The initiation of emergency measures to protect the public after a nuclear accident must be based on immediate measurements of external doses and inhalation doses in inhabited areas. The external radiation exposure from the plume and soil can be determined with dose rate meters. Due to the different biological effects of the individual nuclides, the detection of the inhalation doses calls for nuclide analysis of the air concentration. Radiation exposure calculations of light-water and high-temperature reactors and other nuclear installations proved that only a few nuclides cause the main contribution to the inhalation dose. In the case of reactors, the critical nuclide is 131I. After examining accidents in other nuclear facilities, different nuclides, e.g., strontium and plutonium, may become relevant.