The unified energy dependence of the induced fission lifetimes obtained by the experimental crystal blocking technique for heavy nuclei with Z = 91 – 94 in the range of initial excitation energy from 5 to 250 MeV was analyzed. It was demonstrated that for the excitation energies of investigated nuclei up to 60 – 70 MeV the fission lifetimes can be described in the framework of the statistical theory of nuclear reactions taking into account the double‐humped structure of the fission barrier and the lifetimes of both classes of excited nuclear states realized in the first and second potential wells. However, for the excitation energies above 70 MeV it is needed to consider the dynamical effects in the fission channel. Analysis of the experimental data in this energy range allows us to extract information on the magnitude of nuclear viscosity. © 2004 American Institute of Physics