ventilation, extents and position of obstacles etc., that may lead to accumulation of hydrogen at lower levels. However, the released gas will usually rise to the ceiling.
The gas will accumulate, and large flammable gas envelopes may be created, if no measures are taken for shutdown of release or effective dilution and removal of the gas. A release scenario showing a 10 g/s release of hydrogen inside a process container of 40 m2 is illustrated in figure 4. The calculations, carried out with the CFD code FLACS , ref. /12/, indicate that even large ventilation rates (300 volume changes per hour) will have limited effect on releases of this size.
Figure 4 “Snapshot” of hydrogen gas cloud, showing the gas envelope with H2-concentration in air > ½ LFL (2 vol%), at three different timesteps. Release rate 10 g/s, sonic velocity. Ventilation capacity 300 volume changes per hour. Release position is about 1.5 m above ground level, halfway between the end walls and close to one of the sidewalls. Release direction is conservatively assumed to be vertically downwards.
a) 4 s after release start
b) 10 s after release start