Chemical compounds are used in torture in a variety of ways. Acids are use to burn. Salt or pepper is poured into open wounds. Tear gas is fired into cells containing prisoners or directly into faces. Hoods are impregnated with noxious chemicals like insecticides and then placed on prisoners until they nearly suffocate. Carbonated water is forced into nasal passages.
Chemical torture has been reported in the following countries:
[Africa] Madagascar, Zambia
[America] Canada, El Salvador, Guatemala, Mexico, USA
[Asia] India, Sri Lanka