Rapid decompression

[Carlobrand]

You're a steward aboard a free trader. You are inbound from jump to a little frontier outpost of a world, not one of the Captain's better decisions but you don't get much of a say in such things. You are serving drinks in the lounge to your few passengers, the landing some 5 hours off, when a brilliant flash and wave of heat fill the lounge. There is a sudden howling sound, wind where there should be no wind, klaxons sounding and strobes going off to warn of dropping air pressure, and the passengers cry out and gasp in alarm - there is a hole in the exterior wall large enough to put your fist through. And then the Captain announces battle stations.

So, how long do you have before the air's gone?

I don't know if there's a canon example of being in this situation, but there's this interesting site, discusses vacuum exposure and - in this instance - the formulae to calculate just how long you have.

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

For those of us who are weaker in math, the interesting bit is at the end; they run the numbers for a 10 cubic meter space with a 1 square centimeter hole in the wall, for a drop from 1 atmosphere to 0.5 atmosphere, which is about the point where people start passing out (unless you flood the area with O2 to buy them a little more time). Ends up being 344 seconds, and the equation is such that we can scale up for larger spaces and/or larger holes.

Passenger section on the venerable Free Trader, based on that Starship Operator's Manual deck plan, is about 24 dTons - 6 staterooms and their associated common areas and such. 324 cubic meters. Not all of that's free air - there's the between-deck machine spaces, the furniture, and all that stuff. Let's say we have about 3/4 of that as air space: 243 cubic meters. Assuming a 1 cm hole, we have 8359 seconds. For this example, we're going to say our hole is 100 square centimeters - handily enough to put your fist through. That sound workable for a 250 megawatt laser or a 15 cm HEAP missile hitting a Striker-armor-40 hull? Might be smaller, might be larger, but it's a starting point. End result: everyone has about 84 seconds to get out of there or get into rescue balls. Say a minute and a half.

Could be shorter, could be longer depending on the actual size of the hole. If we assume every stateroom has a rescue ball handy and there are several also in the lounge, the passengers should need no more than 15-20 seconds to get to one and close up - maybe 30 if they spend a few seconds being shocked and wondering how to react. Assuming the hole is readily apparent, there's also plenty of time for the steward to slap something over it, but it's a little short if the hole happens to be in an unoccupied room and they have to spend time finding it.

Now, it would be helpful to have the steward able to move about, try to find and patch the hole or help panicky passengers. He needs air, and he needs a way to protect his body so that he can breathe. However, protecting the body alone serves no use unless he can act - and there's this weird thing in vacuum where your exposed body swells up. Same site, another page:

"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."

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

(about halfway down)

MegaTrav has a "body pressure suit". TL 10, can be worn under clothes, serves as protection against vacuum if worn with a vacuum belt and with gloves and helmet. My thought is to make this required shipboard equipment for certain on-duty positions - the steward (so he can aid passengers in an emergency), the pilot and the engineer. Or maybe the medic, the pilot and engineer would be better. It's a bit pricey, Cr15,000 plus another Cr250 for a 20-minute air kit, but seems like a good idea for the ship's locker. Either that, or just one of these for the steward (or medic) and a regulation requiring one pilot and one engineer in vac suits but for helmet and gloves - they can throw those on quick if a hole takes air from the bridge or engine room.

 

[Timerover51]

A 15cm shaped charge will have an effective penetration of 90cm of steel armor plate, giving an internal hole of roughly 2 to 2.5 centimeters in diameter, plus a very hot jet of flame as well inside of whatever is hit. The jet is also going to be pretty long. All of the displaced metal of the hull is coming in as well, part of it in the jet and the rest is extremely high velocity fragments. You do not simply get a bright light and feeling of heat. You also are going to get a significant pressure pulse as well, and a very loud noise. As a rough estimate, anyone inside of the compartment hit is going to be deafened, stunned, and possibly dead, depending on where they are.

