The issue of major chemical accidents in the Czech Republic is first mentioned from a historical point of view. The following are the main hazardous impacts of chemical accidents. The next part is a comparison of the accidental impacts of major emergencies, such as toxic leakage, explosion and fire, even with examples of several typical chemical substances. Some factors of the main hazardous chemicals with a focus on toxic substances are discussed in detail. The modelling of accident impacts is presented in the next section on a detailed comparison of the accident impacts of nine main industrial chemical toxicants. The article also draws attention to the serious danger of the possible misuse of toxic substances in particular for hostile acts of chemical terrorism.