RS Classic: The Truth About Decompression

>> Wednesday, June 9, 2010

Another science related blog thanks to my odd associative logic. I hope you enjoy it.

Part of what I want to do here, and I haven’t really pursued this yet, is talk about fiction, things I write and things I like to read. Oddly enough, this current stream of science related blogs is much like how I do a novel, with one things making me think of something else. Truly, I’m almost a study in associative thinking.

So, in that vein, here’s another topic that the last topic made me think of: the effects of vacuum on people.

Now, most people think depressurization (exposure to vacuum) is like the movies. Spontaneous eyeballs popping out of one’s head, perhaps a messy explosion. Bad news for those that like that kind of gore (but good news for the rest of us): uh, no. Truth is, though it’s not the way I’d want to go out, an explosion is unlikely unless you try to hold your breath (psst, that won’t help you). Skin is more than capable of taking the 1 atm pressure differential.

So, what is it like? Well, for those that have experienced it and lived (and there are some), it wasn’t fun. Saliva boiling away in your mouth is one of the things generally remembered without joy. Flesh does swell from this ebulism and unconsciousness comes quickly, usually within seconds. It’s happened in vacuum test chambers (and kudos to the folks that run those facilities by the way, they can repress chambers from a hard vacuum to 10.2 psia (703 mbar) in a matter of seconds, where a lock observer can get in and help rescue the victim. Within 30 seconds, everything’s back to normal). People exposed to hard vacuum, if they can be repressed quickly, may get the bends and have other short term discomforts or conditions but usually recover completely if exposure is less than 90 seconds. This might not be true if the decompression is rapid, as alveoli in the lungs can rupture as can sinuses and ear drums. In fact, even small pressure drops can be fatal if they are very rapid.

An interesting study of vacuum without actually going out into space were the very high altitude jumps performed as several series. In the Excelsior jumps, Joe Kittinger made a number of altitude record parachute jumps in a pressure suit culminating in the highest at 102,800 where his glove sprang a leak and that hand swelled and was very painful, but three hours later, it was back to normal.

But, if one goes slowly and has sufficient oxygen to provide the appropriate partial pressure of oxygen, though, one can survive. In fact, those who go out in the suits go out in suits with a total pressure of about 4.3 psia (296 mbar), though they have to go in 100% oxygen to do it. Why, you might ask? Because every bit of extra pressure used in the suit, they have to work against it to move. What I mean is, good luck finding an EVA astronaut who isn’t in excellent shape: EVA is hard work. But I digress.

Now, have we had ugly Hollywood type decompressions? Sadly, yes, though it wasn’t with 1 atmosphere, but actually involved diving pressures. Wikipedia has a good article on the Byford Dolphin calamity but I warn you, it’s not for the weak-stomached. No pictures, but the description is horrific. In that case, the explosive decompression was a differential pressure of ~60 atmospheres. In that scenario, the effects on people were pretty brutal.

Now, interested in some little known information you won’t hear every day on vacuums? In my first job, I worked in a facility that had a number of vacuum and environmental chambers. Apparently, early in the space program, they had “played with” a number of different creepy crawlies in the vacuum jars. Arachniphobiacs will be pleased to note that spiders pumped down to vacuum will explode. Take that, you brown recluse you.

Cockroaches, however, will just lie still and, even if you leave them at vacuum for several days, when you pump it back to ambient, they’ll start to move again like nothing happened.



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