Shipboard safety and security

[Carlobrand]

If your compartment is already in vacuum and it takes a hit you will not have any problems like sudden gusts of wind slamming you onto sharp pointy torn bulkheads. ...

I was given to understand that this is not as big a problem as movies like to make it. Mythbusters did the explosive decomp thing which, admittedly, was not to vacuum but did suggest the only person who had to worry about wind would be the person immediately adjacent to the hole - who frankly is least likely to survive whatever made the hole in the first place.

If I understand the physics correctly, it's rather like a bathtub drain situation: the farther from the hole, the more volume you're dealing with so the lower the velocity of air movement. It exits the hole at the speed of sound but a few hole radii farther out there's much more air trying to crowd in so much slower speeds. 3 or 4 radii out and its noticeable but not something that's going to suck you in. Or am I not understanding that one right?

...Shock waves are not conducted by vacuum so you do not have overpressure injuries. ...

That's an excellent point that I hadn't considered.

...Yes a 250 MW laser pulse will cause explosions, but there is not an explosion like an explosive filled shell produces, it's more like what happens when a squish round hits, a bunch of armor bits fly away from the inner surface. (The KE to do this comes from the laser vaporizing some amount of armor from the surface.)

I hadn't realized lasers caused spalling, but on checking it I find a number of sources talking about laser spalling in a variety of materials. That's interesting. As I understand it, the sudden superheating of the affected material causes a compression wave that travels through to the other side and results in spalling on the far side. I would think it would be standard to have some elastic sandwiching material inside that would absorb the compressing wave to prevent that, given that lasers are so common a weapon.

 

[Enoki]

If your compartment is already in vacuum and it takes a hit you will not have any problems like sudden gusts of wind slamming you onto sharp pointy torn bulkheads. Shock waves are not conducted by vacuum so you do not have overpressure injuries. Yes a 250 MW laser pulse will cause explosions, but there is not an explosion like an explosive filled shell produces, it's more like what happens when a squish round hits, a bunch of armor bits fly away from the inner surface. (The KE to do this comes from the laser vaporizing some amount of armor from the surface.)

You'd have at most 15 psi in the compartment. That's sea level air pressure, give or take a pound. You might well have less. That's not going to "slam" anyone anywhere as actual experiments, even the somewhat crude ones Mythbusters used show. That's not a problem.

An explosion causing a blast effect will do so whether there's air in the compartment or not. The expanding gas of an explosion itself will do it.

It's HESH not "squish" by the by...

A laser or energy weapon hit is more like a HEAT round. It cuts its way through the hull by vaporizing and melting the material in its way. At most these weapons might cause some degree of material to spray off like in oxy-acetylene metal cutting.

Laser metal cutting.

In either case, until the torch / laser actually penetrates all the spray, sparks, etc., are on the outside of the ship. So only as the laser or whatever finishes penetration do you get a spray into the ship, which is a lot less than on the outside.
Spalling, doesn't happen like in a HESH hit where the material on the inside of the wall comes off in a large slab and hurtles through the compartment like fragments from an HE round explosion.
Here you have small sparks of material flying into the space. Even without an atmosphere, they'll still be present simply because they are hot material forced away from the penetration.

Again, no benefit is accrued by lack of an atmosphere except for the possibility of a secondary ignition of some existing material in the space that can burn.

If you were to cover the inside surface of the hull with a fireproof layer of insulation like is done on many ship bulkheads...

It would absorb most or all of that spray and prevent it from combusting anything in the compartment in any case.

 

[Carlobrand]

...
An explosion causing a blast effect will do so whether there's air in the compartment or not. The expanding gas of an explosion itself will do it.
...

I'm not sure you and he are talking about the same thing. A blast in atmosphere creates a shock wave which travels through air and, on hitting a human body, travels through it. The body as a whole is relatively incompressable, but the lungs are not. The result is something called "blast lung" - pulmonary barotrauma. Air pressure in the lungs is briefly spiked by the shock wave, causing damage to lung tissue and possibly causing pneumothorax (air leaking from the lung into the chest cavity through leaks cause by damage, restricting the ability of the lung to expand and take in air.) On x-ray, it has a characteristic butterfly appearance.

https://www.ncbi.nlm.nih.gov/pubmed/16531371

In an explosion in vacuum, one presumes the occupants in a depressurized compartment are at least in pressure suits, and the explosive gases are radiating out into a vacuum. No shock wave as there is no medium to transmit a wave. Primary cause of injury in that scenario is high velocity particles. The suits, by game mechanics, would offer some degree of protection from such fragments, though of course they might be compromised in the process.

