A study of the blast wave shape from elongated VCEs

Abstract

a b s t r a c t Elongated congestion patterns are common at chemical processing and petroleum refining facilities due to the arrangement of processing units. The accidental vapor cloud explosion (VCE) which occurred at the Buncefield, UK facility involved an elongated congested volume formed by the trees and undergrowth along the site boundary. Although elongated congested volumes are common, there have been few evaluations reported for the blast loads produced by elongated VCEs. Standard VCE blast load prediction techniques do not directly consider the impact of this congested volume geometry versus a more compact geometry.This paper discusses an evaluation performed to characterize the blast loads from elongated VCEs and to identify some significant differences in the resulting blast wave shape versus those predicted by wellknown VCE blast load methodologies (e.g., BST and TNO MEM). The standard blast curves are based on an assumption that the portion of the flammable gas cloud participating in the VCE is hemispherical and located at grade level. The results of this evaluation showed that the blast wave shape for an elongated VCE in the near-field along the long-axis direction is similar to that for an acoustic wave generated in hemispherical VCEs with a low flame speed. Like an acoustic wave, an elongated VCE blast wave has a very quick transition from the positive phase peak pressure to the negative phase peak pressure, relative to the positive phase duration. The magnitude of the applied negative pressure on a building face depends strongly on the transition time between the positive and negative phase peak pressures, and this applied negative phase can be important to structural response under certain conditions. The main purpose of this evaluation was to extend previous work in order to investigate how an elongated VCE geometry impacts the resultant blast wave shape in the near-field. The influence of the normalized flame travel distance and the flame speed on the blast wave shape was examined. Deflagration and deflagration-to-detonation transition regimes were also identified for unconfined elongated VCEs as a function of the normalized flame travel distance and flame speed attained at a specified flame travel distance.

Elongated VCE blast waves and structural response

“…This evaluation extends the previous work , examining how the attained flame speed impacts the resultant blast wave shapes and corresponding blast loads immediately downstream of the cloud end along the long‐axis direction. These blast loads were further used to analyze the structural response of conventional structures.…”

“…Although elongated congested volumes are common, there have been few evaluations reported for the blast loads produced by elongated VCEs and the blast loads from the elongated VCEs have not been fully addressed in VCE prediction methods. The authors recently performed an evaluation to characterize elongated VCEs and to identify the resultant difference in blast wave shape compared to those predicted by well‐known VCE blast prediction methodologies. BakerRisk's Blast Wave Target Interaction (BWTI™) computational fluid dynamics (CFD) code was used to investigate the VCE blast loads resulting from elongated flammable gas clouds.…”

“…The authors recently performed an evaluation to characterize elongated VCEs and to identify the resultant difference in blast wave shape compared to those predicted by well‐known VCE blast prediction methodologies. BakerRisk's Blast Wave Target Interaction (BWTI™) computational fluid dynamics (CFD) code was used to investigate the VCE blast loads resulting from elongated flammable gas clouds. The BWTI™ predictions were validated against test data from the recent Buncefield JIP (Joint Industry Program) .…”

“…The influence of the normalized flame travel distance and the flame speed on the resultant blast wave shape was further investigated , and it was determined that the blast wave shape in the near‐field around the congested cloud boundary can be significantly impacted by the cloud aspect ratio and the flame speed attained.…”

Stochastic modeling and analysis of vapor cloud explosions domino effects in chemical plants

“…The authors of [36] propose a method for taking into account channelling and shielding effects when estimating the blast pressure, while in [11], the authors studied the blast wave of elongated VCEs. In fact, most work assumes that the cloud of flammable material participating in the VCE is hemispherical, which is however rarely the case, due to congestion caused by other equipment.…”