Carbon Dioxide (CO₂)

CO₂ is an odourless, colourless gas which does not pose a direct hazard to life because it typically becomes diluted to low concentrations very quickly due to photosynthesis. Volcanoes release more than 130 million tonnes of CO₂ into the atmosphere every year, comparable to the amount released by humans and animals during respiration.

But in certain circumstances, CO₂ may become concentrated at levels lethal to people and animals. Breathing air with more than 30% CO₂ can quickly induce unconsciousness and cause death. Carbon dioxide gas is heavier than air, and the gas can flow into low-lying areas so it is important to avoid small depressions and low areas that might be CO₂ traps.

When a burning piece of wood is lowered into a hole that has a high concentration of CO₂, the fire goes out; a lethal condition for people and animals.

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.

Below is a picture of the effects of carbon dioxide gas on mountain trees in California:

 Picture obtained from http://volcanoes.usgs.gov/Hazards/What/VolGas/volgas.html without permission.

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