Hydrogen Fluoride (HF)

Fluorine is a caustic irritant gas, and is pale yellow in colour. It attaches to fine ash particles, coats grass, and pollutes streams and lakes. Conjunctivitis, skin irritation, bone and teeth degeneration are caused after exposure to the gas.

Excess fluorine results in a significant cause of death and injury in livestock during ash eruptions. Even in areas that receive just one millimetre of ash, poisoning can still occur when the fluorine content of dried grass exceeds 250 ppm.

Small amounts of fluorine can be beneficial, but excess fluorine causes fluorisis, an affliction that eventually kills animals by destroying their bones. It also promotes acid rain effects downwind of volcanoes, like HCl.