Heavy Gas Dispersion Models Research Articles

Risk mapping of Chlorine gas dispersion from a storage plant in a dense urban area of Lahore

In recent times, with the increasing population in urban areas, the adverse events happening due to explosion and dispersion of toxic chemicals has increased. Events like toxic gas dispersion can cause severe environmental issues that endanger human safety and health. Consequence hazard modeling and vulnerable population assessment are critical to predict and minimize the losses. Chlorine is not only utilized in water treatment plants as a disinfectant, but it ca n also lead to some serious concerns to human health. In this paper, the modeling of chlorine release has been investigated for chlorine storage plant by using Heavy gas dispersion model. The modeling results showed that the cloud of chlorine is about 1.9 miles across just downwind of the release for accidental release of chlorine in the summer; however, the probability of fatality is 100 % in a whole year in a distance of 0.36 miles from the Storage Place. As a significant result, the land around the chlorination unit covering a range of approximately 1.9 miles is vulnerable in all wind directions and in the case of South-West direction of the wind, vulnerable population is highly dense, risk prevention in that region should be accounted for. Affected Population and areas at risk are calculated, which illustrates the toxically impacted areas and the population in need of immediate help and evacuation. Such studies can serve as a useful tool for decision-makers to prepare an emergency plan in case of accidental releases.

A dense gas dispersion model based on revised meteorological parameters and its performance evaluation

Heavy gas dispersion is significantly impacted by meteorological conditions. In this study, the widely-used heavy gas dispersion model SLAB is revised by using alternative parametrizations for the meteorological parameters, mixing layer height, and wind speed profile. The Nozaki method and the stability modified logarithmic wind profile evolved from the Monin-Obukhov similarity theory are adopted to calculate the mixing layer height and wind speed profile in the improved SLAB-M model, respectively. Dense gas dispersion model evaluation protocols are used to evaluate SLAB-M, and the datasets from the Jack Rabbit II (JR II) 2015 Trials are used to compare the accuracy of the simulations to observed data. The statistical performance measures (SPMs) of SLAB-M are overall a little better than that of SLAB, and SLAB-M effectively simulates heavy gas dispersion under the different meteorological conditions of the JR II 2015 Trials. Thus, it can better satisfy the requirements of consequence assessment and emergency response for the leakage and dispersion of hazardous gasses.

Modeling the effect of hypothetical chlorine leakage from Malay-Sino Chemical Industries using ALOHA software and development of an emergency evacuation route around Teluk Kalong industrial area

Malay-Sino Chemical Industries in Teluk Kalong is the largest chlor-alkali manufacturer in Malaysia, which may potentially affect the safety of plant workers and nearby residential area in the event accidental chlorine leakage. The dispersion of a hypothetical chlorine leakage from Malay-Sino Chemical Industries in Teluk Kalong industrial area was modelled using ALOHA. The effect of different wind direction, wind speed and time in the meteorological mesoscale area was evaluated. The wind speed ranging from 1.55 to 11.1 m/s obtained from a local weather station was considered. Heavy gas dispersion model was used to determine the concentration of chlorine plume within the area of concern. The leakage rate was set at 702 kg/h. The result showed that the residential area R5 (Kampung Bukit Kuang, and Kampung Sungai Terjun) is affected by the plume dispersed by northern wind at night. A greater hazard zone can be formed under the wind speed below 1.55 m/s. A suitable safety evacuation routes were proposed to reduce the risk of exposure to hazardous gas. Finding from this work is useful to understand the risk of hazardous gas dispersion around Teluk Kalong industrial area.

Influence of monsoon seasons on accidental chlorine leak and dispersion around Gebeng industrial area

This paper presents the prediction of hypothetical chlorine leak dispersion around Gebeng industrial area using Areal Location of Hazardous Atmosphere (ALOHA) software. The effect of the different wind speed and direction to chlorine dispersion in the meteorological microscale area was investigated. The wind speed ranging from 1.32 to 10.7 m/s obtained from a local weather station was considered. Heavy gas dispersion model was used to determine the concentration of chlorine plume within the area of concern. The leakage rate was set to correspond to a leakage from the chlorine tank at 792 kg/h. The result showed that the residential areas R1 and R2 are affected by the plume dispersed by southwest and northern winds, respectively. A greater hazard area was found when the wind speed is below 2.3 m/s. Meanwhile, the hazard zone reduced to nearly half when the wind speed is above 5.4 m/s. The appropriate evacuation routes were developed to reduce risk of exposure to toxic gas. Finding from this work is useful to understand the risk of noxious gas dispersion around Gebeng industrial area.

