Ionization-parameter-sensitive line ratios against Lyman-continuum escape fraction (f_esc) for our sample of HII regions. Panel a: line ratio [O iii]5007/[O I]6300; panel b: [S iii]9068.9531/[S II]6716.31, and panel c: [O iii]5007//[S II]6716.31. In all plots, the blue points are the results using the GALEV model while the red points shows the escape fraction computed using SB99. 1σ ranges of the statistical error of both axes are plotted as gray lines for the GALEV results. Violet points at the left border are those regions which were found to be optically thick. Horizontal dashed lines denote lower limits of the line ratios with high escape fraction, as discussed in the text.