The use of water sprays for mitigating chlorine gaseous releases escaping from a storage shed

Accidental releases of toxic gases in partially confined spaces, like a storage shed, can sometimes be controlled by water sprays. This paper presents the results of experimental field tests during which various water sprays were used to mitigate chlorine gaseous releases. The releases (source strength: 1–4 kg/min) simulated a loss of containment occurring at an industrial chlorine storage installation (5 m³). The mitigation performances of different water sprays were investigated for diverse configurations, and under various atmospheric conditions. The best chlorine concentration reduction was achieved close to the source by a mobile upward water spray, with a maximum concentration reduction of a factor 10 at a distance of 5 m downstream from the source, and for a release flow rate of about 2 kg/min. The good performances of a fixed downward flat fan water spray were also pointed out (mean concentration reduction of a factor 2–5 for the whole series of experiments carried out), with an optimum of effectiveness at a distance of 10 m downstream from the source. In low wind speed conditions (U₁₀<1 m/s), the downward flat fan water spray was more effective for weak release flow rates. The mitigation effectiveness by absorption remained slight (<3%).     

3-D dispersion model for simulation of accidental toxic gas releases in a metropolitan area

Computational fluid dynamic (CFD) simulations were performed to assess the potential chlorine leak scenario in the super-urban area of South Korea, where the human population density is very high and numerous buildings exist near operational water treatment facilities. Flame acceleration simulator (FLACS) was used to predict the consequence from accidental chlorine releases out of one of the water treatment facilities for the nearby area having a size of 5 km × 3 km approximately. The ability to precisely implement 3-D geometries is crucial for a successful 3-D simulation. Thus, a method was proposed to rapidly and accurately implement geometry by importing computer aided-design (CAD) files provided by a government agency, and processing them using Auto CAD and MicroStation software programs. An accidental release from an 18-ton tank was simulated with three different wind directions to determine the expected evacuation distances. Results from the study showed that the endpoint distances varied depending on the density and arrangement of the buildings. Moreover, we employed physical barriers with varying heights for mitigating the effects of toxic gas releases and simulated how effectively they decreased the concentration of released chlorine.     

Design of a system for real-time modelling of the dispersion of hazardous gas releases in industrial plants 2. Accidental releases from storage installations

This paper is the second part of a research programme concerning the modelling capabilities of accidental releases of heavier-than-air toxic gases. The existing theory, which includes the strength of the source and the subsequent development of the released cloud under representative environmental conditions, is described. Comparison of the ZZB-2 system predictions with field data from the Desert Tortoise and Lyme Bay V, ammonia and chlorine releases, shows excellent agreement at distances between ≈ 200 m and a few kilometres from the source. The correlation between observed and predicted cloud concentrations, was in all cases significant at a confidence level better than 95%.     

Cushioning the impact of toxic release from runaway industrial accidents with greenbelts

The three aspects of accidents in chemical process industries which cause most serious damage—explosions, fires, and toxic releases—can all be controlled to some extent if greenbelts are present around the affected industry. We have recently developed and validated a system of methodologies for greenbelt design. In this paper we present the application of these models in designing greenbelts and forecasting their role in cushioning the impact of accidental release of toxic gases. With properly located and designed greenbelts as much as 33% of the accidental release of SO₂, 43% of H₂S, and 51% of NH₃ under stable atmospheric conditions (in which the dispersion is very slow and the release thus has maximum toxic impact) can be absorbed.     

A dynamic approach for evaluating the consequences of toxic gas dispersion in the chemical plants using CFD and evacuation modelling

Accidental releases of toxic gas in the chemical plants have caused significant harm to the exposed occupants. To evaluate the consequences of these accidents, a dynamic approach considering the gas dispersion and behavior evacuation modelling has been proposed in this paper. This approach is applied to a hypothetical scenario including an accidental chlorine release in a chemical plant. CFD technique is utilized to calculate the time-varying concentration filed and evacuation modelling is used to obtain the evacuation routes. The exposure concentrations in the evacuation routes are calculated by using the code of data query. The integrated concentration toxic load model and probit model are used to calculate the probability of mortality of each occupant by using the exposure concentrations. Based on this dynamic approach, a new concept of average probability of mortality (APM) has been proposed to quantify the consequences of different accidental scenarios. The results show that APM decreases when the required detection time decreases or emergency evacuation mode is implemented. The impact of the detection time on APM becomes small as the wind speed increases. The effect of emergency evacuation mode is more obvious when the release occurs in an outdoor space.     

