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Crude oil is often transported by pipelines from remote production sites to refineries. Sometimes oil releases take place, caused by sabotage, corrosion or external impact. In a safety consequence study the main hazards considered are often pool, jet or flash fire. The integral models applied may give somewhat misleading hazard estimates, as a flat terrain surrounding the pipeline is assumed, and the models lack the ability to predict dense gas dispersion for calm and low wind scenarios. In a varied terrain an unrealistic large pool and following pool/flash fire, is often predicted. A major hazard often ignored is vapour cloud explosion. The fractions of volatile components in crude oil are limited. Still, as demonstrated by cascade flow experiments after the Buncefield accident, certain release mechanisms may lead to an enhanced evaporation and the likely generation of flammable vapour clouds. For an oil release it can be assumed that a pressurized oil release generating a vertical oil spray into the air, can lead to the evaporation of significant fractions of flammable vapours of propane, butane and pentane. For major pipeline releses during calm wind conditions (0-0.5 m/s) in a varied terrain, a CFD simulation study demonstrated that very large flammable vapour clouds could be generated and could fill lower lying areas of the terrain. The simulated clouds could be 5-10m deep with likely ignition sources as homes, farm houses and roads inside for 20-30 minutes. Areas with trees and dense vegetation were also inside the gas cloud, and could have led to significant flame acceleration, potentially deflagration to detonation transition (DDT) and severe consequences as seen for the Buncefield accident. For pipelines buried below the ground one possible way to prevent such a scenario will be to avoid the possibility for oil sprays upwards, for instance by covering the pipeline with plates which will remain in place during a major release. If this is not possible, vapour fences may be used to limit the gas cloud migration towards likely ignition sources or areas with dense vegetation. While such scenarios may be rare for unintended releases, the severity of the potential consequences should justify their evaluation as part of a safety study.

Boiling Liquid Expanding Vapour Explosions (BLEVEs) are among the major hazard scenarios to be considered in siting studies as well as transportation safety assessments. The main hazards from BLEVEs consist of blast waves and projectiles, and radiation for flammable and toxicity for toxic substances. Well established relations exist to predict consequences for BLEVEs in the open. With increasing confinement, due to tanks being inside or surrounded by buildings, or tunnels for transport scenarios, the consequences from blast waves become more severe, while the empirical relations can no longer be used to predict the consequences. Blast waves from BLEVEs are partly caused by expansion of pressurized vapour head, partly by the rapid phase change of the boiling liquid, and further pressure waves may be generated by pressure oscillations and combustion. Which mechanism that will dominate the blast generation will depend on the vapour head volume and pressure and the degree of superheat of the liquid. FLACS, a computational fluid dynamics (CFD) model has been applied to model blast waves from BLEVEs. The modelling of the different contributions to blast waves has been validated against experiments. For accurate results, both directional effects due to shape of tank and the cooling during the rapid phase change must be included in the modelling. With the validated modeling approach the CFD model can be applied to predict partially confined BLEVE scenarios, including tunnel scenarios. We consider our modelling approach to be more accurate than similar work published in the past.

As a part of zero emission ambitions within the maritime, and possibly within aviation, liquid hydrogen (LH2) will increasingly be used as fuel in the coming years. In that respect it is important to understand safety aspects of LH2, including gas dispersion and explosion properties. The Norwegian Public Roads Administration commissioned large-scale LH2 dispersion and explosion experiments both indoor and outdoor when developing their first LH2-fuelled ferry. In this article these experiments are simulated using a CFD-model with the aim to validate a modelling approach for gas dispersion from LH2-releases. [ABSTRACT FROM AUTHOR]

Heavy-duty vehicles (HDVs) and trains using hydrogen as fuel have significantly larger tanks than smaller fuel cell vehicles (FCVs). The requirement for depressurization time in case of fire may often be the same, thus there may be a need to dimension the thermal pressure relief devices (TPRDs) for significantly higher release rates than used in FCVs. This CFD-study assesses to what extent higher TPRD release rates than typically used for FCVs may be applied without compromising safety. The study has been performed in collaboration with partners in the MoZEES research centre. [ABSTRACT FROM AUTHOR]

Borehole logs from the northern Barbados accretionary prism show that the plate-boundary decollement initiates in a low-density radiolarian claystone. With continued thrusting, the decollement zone consolidates, but in a patchy manner. The logs calibrate a three-dimensional seismic reflection image of the decollement zone and indicate which portions are of low density and enriched in fluid, and which portions have consolidated. The seismic image demonstrates that an underconsolidated patch of the decollement zone connects to a fluid-rich conduit extending down the decollement surface. Fluid migration up this conduit probably supports the open pore structure in the underconsolidated patch.

