Spatially and temporally resolved in situ measurements of HCN in a steady state tube furnace have been performed using mid-infrared polarization spectroscopy (IRPS). Such measurements are important for the understanding of the detailed HCN chemistry, including pyrolysis, gas phase production, and gas phase consumption. The measurements presented here are in agreement with existing models for HCN chemistry. In particular, it was found that high temperatures and good ventilation result in relatively high peak concentrations of HCN inside the tube furnace. At the same time these conditions also result in high consumption rates of HCN in the hot fire effluents. The results indicate that, although the peak concentrations are highest for high temperatures and good ventilation conditions, the concentration at the exit of the tube are lower for these conditions than those at lower temperatures and under-ventilated conditions.