Vacc Hood

[Carlobrand]

One of the lesser-known dangers of space travel, at least among laymen, is the speed with which a person can be incapacitated when exposed to vacuum. We are familiar with terrestrial circumstances, in which you can hold your breath to buy yourself a couple of minutes - or at the least survive for maybe a minute on the O2 already in your blood. Neither is true in vacuum.

If you try to hold your breath in vacuum, you will quickly suffer a burst lung (pneumothorax), which will most likely be fatal unless advanced medical help is very close at hand to save you from your misjudgment. For this reason, astronauts are trained NOT to hold their breath. One presumes this would be an elementary part of training for all Traveller citizens journeying beyond their world's atmosphere, as ubiquitous as those oxygen mask drills on airlines.

However, if you allow the vacuum to take your breath - thereby preserving your lungs from damage - you run into another problem: the blood gases (including that precious O2) are quickly leached from your blood by the vacuum in your lungs. Within as little as a few heartbeats, your brain is receiving blood stripped of its O2 content, and you fall unconscious. In a sudden depressurization, you could be unconscious in as little as 15 seconds. You can be revived without injury if someone can get you into pressure within about a minute and a half; otherwise, anoxic brain injury and death quickly follow.

To address this (and buy players time to respond to emergencies), I introduced the Emergency Vacuum Hood (vacc-hood). This is simply a clear plastic bag with an elastic band and a very small O2 cylinder, carried in a small pouch on the belt. In a vacuum emergency, the person takes the bag from the pouch and slips it over his head. The action of pulling the bag over the head activates the O2 cylinder, which fills the bag with pure O2 at a carefully metered 0.2 atmospheres, low enough to avoid bursting the lungs. A small pressure relief valve ensures that the pressure in the hood does not exceed external pressure by more than 0.2 atmospheres, so the hood can be used without danger regardless of the rate of decompression. The elastic band provides a seal around the neck - not really tight enough for long-term, but just enough to keep that vital lungful of oxygen around the person's head for a critical few seconds. There isn't much in there, just a lungful, enough to buy the person a couple of minutes to get to safety.

 

[aramis]

Your description is wrong, at least according to NASA data.
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

The issue is simply that the brain shuts the body down when it isn't getting enough oxygen or when it detects too much CO2, and the 60-90 seconds of O2 isn't the issue. You don't lose it out the lungs into vacuum. You build up dangerous CO2 levels, instead. This is because the CO2 and O2 in the blood is chemically bonded, and it requires a 4:1 O2:CO2 ratio to swap out the CO2 for the O2, but the other way is much easier, as hemoglobin readily swaps its carried O2 for the CO2, 1:1.

Note that holding one's breath won't automatically create a pnemothorax, either. I routinely have a differential of 11PSI between my lungs and the outside air, and my dad has a 20PSI difference... we sleep with CPAPs. That's 0.749 Atm of difference for me, and 1.36 Atm for dad.

Given the need to NOTICE the leak, by the time one does, it's likely down to 0.75 ATM or lower.

And, I just tried an experiment. I can hold 6 PSI (startup pressure) on my CPAP so that it doesn't vent out my nose when entered in the mouth, and the opposite.

The alveolar damage is from moisture losses, and their resulting losses of flexibility and function — 90 sec is survivable, more than 2 minutes is unrecoverable.

 

[Spinward Scout]

To address this (and buy players time to respond to emergencies), I introduced the Emergency Vacuum Hood (vacc-hood). This is simply a clear plastic bag with an elastic band and a very small O2 cylinder, carried in a small pouch on the belt. In a vacuum emergency, the person takes the bag from the pouch and slips it over his head.

Sounds like one of these for getting out of a burning building.

http://www.hylinesafety.com/evacu8smokehood.html

Pretty similar purpose - emergency oxygen.

 

[Khan Trav]

So would it be viable to simple stick your head in a plastic baggie? Assuming the ship's cat hasnt been playing with it of course...

 

[aramis]

So would it be viable to simple stick your head in a plastic baggie? Assuming the ship's cat hasnt been playing with it of course...

You need three things to survive:

Oxygen, water, and food.

NASA has established that vacuum is only a major problem on mucus membranes (Eyes, nasal passages, mouth, lungs) and the ear drums. And possibly the urinary tract, rectum, and (gender specifically) the vagina or scrotum, tho' the releases haven't mentioned those.

the "New" pressure suits in development only maintain vacuum integrity on the head and neck, via a yoke. The rest of the suit simply uses dynamic fabric pressure to prevent capillary stretching and thus bruising.

