Carbon dioxide gas can collect in low-lying volcanic areas, posing ...

Fumaroles of cold, dry CO2 such as this one on a lava flow erupted in 1938 from Nyamuragira Volcano, Zaire, can be exceptionally dangerous because the gas discharge is invisible. The density difference between CO2 and air is so great that a sharp boundary can persist between them. Air with 5% CO2 causes perceptible increased respiration; 6-10% results in shortness of breath, headaches, dizziness, sweating, and general restlessness; 10-15% causes impaired coordination and abrupt muscle contractions; 20-30% causes loss of consciousness and convulsions; over 30% can cause death.