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In this study, the consequences of an accidental release of hydrogen within large scale, (>15,000 m3), facilities were modeled. To model the hydrogen release, an LES Navier–Stokes CFD solver, called fireFoam, was used to calculate the dispersion and mixing of hydrogen within a large scale facility. The performance of the CFD modeling technique was evaluated through a validation study using experimental results from a 1/6 scale hydrogen release from the literature and a grid sensitivity study. Using the model, a parametric study was performed varying release rates and enclosure sizes and examining the concentrations that develop. The hydrogen dispersion results were then used to calculate the corresponding pressure loads from hydrogen-air deflagrations in the facility.

To examine the effect of initial turbulence on vented explosions, experiments were performed for lean hydrogen–air mixtures, with hydrogen concentrations ranging from 12 to 15% vol., at elevated initial turbulence. As expected, it was found that an increase in initial turbulence increased the overall flame propagation speed and this increased flame propagation speed translated into higher peak overpressures during the external explosion. The peak pressures generated by flame–acoustic interactions, however, did not vary significantly with initial turbulence. When flame speeds measurements were examined, it was found that the burning velocity increased with flame radius as a power function of radius with a relatively constant exponent over the range of weak initial turbulence studied and did not vary systematically with initial turbulence. Instead, the elevated initial turbulence increased the initial flame propagation velocities of the various mixtures. The initial turbulence thus appears to act primarily by generating higher initial flame wrinkling while having a minimal effect on the growth rate of the wrinkles. For practical purposes of modeling flame propagation and pressure generation in vented explosions, the increase in burning velocity due to turbulence is suggested to be approximated by a single constant factor that increases the effective burning velocity of the mixture. When this approach is applied to a previously developed vent sizing correlation, the correlation performs well for almost all of the peaks. It was found, however, that in certain situations, this approach significantly under predicts the flame–acoustic peak. This suggests that further research may be necessary to better understand the influence of initial turbulence on the development of flame–acoustic peaks in vented explosions.

Experimental data from vented explosion tests using lean hydrogen–air mixtures with concentrations from 12 to 19% vol. are presented. A 63.7-m 3 chamber was used for the tests with a vent size of either 2.7 or 5.4 m 2 . The tests were focused on the effect of hydrogen concentration, ignition location, vent size, and obstacles on the pressure development of a propagating flame in a vented enclosure. The dependence of the maximum pressure generated on the experimental parameters was analyzed. It was confirmed that the pressure maxima are caused by pressure transients controlled by the interplay of the maximum flame area, the burning velocity, and the overpressure generated outside of the chamber by an external explosion. A model proposed earlier to estimate the maximum pressure for each of the main pressure transients was evaluated for the various hydrogen concentrations. The effect of the Lewis number on the vented explosion overpressure is discussed.

Experimental data obtained for hydrogen mixtures in a room-size enclosure are presented and compared with data for propane and methane mixtures. This set of data was also used to develop a three-dimensional gasdynamic model for the simulation of gaseous combustion in vented enclosures. The experiments were performed in a 64 m 3 chamber with dimensions of 4.6 × 4.6 × 3.0 m and a vent opening on one side and vent areas of either 2.7 or 5.4 m 2 were used. Tests were performed for three ignition locations, at the wall opposite the vent, at the center of the chamber or at the center of the wall containing the vent. Hydrogen–air mixtures with concentrations close 18% vol. were compared with stoichiometric propane–air and methane–air mixtures. Pressure data, as function of time, and flame time-of-arrival data were obtained both inside and outside the chamber near the vent. Modeling was based on a Large Eddy Simulation (LES) solver created using the OpenFOAM CFD toolbox using sub-grid turbulence and flame wrinkling models. A comparison of these simulations with experimental data is discussed.

Experimental data from vented explosion tests using stoichiometric methane–air and 18% hydrogen–air mixtures in a 63.7 m3 chamber with a 2.7 or 5.4 m2 vent are presented. Results from experiments conducted using stoichiometric propane–air in 2.42 m3 vessel with a 0.26 m2 vent are also reported. The tests were focused on the effect of fuel, enclosure size, ignition location, vent size, and obstacles on the pressure development of a propagating flame in a vented enclosure. The dependence of the maximum pressure generated on the experimental parameters was analyzed. It was found that the pressure maxima may be caused by pressure transients controlled by the interplay of the maximum-flame area, the burning velocity, and the overpressure generated by an external explosion. A simple model was proposed to estimate the maximum pressure for each of the main pressure transients. The model was found to agree with the experimental data within the experimental uncertainty.

Results of a series of tests on the deflagration of methane-air mixtures in a large vented enclosure are presented. Experiments were made in FM Global’s 63.7 m 3 chamber. The chamber was 4.6 x 4.6 x 3.0 m with a vent opening on one side. Vent areas of either 2.7 or 5.4 m 2 were used. Tests were performed with ignition either at the center of the chamber or at the center of the wall opposite the vent. Methane-air mixtures with methane concentrations close to 9.5% vol. were used in the tests. Pressure data, as function of time, and flame time-of-arrival data were obtained both inside and outside the chamber near the vent. Detailed experimental data is used in the paper to test a three-dimensional gasdynamic model for the simulation of gaseous combustion in vented enclosures. The model is based on a Large Eddy Simulation (LES) solver created using the OpenFOAM CFD toolbox using sub-grid turbulence and flame wrinkling models. Results from the calculations are compared with the experimental data. The capabilities and deficiencies of the model are discussed.

This paper was presented at the Seventh International Conference of Hydrogen Safety (ICHS 2017) in Hamburg on 11-13 September 2017. The paper summarises the results from a blind-prediction study for models developed for estimating the consequences of vented hydrogen deflagrations. The work is part of the project Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations (HySEA). The scenarios selected for the blind-prediction entailed vented explosions with homogeneous hydrogen-air mixtures in a 20-foot ISO container. The test program included two configurations and six experiments, i.e. three repeated tests for each scenario. The comparison between experimental results and model predictions reveals reasonable agreement for some of the models, and significant discrepancies for others. It is foreseen that the first blind-prediction study in the HySEA project will motivate developers to improve their models, and to update guidelines for users of the models. The paper is a deliverable from the project “Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations”, or HySEA (www.hysea.eu), which receives funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement no. 671461. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme and United Kingdom, Italy, Belgium and Norway.