Dispersion of heavy gases - Experimental results and numerical simulations

The hazardous potential of accidental heavy gas releases, especially those involving flammable and toxic gases, is widely known. In order to predict the area in which these gases are in hazardous concentrations, an estimation of the dispersion of these gases must be carried out. While the hazardous area for flammable heavy gases is determined by the lower flammability limit (ca. >1 vol%), the release of toxic heavy gases can result in a much larger hazardous area. Toxic gases, even in very low concentrations (ca. <3,000 ppm), have the potential to be highly damaging. State-of-the-art dispersion models, such as the VDI Guideline 3783, can be used to estimate the dispersion of heavy gases. However, VDI 3783 gives no method for the prediction of the height and width of a heavy gas cloud, which are both required for quantitative risk analysis as well as for a possible coupling of a Lagrangian particle model with the VDI 3783 heavy gas dispersion model. Therefore, further calculation methods were used to describe these dimensions and were evaluated against experimental studies of the length, width, and height of the heavy and neutral gas field. In addition to that the influence of the source height on the heavy gas dispersion was also examined. © 2014 American Institute of Chemical Engineers Process Saf Prog 34: 280–285, 2015

A Review of Mathematical Models for the Atmospheric Dispersion of Heavy Gases. Part I. A Classification of Models

A Review of Mathematical Models for the Atmospheric Dispersion of Heavy Gases. Part I. A Classification of ModelsIn this two part article in its first part models of heavy gas dispersion in the atmosphere are classified and the distinguished groups of models are characterised. In the second part the procedures for the model quality evaluation are described and the main results of model evaluation projects are summarised. Substances released to the atmosphere which have a density greater than the density of the atmospheric air are called heavy gases or dense gases. The dispersion of heavy gases is different from that encountered in the case of neutrally or positively buoyant gases. Specific models have been developed to describe it. The heavy gas dispersion models differ in the complexity and mathematical description. Based on these criteria four main groups of models are distinguished: simple/empirical models, intermediate/integral and shallow layer models, advanced/Lagrangian particle trajectory and Lagrangian puff dispersion models and sophisticated/Computer Fluid Dynamics (CFD) models. This classification is an extension of the classification proposed earlier in the literature.

Sensitivity analysis of probits with respect to Quantitative Risk Assessment of airborne toxic chemicals using IITD-QRA model

This paper deals with the modification of a validated and operational heavy gas dispersion model, namely IIT Heavy Gas (IITHG) model-1, to propose a quantitative risk assessment tool named as IITD-QRA model. IITHG model-1 is modified based on the incorporation of appropriate probit equation and other necessary parameters (e.g., equipment failure rates, weather frequency, average population density etc.) to study the sensitivity analysis of various probit relationships in QRA. The large variation in risk estimates from different probits emphasises the need for cautious interpretation of risk estimates and well tested dose response curves based on experiments.

Comprehensive risk assessment and management of petrochemical feed and product transportation pipelines

Complete information is needed for comprehensive risk assessment and management of pipelines. However, obtaining information using quantitative risk assessment (QRA) (probabilistic model) is not readily possible. Thus, in this research, using probabilistic and indexing models, an algorithm is developed, which overcomes most of the limitations of the models, and is an appropriate technique for the comprehensive risk assessment and management of pipelines. For this reason, 60 feed and product pipelines of the Mahshahr Petrochemical complexes were evaluated and chlorine pipeline was selected based on high-hazard distances for risk analysis. Furthermore, the relative risk indices were also determined in all parts of the pipeline. The failure rate of the pipeline was assessed on the basis of different failure causes. Heavy Gas Dispersion Model developed by ALOHA software was used for the consequence analysis of chlorine gas in different concentrations. Subsequently, the results of the relative risk assessment indices were used as an adjusting factor to correct the pipeline failure rate and to develop an algorithm for the comprehensive risk assessment technique. Finally, sensitivity analysis of the algorithm was carried out. The present algorithm enables the identification of most of the pipeline failure causes. Application of historical incident data is not only important in risk management and emergency response plans, but is also helpful in evaluating the risk by using acceptable risk criterion, such as “as low as reasonably practicable” (ALARP).

Validation of heavy and light gas dispersion models for the safety analysis of LNG tank

This study considered many wind tunnel experiments using isothermal heavy gas and cryogenic gas of the same specific gravity as LNG, and compared the results of time-averaged concentration with those of field experiments, such as the Thorney Island Experiments (1987) and the China Lake Experiments (1987). The laboratory and field measurements agreed well, which suggests that a wind tunnel experiment can simulate important aspects of the diffusion of a cryogenic gas like LNG. These wind tunnel data were also compared with two well-known calculation models, DEGADIS and FEM3. We measured the fluctuation of concentrations for two cases with and without a building, and compared the standard deviation of concentration fluctuation with results calculated by our original numerical code of standard deviation (STD) model. The experimental and numerical results agreed well for unobstructed flows, but there were some discrepancies when a building was present. In addition to the comparison of the standard deviation of the concentration fluctuations, we compared the probability density function (PDF) produced by wind tunnel results with that predicted by a direct numerical simulation (DNS).

