Volcanoes, heat, and air currents

[Yora]

I got an idea for a fantasy adventure and want to make it a bit plausible, so I want to check on the physics involved.

There is a large ancient city that has been abandoned for centuries and for some reason the whole time nobody explored it. But now the heroes are the first people who enter it since it was originally destroyed. Since it would be in an area with volcanic activity, I got an idea:
How about gas from underground rising through cracks, filling all the underground tunnels with a heavier than air gas that made it impossible to explore more than just the streets on the surface? There are places like this, so this part at least works. But lets now say the ruins are at the base of a volcano and some of the tunnels connect to the main crater. If the volcano becomes active again, the hot lava would heat the air in the crater, which then rises. Could cold air be sucked into the crater through the tunnels of the ruins, sucking out all the deadly gas and replacing it with fresh air?

Since it's a fantasy story, a sorcerer could wake up the volcano for just that purpose, venting the tunnels so he can search them for magical treasures.

[halfeye]

I got an idea for a fantasy adventure and want to make it a bit plausible, so I want to check on the physics involved.

There is a large ancient city that has been abandoned for centuries and for some reason the whole time nobody explored it. But now the heroes are the first people who enter it since it was originally destroyed. Since it would be in an area with volcanic activity, I got an idea:
How about gas from underground rising through cracks, filling all the underground tunnels with a heavier than air gas that made it impossible to explore more than just the streets on the surface? There are places like this, so this part at least works. But lets now say the ruins are at the base of a volcano and some of the tunnels connect to the main crater. If the volcano becomes active again, the hot lava would heat the air in the crater, which then rises. Could cold air be sucked into the crater through the tunnels of the ruins, sucking out all the deadly gas and replacing it with fresh air?

Since it's a fantasy story, a sorcerer could wake up the volcano for just that purpose, venting the tunnels so he can search them for magical treasures.
Why wouldn't the lava from the eruption run down the tunnels?

[Bulldog Psion]

I don't see why not. At a minimum, it sounds plausible, and that's usually all you need for a story.

[Tvtyrant]

It could also open a much deeper well, which the heavier gas would fill and leave the upper tunnels.

[Yora]

Why wouldn't the lava from the eruption run down the tunnels?

Oh, that gives me another good idea. It's not really an explosive erruption, just a bit of lava bubbling. Enough to create a strong draft, but not a huge amount of flowing everywhere. However, the lava might slowly rise and could indeed eventually flow into the tunnels, so the characters have to hurry.

[Chronos]

Real caves often have drafts just from the temperature variation from night to day outside. If that's enough to keep air fresh, even with it changing direction twice a day, a through path with a constant heat source shouldn't have any trouble with it.

Also, gases don't actually pool like liquids: Even heavier-than-air gases will diffuse out with time, it's just slower than with light gases. So if the tunnels were uninhabitable, that must mean that there's a continual replenishment of the gases from somewhere. A major geological event like an eruption or an earthquake could easily shift the source of the gas as well, and allow the tunnels to clear out even without volcanic heat. As a bonus, this could also lead to previously-safe tunnels elsewhere becoming uninhabitable.

[Yora]

Yes, earthquake and giving it a few weeks to vent could work.

But I think a sorcerer opening a lake of lava is probably much cooler. :smallbiggrin:

[Kato]

I think it sounds rather plausible. Minor problem might be asking what gas filled the tunnels, but otherwise, if it's isolated enough to not just exchange gases with the surface over time, or have some leak bringing in new gases constantly... I don't see much problem.
I guess if you want to get more detailed, consider what (heavier than air) gases are likely to exist close to volcanoes... First thing that comes to my mind is probably SO2, maybe carbon-oxygen-compounds, not sure about nitrogen-compounds, though. Or just go with heavy noble gases... they probably can be stuck in some subterranean pockets or such.

[Yora]

I know of one Greek temple to Hades, which was in a cave and had the "magic trait" that all animals that enter die. The priests that entered didn't die, because their heads were close to the ceiling, while the animals all were close to the ground and couldn't breath.
I think it's some kind of sulfur compound.

[factotum]

SO2 is the main toxic gas you get from volcanoes, but there are all sorts of other horrible things that can form. Hydrogen fluoride, for instance, which becomes hydrofluoric acid on contact with moist things (like human skin and eyes). You wouldn't want to be anywhere near that stuff!

[cobaltstarfire]

SO2 is the main toxic gas you get from volcanoes, but there are all sorts of other horrible things that can form. Hydrogen fluoride, for instance, which becomes hydrofluoric acid on contact with moist things (like human skin and eyes). You wouldn't want to be anywhere near that stuff!

I don't think Yora is looking for toxicity specifically, the way they have mentioned heavy gas implies they're more looking into how heavier largely non-toxic gases can literally smother you to death in seconds if enough of it comes down on you at once.

Seems like with a tiny bit of poking people and animals have been killed by the sudden release of Carbon Dioxide from volcanos which then travels down hill and asphyxiates the people/animals unlucky enough to be in its path. so maybe those areas you're thinking of are just constantly having CO2 vented into them. What I've read seems to imply that volcanos that release gases in this way do it in a cyclical nature.

