The influence of blockages on backlayering in tunnel fires: A numerical study

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Critical ventilation velocity (CVV) is the most well investigated phenomenon in tunnel fire research. The majority of studies of CVV/backlayering have involved either theoretical analysis or experiments of an open fire in a tunnel, generally with no obstructions in the locality of the fire which could disturb the flow pattern and influence the backlayering behaviour. However, in reality, fires in tunnels do not happen in such idealised situations. Generally there are obstructions due to the vehicle’s construction or adjacent vehicles. Such blockages can modify the flow behaviour and may influence the CVV/backlayering.

This paper presents the findings of a preliminary computational fluid dynamics (CFD) study looking at the influence of overhead blockages and upstream blockages on smoke behaviour at critical ventilation conditions and in the sub-critical regime. Simulations are presented for a reasonably typical two lane road tunnel using the Fire Dynamics Simulator (FDS) model. It is found that certain overhead blockages interrupt the flow sufficiently to significantly reduce the CVV or reduce the backlayering length and temperature in the sub-critical regime. However, upstream blockages and overhead blockages closer to the ceiling have a negative effect, sometimes resulting in backlayering at above the CVV for an unobstructed fire.
Original languageEnglish
Title of host publicationProc. 5th Int. Symp. on Tunnel Safety and Security
Publication statusPublished - 2012
Event5th International Symposium Tunnel Fire Safety & Security - New York, United States
Duration: 14 Mar 201216 Mar 2012


Conference5th International Symposium Tunnel Fire Safety & Security
Country/TerritoryUnited States
CityNew York


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