Scholarly article on topic 'Consequence Evaluation of Toxic Chemical Releases by ALOHA'

Consequence Evaluation of Toxic Chemical Releases by ALOHA Academic research paper on "Earth and related environmental sciences"

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Procedia Engineering
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{"Chemical leakage" / "Areal locations of hazardous atmospheres (ALOHA)" / "Emergency response planning guidelines (ERPG)" / "Immediately dangerous to life or health (IDLH)"}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — J.M. Tseng, T.S. Su, C.Y. Kuo

Abstract Incidence of chemical leakage presents a severe threat to the safety of residents in close proximity, air quality and occupational safety. And as such, the prevention and simulation of chemical leakage has become one of the most important topics in the fields of environmental protection and process safety. In this study, the areal location of hazardous atmospheres (ALOHA) models have been chosen to simulate the release of liquid and gaseous toxic substances of three unnamed plants at a chemical complex. The simulation involves the release of chlorine, epichlorohydrin, and phosgene (these three toxic substances have been chosen for their significantly larger quantities and higher threat to safety) in their storage tanks to analyze the results from the scenario for further analyses and comparisons. The results are then presented in accordance to the emergency response planning guidelines (ERPG) and corresponding immediately dangerous to life or health (IDLH) values. We discovered the spread affection scope of plant C had the higher leaking of phosgene, the next was the plant A for leaking of chlorine, and the final was the plant B for leaking of epichlorohydrin. The results were then used in the deductions of relevant analyses of consequences and risk assessments, which would be made available to the sector in the hopes of minimizing the potential impact from such incidents in the future.

Academic research paper on topic "Consequence Evaluation of Toxic Chemical Releases by ALOHA"

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SciVerse ScienceDirect Procedia

Engineering

ELSEVIER Procedia Engineering 45 (2012) 384 - 389 ;

www.elsevier.com/locate/procedia

2012 International Symposium on Safety Science and Technology Consequence evaluation of toxic chemical releases by ALOHA

J.M. TSENGa*, T.S. SUa, C.Y. KUOb

a Institute of Safety and Disaster Prevention Technology, Central Taiwan University of Science and Technology,666, Buzih Road, Beitun District, Taichung,

Taiwan 40601, China

b Department of Safety, Health and Environmental Engineering, National Yunlin University of Science and Technology, 123, University Rd., Sec. 3,

Douliou, Yunlin, Taiwan 64002, China

Abstract

Incidence of chemical leakage presents a severe threat to the safety of residents in close proximity, air quality and occupational safety. And as such, the prevention and simulation of chemical leakage has become one of the most important topics in the fields of environmental protection and process safety. In this study, the areal location of hazardous atmospheres (ALOHA) models have been chosen to simulate the release of liquid and gaseous toxic substances of three unnamed plants at a chemical complex. The simulation involves the release of chlorine, epichlorohydrin, and phosgene (these three toxic substances have been chosen for their significantly larger quantities and higher threat to safety) in their storage tanks to analyze the results from the scenario for further analyses and comparisons. The results are then presented in accordance to the emergency response planning guidelines (ERPG) and corresponding immediately dangerous to life or health (IDLH) values. We discovered the spread affection scope of plant C had the higher leaking of phosgene, the next was the plant A for leaking of chlorine, and the final was the plant B for leaking of epichlorohydrin. The results were then used in the deductions of relevant analyses of consequences and risk assessments, which would be made available to the sector in the hopes of minimizing the potential impact from such incidents in the future.

© 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Beijing Institute of Technology.