 

[Whipsnade]

One of the lesser-known dangers of space travel, at least among laymen, is the speed with which a person can be incapacitated when exposed to vacuum.

TNE dealt with this issue over a decade ago and, as Wil pointed out, your assumptions are wholly wrong.

There's no need to reinvent the wheel here, especially when the reinvented wheel cannot roll.

 

[aramis]

I'll point out that such a hood can and would prevent as rapid a damage to the lungs and eyes as would occur without protection... Not for the reasons in the blurb, but by simply preventing moisture loss and capillary damage in the lungs. Pure O2, even in low pressures, does damage to the cornea. Not significant in a single use, but... And it would easily prevent the near-immediate loss of consciousness from CO2 non-exchange.

Oh, and the TL14 Tailored vac suit really should be the TL 8 tailored vac suit.

A clarification, by the way: the new suit isn't NASA's, but MIT's. It's based upon some NASA research, however.
Photo at Nat. Geo.

 

[Carlobrand]

With respect, Aramis, your source seems to contradict you: "If you don't try to hold your breath, exposure to space for half a minute or so is unlikely to produce permanent injury. Holding your breath is likely to damage your lungs, something scuba divers have to watch out for when ascending..."

I am somewhat hampered by the need to resort to internet sources for evidence in this kind of public debate - the most authoritative sources charge for the privilege or are incredibly large - or both.

This FAA source has a table on time of useful consciousness:
http://www.faa.gov/pilots/training/airman_education/media/AC 61-107A.pdf

Note the table documents loss of consciousness occurring potentially within a few seconds. The sources that I have ascribe the phenomenon to exchange of blood gases in the lungs - in a nutshell, blood gases are drawn from the blood into the vacuum in the lungs, resulting in O2 saturations dropping very rapidly to below the point at which consciousness can be maintained.

This - be warned - is an 8.2 meg PDF file, the 1991 US Navy Flight Surgeon's Manual

http://www.operationalmedicine.org/TextbookFiles/FlightSurgeonsManual.pdf

From that manual: "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, 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 cabin pressure, intrapulmonary pressure can build up high enough to cause tearing and rupture of the lung tissues and capillaries."

This also is a large PDF file, 5.65 megs, "Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects," a NASA report on some decompression accidents they suffered.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690004637_1969004637.pdf

It includes a mathematical analysis of the pressures involved in lung rupture as well as a description of the incidents. Among other interesting tidbits, it notes that high pressure in the lungs "is dangerous only if it is permitted to expand pulmonary tissue beyond its tensile limits;" it noted that lungs were ruptured by pressure differentials as low as 80mm Hg in rapid decompression but easily survived pressure differentials of twice that value during normal coughing.

This is an indirect reference, for those who can't do the PDFs. It's a website on vacuum by scientist/writer Geoffrey Landis. About halfway down, it quotes the NASA report "Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects," discussing in part a fatal pneumothorax incident involving a pressure suit failure in a vacuum chamber: "...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...'"

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

There's another gent mentioned who experienced decompression but lived. The only difference between him and this poor soul is this guy was seen to cough a bit before falling unconscious. I speculate that something - perhaps a mild respiratory illness or unnoticed lung problem - prevented his lungs from releasing air quickly enough to avoid injury, but I don't have sufficient detail of the incident to draw firmer conclusions.

This is one of those Google book thingies, a page from Principles of Clinical Medicine for Space Flight. I hope it's permissible here. Page 254 opens with a discussion of a near-fatal pneumothorax in a man accidentally decompressed to an equivalent altitude of 74000 feet (about 0.036 atmospheres), then discusses Pulmonary Over-inflation Syndrome, a fancy medical term for what happens when the air in your lungs expands beyond the ability of your lungs to cope. Pressure differentials as low as 0.1 atmospheres were causing damage.

http://books.google.com/books?id=QY...q=pneumothorax due to vacuum exposure&f=false (I'm not entirely sure this will work)

That last involved cadaver studies but the same results are also reflected in studies of diver barotrauma injury.

I hope I haven't violated any rules with this. It's useful information for folk interested in the science end of sci-fi.

I do not know how all that correlates with your CPAP. Frankly, what you describe contradicts my sources, so I don't even begin to know what to say on that subject. My best guess is that the unit pushing gas through the cannula or tube or whatever at 2 atmospheres is not the same as your lungs being suddenly inflated with three or four liters of air. Do your units indicate a flow rate in liters per minute?

