Oxygen Concentration<br> Symptoms<br> <br>21 %<br> None (normal oxygen level)<br> <br>15 %<br> No immediate effects<br> <br>14 %<br> Fatigue, impaired judgement<br> <br>10 %<br> Dizziness, shortness of breath, deeper and more rapid breathing<br> <br>7 %<br> Stupor sets in<br> <br>5 %<br> Minimum amount that will support life<br> <br>2 % - 3 %<br> Death within 1 minute<br> <br><br>Search the web for CONFINED SPACE OXYGEN CONCENTRATION. There is a lot of information about how much O2 is needed to sustain life. The time it takes to die is dependent on a number of factors including the rate at which oxygen is depleted, if other gases are in the area that have negative effects, other hazards, etc. Basically you want to keep the O2 between 19% and 23%. Lower than that you start having problems. Higher than that and you get into highly explosive environments.