The results of physical modeling of fires for road tunnels

Abstract

The paper gives the results of a fire development study using physical models of inclined vehicular traffic tunnels scaled 1:60. The tunnel inclination varied within 0-10% with a 2% increment. The fire strength initiated and developed in a natural tunnel varied within 5-15 MW with a 5 MW increment. The length of the natural tunnel was 360 m, width: 8 m, height: 6 m, cross-sectional area: 48 m2, and the tunnel width and height ratio: 1.33. The model of the natural tunnel of the given geometry was made of a 2-mm-thick stainless steel sheet with an appropriate scale. The sizes of the tunnel model are: length: 6 m, width: 0.16 m, height: 0.12 m, and cross-sectional area: 0.0192 m2. By doing experiments on this model, we studied the nature of propagation of gases (smoke) emitted during the fire initiation and development, specified the impact of the gradient factor on the rate of variability of the critical velocity and backlayering distance. The said characteristics were studied according to the air temperature variability in the tunnel model. The air temperature was measured with K-type thermocouples equipped with open and closed detectors. Maximum measuring temperature was 800°C. The thermocouples were installed in the ceiling of the tunnel model along the entire length, with 5 and 10 cm increments. The fire was modeled with natural gas. Ventilation air was supplied into the model by an axial fan from one portal of the model. The velocity of the ventilation air was measured with an anemometer, and the air discharge was calculated at every moment according to the velocity. The required strength of the modeled fire was provided by natural gas, and the measurement was done with a volumetric and mass regulatory meter. Simultaneous data collection, processing, analysis and digital transmission of data from the K-type thermocouples, anemometers and natural gas flow meters were provided with DT-85 Datataker. The obtained results can be used to develop road tunnel ventilation projects that take into account the impact of fires on ventilation.