Hydrogen–air deflagrations: Vent sizing correlation for low-strength equipment and buildings

• Vent sizing technique based on hydrogen–air combustion advances is presented.
• The deflagration–outflow interaction number is quantified by physical SGS models.
• The correlation has improved predictive capability for hydrogen safety engineering.
• The correlation allows an increase of cost-effectiveness of explosion protection.

This paper aims to improve prediction capability of the vent sizing correlation presented in the form of functional dependence of the dimensionless deflagration overpressure on the turbulent Bradley number similar to our previous studies. The correlation is essentially upgraded based on recent advancements in understanding and modelling of combustion phenomena relevant to hydrogen–air vented deflagrations and unique large-scale tests carried out by different research groups. The focus is on hydrogen–air deflagrations in low-strength equipment and buildings when the reduced pressure is accepted to be below 0.1 MPa. The combustion phenomena accounted for by the correlation include: turbulence generated by the flame front itself; leading point mechanism stemming from the preferential diffusion of hydrogen in air in stretched flames; growth of the fractal area of the turbulent flame surface; initial turbulence in the flammable mixture; as well as effects of enclosure aspect ratio and presence of obstacles. The correlation is validated against the widest range of experimental conditions available to date (76 experimental points). The validation covers a wide range of test conditions: different shape enclosures of volume up to 120 m3; initially quiescent and turbulent hydrogen–air mixtures; hydrogen concentration in air from 6% to 30% by volume; ignition source location at enclosure centre, near and far from a vent; empty enclosures and enclosures with obstacles.