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Blast waves from explosion sources such as a pressure vessel burst (PVB) exhibit both positive and negative phases, and the relative magnitude of the positive and negative phases is a function of standoff distance from the explosion source to the target of interest. When an incident blast wave reaches a target building, the blast wave will be reflected off the front wall (i.e., that facing the blast source). Both the blast wave positive and negative phases are affected by this reflection process. A fully reflected blast wave would be produced if the incident blast wave reflected off an infinitely tall and wide wall in a normal orientation. However, when an incident blast wave reflects from a facing wall of finite size, rarefaction waves are created at the edges of the wall and roof, which then sweep inward across the wall. The rarefaction waves result in a clearing effect for both the positive and negative phases. Clearing relieves some of the applied positive phase blast load on the reflected wall. However, clearing may either relieve or enhance the applied negative phase blast load, depending on the blast wave profile and the wall dimensions. This paper focuses on the determination of negative phase clearing as a function of blast wave and structure parameters. Blast load adjustment factors (i.e., ratio of cleared to fully reflected blast loads) are introduced to characterize blast clearing as a function of these parameters. The purpose of the evaluation described in this paper was to generate a database of the blast clearing for engineering modeling of blast-structure interaction.

An incident blast wave interacting with a building will diffract around the side walls and roof, resulting in reduced blast loads on the back wall. There is also a region behind the back wall where the blast loads will be attenuated (i.e., lower than the incident blast loads). This paper focuses on defining the attenuated blast load region as a function of the blast wave strength and building dimensions. Characteristic parameters are utilized to present the analysis results, including wave length, wave length normalized by a characteristic building dimension, and normalized standoff distance from the building back wall. Blast load adjustment factors (i.e., ratio of the diffracted to incident blast load) are used to define the blast load attenuation as a function of these characteristic parameters. The purpose of this work was to generate a database of the shock attenuation behind a structure for engineering modeling applications.

This paper summarises the results from a blind-prediction benchmark study for models used for estimating the consequences of vented hydrogen deflagrations, as well as for users of such models. The work was part of the HySEA project that received funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement no. 671461. The first blind-prediction benchmark exercise in the HySEA project focused on vented explosions with homogeneous hydrogen-air mixtures in 20-foot ISO containers. The scenarios selected for the second blind-prediction study focused on vented deflagrations in inhomogeneous hydrogen-air mixtures resulting from continuous stratification of hydrogen during vertical jet releases inside 20-foot ISO containers. The deflagrations were vented through commercial vent panels located on the roof of the containers. The test program included two configurations and four experiments, i.e. two repeated tests for each scenario. The paper compares experimental results and model predictions and discusses the implications of the findings for safety related to hydrogen applications. Several modellers predicted the stratification of hydrogen inside the container during the release phase with reasonable accuracy. However, there is significant spread in the model predictions, especially for the maximum reduced explosion pressure, and including predictions from different modellers using the same model system. The results from the blind-prediction benchmark studies performed as part of the HySEA project constitute a strong incentive for developers of consequence models to improve their models, implement automated procedures for scenario definition and grid generation, and update training and guidelines for users of the models. publishedVersion

A pressure vessel burst (PVB) is an explosion scenario commonly encountered at chemical processing and petroleum refining facilities. Existing methodologies are available to predict the blast loads resulting from a spherical or cylindrical PVB source, with the PVB source either at grade or at an elevation. In the case of an elevated PVB source, the resulting blast wave will reflect from the ground at an angle. This ground level reflection will result in the formation of a Mach stem at certain angles between the incident blast wave and ground, with the required angles dependent on the blast wave overpressure. The triple point associated with the Mach stem moves upwards as the Mach stem progresses forwards, which can create a region of high blast pressure. This paper focuses on the investigation of a methodology that can be used to determine the high-pressure region generated by the Mach stem, along with the associated blast pressure, as a function of the PVB source elevation and incident blast pressure.