 

[Spinward Scout]

You need three things to survive:

Oxygen, water, and food.

Four. Shelter from the elements (or lack of). Heat, Cold, Rain, Meteors, etc... Of course in vacuum, there's nowhere for the heat of your body to dissipate to. But shielding from radiation is definitely required. A space suit isn't only needed just to keep the air in.

 

[aramis]

I do not know how all that correlates with your CPAP. Frankly, what you describe contradicts my sources, so I don't even begin to know what to say on that subject. My best guess is that the unit pushing gas through the cannula or tube or whatever at 2 atmospheres is not the same as your lungs being suddenly inflated with three or four liters of air. Do your units indicate a flow rate in liters per minute?

Nope, only for sustained pressure. CPAP stands for Continuous Positive Air Pressure. It maintains a positive pressure over ambient (as I'm only couple hundred above MSL, ambient is about 14.65 PSI or so. But 1 Atm differential isn't a problem - if it were, CPAPs would be killing people.

And the flow rate is sufficient I can't inhale fast enough to prevent outflow at a mere 6psi over ambient; the hose is 25mm interior diameter, and the nasal devices are 2x 1cm openings. So the rate is sufficient to "suddenly fill" my lungs to 1.3 atm. And the kick-up to 11psi is under 1 second to reach pressure... or to drop it.

Look for newer sources, by the way... NASA and the Russian Space Agency have newer data that shows the old "Vacuum kills you quick by pneumothorax" is wrong. Vacuum can, but usually doesn't, cause pneumothorax. Your NASA source is a 1969 document pulled together over several years prior.

Key wording in this source: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

If you don't try to hold your breath, exposure to space for half a minute or so is unlikely to produce permanent injury. Holding your breath is likely to damage your lungs, something scuba divers have to watch out for when ascending, and you'll have eardrum trouble if your Eustachian tubes are badly plugged up, but theory predicts -- and animal experiments confirm -- that otherwise, exposure to vacuum causes no immediate injury. You do not explode. Your blood does not boil. You do not freeze. You do not instantly lose consciousness.​

(Coloring mine)

Note that the answer was given in 1997.

The purple: pneumothorax constitutes relatively permanent injury. One that requires medical intervention.
The orange: Note that the mechanics are somewhat different depending on if one is suited or not, but unlike divers, where decompression is often multiple atmospheres, we're not talking about pressure differentials the human body can't handle. Free-diving to 2 Atm is common. Air flight to 670 mBarr is common; an explosive decompression accident at 10K feet has little to no decompression injury, and even at 24000, only minor barotrauma - See the Aloha Airlines incident, with one fatality... from ejection from the plane. 8 Major injuries - and most of the injuries were reported as being hit with things, not the exposure to 24000' and its 5.5 psi... sudden loss of about 1/3 atmosphere (since they don't maintain the aircraft at surface pressure, but several thousand feet, to reduce hull stress).
The blue: This is the biggest reason to let go. Ear damage. It's the #1 barotrauma injury, and, according to my diver friends (one's a welding inspector), the most dangerous. Worse than the bends, worse than narcosis. In some individuals, 2psi can rupture. In others 30 psi won't. It's all morphology and rapidity of decompression.

Likewise, the rate of decompression is important. In a "slow" decompression (the most likely case, really - most real world decompressions to vacuum have been gradual - not sufficient to pop eardrums, while many divers can wind up emergency surfacing from 2 atm or more, and some will force exhale, adding to the pressure differential...)

Referencing the Aloha Flight 243, no one was hospitalized for barotrauma - which would have been the case for pneumothorax. The major injuries all included object impact trauma, tho' two had "effusion from the ears" (NTSB report, pp 27-28) along with, and many had minor barotrauma. Which, if it parallels diving, is going to be mostly ear issues.

Also note: No current space suits run 1 Atm - most are now at 0.56 Bar and 100% O2 (which is close to dangerous levels long term, but for short term, no problem), and used to be 0.3 or 0.4 bar.

Even the ISS cabin is not kept at 1 Atm... it's kept at 14.0, not 14.7 PSI. This was in fact a problem for the shuttle missions, as it meant having to depressurize the cabin slightly on the shuttle.

It's a good item; it's a bad writeup based upon old and incomplete datasets.

