Carbon ignition curves in the ocean of a neutron star with mass M = 1.4   M_⊙ and radius 12 km, according to different models: solid line corresponds to Eq. (26), long-dashed line to Eq. (25), short-dashed and dotted lines, respectively, to the original and modified approximations of Fushiki & Lamb (1987), Eq. (24). For comparison, the ignition curve without account of conductive cooling is plotted by the dot-dashed line.