Abstract: A ventilation device that enhances the longitudinal thrust of a fan (2) installed within a tunnel, by the introduction of a convergent nozzle (7) to accelerate the outlet flow (8). An angled transition piece (6) can turn the flow by a specific angle (36). Multiple fans can be connected to common inlet and outlet plenums, supplying one or more convergent nozzles. Bi-directional flow can be achieved by fitting convergent nozzles to both sides of a fan, with bypass dampers optionally installed between the fan and the two nozzles. The nozzle trailing edge can be shaped with multiple lobes, chevrons or tongues, and the fan centre-body can be shaped with multiple lobes. A fire suppression agent such as water mist can be supplied into the ductwork between the fan and the nozzle trailing edge. Acoustic silencing can be achieved using the absorbent material on the nozzle and fan centre-body.