Minimum and maximum observed [OI] line intensities over all positions for the ³P₁–³P₂ and the ³P₀–³P₁ transitions (upper and lower panels, respectively) versus shock velocity for C- (blue) and J-type shocks (red) from FPDF’10. The shaded area indicates the observed upper and lower line intensity limits. Observed intensities intercept only the J-shock predictions, constraining the shock velocities to 15–25 km s^-1.