Blast mitigation by water mist: the effect of the detonation configuration

Abstract

In this paper, blast mitigation using water mist was evaluated to assess the operational capability of the use of firefighting systems implemented in ships or infrastructures to reduce blast effects. In particular, we tried to determine the mitigation that could be obtained in specific situations. A tunnel equipped with a water mist system enabled us to assess the mitigation impact of water mist on a blast. Blast effects were evaluated using four pressure gauges on the tunnel walls and one pressure gauge at the end of the tunnel. As a first step, we evaluated the mitigation efficiency based on water mist characteristics (the droplet size and the water load) when the charge was detonated inside the mist, the tunnel being either open or closed. Then, we assessed the mitigation efficiency when the charge was detonated outside the mist with only the blast wave propagated in the mist. The reduction in the initial overpressure and the maximum impulse were higher when the charge exploded inside the water mist, and this is most likely due to the quenching of secondary reactions by the water mist. To obtain a better understanding of mitigation mechanisms, shock tube experiments were conducted. The break-up of water drops in the high-speed airstream behind the shock wave was observed, but the presence of mist had no significant effect on the shock wave profile. This is in line with the importance of fireball extinguishment in the mitigation process.