Risk assessment of major hazards: the effect of ground slope

Liquefied gases, such as chlorine and ammonia, are stored in large quantities at industrial sites. If released accidentally, they form a heavy gas cloud that has the potential to kill or injure large numbers of people. The dispersion of such a cloud is thus of interest to the risk assessment community [Nussey, Pantony, & Smallwood, 1992. HSE’s risk assessment tool, RISKAT. In: Major Hazards: Onshore and Offshore. pp. 607–638].Little is understood about the effect of slope on risk. Here, the risk (probability) of being exposed to the gas cloud, given a release, is considered; probability language is needed because wind direction is assumed to be a random variable.This paper shows how the risk of being exposed to toxic gas released over a slope may be estimated using simple physical modelling.The physical model used is that of Tickle [J. Hazard. Mater. 49 (1996) 29], who showed that a finite-volume instantaneous release on an inclined plane can form a stable wedge-shaped cloud that moves down the line of greatest slope. Nonzero windspeeds are accounted for by following Tickle’s suggestion of vectorially adding windspeed to the advection induced by the slope.A range of windspeeds and slopes are considered. The slopes substantially affect the risk in the sense that the predicted risk contours are far from circularly symmetric.     

Ammonia large scale atmospheric dispersion experiments in industrial configurations

A programme of large-scale experiments for atmospheric dispersion was carried out by INERIS over a period extending from December 1996 to April 1997. The objectives of the test campaign were to measure anhydrous ammonia concentrations in a range of few meters to 2 km from the release, in order to generate data to be used to improve 2-phase discharge and dispersion modelling.

The discharges were released from a 6-tonne storage tank of pressurised liquid ammonia and through a discharge device with an outlet diameter of 2 in. Fifteen trials were carried out with various release configurations corresponding to industrial situations (impinging jets on the ground and on a wall at various distances, release through a flange without seal…). The quantity of ammonia discharged from the liquid phase varied according to the tests, from 1.4 to 3.5 tons for durations between 7 and 14 min and, therefore, at flow rates between 2 and 4.5 kg/s. Approximately 200 sensors were settled downwind to measure ammonia concentrations and temperature in the plume. These tests showed that for discharges with identical flow rates the distances corresponding to the same concentration vary a lot according to the configurations. These distances tend to be reduced by the presence of obstacles or retention dikes that collected liquid ammonia. In the paper, the main experimental results are presented. In order to enable the comparisons with numerical predictions, more detailed information are given in [Bouet R. (1999). Ammoniac—Essais de dispersion atmosphérique à grande échelle. INERIS rapport, ref INERIS-DRA-RBo-1999-20410 (available at http://www.ineris.fr/recherches/recherches.htm).     

Utilization of regression technique to develop a predictive model for hazard radius from release of typical methane-rich natural gas

The aim of hazardous area classification around equipment handling or storing of flammable fluids is to avoid the ignition of those releases that may occur from time to time in the operation of these equipment. There is a point source approach for the classification of hazardous areas which can estimate hazard radius by using hole size and release pressure. Methane-rich natural gas is widely used or produced in the process industries. Till date, there exist no reference that represents hazard radii for the wide range of possible hole sizes and release pressures of this fluid. The aim of the present study was to propose a predictive model for estimation of hazard radii due to releases of typical methane-rich natural gas based on hole size and release pressure. In this study, a complete database of hazard radii due to a broad range of hole sizes and release pressures was provided using available discharge and dispersion models. A regression-based model for estimation of hazard radii was developed based on the provided database. Performance investigation of the proposed model and a case study showed that the results are reliable with an acceptable standard error.     

Real-time response system for the prediction of the atmospheric transport of hazardous materials

Human urge of exploiting earth resources has resulted into unprecedented industrial development in the last century resulting into production of large quantities of hazardous chemicals. Chemical, petrochemical, nuclear, biomedical and pharmaceutical industrial accidents release large quantities of hazardous chemicals into the atmosphere. The accidental discharge during production or storage or transportation have subjected the population to be exposed to exceptionally high concentration levels of hazardous chemicals, taking them by surprise, unprepared with fatal consequences. An emergency planning organization has to be trained to combat this situation in the shortest possible time to minimize the number of causalities. The present paper focuses on computation of dispersion model, using emission source, accident location and online metrological data near to the sources, to provide necessary and accurate results swiftly. The predicted ground level concentrations with the hazardous nature of the chemical, speed and direction of plume, the emergency team will be supplied with all the information in graphical easy to grasp form, superimposed over a GIS map or the latest satellite image of the area.

