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Vapor cloud explosions (VCEs) can cause significant damage to nearby buildings, facilities and infrastructure with potential loss of life and significant business interruption, so the accuracy of predicting blast loads on facility buildings is critical in estimating these losses. Closely spaced buildings and process equipment outside of the congested region of a VCE provide a complicated flow field for an expanding blast wave. Their presence can channel and shield the blast, resulting in significant effects on the blast load magnitude and waveform shape. Currently, the most common way to estimate applied blast pressures resulting from VCE's is to use simplified methods that account for the total energy from the stoichiometric portion of the vapor cloud, fuel reactivity, and level of congestion and confinement, such as the TNO Multi-energy, equivalent TNT, CAM, and BST methods. These simplified tools assume an unobstructed line-of-site condition, which can overestimate and/or underestimate blast loads. This paper illustrates the use of a fast-running Computational Fluid Dynamics (CFD) approach that can account for channeling and shielding effects without having to use a turbulent combustion model. This approach provides a convenient tool for designers and process safety planners to more accurately quantify the hazard from postulated VCE hazards that include site-specific channeling and shielding effects. The accuracy of the approach is demonstrated via comparisons of CFD simulations to experimentally measured waveforms. Computed pressure and impulse are also compared to the BST predictions for unobstructed and obstructed sites.

A common terrorist threat worldwide is the use of large vehicle bombs to attack high value targets. Detonation of large yield devices can cause significant damage to nearby buildings, facilities and infrastructure with potentially high loss of life and large economic losses. Blast pressures can have major consequences on critical facilities such as nuclear power plants, causing economic loss, environmental damage and system failure. Closely spaced structures in a dense configuration provide a complicated setting for evaluating airblast pressures caused by explosive devices. The presence of multiple buildings can channel the airblast, resulting in significant effects on load magnitudes at range from the detonation. Buildings reflect propagating blast waves causing increased loading at some locations and reduced loads elsewhere due to shielding from direct blast waves. The complex interaction between structures, streets, alleys and geographical terrain can have a major impact on structural loads. Currently, the most common way to estimate airblast pressures resulting from above ground explosive detonations is to use fast running, approximate blast tools such as CONWEP. These simplified tools may not provide accurate guidance on airblast pressures in complex environments. The following paper illustrates the use of Computational Fluid Dynamics (CFD) calculations of complex building configurations to quantify the resulting blast environment. Comparisons with simplified methods are presented. An approach to using a database of CFD simulations, customized for a specific site, to provide a fast running blast assessment tool is described. This approach provides a convenient, fast running tool for designers and security planners to visualize and accurately quantify the hazard from any threat size and location within the area of interest.Copyright © 2012 by ASME