Heavy gas dispersion: integral models and shallow layer models

Integral models for heavy gas dispersion approximate a dispersing cloud in terms of a small number of variables; each of these is ultimately a function of an independent variable which is usually time (instantaneous releases) or downwind distance (continuous releases). This type of model is used almost exclusively in risk assessment [HSE’s risk assessment tool, RISKAT, in: Major Hazards: Onshore and Offshore, October 1992, pp. 607–638; Ann. Rev. Fluid Mech. 21 (1989) 317], but many distinct integral models exist. The code comparison exercise of Mercer et al. [CEA/AEA exchange agreement on external event. Comparison of heavy gas dispersion models for instantaneous releases: final report, Technical Report IR/L/HA/91/6, Health and Safety Laboratory, Sheffield, June 1991; J. Hazard. Mater. 36 (1994) 193] presented the results from a number of integral models in a common format; Mercer found that the range of predictions for some scenarios exceeded three orders of magnitude. Here, the TWODEE shallow layer model [J. Hazard. Mater. 66 (3) (1999) 211; J. Hazard. Mater. 66 (3) (1999) 227; J. Hazard. Mater. 66 (3) (1999) 239] is added to Mercer’s code comparison exercise. The physical assumptions used in shallow layer models differ profoundly from those used in integral models and the implications of these differences for risk assessment are discussed. TWODEE was used to simulate four representative cases considered by Mercer. In terms of cloud averaged concentration (CAC) vs. centroid position, the present model gave predictions that were consistent with the integral models used by Mercer. As the model neglects horizontal diffusion for passive clouds, overprediction at large downwind distances was expected, but not generally observed.

Development and test of an evaluation protocol for heavy gas dispersion models

In order to improve the quality (i.e. fitness-for-purpose) of models used to describe the atmospheric dispersion of heavy gas, an evaluation methodology has been developed and tested through a small evaluation exercise. This activity was carried out by the Heavy Gas Dispersion Expert Group, which was set up by European Commission's Model Evaluation Group. Its objective was to develop a protocol for evaluation of the models and to make an overview of the experimental data available for such an evaluation. The main results of the Expert Group's activities are: (i) a tested heavy gas dispersion model evaluation protocol, (ii) a list and classification of available models and (iii) a list and classification of relevant data-sets. Furthermore, it is concluded that there is a need for a more extensive evaluation exercise and that the scientific evaluation requires more attention.

The homogeneous equilibrium approximation in heavy gas dispersion models

The dispersion of heavier-than-air aerosol clouds is of great relevance to the analysis and assessment of hazards in the chemical and petrochemical industries. There are many simple mathematical models for heavy gas dispersion but, in most cases, two-phase dynamics are either ignored or treated in a very simple way, without any convincing scientific justification. In fact almost all of those models which do treat two-phase phenomena rely on the homogeneous equilibrium assumption, whether they be for jet dispersion, for gravity dominated dispersion, or for any other aspect of a two-phase release. Here the authors test the homogeneous equilibrium model against a more sophisticated aerosol approach, in the context of two-phase ammonia clouds released in dry and moist air. It is shown that the simpler model does indeed provide a good description for some envisaged release situations, and guidance is given on where the homogeneous equilibrium model is not likely to be adequate. The homogeneous equilibrium model seems to be adequate for evaluating the dispersion of heavier-than-air clouds containing droplets smaller than 100 micrometers. In this paper the dispersion model DRIFT is compared with the aerosol model AERCLOUD.

Comparison of heavy gas dispersion models for instantaneous releases

In recent years several new heavy-gas dispersion codes have been developed. Some of these were specifically based on an analysis of the Thorney Island Heavy Gas Dispersion Trials, others were developed independently of these trials. A code-comparison exercise was considered to be a valuable contribution to the validation of these codes, though no direct comparison with experimental data has been made. Results for the following codes have been obtained: denz (a number of versions), cigales, degadis, drift, eole, gastar and slab. Also, results from the Britter and McQuaid Workbook (BMW) have been included. Twenty-five cases have been considered; five release conditions in five meteorological conditions. All the releases are isothermal and near-instantaneous, with an initial gas density twice that of air. The most significant finding from this work is that there are still substantial differences between model codes. The major differences occur for releases at low wind speed, in Pasquill F stability and with a large roughness length. It is precisely for these conditions that experimental data are lacking. No statement can be made regarding which model is ‘best’, since no comparison with experimental data has been made. The question of independent model evaluation is an important one and is being addressed elsewhere.

