Density dependence (logscale) of the [O III]52 μm/[O III]88 μm, [N II]122 μm/[N II]205 μm, and [S III]19 μm/[S III]33 μm line flux ratios for different temperatures. The various line flux ratios are sensitive to different density regimes. The results from [N II]122 μm/[N II]205 μm and [S III]19 μm/[S III]33 μm are indicated in red and green dots, respectively, and for [O III]52 μm/[O III]88 μm we show the upper density limit (blue dots).