I saw this on the you tube and thought some of you adventurous types might enjoy it. https://www.bing.com/videos/search?...125E53161DAB1E2F8D1A125E53161DAB1E2&FORM=VIRE
If you don't have an idea of the Oxygen levels down a hole like that, it may be your last adventure. I monitor confined spaces for a living; https://www.ehstoday.com/fire_emergencyresponse/ehs_imp_77598 Human beings normally breathe air that is 20.9 percent oxygen by volume under normal atmospheric pressure conditions. When the concentration of oxygen decreases even slightly by a little more than 1 percent to 2 percent, people immediately begin to feel the effects. Healthy individuals are unable to work strenuously and their coordination may be affected in oxygen environments of 15 percent to 19 percent. With the depletion of oxygen to a mix of only 10 percent to 12 percent, respiration increases, lips turn blue and judgment is impaired. Fainting and unconsciousness begin to occur at 8 percent to 10 percent oxygen. Death occurs in 8 minutes at 6 percent to 8 percent oxygen; recovery is possible after 4 to 5 minutes if oxygen is restored. These values are approximate and may vary greatly depending on an individual’s health, physical activity and the specific working environment that they encounter.