• Hydrogen risk assessments and safety assessments. • Consequence tools – screening models and CFD. • Liquid and compressed hydrogen. • Assessment of explosion incident. • DDT and detonation. With the ambition to cut emissions from transport hydrogen fuelled vehicles and marine vessels are now being introduced several places in the society. To support this development there is a need for infrastructure to produce and transport gaseous and liquid hydrogen. The properties and safety challenges related to the use of hydrogen are very different from those of conventional fuels, thus safe design may require unconventional solutions. Hydrogen has extreme properties in many ways. It is buoyant when in gas phase while a liquid hydrogen spray will develop a dense plume. The reactivity is higher, flammable range wider and the ignition energy lower than for conventional fuels. Flames may be invisible, and radiation is low. When performing risk assessments for land planning purposes, bunkering assessments or passenger and crew safety these aspects must be reflected. Properties like the positive buoyancy, strong dilution for sonic releases into air, and a low reactivity and energy content for concentrations below 10% must be exploited during design to ensure acceptable risk levels. In this article a two-level risk assessment and design optimization approach is presented in which risk screening with rapid consequence calculations and frequency assessments for release, dispersion, fire and explosion can be performed during concept selection phase with indicative hazard distances estimated. Possible risks of concern are in this way identified, and design can be adjusted, or mitigation measures introduced. For final design risk assessment CFD calculations can be performed for more precise consequence estimates. The risk assessment approach is described with illustrating examples. The focus is not only to ensure safety, but to do so in a cost-efficient and practical way. [ABSTRACT FROM AUTHOR]

Across the metal industry the risk of explosions due to liquid water trapped in molten metal is very real. Accidents, often killing one or a few employees, or blowing out walls, are common in the metal industry. Despite awareness of such explosions it can be challenging to predict consequences and thus evaluate vulnerability and design safety measures. In a recent risk assessment an attempt was made to estimate consequences from water explosions in molten metal furnaces using a combination of spreadsheet calculations and a CFD-tool. With the spreadsheet source terms for blast waves were estimated, calculating how pockets of water within milliseconds could accelerate and throw molten metal at high velocities out of the furnace, and at the same time generate strong pressure waves. Using the CFD-tool FLACS the pressure wave propagation was calculated. The effect of a heavy metal hood above the furnace, with a limited area door opening in one direction would help protect the building and employees against projectiles. The hood would also prevent damaging shockwaves from the explosion to reach wall/roof surfaces in directions of main concern. Using this modelling methodology the amount of water entrained in molten metal required to cause critical damage to building was estimated. Based on a qualitative/quantitative assessment it was thereafter concluded that the potential for water explosions to severely damage the building with the actual furnace design and hood was very limited. The study approach and results from calculations are described in this article. [ABSTRACT FROM AUTHOR]

With the ambition to cut emissions from transport hydrogen fuelled vehicles and marine vessels are now being introduced several places in the society. To support this development there is a need for infrastructure to produce and transport gaseous and liquid hydrogen. The properties and safety challenges related to the use of hydrogen are very different from those of conventional fuels, thus safe design solutions may require unconventional solutions. Hydrogen has extreme properties in many ways. It is buoyant when in gas phase while a liquid hydrogen spray will develop a dense plume. The reactivity is higher, flammable range wider and the ignition energy lower than for conventional fuels. Flames may be invisible and radiation is low. When performing risk assessments for land planning purposes, bunkering assessments or passenger and crew safety these aspects must be reflected. Properties like the positive buoyancy, strong dilution for sonic releases into air, and a low reactivity and energy content for concentrations below 10% must be exploited during design to ensure acceptable risk levels. In this article a two level risk assessment and design assistance approach is presented in which risk screening with rapid consequence calculations and frequency assessments for release, dispersion, fire and explosion are performed during design review with indicative hazard distances estimated. Possible risks of concern are in this way identified, and design can be adjusted or mitigation measures introduced. When required more accurate CFD calculations are thereafter performed for more precise consequence estimates. The risk assessment approach will be described with examples illustrating the approach. [ABSTRACT FROM AUTHOR]

