Pressure vessel burst (PVB) is a class of explosion for which there are hazards at virtually all chemical processing facilities. PVBs present both airblast and fragmentation hazards. Blast prediction methods specific to PVBs were first developed in the 1970s and revised blast curves were published in 1995. The published blast curves were developed for spherical vessel bursts, whereas most pressure vessels in use in industry are cylindrical. Blast effects around a bursting cylindrical vessel are not uniform as with a spherical vessel. The blast to the side of a cylindrical vessel is stronger than off the ends, creating non-circular pressure contours. The directional effects diminish with distance as the expanding shock wave approaches a spherical shape. A correlation was developed in the 1970s to account for directional effects using high explosive test data, the best available resource at the time. Like all test programs, pressure transducers extended to limited distances from the explosive charge, yet the data are often extrapolated to a far greater distance. This paper presents the results of recent work on directional effects specific to bursting cylindrical pressure vessels and provides new correlations for blast overpressure and impulse for a range of vessel geometries and burst conditions. The results can be used to predict the airblast hazards from cylindrical PVBs over the range of standoff distances for which directional effects exist.

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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.

Pressure vessel burst (PVB) is an explosion scenario commonly encountered at chemical processing facilities. PVBs pose both blast and fragmentation hazards. Blast prediction methods specific to PVBs were first developed in the 1970s and revised blast curves were published in 1995. The published blast curves were developed for spherical vessel bursts. However, most pressure vessels are cylindrical rather than spherical. The blast wave originating from a cylindrical PVB is not spherical (i.e., as with a spherical vessel). Rather, the blast to the sides of a cylindrical vessel is stronger than on the ends, creating non-spherical pressure contours, particularly near the vessel. The cylindrical vessel directional blast effect has recently been investigated by the authors, resulting in a correlation to account for the directional effects. However, it was assumed in the prior work that the vessel was at ground level. This paper extends the prior work to elevated PVBs. Both elevated spherical and cylindrical PVBs are examined to provide new correlations for blast overpressure and impulse for a range of vessel geometries and burst conditions.

The industrial gas and liquefied natural gas (LNG) industries routinely perform equipment pressure testing pneumatically, rather than hydraulically, due to the necessity for keep piping and equipment dry. Hazards associated with potential failure of pneumatically pressurized equipment under test are well understood, but today, there is no commonly recognized industry guidance on recommended safety distances to protect personnel during such tests. Air Products, Air Liquide and BakerRisk have worked together to develop such guidance for the testing of vessels, process pipes and pipelines, and present in this article new, simple to use correlations, with results also presented in the form of lookup tables. These new correlations are based on the application of established methods, validated against previously published independent test data and new test data presented here for the first time. © 2018 American Institute of Chemical Engineers Process Saf Prog 38: e12025, 2019