Or even a minor accident that through accident magnification turns into a big deal. If you're at all claustrophobic, find something else to do. Make sure someone who knows what they're doing is leading your party. For cavers this usually means a helmet lamp or two and a backup flashlight or two, with spare batteries and bulbs. We have all done it, and it feels much better with a helmet on.
Warm clothing is necessary for all Colorado caves.
Careful cavers avoid leaving even footprints. Join the NSS, go caving with experienced people, listen to the advice. Cavers know where the caves are, know how to teach good caving, will help to expand your skills, and are usually friendly and fun. In many caves, a misplaced hand or too-late head duck will result in damage that will not be replaced in 1,000 years, much less your lifetime. On the other hand, mines were dug recently, are supported by rotten timbers, and are sometimes filled with deadly gases like carbon monoxide.