 

[Enoki]

I'm not sure you and he are talking about the same thing. A blast in atmosphere creates a shock wave which travels through air and, on hitting a human body, travels through it. The body as a whole is relatively incompressable, but the lungs are not. The result is something called "blast lung" - pulmonary barotrauma. Air pressure in the lungs is briefly spiked by the shock wave, causing damage to lung tissue and possibly causing pneumothorax (air leaking from the lung into the chest cavity through leaks cause by damage, restricting the ability of the lung to expand and take in air.) On x-ray, it has a characteristic butterfly appearance.

https://www.ncbi.nlm.nih.gov/pubmed/16531371

In an explosion in vacuum, one presumes the occupants in a depressurized compartment are at least in pressure suits, and the explosive gases are radiating out into a vacuum. No shock wave as there is no medium to transmit a wave. Primary cause of injury in that scenario is high velocity particles. The suits, by game mechanics, would offer some degree of protection from such fragments, though of course they might be compromised in the process.

The shock wave in a vacuum is that bubble of expanding gas. While the effect will be less than in a pressurized compartment, it will still be there. Given the small internal volume of the space usually, either way you're hit. The shockwave can also bounce off the bulkheads (assuming they don't rupture) and cause double and triple points where they magnify their effect as they reflect back.

Vacuum or pressurized you get a shockwave from an explosion. The difference is in an atmosphere the gas has to go somewhere as the explosion occurs so it does increase the effect of the shockwave to some degree. If the space were large or external to the ship, it makes zero difference as the volume makes the expanding gases too volumous to generate great pressures.

What I'd be far more worried about is fragmentation. Large chunks of shell, or pieces of spaceship flying around and hitting things will cause secondary damage. Lack of an atmosphere will increase their value and danger greatly as they won't be slowing down due to air resistance.
In most HE type explosions of a shell, the bulk of the fragments are very small and not dangerous as they quickly lose their velocity in an atmosphere. Without one, these small and micro-fragments become killers. They could puncture your vac suit in an instant with their high velocity and small size.
I'd place that danger far ahead of blast effects just as blast if not contained on Earth is less dangerous than fragments from an HE shell to people nearby.

 

[Carlobrand]

The shock wave in a vacuum is that bubble of expanding gas. While the effect will be less than in a pressurized compartment, it will still be there. ...

The effect will be a lot less. Expanding gases from a blast in atmosphere compresses the surrounding air. That compressed wave then radiates outward. It loses pressure as it expands, so it's weaker as it expands, but it transmits the force of the blast pretty effectively, and it doesn't take much of a pressure differential to damage the lungs. In vacuum, you have the solid - say a stick of dynamite - converted to a hot gas by the chemical reaction. Now, air in a 1 dTon volume, at 1.19 g/L (standard temp and pressure), masses 16 kg. Your stick of dynamite in vacuum, on the other hand, converts itself into 190 grams of hot gas containing about 1 megajoule of energy, expanding spherically into the vacuum (except of course where it hits something and reflects). That's a lot of heat and a lot of speed but not much mass, certainly not as compared to the same energy delivered to your body through a 1-atmosphere gaseous medium.

 

[Enoki]

I did try to indicate that. But, blast is usually not the primary casualty agent in weapons effects, fragmentation is. It is far more effective than blast at damaging stuff and hurting people. A vacuum makes fragmentation far, far more effective as there is no resistance to movement.

 

[warwizard]

I was just saying the pumping down limits the concussion waves rebounding off bulkheads and killing you where the metal bits would not reach, also it reduces the risks of fires, though the challenger destruction shows that mixing LOX and LH2 will produce a boom even if you are at a low pressure environment, so the design of the ship or what it is carrying may make all these steps moot. It's like the crews of ships carrying iron ore in the world wars did not bother with survival gear and such , cause their ship would sink in as little as 20 seconds, not enough time to make it to the deck. Where as the dry goods carriers the sailors slept in their survival gear.

