Abstract
Fire is the most deadly risk during tunnel operation. Early rapid response and a reasonable smoke control plan are very important to evaluate tunnel fire performance. In order to study the relevant time factors for smoke management in a highway tunnel, firstly, the logical sequence and time of the fire alarm system (FAS) startup are investigated and analyzed. Then, according to the one-dimensional fluid mechanics model, the time rule of adjusting the airflow field in the tunnel from the normal operation stage to the emergency ventilation state is analyzed theoretically. Finally, the abovementioned theoretical formulas are verified through the employment of model experiments. The analysis shows that the time that passes from the start of the fire to when the exhaust fan is activated is close to 3 minutes. The time required to form a stable critical wind speed, however, is close to 7 minutes, which is longer than the 5 minutes it takes for the fire to reach its maximum temperature. Due to inertia, it takes about 0.5 to 2 minutes for the air velocity in tunnels of different lengths to drop from the traffic piston wind speed to the critical wind speed. If reverse smoke extraction is required, however, the duration is between 3 and 8 minutes. The conclusion is of guiding significance for the preparation of the emergency linkage control scheme for tunnels, as well as for the setting of initial boundary conditions for CFD fire simulations.
Highlights
As highway tunnels are relatively closed in their shape, fires in these tunnels can become extremely dangerous when not effectively controlled
For tunnel fire rescue evacuations, scholars have studied the tunnel evacuation simulation system [11, 19] and simulation methods [8], the establishment of an emergency evacuation simulation model [20], and the ideologies of self-rescue personnel [21, 22]. Despite all of these studies, two time-related boundary conditions have been ignored in the current experimental studies and CFD software-based numerical simulation of fire dynamics. e first is the start time of the fire alarm system (FAS) and ventilation equipment. e second is the time required, taking into consideration the inertia of the air in the tunnel, to get from the flow field in the normal operation stage to the stable flow field in the fire emergency ventilation stage. e fire rescue stage is a race with “death,” which should be run without delay
It is a series of movements, each of which takes a certain amount of time and has a certain sequence between them. e process from the start of the fire to the start of the smoke exhaust fan includes fire detection (20 s), alarm acknowledge (60 s), opening of the electric combined air valve of the smoke exhaust blower (20 s), and opening of the smoke exhaust fan (60 s). e total time is 160 s, nearly 3 minutes
Summary
As highway tunnels are relatively closed in their shape, fires in these tunnels can become extremely dangerous when not effectively controlled. For tunnel fire rescue evacuations, scholars have studied the tunnel evacuation simulation system [11, 19] and simulation methods [8], the establishment of an emergency evacuation simulation model [20], and the ideologies of self-rescue personnel [21, 22] Despite all of these studies, two time-related boundary conditions have been ignored in the current experimental studies and CFD software-based numerical simulation of fire dynamics. Erefore, in order to better guide the performance-based designs for tunnel fire control, formulate efficient fire rescue evacuation plans, and improve the consistency between fire simulations and actual fire scenes, this paper intends to carry out analysis and research on the abovementioned two time-related boundary conditions For the analysis of tunnel fire safety, the detection, alarm, and equipment startup time should be taken into account [23]. erefore, in order to better guide the performance-based designs for tunnel fire control, formulate efficient fire rescue evacuation plans, and improve the consistency between fire simulations and actual fire scenes, this paper intends to carry out analysis and research on the abovementioned two time-related boundary conditions
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