# Experimental Study of Explosion Mitigation by Deployed Metal Combined with Water Curtain
## 1 Introduction  
The protection of people and structures against the effects of blast waves from terrorist attacks or industrial hazards is of significant interest. It is well known that protective barriers are an effective way to reduce blast loads and to mitigate the adverse effects. Protective solid barriers are usually made of reinforced concrete, concrete masonry unit or steel-concrete-steel composite materials. These barriers are very rigid and have negligible deformation. In urban areas, other protective barriers could be envisaged for facades. The blast wave would be absorbed, deflected or disrupted to be ultimately reduced before it reaches its intended target. Perforated plates disrupt blast waves: it has been shown that grids or perforated plates modify the flow field by introducing new shock waves, regions of vortices and considerable turbulence in which the energy of the incident shock wave can be dissipated [1, 2, 3]. Moreover, grids or perforated plates could be modern architectural design elements which can be used outside buildings. The use of water walls for mitigating the damages from blast waves generated by an explosion has also been described [4], although there is only limited literature on this topic. It seems that the mitigation stems from the fact that the blast wave is obstructed, reflected and diffracted by the water wall. Consequently, it could be an advantage to add a water cover to the grids or perforated plates in order to protect building facades or walls. Recently, the shock wave attenuation performance of protective barriers made of woven wire mesh was investigated [5]. The woven wire mesh was located about 5 m in front of a wall and no obvious mitigation was observed behind the barrier. The woven wire mesh had a very high porosity and this probably explains such results. Two previous studies have been published regarding metal ring meshes, grids or perforated plates combined with a downward-streaming water curtain for blast mitigation [6, 7]. [PERSON] et al. [6] tested a stainless steel ring mesh in combination with a flowing water layer. The charges were detonated 5 m in front of the ring mesh with or without a water cover and the side-onoverpressure was measured on the shock wave path. The reflected overpressure was also measured on a wall located 5 m behind the ring mesh. For the ring mesh alone, they described an initial side-on overpressure reduction of approximately 17% at 50 cm behind the grid and of around 1-6% at 1.5-2.5 m behind the grid. When the ring mesh was covered by water, the initial side-on overpressure was reduced by 56% close behind the ring mesh and by 20% 5 m behind the mesh. As regards the positive impulse, the ring mesh itself caused no reduction. However, a reduction of about 17-31% was obtained behind the mesh by adding a water curtain. The reflected pressure on the wall was slightly decreased by the ring mesh but the addition of a water cover did not improve the attenuation performance. In the second study [7], a transonic shock tube was used to visualize the interaction of a blast wave profile with a metallic perforated plate or with a metallic perforated plate covered by a layer of water. Free-field air blast experiments were also performed. Three grid types with different porosities were tested. The highest attenuation was obtained with the grid having the lowest porosity. The attenuation was of the order of 17-25% 25 cm downstream from the grid and about 25-30% 3 m downstream from the grid. When the grids were covered by a water layer, the initial overpressure behind the plate was reduced for all grid types. The blast mitigation was improved, especially with the grids having a high porosity. Again, the most pronounced reduction (about 35 to 48%) was obtained with the grid having the lowest porosity. The initial overpressure 3 m downstream was also reduced by about 20-30%. The impulse was also reduced by the grids with or without a water film cover.