The influence of wood fires in a 0·3 ×0·3 × 10 m duct on forced ventilation flow was studied in a model tunnel network by measuring tunnel gas mass flow rate, velocity, pressure, and temperature. Comparison of these measurements obtained before and during the fires at various ventilation air velocities provides useful information on the interaction between duct fires and ventilation flow in terms of fire throttling effects and reverse flow phenomena. Results show that duct fires essentially increase flow resistances of the passageways of a tunnel network by virtue of volatile fuel mass injection and high combustion temperatures. In the present tunnel network, the flow resistance in the fire zone was increased by a factor of 6, and upstream and downstream of the fire by ∼1·5. The ventilation air velocity was thus throttled to less than half of its initial value before the fire. Reverse flow occurred when the throttled air velocity was ∼0·6 m/s, which corresponds to a Froude number of ∼7 (based on duct height and ventilation air velocity). The experimental measurements were utilized in a flow network analysis to further elucidate the coupling process between duct fires and ventilation flow.