Hydrogen Jet Vapor Cloud Explosion: Test Data and Comparison with Predictions

Releases of hydrogen at elevated pressures form turbulent jets which may pose vapor cloud explosion (VCE) as well as jet fire hazards. The turbulence induced by the jet release can lead to flame speeds sufficient to produce damaging blast loads if the release is not immediately ignited, even in the absence of confinement or congestion. The VCE hazard posed by such high pressure hydrogen releases is not well-recognized, and there is no well-established methodology to predict the associated VCE blast loads.

Air Products commissioned a series hydrogen jet release tests, aimed primarily at measuring the thermal flux from ignited open air hydrogen jets. The hydrogen jets were created by depressurizing a high-pressure hydrogen reservoir through a horizontal vent pipe. Pipe diameters of 3/4-inch and 2-inches were tested at a release pressure of approximately 60 barg, giving initial flow rates of roughly 8 and 1 kg/s, respectively. For both release sizes, a single test was performed where the ignition system was not activated until approximately 2 seconds after the release had been initiated, such that the resulting flame propagated into a turbulent flammable gas cloud of limited volume. Blast loads were measured at 10 m and 20 meters off the jet centerline.

BakerRisk compared the data from the Air Products hydrogen jet VCE tests with predictions made using the FLACS computational fluid dynamics (CFD) code. FLACS was first used to evaluate the flammable clouds resulting from the jet releases up to the time of ignition. FLACS was then run with a range of grid sizes for the 2-inch release case in order to determine a grid size which gave reasonable agreement with the measured peak pressure and pressure history. The grid size giving the best agreement with the 2-inch release case data was then used to evaluate the ¾-inch release case.

This paper presents the data from these two hydrogen jet release VCE tests along and the comparison with the FLACS predictions. Based on these results, the feasibility of using FLACS as a general predictive tool for the blast loads from such hydrogen releases is discussed.