Influence of height of confined space on explosion and fire safety

• We determine the structure of flow behind blockages in a confined space.
• Turbulent intensity is enhanced by interacting shocks from blockages.
• Larger heights of confinement do not generate turbulence behind obstructions.
• Explosions are shown to be more likely in confined space having small heights.

Experiments were carried out in the test section of a wind tunnel to simulate the role of the heights of confined space on formation of shock waves due to a high-speed subsonic flow of air interacting with blockages placed in the flow path. The blockage ratio considered was 0.13 and the medium used was air. A Mach stem shock wave structure was seen to be formed in the flow field downstream of the blockages for small heights of the test section while no shock waves were formed for larger heights of the test section. The turbulent velocities, turbulent intensities and length scales of turbulence were also measured. Test sections of smaller heights were shown to generate higher levels of turbulence in the flow field following the blockages due to the complex shock interactions. As a result, ignition of combustible gas mixtures from an accidental release or leakage in a confined space having small height could form a turbulent flame brush or a detonation. The requirement of larger heights of confined spaces is seen to be desirable from explosion safety point of view.