Is your Striker Amor 40 hull equal to 90 centimeters of steel plating? Note, 90 centimeters of steel armor is going to weigh about 1400 pounds per square foot of surface covered, not counting the necessary structural support for all of the weight. Higher density does not help that much, as shaped charge penetration scales to the square root of density, so heavier materials are less effective against penetration as an equal mass of lighter materials.

That size of precision shaped charge should punch a near caliber size hole through about 2 diameters thickness of steel plate, or a roughly circular hole of 15cm through 30 centimeters of steel. To stop a shaped charge, you need mass. Claiming that 2.5 centimeters of hull metal is equivalent in strength to 30 centimeters of steel plate does not cut it.

 

[Carlobrand]

A 15cm shaped charge will have an effective penetration of 90cm of steel armor plate, giving an internal hole of roughly 2 to 2.5 centimeters in diameter, plus a very hot jet of flame as well inside of whatever is hit. The jet is also going to be pretty long. All of the displaced metal of the hull is coming in as well, part of it in the jet and the rest is extremely high velocity fragments. You do not simply get a bright light and feeling of heat. You also are going to get a significant pressure pulse as well, and a very loud noise. As a rough estimate, anyone inside of the compartment hit is going to be deafened, stunned, and possibly dead, depending on where they are.

Is your Striker Amor 40 hull equal to 90 centimeters of steel plating? Note, 90 centimeters of steel armor is going to weigh about 1400 pounds per square foot of surface covered, not counting the necessary structural support for all of the weight. Higher density does not help that much, as shaped charge penetration scales to the square root of density, so heavier materials are less effective against penetration as an equal mass of lighter materials.

That size of precision shaped charge should punch a near caliber size hole through about 2 diameters thickness of steel plate, or a roughly circular hole of 15cm through 30 centimeters of steel. To stop a shaped charge, you need mass. Claiming that 2.5 centimeters of hull metal is equivalent in strength to 30 centimeters of steel plate does not cut it.

Striker unfortunately did a poor job of reflecting the power of HEAPs. The Striker 15cm HEAP at TL13+ has a penetration of 49, or 73.4 cm of steel. At our tech, it's 51.9 cm. But that's neither here nor there. I was actually trying to describe a surprise laser hit. I seem to have done a rather bad job of it. I'd have hoped the captain had the sense to call battle stations before a missile hit if he'd seen a missile inbound.

(And, yes, I expect there'd be spalling associated with the sudden explosive vaporisation of a piece of hull under a powerful laser, but I figured the lounge was big enough I could gloss over that and get to the decompression part.)

MT handles the ship hull pretty much the same way Striker builds tank armor, but that leaves it depending on TL as to whether it's a foot of steel or a couple inches of superdense. High Guard doesn't go into details about how the hull is made, just that added armor takes up X% of the ship. The basic unarmored hull is declared by Striker to be equivalent to 33.6 cm of steel (irrespective of TL), so it's not even going to stop a Striker 15 cm HEAP, much less the real-world ones you mention. I'm really not intending the thread to debate the effectiveness of superdense or bonded superdense armor since in this case the shot clearly bored through the hull and we're more interested in what happens after. However, that's an interesting description and some interesting data.

I'm a bit confused though: you say at one point I can expect a 2.5 cm hole and at another point that I can expect a caliber-size hole, i.e. 15 cm. The difference is the difference between having a half hour and having less than a minute before you're unconscious (assuming you haven't been killed in the initial weapon strike). Which is correct?

 

[Timerover51]

I'm a bit confused though: you say at one point I can expect a 2.5 cm hole and at another point that I can expect a caliber-size hole, i.e. 15 cm. The difference is the difference between having a half hour and having less than a minute before you're unconscious (assuming you haven't been killed in the initial weapon strike). Which is correct?

The 2.5 centimeter hole assumes that it has punched through 90 centimeters of steel plate. The caliber-size hole assumes that it has punched through a plate of 1 to 2 calibers in thickness, i.e. 15 to 30 centimeters of steel plate.

