Explosive Decompression In a Vacuum
Created | Updated Jul 27, 2009
"A slight hiss built into a deafening roar of rushing air as the outer hatchway opened onto an empty blackness studded with tiny, impossibly bright points of light. Ford and Arthur popped out into outer space like corks from a toy gun. [...] The Hitchhiker's Guide to The Galaxy says that if you hold a lungful of air you can survive in the total vacuum of space for about thirty seconds. However, it does go onto say that what with space being the mind-boggling size it is, the chances of getting picked up by another ship within those thirty seconds are two to the power of two-hundred and seventy-six, seven hundred and nine to one against
[The Hitchhiker's Guide To The Galaxy ; Chapters 7-8]
This is one of those common-knowledge question that always surprises people especially if they garner too much of their general knowledge from movies. From no lesser source than NASA, we can officially debunk one or two myths immediately...
Would your blood boil?
No. The blood in your veins is at a higher pressure than the outside environment because of the elastic nature of the blood vessels and the activity of the circulatory system.
A typical blood pressure might be 80/120. Between heartbeats the blood pressure is 80 Torr (equal to about 100 mbar) above external pressure.
Pressure can depress the melting and boiling points of solids and fluids which is how you can get super-cooled water for example. similarly solutions alter the point of changing state at a given pressure. At an atmospheric pressure of 1 for example salt is used to melt snow and is erroneously used in cooking pasta by people who think this raises the boiling point thus making the water hotter. Though the effect is true it would require 2 ounces of salt would to raise the boiling point of one litre of water at normal atmospheric pressure.
6 grams of salt is fatal so 2 ounces is more than 9 times that amount.
Why mention this, because simplistically blood can be thought of as a water solution.
So what happens to blood at a normal blood pressure in a vacuum where atmospheric pressure is zero?
At a blood pressure of 80 Torr the boiling point of water is 47 degrees Celsius (116 F). This is well above body temperature of 37 C (98.6 F) so blood won't boil.
Provided your blood-pressure stays above that and doesn't drop precipitously or stop all together then your blood will not boil in your veins. However if your heart stops then you've a whole other set of problems to worry about.
Would you flash-freeze?
No. Heat understood as energy is transmitted through convection, conduction and radiation, so although our hapless bathrobe-clad Arthur would be radiating his body heat away (space is colder than he is) he wouldn't freeze. Also the evaporation of moisture on his skin would feel 'cool'.
Would you inflate and burst?
No. You do not explode because of the containing effect of your skin, the expansion of gases in places like the lungs, throat and digestion tract are no more severe that would happen under normal ascent - the same degree of expansion occurs just faster. gasses also emerge out of solution in your blood - giving rise to symptoms associated with
decompression sickness.
This is conceivable if one thinks of compressed oxygen cylinders the gas in these tanks may be at pressures many hundreds of times the external pressure, but the thin layer of steel doesn't explode. Now skin isn't steel but it does prevent astronauts popping open in space.
Partial Exposure
Partial exposure to a vacuum isn't deadly at all.
Joe Kittinger's hand was exposed to the vacuum of the edge of space during his parachute jump from 103,000 feet. He remarked it was painful and swollen on ascent but his hand returned to normal when he landed. 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."
Later when he was at the peak of his ascent he wrote
"At 103,000 feet, circulation has almost stopped in my unpressurized right hand, which feels stiff and painful."
Upon landing:
"Three hours later the swelling will have disappeared with no ill effect."
In David Shayler's instructive 'Disasters and Accidents in Manned Spaceflight there is a bit more elaboration:
"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." [pages 36-37]
As for accidents in space, On the eighth launch of the space shuttle
Atlantis, one astronaut experienced the first ever injury in space. After returning to the shuttle he complained that his gloves was chaffing. Further examination revealed a puncture: there was a perforation in the pressure-bladder between his thumb and forefinger. The rupture hadn't led to explosive decompression and the tear was only a small 1/8 hole which had been sealed by the astronaut's skin when the glove had been torn open. He had bled into space but his blood coagulated around the injury and the hole, sealing it. It was only after the gloves was removed that the red mark was revealed. Apparently he was so pumped with adrenaline that he hadn't noticed at the time.
In both cases they suffered initial problems consistent with exposure to a vacuum but no long-lasting damage.
Total Exposure
However, total exposure to a vacuum is deadly before you get the idea that it isn't - it's just not deadly in the ways people imagine or movies depict.
Many post-mortem autopsies confirm: the primary cause of death is asphyxiation followed by heart failure.