The emergency team has to be trained for all past scenarios and their preparedness, response and actions must be practiced regularly to be able to abate chemical releases accidentally or intentionally.

Accidental releases of chlorine and ammonia gases in residential and industrial areas are simulated. The predicted ground level concentrations in the effected areas are shown after different time intervals. For low vapor pressure chemical, the dispersion time is large and concentration levels are low but persist for prolonged time while for volatile chemical, the concentrations are high in short time and recovering to safe environment is quick.     

CFD analysis of the dispersion of toxic materials in road tunnels

The present work is aimed at analyzing the evolution of accidental scenarios deriving from the release of toxic materials inside a tunnel. This scenario, compared to the more frequently investigated cases of fire, followed by smoke dispersion, may involve a large variety of common products characterized by widely differing physical properties; nonetheless it has been analysed in the literature less than expected. The present study compares the dispersion of two common toxic chemicals (chlorine and ammonia), in order to derive some preliminary information about the influence of the physical properties and the release rate. A reference road tunnel geometry is assumed, while the release occurs from ground level, at the centre of one lane and in the middle of the tunnel. Two study cases involving a road tanker, transporting the product as liquefied gas under pressure, were considered: a catastrophic release, from a 220 mm hole, emptying the tanker in a few tens seconds (case A), and a continuous release, from a much smaller hole (15 mm), lasting 5 min (case B). For the sake of simplicity, the release is assumed to be in gaseous phase; the dispersion of the toxic is simulated for the 5 min period following the start of the release using a CFD (Computational Fluid Dynamics) analysis, according to an RANS (Reynolds-Averaged Navier–Stokes) approach with the standard k–ε turbulence model, assuming no ventilation conditions. Structured curvilinear grids with hexaedric cells, refined according to the local concentration gradient, are used. For case A scenarios, especially for the whole release duration, dispersion is mainly governed by the “plug-flow” effect caused by the large volume of toxic entering the tunnel in a rather short time; then, the role of diffusivity and gravity becomes more important. Chlorine, heavier than air and with lower diffusivity than ammonia, progressively accumulates towards the floor; the dispersion of ammonia, which is lighter than air, appears more influenced by diffusivity than by gravity, since a limited stratification is observed. These trends are more evident for case B scenarios, where the toxic flow rates are much lower. It is expected the results will give some useful insight into the dispersion phenomenon within highly confined spaces and maybe also provide some suggestion about ventilation systems design and emergency procedures.     

Using computational fluid dynamics (CFD) for blast wave predictions

Explosions will, in most cases, generate blast waves. While simple models (e.g., Multi Energy Method) are useful for simple explosion geometries, most practical explosions are far from trivial and require detailed analyses. For a reliable estimate of the blast from a gas explosion it is necessary to know the explosion strength. The source explosion may not be symmetric; the pressure waves will be reflected or deflected when hitting objects, or even worse, the blast waves may propagate inside buildings or tunnels with a very low rate of decay. The use of computational fluid dynamics (CFD) explosion models for near and far field blast wave predictions has many advantages. These include more precise estimates of the energy and resulting pressure of the blast wave, as well as the ability to evaluate non-symmetrical effects caused by realistic geometries, gas cloud variations and ignition locations. This is essential when evaluating the likelihood of a given leak source as cause of an explosion or equally when evaluating the potential risk associated with a given leak source for a consequence analysis.In addition, unlike simple methods, CFD explosion models can also evaluate detailed dynamic effects in the near and far field, which include time dependent pressure loads as well as reflection and focusing of the blast waves. This is particularly valuable when assessing actual near-field blast damage during an explosion investigation or potential near-field damage during a risk analysis for a facility. One main challenge in applying CFD, however, is that these models require more information about the actual facility, including geometry details and process information. Collecting the necessary geometry and process data may be quite time consuming. This paper will show some blast prediction validation examples for the CFD model FLACS. It will also provide examples of how directional effects or interaction with objects can significantly influence the dynamics of the blast wave. Finally, the challenge of obtaining useful predictions with insufficient details regarding the geometry will also be addressed.     

