite may occur if proper protective clothing is not worn or available.
    (e) Pressure.


How Fast Will A Spaceship Decompress If It Gets Punctured?

The decompression time will depend on how big the hole is. For a fast estimate, you can assume that the air exiting through the hole will travel at the speed of sound. Since the atmosphere drops in pressure as it moves through the hole, the effective rate at which the atmosphere leaves is at about 60% of the speed of sound, or about 200 meters/second for room-temperaure air (see derivation by Higgins):

P = Po exp[-(A/V)t*(200m/s)]

This gives you a quick rule of thumb, the one-one-ten-hundred rule:
A one square-centimeter hole in a one cubic-meter volume will cause the pressure to drop by a factor of ten in roughly a hundred seconds.
(for quick approximations; only roughly accurate). This time scales up proportionately to the volume, and scales down proportionately to the size of the hole. So, for example, a three-thousand cubic meter volume will decompress from 1 atmosphere to .01 atmosphere through a ten square centimeter hole on a time scale of a sixty thousand seconds, or seventeen hours. (it’s actually 19 hours by a more accurate calculation).

The seminal paper on the subject is by Demetriades in 1954: “On the Decompression of a Punctured Pressurized Cabin in Vacuum Flight.”

The decompression rate can be derived for laminar viscous flow (that is, near atmospheric pressure) using Prandtl’s equation in the limit Po/P is zero, and assuming a simple aperture (a pipe of zero length). The gas flow conductance is Cvisc= 20 A liters/second (for A in square centimeters). As the pressure decreases the flow changes to molecular flow, and the depressurization rate decreases by about a factor of two. This is for air at 20 C; for the case of pure oxygen, the leak rate is about 10 percent slower.

For reference, when the pressure drops to about 50% of atmospheric, the subject will be entering the region of “critical hypoxia”; when the pressure drops to about 15% of atmospheric, the remaining time of useful consciousness will have decreased to the 9-12 seconds characteristic of vacuum.

Professor Andrew J. Higgins of McGill University had written a more detailed answer to the question of how fast a spacecraft will decompress through a given size hole; which I have reprinted with his permission here.

References

  1. Charles E. Billings, “Barometric Pressure,” in Bioastronautics Data Book, Second edition, NASA SP-3006, edited by James F. Parker and Vita R. West, 1973.
  2. Arnauld E. Nicogossian, Carolyn L. Huntoon and Sam L. Pool, Space Physiology and Medicine, 2nd Edition, Lea and Febiger, Philadelphia 1989.
  3. Emanuel M. Roth, Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects, NASA CR-1223, November 1968.
  4. Tam Czarnik, “Ebullism at 1 Million Feet: Surviving Rapid/Explosive Decompression” (unpublished review, 1999).
  5. Richard Harding, Survival in Space: Medical Problems of Manned Spaceflight, Chapter 3: “Pressure and density”, Routledge, New York 1989.
  6. Paul W. Fischer, Chapter 2: High-altitude Respiratory Physiology, in USAF Flight Surgeon’s Guide.
  7. U.S. Naval Hospital Flight surgeon Manual, 3rd Edition 1989 (see also 2nd edition, 1998).
  8. M. A. Bodin, “Brief Human Vacuum Exposure in Relation to Space Rescue Operations,” Journal of the British Interplanetary Society, Vol. 30, Feb. 1977,p.55
  9. Dacid J. Shayler, Disasters and Accidents in Manned Spaceflight, Springer-Praxis Books in Astronomy and Space Science, Chichester UK, 2000.
  10. Hypoxia information on Everest page
  11. S. T. Demetriades, “On the Decompression of a Punctured Pressurized Cabin in Vacuum Flight,” Jet Propulsion, January-February, 1954, pp. 35-36.
  12. M. Saad, Compressible Fluid Flow, 2nd Ed., Pearson Education, 1998.

See also:

  • Andrew A. Pilmanis, and William J. Sears, “Physiological hazards of flight at high altitude,” The Lancet, Volume 362, Supplement 1, December 2003, Pages s16-s17, doi:10.1016/S0140-6736(03)15059-3. Cited in Tubious, Nov. 2007.

For more technical details, a paper discussing the medical effects of sudden vacuum exposure on a human, and discussing the emergency medical response to a decompression emergency, can be found in Dr. Tam Czarnik’s paper Ebullism at 1 Million Feet.

about the author

Geoffrey A. Landis is a scientist now working at the NASA Glenn Research Center. He has been on the science team of the Pathfinder mission to Mars and the Mars Exploration Rovers mission. His novel Mars Crossing is available from Tor Books, and his short-story collection Impact Parameter (and other quantum realities) from Golden Gryphon.

Disclaimer

When the original version of this document was written, the author was not employed by NASA. This document is not a work of the U.S. government, and any opinions expressed in it are the views of the author, and not NASA or the U.S. government.

http://www.geoffreylandis.com/vacuum.html

Leave a comment