Based on the material in the Classic Version of Traders and Gunboats, the adventure Chamax Plague, and the adventure Annic Nova, the hull thickness and bulkhead thickness of a commercial starship is about 10 millimeters in thickness of steel. The standard internal partition should be about 1 millimeter of steel plate equivalent, or maybe 3 millimeters of aluminum. That is based on, in the Annic Nova, 200 millimeters of steel armor requiring 20,000 damage points from laser fire or a cutting torch to cut through, while ship bulkheads require 1000 damage points and internal partitions require 100 damage points. Ten millimeters is pushing it to stop full rifle caliber AP rounds, such as the WW2 .30-06 round. Because the ship bulkhead present a flat face to the internal pressure of the ship, and they are intended to maintain internal pressure in the event of damage elsewhere, they may actually be thicker than the ship hull. In Chamax Plague, the Chamax acid ate through the ship hull and the ship bulkheads, apparently with equal ease.

I will not comment on the handwavium used as armor in Strker and later versions of Traveller.

 

[Vladika]

As to the air problem, I'd suggest the ship of the future would have the equivalent of "Momsen lungs", strategically placed about the ship. That or small oxygen tanks and masks, just for such an eventuality.

With compressed gas, oxygen in this case, and a regulator, the body would be able to breath at the original atmospheric pressure for a short while.

Making your way to a nearby airlock would probably be best as they cycle in 10 seconds IIRC. There you would access a handy vacc suit and don it while in the lock, cycle the lock and reenter the ship proper.

Not ideal of course, but doable.

 

[SpaceBadger]

Hole's a bit large for a "finger in the dike", but how about a serving tray across it, or something soft like a sofa cushion?

I think that's be my priority, anyway, if I could see the actual hole and it looked small enough to plug and stop the loss of any further atmo.


EDIT: Seems I remember an SF story where a self-sacrificing brave soul "turned the other cheek" and sat himself up against the hole - not centered, where it could suck out his innards, but with one buttock solidly in place. Injury was one heck of a blood blister, IIRC, but he was a hero who saved the day - even if he couldn't sit down for awhile without a special cushion.



*

 

[Vladika]

Hole's a bit large for a "finger in the dike", but how about a serving tray across it, or something soft like a sofa cushion?

I think that's be my priority, anyway, if I could see the actual hole and it looked small enough to plug and stop the loss of any further atmo.


EDIT: Seems I remember an SF story where a self-sacrificing brave soul "turned the other cheek" and sat himself up against the hole - not centered, where it could suck out his innards, but with one buttock solidly in place. Injury was one heck of a blood blister, IIRC, but he was a hero who saved the day - even if he couldn't sit down for awhile without a special cushion.



*

Between that, and handy duct tape*, it should do the trick.

* Ubiquitously everywhere around a ship. Just because.:devil:

 

[CosmicGamer]

Not sure how the different versions of Traveller handle things so some may assume one solid ships hull and the following may not apply.

Current space hull design is going in the direction of several solid hull layers with "filler". Some of the layers in in the hull can help absorb damage and some can help reseal the hull - perhaps not completely, but enough that decompression is less rapid.

The concept here that the outer hull is sacrificial and easily penetrated by something (like a shaped charge). The filler layers of material help distribute the energy across a wider area of each successive solid layer of armored hull and then one of the last layers is a material designed not to stop penetration but to help reseal the breach.

So that said, while I recognize that the more technical info on blasting through steel and decompression times is useful to help form a picture, for me, the possible futuristic materials and methods of hull design allow for quite a bit of room for GM fiat.

 

[Carlobrand]

As to the air problem, I'd suggest the ship of the future would have the equivalent of "Momsen lungs", strategically placed about the ship. That or small oxygen tanks and masks, just for such an eventuality.

With compressed gas, oxygen in this case, and a regulator, the body would be able to breath at the original atmospheric pressure for a short while. ...

There is a point at which reduced pressure outside of the body will lead to ruptured lungs if you try to take in air, but I don't know what that pressure is, nor do I know what pressure differential the lungs can take - i.e. if some poor sap tries to hold his breath while the lounge is still at 1 atmosphere, at what level of pressure will he face pulmonary barotrauma as the pressure drops?

