Outburst parameters for giant flares (coloured areas) and normal flares (dotted lines) vs inner truncation radius of quiescent geometrically thin disc. From top to bottom, from left to right: Mass involved in a flare (14), estimated peak accretion rate (13), characteristic flare duration (5), and rise time (11). The upper boundaries of the coloured areas correspond to the case when the disc is heated to the radius R_out,max, the lower boundaries to the conservative assumption R_out = R_trunc + z₀ (see Sect. 4). The lower grey line illustrates the limits for intermediate masses. For 10⁹ M_⊙, ionisation instability always ignites a giant flare.