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.     

Minimizing concentrated malodorous gases from a sulphate pulp mill by applying some risk analysis methods

The significance of accidental releases has increased during the past few years. The reason for this is that the level of continuous process emission has gone down, partly due to more stringent environmental regulations and partly due to technical improvements. The aim of the study was to minimize accidental releases from a sulphate pulp mill. Some well-known methods of risk analysis were used as a tool. This article presents the application of risk analysis to reduce accidental releases of concentrated malodorous gases from a sulphate pulp mill. This particular objective was chosen not only because of the inconvenience caused by the smell but also the possible health hazards which have been of growing concern recently. In this study, risk analysis has proved to be a recommendable tool in environmental protection of sulphate pulp mills. However, only thorough advance planning before analysis begins can guarantee the most efficient and beneficial results of risk analysis. The aim of the examination and the resources available have an effect on the selection of the method and also on the level of examination.     

Heavy gas dispersion by water spray curtains: A research methodology

The mitigation of the consequences of accidental releases of dangerous toxic and/or flammable cloud is a serious concern in the petro-chemical and gas industries. Nowadays, the water-curtain is recognized as a useful technique to mitigate a heavy gas cloud. The paper presents a research methodology, which has been established and undertaken to quantify the forced dispersion factor provided by a water-curtain with respect to its configuration.

The method involves medium-scale field tests, Wind-Gallery tests and numerical simulations. These different approaches are discussed and exemplified by typical results emphasizing the observed concentration reduction due to the water-curtain.     

Quantitative risk analysis of toxic gas release caused poisoning—A CFD and dose–response model combined approach

Some major toxic gas release accidents demonstrate the urgent need of a systematic risk analysis method for individuals exposed to toxic gases. A CFD numerical simulation and dose–response model combined approach has been proposed for quantitative analysis of acute toxic gas exposure threats. This method contains four steps: firstly, set up a CFD model and monitor points; secondly, solve CFD equations and predict the real-time concentration field of toxic gas releases and dispersions; thirdly, calculate the toxic dose according to gas concentration and exposure time; lastly, estimate expected fatalities using dose–response model. A case study of hydrogen sulfide releases from a gas gathering station has been carried out using a three dimension FLUENT model. Acute exposure fatalities have been evaluated firstly with a simplified ideal model which assumes workers stay at original exposure location without moving. Then a comparison has been made with a more realistic model which assumes workers start evacuating according to a prearranged course as soon as hydrogen sulfide detection system alarms. These two models represent the worst and best emergency response effects, respectively, and the analysis results demonstrate significant differences. Results indicate that the CFD and dose–response combined approach is a good way for estimating fatalities of individuals exposed to accidental toxic gas releases.     

Transient large-scale chlorine releases in the Jack Rabbit II field tests: Rainout source data analysis from video records

Sponsored by the U.S. Department of Homeland Security Science & Technology (DHS S&T) Chemical Security Analysis Center (CSAC), the U.S. Department of Defense (DoD) Defense Threat Reduction Agency (DTRA), Transport Canada, and Defence Research and Development Canada (DRDC), the Jack Rabbit II tests were designed to release liquid chlorine at ambient temperature in quantities of 5–20 T for the purpose of quantifying the behavior and hazards of catastrophic chlorine releases at scales represented by rail and truck transport vessels. In 2015, five successful field trials were conducted in which chlorine was released in quantities of 5–10 tons through a 6-inch circular breach in the tank and directed vertically downward at 1 m elevation over a concrete pad. In 2016, three additional trials were conducted with releases of 10 tons also through 6-inch circular breaches at different release orientations. A final 20 ton test was conducted in 2016. Data from the test program is available. This paper summarizes an analysis of the available data from the concrete pad including analysis of the temperature measurements above and below grade in the concrete pad. Assessment of the chlorine rainout is estimated based on temperature measurements and available video data analysis.     