高压管道天然气泄漏扩散过程的数值模拟

采用CFD模型的方法对高压管道内的天然气泄漏和扩散过程进行了数值模拟。其结果表明,从高压管道泄出的天然气在大气中主要表现为高速射流的泄漏过程和随后的扩散过程。在泄漏过程中,天然气在泄漏口附近为欠膨胀射流,整个泄漏过程具有一定的高度;在扩散过程中,天然气在浮力作用下以向上扩散的形式发展。研究了不同环境风速对扩散过程的影响,较大的风速可以使天然气向下风方向更远的距离扩散,从而增大了天然气爆炸危险浓度的范围。研究结果可     

Numerical simulation of LNG dispersion under two-phase release conditions

The use of LNG (liquefied natural gas) as fuel brings up issues regarding safety and acceptable risk. The potential hazards associated with an accidental LNG spill should be evaluated, and a useful tool in LNG safety assessment is computational fluid dynamics (CFD) simulation. In this paper, the ADREA-HF code has been applied to simulate LNG dispersion in open-obstructed environment based on Falcon Series Experiments. During these experiments LNG was released and dispersed over water surface. The spill area is confined with a billboard upwind of the water pond. FA1 trial was chosen to be simulated, because its release and weather conditions (high total spill volume and release rate, low wind speed) allow the gravitational force to influence the cold, dense vapor cloud and can be considered as a benchmark for LNG dispersion in fenced area. The source was modeled with two different approaches: as vapor pool and as two phase jet and the predicted methane concentration at sensors' location was compared with the experimental one. It is verified that the source model affect to a great extent the LNG dispersion and the best case was the one modeling the source as two phase jet. However, the numerical results in the case of two phase jet source underestimate the methane concentration for most of the sensors. Finally, the paper discusses the effect of neglecting the ?9.3° experimental wind direction, which leads to the symmetry assumption with respect to wind and therefore less computational costs. It was found that this effect is small in case of a jet source but large in the case of a pool source.     

Method to analyze the regional life loss risk by airborne chemicals released after devastating earthquakes: A simulation approach

Widespread chemical plants render human life more vulnerable to major natural disasters such as earthquakes. Recognizing the potential cascading threats initiated by a devastating earthquake, a general methodology for assessing the life loss risks introduced by airborne hazardous chemical dispersion following seismically induced chemical release (SICR) was proposed. With a 600 km × 600 km region in North China as a demonstrative study area, the dispersion of ammonia released from multiple relevant chemical plants that were supposed to be damaged by a devastating earthquake was simulated in a probabilistic manner. Using an ammonia toxicity-fatality relationship and its toxicity concentration threshold, regional life loss and spatial spread were evaluated. The life loss risk was found to be non-prominent but would be very contingent on unfavorable meteorological conditions. Non-parametric correlation analysis revealed that the respective effects of meteorological mixing parameters on the risk exhibit new features in a disaster context, that is, stronger mixing would cause elevation of risk in a region. This preliminary research implied that the risk of chemical-induced life loss after a devastating earthquake deserves attention and a thorough uncertainty evaluation in the future.     

A modified steady-state model for evaluation of ammonia concentrations behind a water curtain

Water curtain system has been proved an effective mitigation measurement for ammonia spill dispersion. Calculating of ammonia cloud concentration with water curtain was less studied. This paper presents a steady-state calculation model to calculate open and forced ammonia spill dispersion. The formula of ammonia absorption was built and integrated into the calculation model. The calculated downwind ammonia concentrations for open and forced spill dispersion were reproduced and compared with literature using a statistical method. In addition, the relationship between ammonia concentration in water droplet and the droplet diameter was studied. The results display that the formula of ammonia absorption is suitable for calculating mass transfer process between the ammonia cloud and the water curtain. The calculation model presents good performances for open and forced ammonia spill dispersion. This study indicates that the calculation model can be satisfactory in determining the impact of open and forced ammonia spill dispersion and the design of water curtain mitigation system.     

城市公路隧道火灾近火源区长度的研究

为对近火源区长度进行研究,以城市公路隧道为研究对象,采用理论分析与数值模型相结合的方法,探究了大火源功率、有效顶棚高度和火源横向位置对近火源区长度的影响,对36个工况的数值模拟和温度场变化规律的研究与分析。结果表明:火焰未撞击顶棚时,火源功率对近火源区长度几乎没有影响;当火焰持续撞击顶棚并形成水平扩展火焰时,近火源区长度受火源功率和有效顶棚高度影响较大,其无量纲形式与无量纲火源功率的2/3次方呈线性关系;随着火源与侧壁距离的减小,近火源区长度呈自然指数增加趋势;火源贴壁时,近火源区长度是火源位于隧道中部时的1.866倍;提出了近火源区长度预测模型,基本揭示了烟气由过渡阶段转入一维蔓延阶段起始位置的变化规律,能够为定量研究各阶段烟气流动特性提供参考依据。     