 

[aramis]

There is a point at which reduced pressure outside of the body will lead to ruptured lungs if you try to take in air, but I don't know what that pressure is, nor do I know what pressure differential the lungs can take - i.e. if some poor sap tries to hold his breath while the lounge is still at 1 atmosphere, at what level of pressure will he face pulmonary barotrauma as the pressure drops?

That pressure is well below that found at 20000' MSL. People can breath the pressure at the top of K2 (28,251', probably 325 mBar) with only supplemental oxygen, not supplemental pressure.

I've heard of bailouts at 50,000' without pressure support - a measly 110 mBar - without bleeding from the lungs.

Plus, there's the NASA vacuum exposures.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

 

[JimMarn]

Hole's a bit large for a "finger in the dike", but how about a serving tray across it, or something soft like a sofa cushion?

I think that's be my priority, anyway, if I could see the actual hole and it looked small enough to plug and stop the loss of any further atmo.


EDIT: Seems I remember an SF story where a self-sacrificing brave soul "turned the other cheek" and sat himself up against the hole - not centered, where it could suck out his innards, but with one buttock solidly in place. Injury was one heck of a blood blister, IIRC, but he was a hero who saved the day - even if he couldn't sit down for awhile without a special cushion.



*

I remember reading that as a short story. I'm not sure who the author was though.

 

[aramis]

One other thought on the pressure drop = bleeding score: certain individuals can start bleeding from a mere 200mBar drop - but that's due to a pre-existing aneurism.

 

[Carlobrand]

That pressure is well below that found at 20000' MSL. People can breath the pressure at the top of K2 (28,251', probably 325 mBar) with only supplemental oxygen, not supplemental pressure.

I've heard of bailouts at 50,000' without pressure support - a measly 110 mBar - without bleeding from the lungs.

Plus, there's the NASA vacuum exposures.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

Okay, we know you can survive if you don't hold your breath - assuming you get back into air quick enough. Question is when are you at risk of injury if you do? I've got sources suggesting it can occur in as little as an eight of an atmosphere difference. Of course, much depends on circumstance and luck: the average person's maximum lung capacity is 6 liters and the lungs don't seem to get smaller than about 1.2 liters on the exhale unless you hurt yourself, but he/she typically draws around a 0.5 liter breath, so unless he actually draws deep and holds, he's got a bit of room to expand. I presume that 6 liters represents how much expanding the typical set of lungs will take before they go pop.

 

[aramis]

Okay, we know you can survive if you don't hold your breath - assuming you get back into air quick enough. Question is when are you at risk of injury if you do? I've got sources suggesting it can occur in as little as an eight of an atmosphere difference. Of course, much depends on circumstance and luck: the average person's maximum lung capacity is 6 liters and the lungs don't seem to get smaller than about 1.2 liters on the exhale unless you hurt yourself, but he/she typically draws around a 0.5 liter breath, so unless he actually draws deep and holds, he's got a bit of room to expand. I presume that 6 liters represents how much expanding the typical set of lungs will take before they go pop.

half an atmosphere overpressure isn't much of an issue - that's a pretty typical treatment for sleep apnea. I can hold +1/3 Bar (which is what my CPAP pushes. I've got just a hair over 6.5L exhalation capacity - I just had it tested - and nightly breathe 1.3 Bar at-the-mask while in 1 Bar atmosphere; I can take a deep breath, and hold it while removing the mask. My folks' CPAPs are set for over 1.5 Bar)

There's an awful lot of wrong common knowledge about decompression and lung pressure tolerances.

 

[Carlobrand]

half an atmosphere overpressure isn't much of an issue - that's a pretty typical treatment for sleep apnea. I can hold +1/3 Bar (which is what my CPAP pushes. I've got just a hair over 6.5L exhalation capacity - I just had it tested - and nightly breathe 1.3 Bar at-the-mask while in 1 Bar atmosphere; I can take a deep breath, and hold it while removing the mask. My folks' CPAPs are set for over 1.5 Bar)

There's an awful lot of wrong common knowledge about decompression and lung pressure tolerances.

