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Fire Ventilation in Road Tunnels: Some Investigations about Critical Air Velocity

DOI: 10.1615/ICHMT.2004.IntThermSciSemin.1170
pages 929-935

Fabio Peron
Department of Building Construction, IUAV University of Venice, Dorsoduro 2206, 30123 - Venezia, ITALY

Luca Porciani
Department of Building Construction, IUAV University of Venice, Dorsoduro 2206, 30123 - Venezia, ITALY

Mauro Strada
Department of Building Construction, IUAV University of Venice, Dorsoduro 2206, 30123 - Venezia, ITALY


A very important factor in people's safety during road tunnel fires is an efficient smoke evacuation strategy. In most cases this could be achieved by longitudinal ventilation, obtained using jet fans in order to force the smoke out of the tunnel at one of the exit portal.
Usually the most relevant factor in the design of this kind of equipment is the control of the so called "critical air velocity", that is the minimum value of longitudinal air velocity in the cross section of the tunnel to be achieved by jet fans in order to keep safe the portion of it between the place where the fire occurs and the portal from which vehicles enter. Giving the definition of "backlayering" as the movement of smoke contrary to the ventilation flow, critical velocity has to be intended as the minimum value of air velocity that realizes a null backlayering.
In this study some Computational Fluid Dynamics simulations were performed for a test tunnel with different values of fire power and the resulting values of critical velocity are compared with what could be obtained from algorithms found in literature. Some considerations are presented about the matching between the found results in order to get possible guidelines in using CFD tools in the ventilation design and prediction processes.

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