Impact of leakage location and downwind storage tank on the gas dispersion in a typical chemical tank storage area

Toxic gas leakage in a tank area can have catastrophic consequences. Storage tank leakage location (particularly for high leakage) and downwind storage tanks potentially influence gas diffusion in tank areas. In this study, we developed a numerical and experimental method to investigate the impact of a high leakage location and downwind storage tank on gas diffusion based on three (1.05H, 0.90H, and 0.77H, H was the tank height, 22m) leakage field experiments on the leeward side of storage tank, which have been not conducted before. The experiments revealed an unexpected phenomenon: the maximum ground concentration first decreased and then increased with increasing leakage height. The simulations illustrated that the differences in micrometeorological conditions caused the maximum ground concentration of gas emitted from the roof to be higher than that emitted from the tank wall near the storage tank height. The downwind storage tank 1) had little influence on the entire diffusion direction but altered the local diffusion pattern; 2) reduced the maximum ground concentration (∼18.7%) and the distance from the emission source (approximately a storage tank diameter); and 3) had strong influences on the concentration, velocity, turbulence, and pressure on the leeward side. The concentration negatively correlated with the velocity, pressure, and turbulence in the middle of the two storage tanks on wind centerline. Our results can improve understanding of gas dispersion in tank areas and provide references for mitigating loss and protecting lives during emergency response processes.     

Effects of release pressure on the transportation characteristics in pipeline and the diffusion behaviors in enclosure space of typical gas extinguishing agent

Reducing the release pressure of fire extinguishing systems can decrease potential safety hazards in large transport airplanes. To explore whether reducing the release pressure can achieve the release effect required by the airworthiness standards or not, the transportation characteristics in the pipeline and diffusion behaviors in the enclosure space of a typical fire extinguishing agent (Halon 1301) were investigated under five release pressures in the present study. The effects of the release pressure on the degree of superheat, injection duration, jet structure, and concentration distribution of Halon 1301 were analyzed. The results show that both of the degree of superheat and the injection duration decrease with an increase in the release pressure. The supplement of bubble expansion in the fire extinguishing agent can slow down the pressure decrease in the vessel. Both of the maximum and mean values of the pipeline differential pressure increase with an increase in release pressure. The maximum value of the jet angle decreases linearly with the increase in release pressure, and the jet deflects upward owing to the effects of buoyancy. The maximum concentration value decreases with an increase in the distance from the nozzle. The maximum concentration values in the near field from the nozzle increase with an increase in the release pressure. Under five release pressures, the concentration and holding time (duration above 6% volume concentration) of Halon 1301 on the centerline of the jet meet the requirements of airworthiness provisions.     

Evaluation of hazard range for the natural gas jet released from a high-pressure pipeline: A computational parametric study

In the present study, the hazard range of the natural gas (NG) jet released from a high-pressure pipeline was investigated. A one-dimensional integral model was combined with a release model to calculate the length and width (i.e., size), and the shape of NG jet release. The physical parameters affecting the jet release of NG were categorized into three types: source release, environmental and time parameters. The effects of each type of parameters on the gas jet release rate, size and shape were evaluated systematically. The results show that all of these parameters have important influence on the hazard range of NG jet release. The source release parameters, including the pipeline length, the operation pressure of the pipeline, the release hole diameter and the pipe diameter, dominate the gas release rate through a hole and therefore the length and width of gas jet release. The gas jet release rate and size are found to be highly correlative with these parameters in terms of power curve regression analysis. The environmental parameters including the atmospheric stability, the ambient wind speed and the source height, have no influence on the gas jet release rate but have influence on the hazard range of gas jet by the turbulent mixing and dilution of NG with air. The time parameters including the concentration averaged time and the valve closing time which are related to the unsteady state jet release of NG, also show the influence on the hazard range of gas jet release. The results show that the decreasing valve closing time and increasing gas concentration averaged time are in favor of reducing the length and width of gas jet release. In addition, these computational parametric studies indicate that the parameters of source release and time have no significant influence on the shape of gas jet release (i.e., jet length/width ratio, LWR) which can maintain the values between 7 and 8. However, the environmental parameters have influence on the shape of gas jet release. These comprehensive investigations provide useful database of evaluating the hazard range for NG jet released from a hole on a high-pressure pipeline and also provide the foundation of decision-making for further fire and/or explosion evaluation and people evacuation.     

