Abstract: An actuating unit for a sprinkler in automatic fire extinguishing systems; the actuating unit contains an explosive liquid which ensures short triggering times with good overall usability, in which the explosive liquid is or contains a substance derived from a halogen-free or halogenated hydrocarbon in such a way that, in its structural formula: a) I) at least one CH.sub.2 group is replaced by oxygen (O), sulphur (S), sulphinyl (SO.sub.2) or ii) at least one CH group is replaced by nitrogen, b) there are no hydrogen atoms directly bonded to oxygen, nitrogen or sulphur, and c) iii) there are at least two oxygen atoms with two single bonds, or iii) there are at least two carbonyl groups, or iv) there is at least one oxidized sulphur atom (so or SO.sub.2), or v) at least one nitrogen atom is characteristic for amide, imine or nitrile.