[O I] 63/145 µm intensity ratio versus [O I] 145 µm intensity. The light grey to black curves show a grid of radiative transfer models for four values of N(O): 2×10¹⁶, 2×10¹⁷, 2×10¹⁸, and 2×10¹⁹ cm⁻², from left to right, at 200 and 500 K. Tick marks denote log n_H (in cm⁻³) and are separated by one decade along curves of constant N(O). The colored squares show the observed values in LSR velocity bins of 5 km s⁻¹ toward Peak 1 (filled squares) and averaged over the BN/KL outflow (open squares). Red squares correspond to the redshifted line wing, while blue squares correspond to the blueshifted line wing. Green squares correspond to OMC-1 velocities (see Tables D.2 and D.3).