Accidental Releases of Hydrogen in Maintenance Garages: Modelling and Assessment

This study investigates the light gas dispersion behaviour in a maintenance garage with natural or forced ventilation. A scaled-down garage model (0.71 m high, 3.07 m long and 3.36 m wide) equipped with gas and velocity sensors was used in the experiments. The enclosure had four rectangular vents at the ceiling and four at the bottom on two opposing side walls. The experiments were performed by injecting helium continuously through a 1-mm downward-facing nozzle until a steady state was reached. The sensitivity parameters included helium injection rate, the elevation of the injection nozzle and forced flow speeds. Exhaust fans were placed at one or all of the top vent(s) to mimic forced ventilation. Numerical simulations conducted using GOTHIC, a general-purpose thermal-hydraulic code, and calculations with engineering models were compared with experimental measurements to determine the relative suitability of each approach to predict the light gas transport behaviour. The GOTHIC simulations captured the trends of the helium distribution, gas movement in the enclosure, and the passive vent flows reasonably well. Lowesmith’s model predictions for the helium transients in the upper uniform layer were also in good agreement with the natural venting experiments.