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a b s t r a c tSafety studies for production and use of hydrogen reveal the importance of accurate prediction of the overpressure effects generated by delayed explosions of accidental high pressure hydrogen releases. Analysis of previous experimental work demonstrates the lack of measurements of turbulent intensities and lengthscales in the flammable envelope as well as the scarceness of accurate experimental data for explosion overpressures and flame speeds. AIR LIQUIDE, AREVA STOCKAGE ENERGIE and INERIS join in a collaborative project to study un-ignited and ignited high pressure releases of hydrogen.The purpose of this work is to map hydrogen flammable envelopes in terms of concentration, velocity and turbulence, and to characterize the flame behaviour and the associated overpressure. These experimental results (dispersion and explosion) are also compared with blind FLACS modelling.

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Releases of hydrogen at elevated pressures form turbulent jets in unconfined & uncongested regions may trigger vapor cloud explosion (VCE) as well as jet fire hazards. In the case of a delayed ignition of an unconfined & uncongested jet the turbulence induced by the jet release can lead to flame speeds sufficient to produce damaging blast loads, even in the absence of confinement or congestion. The VCE hazard posed by such high‐pressure hydrogen releases is not well‐recognized. The authors have previously presented test data and computational fluid dynamic (CFD) modeling analyses which characterize high pressure hydrogen releases and the associated VCE hazard in unconfined & uncongested regions. The current paper provides an overview of this VCE hazard. It presents both CFD simulations and a new simplified method. The new method determines the blast strength based on a blast curve method (i.e., TNO multienergy or BST) with the strength index correlated to the mass flow rate of the accidental release. The paper discusses also the implications of such events for building siting analyses and risk assessments. © 2018 American Institute of Chemical Engineers Process Process Saf Prog 37:397–410, 2018