[en] In order to measure removal efficiency under accident conditions at high temperatures and high humidity a test material is required which does not change under stresses of this kind. In the newly developed TiO₂ process a water-insoluble, thermally stable solid condensation aerosol, produced with the aid of a plasma is used. The investigation involves removal of aerosol samples by means of Nuclepore filters and subsequent analysis by means of absorption spectroscopy. The high sensitivity of the process permits reliable determination of decontamination factors of the order of 10⁵. In comparative tests using the standard test aerosols Dop, Nacl and Uranin under ambient conditions, the TiO₂ process yielded decontamination factors which were on average greater by a factor of 2 than the corresponding values obtained with the various other processes. Initial tests at temperatures up to 180⁰C were carried out on the 'Taifun' test rig. No major variations in removal efficiency were observed with the trade high-temperature particulate filters used; nor was any structural damage resulting from the temperature stress detected. (author)