液氨储罐泄漏扩散模型的改进研究

针对液氨储罐孔洞泄漏的实际工况,综合考虑泄漏及由于泄漏导致液氨闪蒸造成 的罐压变化,以及储罐的许用压力,对其连续泄漏过程进行了分析,以此改进现有的泄漏扩 散后果分析模型,获得较忽略这些因素更为严重的后果.最后针对灾难性事故发生前连续泄 漏最大持续时间的影响因素进行了分析.结果表明,环境温度与初始罐压对其影响较大,是决定...     

Analyzing effective factors on leakage-induced hydrogen fires

Currently, novel energy resources are receiving increasing attention as a response to the limitation in fossil fuels as well as their adverse effects on human health. Hydrogen, one of the most abundant elements on the earth, can be regarded as a new energy source to replace fossil fuels. Therefore, safety assessment of the relating processes is very crucial by increasing use of hydrogen as a fuel source. In this regard, consequence analysis for risk assessment and power reduction is very important. The present study aims at modeling hydrogen dispersion along with consequence analyses for such events as jet fire and flash fire. The model was validated by using the data derived from a study on hydrogen leakage in supply pipelines in the laboratory of the University of Pisa. Modeling results reveal that ambient conditions will impose a milder impact on leakage consequences if internal pressure is high in release source. The safe distance was also estimated to be 14 m. Dispersion consequence modeling was performed, followed by the evaluation of the effect of environmental (i.e., stability, ambient temperature, surface roughness, wind speed, and humidity) and process (i.e., vessel temperature and pressure, leakage diameter, and releasing point height) parameters on maximum size flammable vapor cloud and maximum level jet fire radiation on the ground. The size of flammable vapor cloud (consequence dispersion index) and the maximum flux of radiation were affected by process parameters more than ambient parameters. Leakage diameter and the vessel pressure were found to have the highest impact on the operational parameters.     

液化危险品储罐泄漏——扩散监测及仿真预警系统

根据国家八五科技攻关专题“易燃易爆重大危险源监控及预警技术研究”技术总结报告提供的素材，通过对危险品储罐的安全状态实时监测、建立泄漏扩散预测模型及其计算机仿真装置，构成监控危险源的预警系统，为预防重大事故、保障安全生产提供技术支撑     

Release and dispersion behaviour of carbon dioxide released from a small-scale underground pipeline

The development of carbon capture and storage (CCS) brings challenges for safety issues regarding carbon dioxide (CO₂) transmission pipelines. Once a pipeline is punctured or full-bore ruptured, the leaked CO₂ is hazardous to personnel and the environment. Small-scale devices were established with the aim of studying the release and dispersion behaviour of gas and liquid CO₂ from a punctured underground pipeline. A sandbox was built to simulate the underground conditions. The parameters of the sand used in the experiments were tested. CO₂ concentrations on the ground and temperatures around the release orifice in the sand were analysed. The results indicate that in the CO₂ gas release experiments, the CO₂ concentration on the sand surface decreases with increasing horizontal distance in the form of a power function. CO₂ concentrations in upward release are slightly larger than those in horizontal release at the same location but are obviously bigger than values in downward release. The temperature-drop region is much smaller than that in air. A frozen ice ball can be generated near the release orifice during the gas phase of the CO₂-release process. In the liquid phase of CO₂-release experiments, a large amount of dry ice is generated near the release orifice. Dry ice can only be generated in the area close to the release orifice, especially in the near-field area.     

CFD simulations of ammonia dispersion using “dynamic” boundary conditions

Ammonia is stored in liquid form at ambient temperature and under high pressure. During an accident, ammonia will flash out of the vessel and disperse in the surrounding area. This paper provides a comparison of the results obtained by the FLADIS field experiments and those of CFD modeling by Fluent 6.3. FLADIS experiments were carried out by the Risø National Laboratory using pressure liquefied ammonia. Time series of meteorological conditions as wind speed, wind direction and source strength were determined from the experimentally measured data and used as the inflow boundary conditions. Furthermore, for more realistic simulation of air flow in the computation domain for the desired atmospheric stability, periodic boundary conditions were used on both side boundaries. The initial two-phase flow of the released ammonia was also included. The liquid phase was modeled as droplets using discrete particle modeling, i.e., the Euler–Lagrangian approach for continuous and discrete phases.