[halfeye]

I don't think Yora is looking for toxicity specifically, the way they have mentioned heavy gas implies they're more looking into how heavier largely non-toxic gases can literally smother you to death in seconds if enough of it comes down on you at once.

Seems like with a tiny bit of poking people and animals have been killed by the sudden release of Carbon Dioxide from volcanos which then travels down hill and asphyxiates the people/animals unlucky enough to be in its path. so maybe those areas you're thinking of are just constantly having CO2 vented into them. What I've read seems to imply that volcanos that release gases in this way do it in a cyclical nature.
According to Wikipedia, CO2 is actively toxic, not just inert and anoxic.

http://en.wikipedia.org/wiki/Carbon_dioxide


CO2 is an asphyxiant gas and not classified as toxic or harmful in accordance with Globally Harmonized System of Classification and Labelling of Chemicals standards of United Nations Economic Commission for Europe by using the OECD Guidelines for the Testing of Chemicals. In concentrations up to 1% (10,000 ppm), it will make some people feel drowsy and give the lungs a stuffy feeling.[81] Concentrations of 7% to 10% (70,000 to 100,000 ppm) may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.[83] The physiological effects of acute carbon dioxide exposure are grouped together under the term hypercapnia, a subset of asphyxiation.

[cobaltstarfire]

According to Wikipedia, CO2 is actively toxic, not just inert and anoxic.

http://en.wikipedia.org/wiki/Carbon_dioxide

Uh, read what you quoted again, it says CO2 is not toxic but an asphyxiant.

The thing that came to mind at first when I was reading Yoras post was argon though, which also isn't toxic, and doesn't come from volcanoes but it sure will kill you good and fast in high enough quantities. Or give you a pretty nasty headache in lower quantities similar to what is described for CO2.

I can say that another thing Yora can do if they want to throw things like heavy air at their PC's is have them start making fort checks at first to not get nauseous and headache. In my experience it only takes about 15-20 minutes of light exposure to start feeling like you're hung over, or coming down with the flu. Stepping out for a 5-10 minutes is enough to start to feel better for some people, but for others they'll feel ill for the rest of the day even with regular breaks.

[Kato]

I can say that another thing Yora can do if they want to throw things like heavy air at their PC's is have them start making fort checks at first to not get nauseous and headache. In my experience it only takes about 15-20 minutes of light exposure to start feeling like you're hung over, or coming down with the flu. Stepping out for a 5-10 minutes is enough to start to feel better for some people, but for others they'll feel ill for the rest of the day even with regular breaks.

A large-ish problem with heavier than air gases is getting them out of your lungs. Depending on how deep you breath they can gather in the lower parts of your lung and you need to take proper, deep breaths to get them out. That, or place yourself upside down to let them flow out.

[halfeye]

Uh, read what you quoted again, it says CO2 is not toxic but an asphyxiant.

Yeah it starts off saying something like that, but then you get this bit:


Concentrations of 7% to 10% (70,000 to 100,000 ppm) may cause suffocation, even in the presence of sufficient oxygen

If it kills in the presence of sufficient oxygen, it's toxic by my definition.

[Yora]

But it doesn't cause any damage. The problem is that removing CO2 from the body has priority over absorbing O2 (or we would inflate and burst). The blood cells carry CO2 to the lung, put it into the air inside the lung, and pick up a new molecule for their next trip through the circulatory system. Usually there is over 500 times more O2 in the air than CO2, so (I assume) the new molecule that gets picked up is most likely O2. If you increase the amount of CO2 200 times, and the ratio gets to something like 1:4 instead of 1:500, lots of blood cells will run through the whole circulatory system carrying CO2; neither delivering oxygen, nor removing any CO2 that needs to be transported out of the body.
Everything works normally, nothing gets damaged. It just doesn't get enough oxygen to your cells.

(I am guessing here on the process that makes blood cells drop off CO2 and picking up O2, but however it really works, the effect on the O2 and CO2 in the blood and the body cells is the same.)

[factotum]

If it kills in the presence of sufficient oxygen, it's toxic by my definition.

Oxygen itself will kill you under some circumstances (e.g. at very high pressures)--that makes it toxic too, by your definition? Pretty darned strange definition, if that's the case.

[halfeye]

Oxygen itself will kill you under some circumstances (e.g. at very high pressures)--that makes it toxic too, by your definition? Pretty darned strange definition, if that's the case.
Will it? I am not aware of that. I mean anything at high pressure will do you damage if there's a pressure differential and you're all that's between the two pressures, you mean high pressure oxygen will kill you without a pressure differential to physically injure you?

By toxic I mean that nitrogen at normal temperatures and pressures is not toxic. If you dive in scuba gear, quite deep, the nitrogen in compressed air becomes narcotic, then I would say it's mildly toxic, though not usually lethally so. You couldn't replace that nitrogen with CO2, it would kill you straight off, even mixed with oxygen, that sounds like toxicity to me.

