We suggest that large-scale turbulence dissipation is concentrated along caustic networks (that appear due to vortex sheet instability in three-dimensional space), leading to an effective fractal dimension D eff = 5/3 of the network backbone and a turbulence intermittency exponent µ = 1/6. Actually, D ef f < 5/3 and µ > 1/6 due to singularities on these caustic networks. It is shown (using the theory of caustic singularities) that the strongest (however, stable on the backbone) singularities lead to D eff = 4/3 (an elastic backbone) and to µ = 1/3. Thus, there is a restriction of the network fractal variability: 4/3 < D eff < 5/3, and consequently: 1/6 < µ < 1/3.Degeneration of these networks into a system of smooth vortex filaments: D ef f = 1, leads to µ = 1/2. After degeneration, the strongest singularities of the dissipation field, ε, lose their power-law form, while the smoother field lnε takes it. It is shown (using the method of multifractal asymptotics) that the probability distribution of the dissipation changes its form from exponential-like to log-normal-like with this degeneration, and that the multifractal asymptote of the field lnε is related to the multifractal asymptote of the energy field.Finally, a phenomenon of acceleration of large-scale turbulent diffusion of passive scalar by the singularities is briefly discussed.All results are based on experimental data.