Users of extinguishing agent additives for solid-substance fires often face difficulties in evaluating the available products on the market, as they lack a sound basis for their decision. The main aim of the present work was to develop a testing methodology that allows to quantify the extinguishing effect of additives for solid-substance fires, which could support users in their purchasing decision. To begin with, an overview of common extinguishing agents is given along with their field of application and their extinguishing effect. Furthermore, fire tests that are conducted by fire departments, private and governmental research institutions worldwide are described and categorized, and their advantages and disadvantages are discussed. The testing methodology that was developed in the thesis’ practical part was aimed at being easily practicable in laboratory environment. A sufficiently large number of experiments ensured the validity and significance of the data gained through the extinguishing experiments. In the course of the development of such a methodology, the fundamental test parameters and potential influencing factors were assessed and tested. Finally, a testing methodology could be elaborated that largely met the requirements. However, the human influence on these experiments turned out to be underrated which limited the reproducibility. Overall, the experiments provided a valuable basis for further developments.