In addition to emissions from road tunnels during normal driving, smoke is also emitted in the event of a fire in the tunnel. Reducing the concentrations of pollutants in the tunnel and their spread outside the tunnel, in the portal areas, is very important. The direction of emission and smoke flow is more difficult to predict in two-way tunnels than in tunnels with one-way traffic, where the airflow direction is uniform due to the piston effect, as vehicles and airflow move in the same traffic direction.
In the case of a tunnel fire a backward movement occurs, that is undesirable and depends on the conditions and factors inside and outside the tunnel. The distribution of air flow in the cross section of the tunnel is also important, which is reflected in the stratification as an important phenomenon, depending on the height of the temperature and air velocity. It should be noted in particular that the level of threat to people who are in the tunnel at the time of the fire is very high, which requires rapid and appropriate action of control systems in terms of significantly reducing the risk by mobilizing the so-called fire scenario.
Setting up a uniform and generally valid model is practically impossible, so engineers use various numerical simulations which using numerical methods allow making acceptable approximations for practice, thus ensuring the prescribed safety requirements for fire management in different tunnel environments at variable energy levels the strength of fires resulting from intense burning indoors.
In order to avoid the catastrophic consequences of fires in road tunnels as much as possible, it is necessary to ensure adequate and appropriate ventilation conditions by taking into account various influencing factors, first in computational models and then in design solutions and their implementations, external winds, intensity and types of traffic flows in the tunnel, switching on and operation of fans with all associated ventilation facilities, etc. The aim is to provide such ventilation conditions or stratification of tunnel air to prevent the dangerous mixing of fresh air and smoke during the evacuation of people from the tunnel or the evacuation to specially designed spaces. Therefore, there is an essential requirement in the profession that, if possible, two-pipe tunnels be built, wherein in case of emergencies, evacuation to an adjacent tunnel pipe through crossbars built at prescribed longitudinal distances is possible.
The aim of the research was to ensure that hot flue gases under the ceiling are kept as long as possible through appropriate calculation models and comparisons with classical calculation methods that simulate different fire scenarios and technical solutions for ventilation in road tunnels, which realistically allows most participants safe withdrawal from a tunnel or an adjacent tunnel pipe.
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