Shock wave attenuation in a straight tunnel (or pipe) can be evaluated using existing methodologies. Shock attenuation is enhanced when there are right-angle turns along the length of the tunnel over which the shock is transmitted. A repeated set of such turns is generally defined as a blast trap. Little guidance is available in the open literature regarding the blast attenuation enhancement due to a right-angle turn or a blast trap in a tunnel. This paper presents guidance for shock wave attenuation as a function of the number of right-angle turns and blast wave parameters (i.e., peak pressure and duration). Characteristic parameters are utilized in order to define shock wave properties and tunnel dimensions. The shock attenuation due to up to four consecutive right-angle turns is evaluated. The purpose of this work is to provide a database of the shock attenuation within a tunnel due to multiple right-angle turns for use in designing tunnel structural components and evaluating the response of such components to postulated transmitted shock loads.

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 well-known 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.

Drag loads due to the gas flows generated by vapor cloud explosions (VCEs) can damage piping and vessels, particularly near or in the flammable cloud. There is little guidance available to the piping and vessel designer regarding the magnitude of such drag loads, beyond evaluating drag loads on a case-by-case basis [e.g., using computational fluid dynamics (CFD)]. This paper presents a newly developed set of drag loads vs standoff distance for a range of flame speeds and vapor cloud sizes. Nine flame speeds were evaluated, up to and including supersonic flame speeds. Cloud sizes are characterized using energy scaled standoff distances (i.e., Sachs scaling). The purpose of this work is to provide a database of drag loads that can be used to evaluate the structural response of piping, vessels, equipment, and supporting structures. The database presentation is similar to that used for existing VCE blast load charts, such as those used in the Baker-Strehlow-Tang (BST) and TNO MEM (Multi-Energy Model) methods.

The purpose of the research was to improve prediction of response of buildings to blast waves by including the negative phase and considering clearing of both positive and negative phases. Commonly used structural design practices, which trace their origins to military design manuals, often ignore the negative phase as well as positive phase clearing. For high explosive threats, this approach is conservative in most circumstances. However, negative phase clearing had not previously been studied for blast waves, and the implications for structural response had not been evaluated. This paper presents results of modeling negative phase blast clearing behavior for a typical blast wave and discusses the differences from positive phase clearing. The implications of including positive and negative phase clearing in building blast damage analysis are also investigated through single-degree-of-freedom (SDOF) analyses. Blast waves from explosion sources like a vapor cloud explosion (VCE), pressure vessel burst or high explosive exhibit both positive and negative phases, and the relative magnitude of the positive and negative phases varies among explosion sources and the specific circumstances of each source. A fully reflected blast wave is produced if an incident blast wave were to strike an infinitely tall and wide wall in a normal orientation. Both the positive and negative phases of the blast wave are enhanced by the reflection process. However, when an incident blast wave strikes a wall of finite size in a normal orientation, rarefaction waves are created at the edges of the wall, and the rarefactions sweep down from the roof and inward from sides. The rarefaction waves result in a clearing effect for both the positive and negative phases. Clearing relieves some of the applied blast load on the reflected wall for the positive phase. However, this is not always the case for the negative phase. As shown by the results presented in this paper, clearing may either relieve or enhance the applied negative phase blast load, depending on the duration of the blast wave and the wall dimensions. The impact of negative phase clearing on structural response for generic building components was also investigated. Nonlinear SDOF methods were used to characterize response in terms of peak positive and negative displacements. It was found that the influence of the negative phase is significant and the peak structural response can occur during negative (outward) displacement.

High-pressure pipeline ruptures are a credible explosion hazard at many industrial facilities. The blast field generated by a pipe rupture is highly directional. However, there have been few evaluations of the directional blast loads produced by pipe ruptures. This paper addresses the blast loads generated by a typical “fish mouth” type pipe rupture. The effects of five key parameters on the resulting directional blast field were examined: rupture opening speed, final rupture opening area, pipe diameter, initial gas pressure, and initial gas temperature. The resultant blast loads were compared to those based on existing blast curves for Pressure Vessel Bursts (PVB), the most common of which is based on an assumption of a spherical vessel geometry and instantaneous failure of the entire pressure vessel boundary. The effective gas volume (i.e., number of pipe diameters) required to achieve reasonable agreement between the blast load based on existing PVB blast curves and that resulting from a high-pressure pipeline fish mouth rupture for a specified direction was determined.

