Toward a Reliable Methodology for Assessing Overpressure in Hydrogen Vents

The oil, gas, and chemical industries continually face risks from accidental releases of flammable gases, which can lead to severe consequences if ignited after a delay. Hydrogen, gaining popularity as an alternative fuel, poses specific challenges due to its explosion hazards. Ensuring safety requires a thorough understanding and prediction of gas explosion outcomes. With the anticipated increase in hydrogen production and usage in both public and industrial settings, establishing safe venting guidelines is essential. There is no industry-standard methodology for hydrogen venting that reliably estimates overpressures from deflagration and detonation, following the delayed ignition of flammable clouds. This study aims to address this gap by building on a methodology introduced in earlier works. The methodology involves determining the mass of hydrogen contributing to the blast loads in the cloud through dispersion calculations using standard consequence modeling software (e.g., FRED, PHAST) and engineering judgment. The article also discusses the limitations of the predictive capabilities of unconfined and uncongested deflagration/detonation models when tested against the available experimental data (i.e., large under-/overpredictions in overpressure estimates). An updated methodology is proposed based on a scaling that relates the vent release conditions (i.e., pressure and diameter) to the visible flame velocity in nonuniform, nonquiescent flammable clouds. A map of expected overpressures as a function of pressure and vent diameter is provided.