Characteristics of smoke extraction by natural ventilation during a fire in a shallow urban road tunnel with roof openings

A set of burning experiments were conducted to investigate the effect of vertical shaft geometry on natural ventilation in urban road tunnel fires. Results show that using vertical shafts to discharge smoke leads to a boundary layer separation near the right-angle connection of the shaft and the tunnel ceiling. In a low shaft, the turbulent-boundary-layer separation phenomenon causes relatively large-scale vortexes and restricts smoke from being exhausted, resulting in a negative effect on natural ventilation. Replacing the right-angle connection with the bevel-angle connection was proposed to split one separation point into two separation points, to attenuate the negative effect. The detailed characteristics of the separation phenomenon were analysed and the proposition was verified by Large Eddy Simulation. Results show that there are no relatively large-scale vortexes in shafts with bevel-angle connections, resulting in improved natural ventilation effectiveness. For lower shafts, the advantage of using the bevel-angle connection is more significant, and for shafts of the same height, the mass flow rate of smoke discharged by shafts with the bevel-angle connection increases up to 1.5 times of that by shafts with the right-angle connection. For relatively high shafts, it is about 1.2 times.

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Evaluation of Natural Ventilation on Temperature and Pressure Distribution in a Road Tunnel Fire with Vertical Shaft

International Letters of Chemistry Physics and Astronomy ◽

10.18052/www.scipress.com/ilcpa.55.79 ◽

2015 ◽

Vol 55 ◽

pp. 79-85

Author(s):

I. Benabdelaziz ◽

M. Bouterra ◽

Afif El Cafsi ◽

A. Belghith

Keyword(s):

Natural Ventilation ◽

Pressure Field ◽

Reduction Rate ◽

Vertical Shaft ◽

Road Tunnel ◽

Urban Road ◽

Eddy Simulation ◽

Tunnel Fire ◽

Large Eddy ◽

Temperature And Pressure

This paper has analysed the influence of plug-holing on thermal and pressure field evolution in urban road tunnel fires with vertical shaft by Large Eddy Simulation (LES). Results show that the temperature reduction rate is about 70 % at the tunnel half and it increases about 80 % at the ceiling level. The pressure field is characterized by a pseudo-periodic behavior which reaches a maximum reduction rate (78 %) in case of natural ventilation. The numerical tool used is FDS (version 5).

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Should We Expect a Disastrous Fire Accident in an Urban Road Tunnel? Literature Data Review and a Case Study for Selected Tunnels in Poland

Sustainability ◽

10.3390/su13116172 ◽

2021 ◽

Vol 13 (11) ◽

pp. 6172

Author(s):

Krystian Szewczyński ◽

Aleksander Król ◽

Małgorzata Król

Keyword(s):

Time Horizon ◽

Road Traffic ◽

Traffic Intensity ◽

Road Tunnel ◽

Urban Road ◽

Road Tunnels ◽

High Uncertainty ◽

Fire Outbreak ◽

Fire Accident

Urban road tunnels are a reasonable remedy for inconvenience due to congested road traffic. However, they bring specific threats, especially those related to the possibility of fire outbreak. This work is a case study for selected urban road tunnels. Considering tunnel specificity, road traffic intensity, and structure and based on the literature data for vehicle fire probability, the chances of a fire accident were estimated for selected tunnels in Poland. It was shown that low power tunnel fires could be expected in the 10–20-year time horizon. Although such threats cannot be disregarded, tunnel systems are designed to cope with them. The chances of a disastrous fire accident were estimated as well. Such events can occur when an HGV with flammable goods or a tanker are involved. Such accidents are fortunately very rare, but, on the other hand, that is the reason why the available data are scanty and burdened with high uncertainty. Therefore, a discussion on the reliability of the obtained results is also provided.

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