Vapor Cloud Explosions Involving Separated Congestion Volumes – Application of the BST Method

Vapor Cloud Explosion (VCE) overpressure calculations for potential flammable vapor release scenarios deliver critical information for the design and construction of contemporary oil & gas processing facilities. Multiple techniques exist for modeling the effects of overpressure hazards, from simplified empirical models to increasingly robust complex computational fluid dynamics (CFD) models. Alternatively, empirical models (e.g., TNT method, TNO method, BST method) function at a lower computational cost and are capable of reasonable overpressure estimates.

The Baker–Strehlow–Tang (BST) method is a commonly used empirical model for overpressure hazards, offering the means to adjust computation for different fuel types, level of congestion, and the size/position of the congested vapor cloud volume(s). However, a challenge when applying the BST method is appropriately defining these parameters to depict complex, real-world configurations of congestion volumes. The BST method allows the user to designate a congestion level but assumes that the volume sees uniform congestion throughout, something atypical for many industry applications. Furthermore, the BST method is not directly capable of quantifying the effects of multiple congested volumes positioned in series with separation. CFD tools, however, can handle such complicated physical geometry scenarios but often at the cost of computational time and expense.

In this paper, we evaluate the validity of assumptions used in our application of the BST method to quantify VCEs within a series of multiple complex congestion volumes that are separated but occupied by a continuous flammable cloud, an extension of previous works evaluating the degree if congestion within a single volume. Empirical overpressure results will then be compared to simulations that were prepared using a commercial CFD package, to determine the accuracy and reliability of BST congestion simplifications.