I realize that this is a very late reply, but that it would be useful information to have:
This chart should give some idea of potential hazardous gases:
http://miningquiz.com/2013_Coal_Contest ... sChart.pdfThe primary threat in underground hard rock mines, aside from oxygen deprivation, is hydrogen sulfide. It is a decomposition product of sulfide ores and minerals such as galena, pyrite, and sphalerite, and smells like rotten eggs. The real issue with the stuff is that it is water-soluble, and will liberate out of stagnant water if the water is disturbed- do NOT disturb stagnant water when underground in hard rock mines! H2S can be smelled at 0.01-0.015ppm. You start encountering physiological effects around 2-5ppm, such as eye tearing, fatigue, headaches, nausea, or conjunctivitis (gas eye). The TLV set by OSHA is 20ppm. I got "nuked" by a combination of H2S and black mold at a lead-zinc mine in New Mexico after standing in front of the gated portal, taking photographs of the main haulage drift for a few minutes and relaxing for a few minutes. My eyes were burning and tearing up for several hours after that- it was NOT a pleasant experience. The fact that I'd been up since 0415 that morning (got some sleep on the road) and driven through a nasty ice storm in the Texas panhandle may have had something to do with it. Some research later indicated that the mine's entire second level was full of gas as early as the 1920s, and a vent raise was never constructed as best I could tell.