The state dependent quenching mechanism of metastable antiprotonic He atoms by contaminants is suggested to explain existing experimental data. The effect of antiproton transfer from the antiprotonic He to noble gas contaminants is shown to play a significant role. Preliminary estimations have been done in the framework of the coupled channels model. The obtained results support the idea of strong dependence of quenching cross-sections on the antiprotonic states quantum numbers and enable to explain qualitatively existing discrepancies between experimental results, obtained for different contaminant densities. New observable effects are predicted.