Edit: One other thing: The Pneumothorax in the individuals cited may come from post-accident resuscitation attempts - humans performing CPR can generates several ATM of pressure on the lungs, and Pneumothorax is common in resuscitations, according to my last CPR class (almost 2 years ago).

Edit2: Your cited math study is from 1969. More recent studies don't support it, nor do explosive decompressions in aircraft. Alveolar edema is much more of a problem... which a controlled exhale to sustainable pressure can reduce.

http://www.ncbi.nlm.nih.gov/pubmed/11874646
http://www.aloha.net/~icarus/243pg4.htm
http://www.airdisaster.com/reports/ntsb/AAR89-03.pdf
http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=45

 

[Carlobrand]

Now see, this is why I'm glad I found this group. Where else can a person discuss such things?

Whipslade, for the record: I've no idea what TNE did or did not deal with. Like many, I took the assassination of Strephon as a very bad sign for the game's direction. Other than a copy of the Imperial Encyclopedia, I stopped investing at that point. Strange since I'm a Striker fan, but I like my wargaming complicated and my roleplaying simple and loose. Bits and pieces of the material have fallen into my lap since, courtesy of my wife's bookselling business, but that's about it. I am grateful to anyone who wants to point out sources to correct my more egregious points of ignorance, as Aramis has been so patient to do ... provided of course that I am not compelled to sell my firstborn to afford those sources. She is, after all, in college and would likely resent that - not to mention the legal complications involved.

Aramis, I think we both agree it's possible to avoid injury related to decompression. The key point of difference seems to be whether injury will occur if you do not or can not release that lungful of air as your cabin goes to vacuum around you. Aloha 243 involved a drop from roughly 2/3 atm to roughly 1/3 atm. Not exactly a drop from one to nothing, but a big drop nonetheless and with no lung injuries resulting. Still, we agree you can drop from 1 to zero without (immediate) injury if you don't hold your breath, and we have nothing saying anyone on Aloha just happened to be holding their breath at the time of the incident. Probably not, so that incident doesn't tell us anything about the lung's ability to withstand pressure differentials.

However, there seems to be wide variation, both related to rate of decompression and individual variability, as you point out. You're using a tool that appears to be hitting you with close to an atmosphere above normal air pressure, and clearly the FDA thinks it's safe to sell those devices. Yet, the news today features the story of a teenager who died from an apparent embolism after taking helium straight from a helium tank at a party (while her friends playing the same game at the same party were uninjured). And then there's ongoing controversy in the medical community about the potential for injury from mechanical ventilators. There seems to be a "bad luck" factor involved, perhaps individual variation or unnoticed minor damage from past illnesses that make a handful of people more vulnerable than the general population. Certainly that would account for the handful of reports of lung injuries from quite shallow dives while divers in general report doing the same with no ill effect. I'd be tempted to experiment - me, an inverted bucket, and the local pool - but with my luck I'm very likely to be among the unlucky few. And, I'm slow, not stupid.

I don't consider the 1969 study entirely invalid - it too documented some animal research, and I unfortunately do not have access to your NIH link to compare its findings to those. However, your speculation regarding CPR is a good one, sufficient to raise significant doubt as to the cause of that victim's pneumothorax. That does however leave me scratching my head in bafflement at the evidence presented in Principles of Clinical Medicine for Space Flight, which has a 2008 copyright date.

Leaving aside the injury question, it remains an issue gamewise - as far as characters are concerned - that their opportunity to take action in the event of a serious incident may be pretty narrow, mere seconds of consciousness. Survivable or not, it's no great fun sitting there watching the clock and hoping one of the other players remembers to save you if you pass out. However, given the extraordinary strength of those spacecraft hulls, it's honestly difficult to think of anything causing a decompression so rapid (without killing the crew directly) that the crew won't have time to slap on a patch or retreat to another compartment. On the other hand, it's hard to imagine an airplane spontaneously losing a large section of fuselage, and a game master inclined to the dramatic might be tempted to treat his players to "Aloha Airlines in Space" just to get their adrenaline moving. "Hey, design defect. Didn't you get the recall notice?"

If so, I hope he is equally inclined to give them the tools needed to handle the situation.

That actually sounds rather fun, in a fiendish sort of way.

 

[aramis]

It didn't take anything special to hit the NIH link; perhaps my state has paid for a subscription.

As for the resuscitations: Every study I've seen citing 1atm to vacuum coupled to pneumothorax has included resuscitation attempts as standard protocol. It confounds the data. Especially animal studies, where it's less of an ethical issue.