Modelling heavy gas cloud transport in sloping terrain

A model is presented for the transport of a denser-than-air gas cloud on a slope. We discuss the structure of the model and derive detailed model equations for the special case in which the wind is directly uphill or downhill. The model was designed as a hazard analysis tool, and its com- puter implementation can be used as a subprogram in heavy gas dispersion models. We have compared model predictions with results of the Thorney Island phase I field experiments. Although these trials were conducted on flat terrain, the comparison is useful for understanding the cloud transport processes. We have also analysed numerical calculations of heavy gas cloud dispersion on a slope.

Estimation of Vulnerable Zones Due to Accidental Release of Toxic Materials Resulting in Dense Gas Clouds

Heavy gas dispersion models have been developed at IIT (hereinafter referred as IIT heavy gas models I and II) with a view to estimate vulnerable zones due to accidental (both instantaneous and continuous, respectively) release of dense toxic material in the atmosphere. The results obtained from IIT heavy gas models have been compared with those obtained from the DEGADIS model [Dense Gas Dispersion Model, developed by Havens and Spicer (1985) for the U.S. Coast Guard] as well as with the observed data collected during the Burro Series, Maplin Sands, and Thorney Island field trials. Both of these models include relevant features of dense gas dispersion, viz., gravity slumping, air entrainment, cloud heating, and transition to the passive phase, etc. The DEGADIS model has been considered for comparing the performance of IIT heavy gas models in this study because it incorporates most of the physical processes of dense gas dispersion in an elaborate manner, and has also been satisfactorily tested against field observations. The predictions from IIT heavy gas models indicate a fairly similar trend to the observed values from Thorney Island, Burro Series, and Maplin experiments with a tendency toward overprediction. There is a good agreement between the prediction of IIT Heavy Gas models I and II with those from DEGADIS, except for the simulations of IIT heavy gas model-I pertaining to very large release quantities under highly stable atmospheric conditions. In summary, the performance of IIT heavy gas models have been found to be reasonably good both with respect to the limited field data available and various simulations (selected on the basis of relevant storages in the industries and prevalent meteorological conditions performed with DEGADIS). However, there is a scope of improvement in the IIT heavy gas models (viz., better formulation for entrainment, modification of coefficients, transition criteria, etc.). Further, isotons (nomograms) have been prepared by using IIT heavy gas models for chlorine, which provide safe distance for various storage amounts for 24 meteorological scenarios prevalent in the entire year. These nomograms are prepared such that a nonspecialist can use them easily for control and management in case of an emergency requiring the evacuation of people in the affected region. These results can also be useful for siting and limiting the storage quantities.

Vulnerability analysis for airborne release of extremely hazardous substances

This study deals with the important key ingredients of risk assessment pertaining to vulnerability analysis in respect of accidental release of the hazardous materials and industrial siting and planning. A wide range of mathematical modelling techniques ranging from very crude to sophisticated heavy gas dispersion models have been discussed and compared. Case studies have been undertaken for the recent industrial accidents in India with the help of appropriate mathematical models developed for this purpose. Simulations have also been performed under worst meteorological conditions for the accidental release of toxic material such as chlorine(Cl 2) stored at an industrial site. The role of meteorology and dispersion modelling is shown for industrial siting and planning. Also intercomparison is made in respect of various operational models (for dispersion of toxic chemicals due to accidental release in the atmosphere) by simulating the dispersion scenario due to the recent industrial accident in Chembur, Bombay resulting in the spillage of 2 t of Cl 2. The paper ends with the current practices in the quantification of health hazards and with the specific issues where more research is needed.

Comparison of thorney island data with heavy gas dispersion models

The major objectives of this work were to provide information on the dispersion of large-scale instantaneous releases of heavier-than-air gases and to

Development and application of heavy gas dispersion models of varying complexity

The data which has been obtained from the Thorney Island trials has already been put to good use in model validation and development. This paper demons

Heavy gas dispersion models

This paper reviews fifteen current mathematical models for the dispersion of accidental releases of heavy gases until they dilute with air to non-flammable or non-toxic concentrations. The models are broadly classified into K-theory models (5 in number) and slab models (10 in number). In addition, 4 jet release models are given that can describe elevated releases of heavy gases.For each model, a description is given of the mechanistic features claimed, the applicability to differing types and geometries of release, the ease of availability to users, and the degree to which calculated results have been compared with field data. To facilitate comparison, these characteristics are listed in a common tabular form for each model.

Heavy gas dispersion model with liquified release

A model simulating liquified gas release, evaporation and dispersion of the resulting heavy gas cloud simultaneously is obtained by slightly modifying Eidsvik's (1980) heavy gas dispersion model.