As it happens, fires in coal mines, coal seams, and other underground sources of carbon-bearing rock are extremely widespread. It makes me wonder just how much Carbon is being paired up with Oxygen and shot off into the atmosphere through these cracks and crevices, to say the least of any toxins borne in the coal such as Benzene (a liquid, thankfully) and lead. It's been a while since I studied up on coal fires, so I headed to Wikipedia. I started with what was, to me, the most obvious starting-point article "Coal Seam Fire"::
http://en.wikipedia.org/wiki/Coal_seam_fire"A coal seam fire or mine fire is the underground smouldering of a coal deposit, often in a coal mine. Such fires have economic, social and ecological impacts. They are often started by lightning, grass, or forest fires, and are particularly insidious because they continue to smoulder underground after surface fires have been extinguished, sometimes for many years, before flaring up and restarting forest and brush fires nearby. They propagate in a creeping fashion along mine shafts and cracks in geologic structures."
Aside from being written by a Canadian or some other type with the affinity for those precious extra "U"s (I'm partial to "colour" myself, but mostly to irk fellow Americans), this article related very closely to my recent DF experiences. Having embarked at a flat desert with a thick, healthy, 4-z layer of Limestone just racing with seams of coal and lignite, I could probably have gotten by without ever using magma. Nonetheless, I wanted to bring magma to the surface and at one point there was coal in the path of the pump stack. As far as I know, walls and floors presently NEVER ignite under any circumstances, even if they're made of soap or silver they can hold in magma for all eternity. Despite this, I imagine the worst-case scenario where magma ignites a coal vein or a coal flooring and gradually burns through from the magma source into my fort's dining hall, so I ended up flooring it all over with Bauxite and replacing coal walls with Bauxite Blocks. Wasn't necessary, but half of DF is pretending, right?
This leaves me wondering if a percentage of natural caverns weren't once coal veins that burned away over the course of tens or scores or hundreds of years, leaving an extremely organically-fertile cavern behind which nourishes all manner of underground life. I wouldn't be surprised if such a cave needed a few decades of bioremediation through natural microbes to "clean up" the cavern a bit before it stopped being a toxic environment. Then again, there's a host of adapted lifeforms for most any niche you can imagine...
Now, to the !!Fun!! part of the thread. They mention Lightning, Grass Fires, and Forest Fires as sources of ignition of these veins. While coal is a valuable natural resource in DF, it's presently not very dangerous like say, magma or a running underground river might be. Natural resources must be protected if they are to be harnessed completely and safely. I'd really like to see these veins serve as a source of significant danger at some point, with ignited veins burning away amidst an unreasonable volume of smoke at a rate of 1 tile of exposed surface area per 9 months or something in that... ... ...vein. >_> *dodges pun-seeking missiles* I imagine that in order to extinguish a coal vein, the entire tunnel would require flooding. Extinguishing it with mining picks, well, suffice to say I imagine it would be a disaster, assuming one could not get into an oxygen-deprived cave and manage the endurance to swing a pick for enough time to break down all of the burning rock face without igniting the newly-exposed faces with the existing burning material. I'd definitely like to see veins have a chance to ignite in proximity to fire or magma. Lightning doesn't currently exist but it surely could, even if it had to be done in a cheesy fashion with a pause-recenter event if anything meaningful was struck by lightning. How to render lightning in 2D ASCII, however...? With lightning, we could have natural grass fires, and more reasons to fear the overworld prison reserved for the races rejected by the stone.
All of this makes me wonder at the structural role in organic substances that fill a layer or reservoir or vein like this. Once removed, do these voids left over from oil drilling, coal mining, etc. provide an opportunity for underground collapses or geologic instability? Could all those drained oil reservoirs simply collapse, on a massive (many many acres) scale, causing depression of the land above? Could a burned-out coal seam effectively behave as a faultline?
Another bit scares me just slightly, from the same wiki article:
Global coal fire emission are estimated to include 40 tons of mercury going into the atmosphere annually, and three percent of the world's annual CO2 emissions.
Oh, methyl mercury poisoning. Why must I be a fish-lover? Personally, I don't believe that CO2 is a "greenhouse gas"; CO2 is the main or only means by which plants obtain carbon with which to grow and build their bodies. If you increase the supply they will eat more. In the study of horticulture I learned to burn a tea candle periodically when growing indoor plants as a "snack." Please no off-color jokes here, I don't grow marijuana. I do have a selection of
Spider Plants and
whatever these are called, however. Any amount of mercury is pretty much a horrible thing for the ecosystem since it is a biomagnifying toxin which works its way up the food chain to humans.
I wonder what, if anything, we could hope to do to put out these RL coal fires. The existing one which I had studied previously::
http://en.wikipedia.org/wiki/Centralia,_Pennsylvania#Mine_fire has been burning for 45 years and acknowledged as a lost cause. The city of Centralia was abandoned and a scant 5 or 10 residents remain, the government has even revoked Centralia's ZIP code despite that a few residents refuse to leave their homes. In response, they put up a park bench bearing their stolen ZIP code. True dwarves, here. Burning coal seam? Magma leaking out of the rock above sea-level? Physical gateway to HELL spewing demons? It's fine, this is our home. However, apparently::
"In 2009, Ed Rendell began the formal eviction of Centralia residents. He is facing criticism from some for this move."
To have already lost their hometown in this fashion can leave some people dejected with a feeling that it was all pointless. The last thing they have is the freedom of choice to remain in their homes for better or worse. I'm not sure how I feel about someone else choosing for them that they may no longer do so.
(Attempt #2. This time we have a bit meatier of an OP. Let's remain civil and focused on the topic. Peace, my dwarven brethren! Forget about the previous thread.)