Semi-confined explosion overpressures

The overpressure developed in semi-confined explosions depends on the following key parameters  

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However, confining surfaces increase the danger resulting in a hydrogen+air cloud explosion. It has been shown in [6] that when a H2 + air mixture is ignited in a U-shaped semi-open duct of 90 m volume, the combustion velocity can reach 80 m/ s and compression wave overpressure AP = 2 10" Pa. The turbulence artificially generated in U-shaped duct may cause transition of deflagration to detonation. 

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