Impact of Water Mist Thickness on Shock Wave Attenuation

Explosion protection systems for underground structures are designed to create a suppressing barrier between the site of explosion and the facility to be protected. Studies have shown that water mist, provided that its properties are correctly selected, can effectively reduce shock wave overpressure in tunnels. The influence of droplet sizes and concentration of water in mist on shock wave mitigation processes have been studied by various researchers through experiments and modelling. However, the effect of geometric dimensions of mist on shock wave attenuation in tunnels has not been sufficiently studied. This paper addresses the influence of water mist thickness on blast overpressure under identical mist properties and explosion conditions in the tunnel. The study of such influence is essential for the proper design of the protective system. Experiments were conducted in the tunnel of the underground experimental base of the Mining Institute, Tbilisi, Georgia. The methodology employed envisaged the measurement of overpressures in the tunnel with the mist generated by the spray system. At different stages of experiments, the water mist thickness was 1.6m, 2.6m and 3.8m. Experiments were carried under the following conditions: charge weight - 2 kg; distance from the charge to the mist - 3.5 m, from the charge to the sensors - 11.5 m, droplet size distribution - 10-260μm, Mist density - 1.45 l/s•m3. In the test zone the height of the tunnel was 2.2 m, width - 2.2 m, cross-section - 4.4m2. The results of the experiments showed that the water mist thickness has an influence on the shock wave overpressure. Under the conditions of experiments carried out by us, the increase of the mist thickness by 3.1 times allowed to reduce the overpressure by 34%.