Environmental risk mapping of accidental pollution and its zonal prevention in a city

Accidental releases of pollution can have severe environmental, societal, economic, and institutional consequences. This paper considers the use of risk mapping of accidental pollution events, and zonal prevention measures for alleviating the impact on large urban areas. An Environmental Pollution Accident Risk Mapping (EPARM) model is constructed according to a mapping index system supported by quantitative sub-models dedicated to evaluating the risk arising from different sources of potential accidental pollution. The EPARM approach consists of identifying suitable indexes, assessment of environmental risk at regional and national scales based on information on previous pollution accidents and the prevailing environmental and social conditions, and use of GIS to map the overall risk. A case study of pollution accidents in Minghang District, Shanghai, China is used to demonstrate the effectiveness of the model. The paper also proposes a systemic framework for accidental environmental pollution risk prevention, and detailed countermeasures for specific risk zones.     

Assessing the influence of real releases on explosions: Selected results from large-scale experiments

The research activities in the project Assessing the Influence of Real Releases on Explosions (AIRRE) included a unique series of large-scale explosion experiments with high-momentum jet releases directed into congested geometries with subsequent ignition. The primary objective for the AIRRE project was to gain improved understanding of the effect that realistic releases and turbulent flow conditions have on the consequences of accidental gas explosions in the petroleum industry. A secondary objective was to develop a methodology that can facilitate safe and optimal design of process facilities. This paper presents selected results from experiments involving ignition of a highly turbulent gas cloud, generated by a large-scale, pressurised release of natural gas. The paper gives an overview of the effect on maximum explosion overpressures of varying the ignition position relative to the release point of the jet and a congested region placed inside the flammable cloud, with either a high or a medium level of congestion. For two of the tests, involving a jet release and the medium congestion rig, the maximum overpressures significantly exceeded those obtained in a quiescent reference test. The paper presents detailed results for selected tests and discusses the effect of the initial flow field generated by realistic releases – including turbulence, net flow and concentration gradients – on relevant explosion phenomena.     

Control of accidental releases of hydrogen selenide and hydrogen sulphide in the manufacture of photovoltaic cells: a feasibility study

Industrial and regulatory communities are concerned about the need to control routine and accidental releases of toxic gases. This paper outlines an approach for evaluating control systems for new technologies when there is only limited experience. The approach is illustrated by identifying and evaluating specific options to control releases of hydrogen selenide (H₂Se) and hydrogen sulphide (H cells. Routine emmisions can be controlled with a system composed of a Venturi scrubber, a packed-bed scrubber, and a carbon adsorption bed. Accidental releases can be controlled by the proper design of a ventillation system combined with either a Venturi and packed-bed scrubber and carbon-a or a containment-scrubbing equipment followed by carbon adsorption. The annualized costs of these controls (≈$0.01/Watt-peak (W_p)), are small compared with current (≈$6/W_p) and projected (≈$1/W_p) production costs. Thus, systems which could control accidental releases of highly toxic H₂Se and H₂S in CuInSe₂ photovoltaic cell manufactu These systems can effectively reduce emmisions of toxic gas to levels needed to protect the health of the public.     

A transportation network assessment tool for hazardous material cargo routing: Weighing exposure health risks,proximity to vulnerable areas,delay costs and trucking expenses

The inherent risks associated with accidental releases of hazardous materials during transport have drawn attention and concerns in the recent decades. The aim of this study is to propose a tool for evaluation and comparison of the transportation networks which can be used to assess the routing options between origins and destinations of the cargos for their suitability for transporting hazardous material cargos by tanker trucks and to identify routes which provide lower accidental release risks, lower public exposure risks, and offer economical benefits. Each route segment of transportation networks were evaluated using specific criteria which included health risk and cost of delay in case of an accidental release of materials, trucking cost and proximity to vulnerable areas. Since, the health impact of hazardous materials differ depending on the characteristics of the material being transported as well as release quantities and atmospheric conditions; this paper aimed in providing a tool that can be used to estimate the impact radius (for health risks) after accidental release of hazardous materials by taking into account different atmospheric conditions based on the meteorological data and solar elevation angle. The Gaussian air dispersion model paired with ArcGIS using Python programming were employed to estimate the health risk impact zones by considering the meteorological data, and accordingly to analyze road segments for cost impacts (delay and trucking costs), and the proximity to vulnerable areas. The route assessment tool was demonstrated with a case study. The results of this study can efficiently aid decision makers for transportation of hazardous materials.     

