Hydrogen fluoride is a colourless fuming liquid at room temperatures. With a boiling point of only 19.5 °C, it readily forms a colourless vapour with an irritating odour usually not detectable by smell below about 0.04 ppm.
Hydrogen fluoride is extremely corrosive and poisonous. Both its liquid and vapour cause severe and painful burns on contact with the skin, eyes and mucous membranes. HF vapour if inhaled may cause pulmonary oedema which may not become apparent until 12-24 hours after exposure.
Used in the production of fluorocarbons (e.g. PTFE) and inorganic fluorides, metal refining (e.g. uranium), as a catalyst in the chemical industry and for etching glass and pottery.