Blast walls are frequently considered as a potential mitigation option to reduce the applied blast loading on a building or structure in cases where unacceptably high levels of blast damage are predicted. There are three general explosion types of interest with respect to blast loading: High Explosive (HE), Pressure Vessel Burst (PVB), and Vapor Cloud Explosion (VCE). The blast waves resulting from these explosion types can differ significantly in terms of blast wave shape and duration. The effectiveness of a blast wall depends on these blast wave parameters (shape and duration), as well as the blast wall parameters (e.g., height, width and standoff distance from the protected structure). The effectiveness of a blast wall in terms of mitigating the blast loading on a protected structure depends on the combination of the blast wave and blast wall parameters. However, little guidance is available on the effectiveness of blast walls as a mitigation option for non-HE explosion sources. The purpose of this paper is to characterize the effect of blast wave parameters on the effectiveness of a blast wall and to provide guidance on how to determine whether a blast wall is an effective and practical blast damage mitigation option for a given blast loading.

Pressure vessel burst (PVB) explosions are credible explosion hazards at a number of chemical processing and petroleum refining facilities. PVBs can present both blast and fragment hazards. Blast prediction methods specific to spherical PVBs were first developed in the 1970s and revised blast curves were subsequently published. The directional effects from non-spherical PVBs were recently investigated by the authors, resulting in correlations for blast overpressure and impulse for a range of vessel geometries and burst conditions. The existing blast charts coupled with these correlations provide a well-defined blast prediction method for PVBs. When a PVB blast wave propagates through an enclosure opening (e.g., window or door), the result is an infiltrated blast wave which will propagate downstream into the enclosure. This paper addresses the infiltration of a PVB blast wave through an opening on a wall. The properties of an infiltrated blast wave depend primarily on the incident blast wave peak pressure, positive phase duration and the opening size. The purpose of the work described in this paper is to introduce an equivalent explosion source, characterized by these three parameters, so that the infiltrated PVB blast loads can be evaluated based on the equivalent source and existing blast curves.

Enclosed chemical processes, laboratory facilities, boilers and reformer furnaces are typical examples of facilities and equipment where an internal VCE may be postulated to occur. The applied blast load history on the enclosure surfaces is required in order to assess the response of the enclosure to the postulated VCE. The internal blast pressure history and associated applied blast loads depend on a number of factors, such as: (1) the maximum flame speed attained in a flammable cloud, (2) the ratio of the cloud volume to the total enclosure volume, (3) the cloud location within the enclosure, and (4) the environment temperature. The purpose of work described in this paper was to investigate the dependence of internal blast pressure history and applied blast loads on the aforementioned factors. It was found that the applied loads on the enclosure surfaces can be roughly classified into two regimes: quasi-static and dynamic, depending on the combination of these factors. It can be important to identify the appropriate blast loading regime in order to properly analyze the structural response of the enclosure.Copyright © 2015 by ASME

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.Copyright © 2014 by ASME

A key component of explosion hazard evaluations is the determination of standoffs to given blast overpressure values. Many such evaluations use a simplified methodology that assumes that the blast wave propagates from the explosion source to the target location without interacting with intervening buildings or structures (i.e., without blast wave shielding). This is obviously a perfectly acceptable approach for a screening study, but blast wave shielding effects can be significant in certain circumstances (e.g., within a building group). A methodology was proposed by the UK Health & Safety Laboratory (HSL) in 2001 to account for blast shielding due to buildings/structures between the explosion source and target location. The HSL methodology is based on the blast waves generated by high explosives (HE). This paper extends the blast shielding evaluation to blast waves generated from pressure vessel bursts (PVB) and vapor cloud explosions (VCE). The influences of blast wave shape parameters (overpressure, duration and rise time) on blast wave shielding are examined. The results indicate that the degree of blast shielding is strongly dependent on the source of the blast wave (i.e., on the blast wave shape parameters) and that the shielding factors obtained with HE blast waves are not always directly applicable for PVB and VCE blast waves.