Keywords: Chemical leakage, Areal locations of hazardous atmospheres (ALOHA), Emergency response planning guidelines (ERPG), Immediately dangerous to life or health (IDLH)

1. Introduction

Industrial development in Taiwan has grown at a rapid pace and given the promising trends of economic development, the use of various chemical substances has become inevitable [1]. The use of toxic chemical substances calls for careful handling because the leak of toxic chemical substances caused by improper handling or accidents could result in the dispersion of toxins into the atmosphere, leading to severe environmental pollution and casualties. Considering the density of the population in Taiwan and its limited land size, the general public is exposed to greater threats from such incidents [24]. The petrochemical sector is driven by the manufacturing plants that produce petrochemical raw, intermediate, or final materials. Due to its massive scale of operation, sophisticated procedures and exotic processes that involve powerful chemical reactions, the odds of accidents and disasters such as explosions and fire hazards caused by the leakage of chemicals exposed to important production facilities, production procedures, storage tanks, warehouses, and public facilities in close proximity due to minor negligence are not to be underestimated. Due to the sheer size of facilities at petrochemical plants and sophisticated procedures, a substantial amount of qualified maintenance and repair manpower would be necessary to ensure the stability of manufacturing procedures. And as such, in order to prevent the disruption of production

* Corresponding author. Tel.: +886 4 2239 1647 #6860; fax: +886 4 2239 9934. E-mail address: jmtseng@ctust.edu.tw

1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.08.175

and malfunctioning of equipment/components, petrochemical corporations have adopted advanced risk assessment technologies to maintain equipment inspection quality and equipment reliability after major maintenance.

Having thorough control and knowledge of all on-going operations will help to minimize the threat of potential hazards and facilitate relevant pre-rescue preparations. From the case studies available on the Toxic Chemical Substance Declaration System [5] maintained by the EPA, one will see that the leakage of dimethylbenzene at an unnamed plant in August 2009, the leakage of phosgene at a chemical complex in November 2009 and the leakage at a water purification plant in a chemical complex in December 2009 all involved the release of toxic chemical substances. These leakages had caused physical ailments for residents in the surrounding communities and they had to receive medical assistance. In hindsight, if petrochemical plant operators had forecasted the scale of the impact beforehand, it would have facilitated the pre-rescue preparations and lessened the degree of impact of the toxic gas on the residents [6,7]. However, conventional decision making models are no longer capable of addressing these issues [8].

In this study, the ALOHA (Areal Locations of Hazardous Atmospheres) model has been chosen to simulate the scales of impact (threat zones) in the event of toxic chemical release [9]. Using three unnamed production plants located at a chemical complex in central Taiwan with operations involving toxic chemicals in liquid and gaseous states as subjects. The model is used to simulate the scale of threat zones and dispersion when chlorine, epichlorohydrin, and phosgene (these are chosen because of their relatively larger volume at these facilities and hazard levels) are released from their storage tanks.

2. Research method

2.1. ALOHA model of dispersion

The model of dispersion chosen for the purpose of this research is the ALOHA model, which has been built upon the Gaussian dispersion model of continuous, buoyant air pollution flumes [10]. The latest version of ALOHA model available is version 5.4.1 (published in February 2007). The simulation model was jointly developed by organizations including the United States Environmental Protection Agency (USEPA), Chemical Emergency Preparedness and Prevention Office (CEPPO), and National Oceanic and Atmospheric Administration Office of Response and Restoration (NOAA). In recent years, the ALOHA model has evolved into a PC assistive management software intended for rapid deployment by emergency responders. The ALOHA model of dispersion is a free application provided by NOAA (National Oceanic and Atmospheric Administration) of the United States and EPA (Environmental Protection Agency) and it is the tool for the assessment of toxic gas cloud threat zones recommended by the USEPA. The model is capable of simulating the dispersion model for over 900 chemicals and is primarily used in the simulation of accidental release of hazardous substances [11] and the dispersion of chemical vapor.

2.2. Assumptions of the simulation scenario

With the ALOHA program, manufacturing plants with operations involving toxic chemicals that met the aforementioned criteria have been chosen as the subjects of simulation to obtain the results of simulation scenario and the threat zones of toxic vapor dispersion. Based on the definitions of toxic substance storage format at the subjects' facilities shown in Table 1 and potential incidence of release, two hypothetical scenarios (I and II) have been created with environmental configurations as shown in Table 2.