I don't know that there's any "common knowledge;" just a lot of individual cases that seem to take it all over the place.

 

[savage]

Starship operations include an HVAC system. Decompression in one area would put this system into overtime pumping air into that environment. At TL15 it might be a pretty competent system for brief time periods, although noisy. The intention might be to allow crew members in damaged areas the opportunity to address the issue or escape within a couple minutes.
Objects stuck in the hole could also alter the loss of air for brief periods of time.

On another note, there is still gravity from the gravitic plating and i'd assume a ship heating system other than Air through HVAC.

I would say the player has an opportunity for an action without severe personal damage.

Have you ever been in one of those simulated (or real) hurricanes? Jumped out of an airplane? It's necessary to work harder on the basics like breathing.

 

[JimMarn]

Starship operations include an HVAC system. Decompression in one area would put this system into overtime pumping air into that environment. At TL15 it might be a pretty competent system for brief time periods, although noisy. The intention might be to allow crew members in damaged areas the opportunity to address the issue or escape within a couple minutes.
Objects stuck in the hole could also alter the loss of air for brief periods of time.

On another note, there is still gravity from the gravitic plating and i'd assume a ship heating system other than Air through HVAC.

I would say the player has an opportunity for an action without severe personal damage.

Have you ever been in one of those simulated (or real) hurricanes? Jumped out of an airplane? It's necessary to work harder on the basics like breathing.

Depends on where you are when the hurricane arrives.

but that I mean, on the outer edge of the storm, or near the low pressure eye. I've been in one out in the Atlantic, and several while I was on land.

I don't remember having a problem breathing, but I was indoors and not trying to move around in the face of the wind.

 

[savage]

Depends on where you are when the hurricane arrives.

but that I mean, on the outer edge of the storm, or near the low pressure eye. I've been in one out in the Atlantic, and several while I was on land.

I don't remember having a problem breathing, but I was indoors and not trying to move around in the face of the wind.

Ok i didn't mention the eye of the storm being a different environment. Yes, I've been in them too. Putting your face into the wind can add complexity in a storm. There have been days in January walking in downtown Chicago, when breathing wasn't easy.

My point is that we can get comprehend the situation and a TL15 technology with thousands of years of experience may have developed rather clever temporary fixes to extend life.

 

[Hovtej]

Been There (In Training)

As part of Air Force flight training, we went through a rapid decompression. A large altitude chamber was evacuated as low as it would go while we were in the much smaller airlock entrance. When the large connecting valve was opened we went from near sea level to over 35,000 ft in a few seconds. The airlock filled with fog from the decompression cooling. It felt like I had been punched in the chest as the air escaped from my lungs. While it wasn't true vacuum, we had sufficient time to locate and don oxygen masks. Pressure breathing at altitude is interesting, opposite of Scuba. On commercial spaceflights I'm sure there would be some basic training like current airline briefings and ship lifeboat drills. I've seen a NASA video showing a puncture of a small pressurized compartment to vacuum with an assortment of electronic equipment. In addition to the fog there was some actual smoke as high voltage electronics arced and started small fires which went out as the air escaped.

 

[aramis]

As part of Air Force flight training, we went through a rapid decompression. A large altitude chamber was evacuated as low as it would go while we were in the much smaller airlock entrance. When the large connecting valve was opened we went from near sea level to over 35,000 ft in a few seconds. The airlock filled with fog from the decompression cooling. It felt like I had been punched in the chest as the air escaped from my lungs. While it wasn't true vacuum, we had sufficient time to locate and don oxygen masks. Pressure breathing at altitude is interesting, opposite of Scuba.

35000' is about 238 mBar. Well into what Traveller defines as Very Thin (0.1 to 0.42 Bar; see MT RM 20). And for earth, the "Very thin" range is about 22000' to 50000'... No mask, you suffocate.

http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html