In recent explosion accidents on onshore petrochemical facilities, it has been concluded that a deflagration-to-detonation-transition (DDT) took place, both with Liquefied Petroleum Gas (LPG) and gasoline vapor. DDT has also been observed in a number of large-scale experiments. DDT leads to very high pressures (16-20 barg) and flame speeds (1,600-2,000 m/s) even outside congested regions and has a significant impact on the severity of the near-field and far-field explosion loads. It has not been generally accepted that DDT may be a threat at offshore petrochemical facilities and prediction tools have not been available. Thus, the potential effect of DDT is seldom considered. For Floating production, storage and offloading vessels (FPSOs), and even more Floating liquified natural gas vessels (FLNGs), due to larger dimensions and inventories, operators should be concerned that major explosion scenarios can lead to DDT phenomena. Recently, a DDT prediction parameter was implemented in the Computational Fluid Dynamics (CFD) model FLACS, and with model adjustments it is possible to calculate DDT and effect on explosion loads with good precision. A CFD-based FPSO explosion study is presented evaluating DDT potential and impact. DDT will mainly be a concern for large cloud sizes, often larger than commonly considered for design accidental loads for an FPSO (10−4/year). Mitigation by separation walls is also evaluated. © 2014 American Institute of Chemical Engineers Process Saf Prog 34: 44-57, 2015 [ABSTRACT FROM AUTHOR]

Abstract: The Snøhvit CO2 injection into the Tubåen Formation ended in April 2011. This paper summarizes the Statoil experiences from the injection regarding operational aspects, monitoring and simulation of the CO2 flow in the reservoir. The use of down-hole pressure measurement, in combination with repeated surface seismic data, improved the understanding of the injection process. Detailed interpretation of fall-off pressures in combination with good and updated reservoir models and thorough investigations into the rock mechanical strength of the reservoir rock lead eventually to the abandonment of the original injection reservoir. The storage capacity of the Tubåen Formation is not reached, but the well and the near well reservoir could not receive the necessary volume rate. A PLT -log was run during abandonment confirming pressures and flow scenario and thereby the previous interpretations. The CO2 injection at Snøhvit continues at normal levels in a fallback reservoir. No CO2 has been or will be vented to the atmosphere. [Copyright &y& Elsevier]

To assist in emergency response decisions and planning in case of releases of pressurized liquefied chlorine from railroad tank cars in industrial sites and cities, the FLACS Computational Fluid Dynamics (CFD) model has been used to simulate the transport and dispersion of the dense chlorine cloud. Two accident locations are studied: an actual railcar accident at an industrial site in Festus, MO, and a hypothetical railcar accident at a rail junction in the Chicago urban area. The results show that transport of a large dense gas release at ground level in an industrial site or large city could initially extend a hundred meters or more in the upwind and crosswind directions. The dense cloud may follow terrain drainage, such as river channels. Near the source, the obstacles tend to slow down the dense gas cloud and may constrain it and cause increased concentrations. Farther downwind, the obstacles may cause enhanced mixing and dilution once the cloud has grown larger. In some cases, significant amounts of cloud mass may become “trapped” in obstacle wakes for many minutes after the main cloud has passed. Although the CFD model can account for the details of the flow and dispersion much better than standard widely-used simple dense gas models, many similarities are found among the various models in their simulated variations with downwind distance of the maximum cloud centerline concentration. [Copyright &y& Elsevier]

The FLACS CFD model, which can be used to estimate the flow and dispersion around buildings and other large roughness obstacles, has been evaluated with tracer data from several field experiments involving obstacle arrays. The following experiments were used in the evaluation exercise: Kit Fox (52 trials with puff and plume releases of slightly dense CO2 gas in arrays of billboard-shaped obstacles), MUST (37 trials with puff releases of neutrally buoyant tracer gas in an array of 120 shipping containers), Prairie Grass (43 trials with continuous plume releases of neutrally buoyant tracer gas over a flat agricultural field), and the EMU L-shaped building (a wind tunnel experiment involving a release from an open door in the courtyard area of an L-shaped building). The primary focus is on the maximum concentration on the monitoring arcs. The performance statistics are consistently fairly good, with a median of 86% of the predictions within a factor of two of the observations, a median relative bias suggesting a 20% underprediction, a median relative scatter of about 50%, and a median 20% underprediction of the overall experiment maximum. These results are all well within the criteria of acceptance for dispersion models. Evaluations with the EMU L-shaped building data show that 72% of FLACS predictions are within a factor of two of observations, and that the model can predict the dimensions of the recirculating cavity behind the building within a factor of two. It is suggested that these extensive data sets involving tracer releases in obstacle arrays be used to evaluate other CFD models. [Copyright &y& Elsevier]