This paper presents an analysis of the experimental results and interpretation of the quench propagation runs performed in the QUELL experiment. It is shown, based on experimental data, that the quench propagation in cable-in-conduit conductors with a central channel has two regimes. Scaling relations for the dependence of the normal zone length on the operating current, temperature margin, helium mass flow and propagation time for these two regimes are presented. It is shown that at early times the quench propagation is conduction-dominated, while at late times the pressure-driven regime dominates. An unexpected and previously unpredicted dependence (scaling) of the quench velocity with the temperature margin was observed. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.