So what does happen when you are suddenly exposed to a vacuum?
History records one or two documented cases, some involving space travel but most in high altitude aviation which is similar if not the same.
At the less lethal end there are the symptoms of Decompression Sickness where gasses in the blood come out of solution, and can attack the tissues and joints. This can be very painful and occasionally lethal if the bubbles reach the heart or the brain.
The Soyuz 11 cosmonauts spent several minutes in vacuum when their capsule lost pressure before re-entry. Their bodies showed so little damage that the recovery crew started CPR, and it took a careful investigation to establish they were dead and what had killed them. The failure of a pressure seal killed them and it was established that within death occurred within 40 seconds.
So base measurement: exposure to a vacuum can kill you. No dice.
However if one distinguishes between survival and consciousness (for if you are alone an unconscious the prospects are bleak but if help is at hand then the range narrows or widens accordingly.
At NASA's Manned Spacecraft Centre (now The Johnson Space Centre) a technician test subject was altitude-testing a space suit accidentally exposed to a near vacuum (less than 1 psi.) as he was instantaneously exposed to an altitude of 120,000 feet
He remained conscious for about 14 seconds, which is about the time it took for his O2 deprived blood to go from his lungs up to his brain. The chamber was repressurised within 15 seconds. The man regained consciousness at around 15,000 feet equivalent altitude and later reported that he could feel and hear the air leaking out. His last conscious memory was of the water on his tongue beginning to boil. He suffered no neurological problems and was not hospitalised.
The tolerable exposure to a vacuum to sustain consciousness doesn't get much above that. As that is the rate at which the anoxic blood takes to be circulated and reach the brain.
So it is very unlikely that a human suddenly exposed to a vacuum would have more than 5 to 10 seconds to help themselves.
Equivalent accidents where people are exposed to pure nitrogen atmospheres offer a fairly good approximation of how the body reacts because there's no oxygen present. Sudden loss of consciousness occurs within 10-15 seconds and survival is rare - you get no warning that you're about to keel over.
If immediate help is at hand, although ones appearance and condition will be grave, it is reasonable to assume that recompression to a tolerable pressure within 60 to 90 seconds could result in survival, and possibly in
rather rapid recovery (as was the case with the hapless Houston Technician but was not the case with the Soyuz -11 Cosmonauts)
From the Bioastronautics Data Book in the Chapter: "Barometric Pressure," it says that
"In rapid sequence after consciousness is lost paralysis will be followed by generalized convulsions and paralysis. 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 and embolisms in tissues. 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 distension 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 rapidly; the remainder of the body will also become cooled, but more slowly."
If you are exposed to direct sunlight - you can get a rather severe sunburn
The Hitchhiker's Guide excerpt only mentions holding your breath but assuming Arthur began panicking and hyperventilating - that wouldn't have helped either. The bloodstream of a resting person is already saturated with oxygen; there is no way to pump more in. What hyperventilation does is to flush CO2 out of your body. This matters because the breathing reflex is triggered by CO2 buildup, not oxygen shortage.
(That's why you get no warning of impending unconsciousness in a pure-nitrogen atmosphere.)
Hyperventilation suppresses the breathing reflex so you can fully exploit the air in your lungs. This doesn't help in vacuum since if holding in air by closing the tubes connected to lungs causes greater damage than if the lungs are allowed to deflate. (There's a reason it's called explosive decompression.)
This is confirmed with the sorry tale recorded in another Nasa Document, the ever-thrilling: Rapid (Explosive) Decompression Emergencies In Pressure-Suited subjects by Emmanuel Roth which establishes the lethality of sudden compression but also the effects upon the heart and brain
The un-named 24 year old white male, was subject to a rapid decompression at 30,000 feet in less than 1 second. He was seen visibly to be rigid, and anxious and appeared to be holding his breath. Immediately following decompression he began to cough moderately lost consciousness a few seconds later.
At ground level he was cyanotic, unresponsive, pupils fixed and dilated flaccid and clammy to the touch. 100% oxygen was administered, no heart sounds, blood pressure or pulse could be located; urinary incontinence followed, a respirator was introduced and his airways were not blocked, however he remained utterly unresponsive. After 15 minutes of continued attempts to resuscitate a final injection of adrenalin was administered into the heart with no change.
Post-mortem autopsy found evidence of severe haemorrhaging in his lungs and gas bubbles in his blood vessels throughout his body as well as the rapid collection of moisture in tissues including embolisms in the brain but these would not have been fatal but were consistent with asphyxia and the primary cause of death was cardio-respiratory failure.