The ignition of a flammable gas mixture contained within a piping system can lead to damage or failure of the piping or system components. Flame propagation and acceleration within piping systems have been extensively studied. It has been well documented that, given sufficient flame propagation distance and/or the presence of turbulence generating features, flame acceleration within a pipe can lead to a deflagration-to-detonation transition (DDT). The high overpressures associated with a DDT can increase the potential for deformation or failure of the piping system relative to the loads associated with either a fast deflagration or steady-state detonation. This paper presents the results of numerical evaluations to predict the pressure distributions within a pipe run due to a DDT. The blast overpressure associated with a DDT was found to depend on a number of parameters, including: the rate of flame acceleration prior to the DDT, the length of piping occupied by the flammable mixture, the initial gas pressure and the flammable mixture concentration distribution along the pipe. This paper also provides a comparison of the blast loads associated with a steady-state detonation relative to those due to a DDT.Copyright © 2012 by ASME

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.Copyright © 2011 by ASME

The downhole tool industry commonly conducts tests that require pressurization of a vessel. The most common failure mode is through the launching of end caps, plugs, and fittings as opposed to a catastrophic rupture of the vessel body. This type of vessel failure during high pressure gas testing can produce significant threats to nearby personnel in the form of high energy projectiles and blast waves that must be blocked or dissipated before reaching personnel. Adequately designing a structure to contain this energy depends on how well a worst case scenario event can be modeled. Blast waves ensue from a pneumatic pressure test failure. As a vessel fails, the volume of pressurized gas will expand into the surroundings. A computational fluid dynamics (CFD) model of the pressure vessel and its enclosure will provide an accurate assessment of the blast loads in the environment. This paper describes an experimental test program of a simulated pneumatic pressure vessel failure through the launching of a hypothetical end cap or plug inside an enclosure. The recorded blast loads from three tests at various pressures were compared to simplified two-dimensional CFD model results of the enclosure. Two CFD models were run for each test: the first accounts for the time required for the vessel to open during failure, and the second assumes an instantaneous release of pressurized gas. The CFD results for the first model matched the test results well and provided validation of the modeling approach. The second model indicates the level of conservatism of predicted blast loads when assuming an instantaneous vessel failure. A properly designed pressure testing enclosure can provide a high level of safety in the event of a failure; several types of enclosure designs have proven to be successful, which are discussed in this paper. Equally important is the need to have competent operators with an awareness of the risks involved with pressure testing combined with training and competency programs implemented throughout the industry.Copyright © 2011 by ASME

This paper was presented at the Seventh International Conference of Hydrogen Safety (ICHS 2017) in Hamburg on 11-13 September 2017. The paper summarises the results from a blind-prediction study for models developed for estimating the consequences of vented hydrogen deflagrations. The work is part of the project Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations (HySEA). The scenarios selected for the blind-prediction entailed vented explosions with homogeneous hydrogen-air mixtures in a 20-foot ISO container. The test program included two configurations and six experiments, i.e. three repeated tests for each scenario. The comparison between experimental results and model predictions reveals reasonable agreement for some of the models, and significant discrepancies for others. It is foreseen that the first blind-prediction study in the HySEA project will motivate developers to improve their models, and to update guidelines for users of the models. The paper is a deliverable from the project “Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations”, or HySEA (www.hysea.eu), which receives funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement no. 671461. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme and United Kingdom, Italy, Belgium and Norway., The work described in this paper is a deliverable from the project "Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations", or HySEA (www.hysea.eu), which received funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement no. 671461. The paper is part of the Proceedings from the Seventh International Conference on Hydrogen Safety (ICHS 2017), ISBN 978-88-902391, pp. 639-652.

This paper was presented at the Seventh International Conference of Hydrogen Safety (ICHS 2017) in Hamburg on 11-13 September 2017. The paper summarises the results from a blind-prediction study for models developed for estimating the consequences of vented hydrogen deflagrations. The work is part of the project Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations (HySEA). The scenarios selected for the blind-prediction entailed vented explosions with homogeneous hydrogen-air mixtures in a 20-foot ISO container. The test program included two configurations and six experiments, i.e. three repeated tests for each scenario. The comparison between experimental results and model predictions reveals reasonable agreement for some of the models, and significant discrepancies for others. It is foreseen that the first blind-prediction study in the HySEA project will motivate developers to improve their models, and to update guidelines for users of the models. The paper is a deliverable from the project “Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations”, or HySEA (www.hysea.eu), which receives funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement no. 671461. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme and United Kingdom, Italy, Belgium and Norway.