If I recall correctly, most of the deaths in the St. Paul caves are from people starting makeshift campfires in areas without any ventilation. Seems to be backe

If I recall correctly, most of the deaths in the St. Paul caves are from people starting makeshift campfires in areas without any ventilation. Seems to be backed up by this MPR News article from 2004: http://news.minnesota.publicradio.org/features/2004/04/28_ap_cavedeaths/ http://news.minnesota.publicradio.org/features/2004/04/28_ap... Generally speaking, you don't worry about breathing in caves: if you can get there unaided, then so can ambient air. The risks are mainly when you're traversing a completely flooded portion of the cave (a "sump"), since you can't be certain that the dry passages on the other side have any exposure to the outside atmosphere. Edit: You do have to be wary of rain and flash flooding in the Driftless Area. It's not fun to see little twigs and leaves plastered to the ceiling in, for example, Goliath's Cave, since it means that the entire system can flood under the wrong circumstances. Caves are great fun, but they don't mess around. I'd encourage anyone interested in caving to reach out to their local clubs; we're friendly! For folks in the US, the National Speleological Society maintains a list of "grottos" at https://caves.org/committee/i-o/grottos/new_grotto_page-v2.shtml https://caves.org/committee/i-o/grottos/new_grotto_page-v2.s....