n-Compartment mathematical model for transient evaluation of fluid curtains in mitigating chlorine releases

A simple n-compartment mathematical model is developed to study the effectiveness of fluid curtains and transient behaviour in mitigating the effects of an accidental chlorine release. The model is obtained considering chemical and physical absorption effectiveness of the toxic cloud by a reacting liquid curtain. The characteristics of the curtain and the evolution were deeply studied by means of replicated wind tunnel experimental runs, according to different operating parameters. An analytical solution of the model is presented. A fairly good agreement was verified between the model predictions and the original experimental results here presented.     

Chlorine leakage from bonnet of a valve in a bullet—a case study

This paper deals with the accidental release of chlorine from bonnet of a valve in a bullet installed in a chloro-alkali industry, and the probable causes of the accident and the ensuing sequence of events. Emergency procedures are also discussed. Finally, in the conclusions reached at some useful recommendations, which has been drawn for industrial facilities handling chlorine.     

模拟装置研究绿地系统在暴雨径流污染控制中的作用

采用城市绿地和降雨系统模拟装置,研究绿地系统对实际暴雨径流污染的削减作用.历时60 min,降雨重现期为1 a、3 a、5 a时,绿地系统可以削减雨水径流量.1 a一遇时,绿地系统对雨水径流中COD、氮和磷总量的去除率分别为60.2%,49.2%和61.5%.以无植被裸土为对照,模拟绿地系统对径流雨水中COD、NH+4N及TP去除率较对照组分别提高7.1%,6.2%和4.4%.降雨期间污染物的去除主要依靠土壤和植物根系的截留、吸附和吸收作用;降雨后微生物开始降解吸附于土壤颗粒表面和植物根系上的污染物,降雨后第5～8 d,土壤中微生物数量达到最大值,第14～17 d微生物完成对吸附有机物等的降解,数量恢复到降雨前水平.研究表明, 模拟绿地对降雨地表径流量的削减、径流污染物浓度的削减和污染物总量的控制有较好作用.     

化学品突发性事故预测的不确定性分析

介绍化学品突发性事故预测的不确定性概率统计和模糊数学分析方法。对参数和模式的不确定性分别进行了讨论,计算机系统包括化学品常用数据库、事故识别模块,事故后果分析模块和不确定性分析模块,对液氯泄漏排放事故、液化气（丙烷）两相闪蒸爆炸和管道煤气（CO）泄漏伤害模式实例进行了分析。对连续源和瞬时源的讨论说明泄漏时间的确定对事故分析极为重要。     

Toxic release of chlorine and off-site emergency scenario – A case study

Release of chlorine gas causes deaths and injuries to workers and the public, resulting in the evacuation of communities and adversely affecting the environment as a whole. The off-site emergency plan is an integral part of any major hazard control system. This paper highlights some salient features of the emergency scenario from a chemical plant, which ultimately lead to fatal consequences all around upon releases of toxic chlorine gas. A typical scenario illustrating the dispersion model of chlorine (for three isopleths concentration) has been estimated by Complex Hazards Air Release Model (CHARM) software package. The enlarged form of this model diagram has been outlined on the area map of the study area for contingency planning. As a broad guide line to the district authorities for contingency planning, evacuation time has also been calculated with reference to a concentration level of 3 ppm chlorine.     

Are dispersion models suitable for simulating small gaseous chlorine releases?

Dispersion models are mostly validated on the basis of historical dispersion experiments. The latter imply large quantities of hazardous products (flammable or toxic gases), and are dedicated to study the dispersion of the resulting clouds on great distances from the source to reach a better knowledge of the different phases of gas dispersion (slumping, creeping, passive dispersion…).However, dispersion models have hardly been validated on small releases and therefore require more validation on small plumes of dangerous gases. Indeed, what is their reliability in case of accidents involving small amounts (e.g., chlorine leakages at swimming pools’ installations), and for small distances downwind the gas source? This information is of prime interest in so far as small releases are more likely to occur than larger ones.This paper reports on chlorine small-scale dispersion experiments and deals with the comparison between experimental data of ground level concentrations in the plume and predicted concentrations obtained from several dispersion models.