>>2805474generally all mines are wet when their operating from dust control water and water coming from tooling. In abandoned mines, gases such as H2S generated from decaying wood or other material like sufide / oxide ores gets trapped in mud under large stagnant water bodies. When you disturb this water, the gases are released, often replacing the oxygen atmosphere in the workings. This can cause you to pass out and die from oxygen deprivation. Always watch out for large areas of rust as well, in those areas you can have oxygen depleted environments too.