Consequence Assessment of a 440 L Propylene Y-Cylinder Gas Cabinet in Semiconductor Gas Supply Systems

The use of propylene (C3H6) in semiconductor manufacturing processes is increasing, and conventional 47 L cylinder supply systems are recognized as a primary source of leakage accidents associated with human error due to the need for frequent manual cylinder replacement. In this study, a Computational Fluid Dynamics (CFD)-based dispersion analysis and a preliminary accident consequence assessment—based on explicitly stated assumptions—were conducted for a gas cabinet housing a 440 L Y-type propylene cylinder. The potential for Vapor Cloud Explosion (VCE) was analyzed using a TNT equivalence model that accounts for the internal volume of the semi-enclosed cabinet. Pressure Vessel Burst (PVB) was evaluated using the Brode–Baker–Tang approach, while the fireball resulting from a Boiling Liquid Expanding Vapor Explosion (BLEVE) was assessed using the EFFECTS software. Under emergency ventilation conditions, the steady-state volume of the flammable gas cloud exceeding the Lower Flammability Limit (LFL) was calculated to be 6.9 m3, representing less than 0.2% of the total indoor volume. The distance corresponding to an overpressure of 1 psi was estimated to be 12.0 m for PVB and 13.6 m for VCE. Additionally, assuming that the entire 185 kg inventory participates in fireball formation, the distance corresponding to a radiant heat flux of 5 kW/m2 was calculated to be 104 m. However, this distance represents an upper bound solely with respect to the fraction of material participating in fireball formation and does not account for other input variables in the fireball model. The presented results represent a preliminary consequence analysis based on the specified assumptions. Some of the applied assumptions are conservative; for instance, a constant leak rate and complete participation of the stored inventory in fireball formation were assumed. Conversely, the neglect of liquid pool evaporation and the assumption that vessel rupture occurs at operating pressure are not conservative approaches. The analysis indicates that, while the consequences of overpressure are confined to the immediate vicinity of the gas cabinet, the extent of thermal radiation impact depends on whether accident scenarios initiated by external fires can be prevented. These findings provide consequence-based baseline data for the design of safety systems—such as emergency ventilation, gas detection, automatic shut-off, fire suppression, and protective structures—for facilities utilizing 440 L Y-type cylinders. However, these results alone do not determine whether the installation of such facilities is acceptable from a safety perspective.