[cobaltstarfire]

Yeah it starts off saying something like that, but then you get this bit:



If it kills in the presence of sufficient oxygen, it's toxic by my definition.

Your definition of "toxic" is wrong, you should educate yourself on the correct definition rather than arguing about it.


The reason it will kill you in the presence of oxygen is because it is heavier, as Kato mentioned. The reason heavy gases are dangerous is because it's hard to get them out of your lungs.

By your definition Argon is also toxic, even though it clearly is not, no MSDS sheet is going to list Argon, or CO2 as toxic, because they are not by actual definition toxic, they are asphyxiants. They kill you by suffocating you to death.

And when I say I speak from experience, I say that as a welder. TIG welding uses Argon gas as a shielding metal for welding, MIG welding uses a CO2 mix dependant on what alloy you are welding. I've had to work with the stuff daily. Just because something can kill you good and fast doesn't mean it's toxic.

[halfeye]

Your definition of "toxic" is wrong, you should educate yourself on the correct definition rather than arguing about it.


The reason it will kill you in the presence of oxygen is because it is heavier, as Kato mentioned. The reason heavy gases are dangerous is because it's hard to get them out of your lungs.

By your definition Argon is also toxic, even though it clearly is not, no MSDS sheet is going to list Argon, or CO2 as toxic, because they are not by actual definition toxic, they are asphyxiants. They kill you by suffocating you to death.

And when I say I speak from experience, I say that as a welder. TIG welding uses Argon gas as a shielding metal for welding, MIG welding uses a CO2 mix dependant on what alloy you are welding. I've had to work with the stuff daily. Just because something can kill you good and fast doesn't mean it's toxic.
By toxic I mean poisonous. There was a bunch of stuff turned up somewhere recently about toxic coming from archery, because of poisoned arrows. Here:

http://www.bbc.co.uk/news/blogs-magazine-monitor-31833393

So, you're saying that someone with their head below their lungs would be alright?

If that's so, you're right it's not toxic, but I'm not convinced, we breathe the stuff out, and we wouldn't do that if it was good for us.

[Solaris]

By toxic I mean poisonous. There was a bunch of stuff turned up somewhere recently about toxic coming from archery, because of poisoned arrows. Here:

http://www.bbc.co.uk/news/blogs-magazine-monitor-31833393

So, you're saying that someone with their head below their lungs would be alright?

If that's so, you're right it's not toxic, but I'm not convinced, we breathe the stuff out, and we wouldn't do that if it was good for us.

We breathe an excess of CO2 out. A large amount of it is essential as a part of the blood's pH buffering system, as it's one of the required components for bicarbonate and carbonic acid.
We also breathe out a lot of oxygen gas, too, along with water vapor and nitrogen gas. "You don't want it accumulating in your bloodstream and cells" isn't quite the same as "toxic to breathe". If you don't have CO2 gas in your blood, you won't breathe except by deliberate action.

CO2 is not toxic; it's simply that having too much of it in the air, even when there's adequate O2 levels present, means the body's gas exchange mechanisms don't work nearly as well as they should - the symptoms of CO2 'poisoning' are identical to the symptoms of asphyxiation for a reason. Yora's explanation was quite on the money.

[factotum]

Will it? I am not aware of that. I mean anything at high pressure will do you damage if there's a pressure differential and you're all that's between the two pressures, you mean high pressure oxygen will kill you without a pressure differential to physically injure you?

That's exactly what I mean. Look up "oxygen toxicity"--basically, oxygen is a highly reactive gas, and at higher partial pressures it will start to damage body cells faster than they can repair themselves. This is a definite problem in applications like deep-sea diving and hyperbaric chamber therapy.

It's also interesting to note that nitrogen can have a narcotic effect at high pressures, so divers intending to go below about 250 feet in the water will often be breathing an oxygen/nitrogen/helium mix with the oxygen and nitrogen percentages considerably reduced from what they are in surface air.

[cobaltstarfire]

By toxic I mean poisonous. There was a bunch of stuff turned up somewhere recently about toxic coming from archery, because of poisoned arrows. Here:



{scrubbed}

Look at a MSDS and you will find that CO2, Argon, Helium and Nitrogen are not classified as Toxic, but asphyxiates. Because they suffocate you. Some MSDS sheets depending on the company providing the cylinder may have something under toxicology in relation to what happens in the body as a result of suffocation, there is no poisoning involved, they will all say that they are classified as "Simple Asphyxiant [gas] is nontoxic"

Welders, and welding assistants have died of suffocation due to accidents involving their shielding gas. Not poisoning.

Small populations have been killed via suffocation simply because they were near volcanos that decided to belch up CO2. Not poisoning.

Accidents involving nitrogen in labs, space shuttles, or through playing with fire extinguishers have killed people via suffocation. Not poisoning.

{scrubbed}

[Sith_Happens]

The distinction is rather pointless in the first place. Anything is toxic in high enough quantities.