 

[Enoki]

Fragments, in a normal shell-type HE round travel far further than the blast. For most rounds up to about 6" if you aren't within a few meters of the explosion, blast has little or no effect on you as a casualty agent.
The fragments, on the other hand number in the hundreds to thousands depending on the size of the round. The smallest produce several hundred. A large shell several thousand. The smallest of these, called "micro-fragments" are generally not dangerous beyond a few meters at most, often less distance, due to air resistance.
Without air resistance every fragment is a potential killer up to as much as 20 to 50 meters or more from the point of burst. In a vacuum, they'd travel as far as gravity would let them, that being the only thing acting on their path of flight. Any fragment would impact at several thousand feet per second and small ones would be potentially as lethal as big ones. These would also have a potentially devastating effect on everything in the compartment, wiring, piping, equipment, personnel, and the bulkheads and decks.
Blast wouldn't be the dangerous killer, fragmentation would be. Even with lasers and such, all the hot sparks given off as it penetrates would be extremely dangerous. Getting hit with sparks that are at thousands of degrees C would burn through vac suits, rescue bubbles, and most of the "stuff" in the compartment. They'd stop being dangerous only when they lost their heat through conduction (hitting something) or radiation which is much less efficient than convection (ie., there's an atmosphere present).
Sure, having an insulating blanket on the bulkheads, etc., would help a lot in keeping these down, but it wouldn't stop all of them as the laser burned through.
Fusion or plasma weapons would have inherent splash and that'd be horribly dangerous. Sort of having a blob of molten, boiling steel splash around the compartment.

As for the crew having to have survival gear on all the time, I'd doubt that. Surprise is very hard to obtain in Traveller in terms of space combat. Unless a ship has a black globe or something like that to camouflage it, you're pretty much going to be spotted at ranges that give the enemy as much as hours to get ready for your arrival.
It isn't like a sudden torpedo from a U-boat hitting the ship.

Aside from all that, I doubt that merchant ships engage in combat on a regular basis, unless the Captain is into heavy risk taking. "Hey guys, today we're heading into a war zone!" "Hey crew, this time we're going into an area plagued with pirates!"
Even then, a ship that's got its hatches set isn't going to suddenly completely lose atmosphere if hit.

 

[Carlobrand]

To be clear, we're addressing these issues with respect to shipboard security, where you are likely to be within a few meters of the explosion if it occurs in your compartment - assuming the source can punch through factor 40 armor to explode within the compartment. I don't have my references handy, but I recall there really weren't any crew casualties going on from missiles, lasers or energy weapons unless you were in a ship small enough to take crits.

As a matter of curiosity, what happens in a compartment under pressure if a 250 Mw laser manages to get in there? MT has this collateral effect on those nearby, if I recall.

 

[Enoki]

As a matter of curiosity, what happens in a compartment under pressure if a 250 Mw laser manages to get in there? MT has this collateral effect on those nearby, if I recall.

I'd think the biggest danger would be the slag spraying off the hole it cut in the bulkhead, much like a giant cutting torch.



Scale that up say 1,000 or 10,000 times larger and imagine what's happening in that compartment...

 

[flykiller]

Scale that up say 1,000 or 10,000 times larger and imagine what's happening in that compartment...

can we get the picture scaled down so we can so imagine ... ?

 

[aramis]

[m;]I edited Enoki's post[/m;]
I switched from the [img]yada.yada/yada[/img] to [imgw=600]yada.yada/yada[/imgw].

The posting of oversized pictures is a MAJOR problem for readability. Since many users are on tablets, about 600 wide is the biggest "safe" image...

 

[Enoki]

Sorry, didn't know how to reduce its size on this board.

 

[aramis]

Sorry, didn't know how to reduce its size on this board.

Now you do. IMGW=600 instead of IMG. That easy.

 

[whartung]

Now you do. IMGW=600 instead of IMG. That easy.

How could he have learned that without you telling him, Aramis?

 

[flykiller]

How could he have learned that without you telling him, Aramis?

it's in the "posting rules" box, "bb code" link, at the bottom left of this webpage.

 

[aramis]

it's in the "posting rules" box, "bb code" link, at the bottom left of this webpage.

I need to find that chunk and add a link there to the BBCode FAQ - which said faq does have imgw right below img.

edit: Never mind, I was wrong, flykiller was correct. I did go in and fix the look of the rules reminder, tho'.