Exposure to acid gases such as sulfur dioxide, hydrogen sulfide, and hydrochloric acid can damage eyes and mucous membranes along with the respiratory system and, under extreme conditions, can lead to death. The toxicity of carbon monoxide is well known, although it is rarely abundant enough to cause serious problems. One of the most serious hazards occurs when volcanoes emit large quantities of carbon dioxide. Carbon dioxide is heavier than air and collects in low spots, displacing air in these locations. Hundreds of people have died of carbon dioxide asphyxiation near volcanoes in the past two decades, most of them in Cameroon, Africa, and in Indonesia.
Volcanic gases can also severely damage vegetation.
Direct exposure to concentrated volcanic gas or long-term exposure to dilute volcanic gas has a lethal effect on most types of foliage. Fume clouds from volcanoes also contain water droplets in which acid gases have dissolved. These droplets eventually fall to earth as acid rain. Utility lines, farm equipment, cars, and other metal objects corrode when exposed to volcanic gases or acid rain. Persistent acid rain causes galvanized nails or lead solder in water catchment systems to deteriorate and release heavy metals into drinking water.