3. Results and discussions

ALOHA methods was employed to simulate three toxic materials, such as chlorine, epichlorohydrin, and phosgene, these toxic chemicals have the nature hazardous characteristics for human being and environment. All of the investigation and simulation results are shown in Tables 1-3 and Figs. 1-7.

Chlorine is extensively used in industry about 12,263,257 tons, if the storage and transportation process were in loss control, the accident could be trigger in the next stage, therefore simulation results by this study was an very important information to provide the relevant staff on how many scope was affected and how to have a suitable emergency response during upset situation. Due to the leaking scope was affected by many parameters, such as air temperature, relative humidity, wind velocity, and so on, therefore this study could be use as an consult information for the decision maker in order to have the enough time to take refuge. Because, most of the accidents were caused utterly routed, the emergency response procedure could not be operated in a right track, which induced many people were fall into hazard. Results by this study should be combined with emergency response for dealing with accident in the limit time. We also had analyzed the other toxic chemicals of epichlorohydrin and phosgene, both were also had a great quantity used in industry about 956,880 and 954,588 separately.

J.M. Tseng et al. / Procedia Engineering 45 (2012) 384 - 389 Table 1. Definition of release scenario

Definition

Worst-case scenario

Other release scenarios

Storage tank

Gallon barrel or glass bottle

A storage vessel of toxic substance (filled to its maximum capacity) has been damaged in an accident, causing the release of its contents. The simulation will compute the range of toxic vapor dispersion under the assumption that the contents from the damaged vessel were released completely in 10 minutes.

Leakage of contents at the outgoing valve of A storage vessel of toxic substance (filled to its maximum capacity) caused by a faulty pipeline shaft seal. The simulation will compute the range of toxic vapor dispersion under the assumption that the source of release is equivalent to the pipeline diameter.

Pipeline diameter <2"; assuming complete rupture

Pipeline diameter between 2-4"; assuming the diameter of release to be 2" Pipeline diameter >4"; assuming 20% of the surface area as the point of release

A gallon barrel (or glass bottle) containing toxic substance has been toppled over, leading to a spill of contents from its opening. The simulation will compute the range of toxic vapor dispersion.

Table 2. Configurations of the release scenario for the simulation

Hypothetical scenario of simulation Scenario I Scenario II

Fixed parameters

Temperature (°C) Summer: 29.1; Winter: 18.5

Relative humidity 80.3%

Elevation of wind speed measurement 10 m

Total volume released 2 tons

Model of release Direct release

Elevation of source 35 m

Cloud cover 10

End time 60 min

Model Heavy gas dispersion

Terrain roughness Rural township

Manipulated parameters

Atmospheric stability level F D

Wind speed 1.5 m/s 9.5 m/s

Total duration 10 min 60 min

Source of meteorological data: (Central Weather Bureau, Taiwan, ROC, http://www.cwb.gov.tw/) Table 3. Threat zones of toxic substance release by three unnamed plants at a chemical complex in central Taiwan as computed in the ALOHA simulation

Name of Scenario I Scenario I Scenario II Scenario II

Toxin in effect

plant Threat zone in summer Threat zone in winter Threat zone in summer Threat zone in winter

ERPG-1: 8.1 km ERPG-1: 8.1 km ERPG-1: 2.2 km ERPG-1: 2.2 km

Plant A Chlorine ERPG-2: 5.2 km ERPG-2: 5.2 km ERPG-2: 1.2 km ERPG-2: 1.2 km

IDLH: 3.1 km IDLH: 3.1 km IDLH: 657 m IDLH: 645 m

ERPG-1: 5.2 km ERPG-1: 5.3 km ERPG-1: 1.3 km ERPG-1: 1.3 km

Plant B Epichlorohydrin ERPG-2: 1.9 km ERPG-2: 1.9 km ERPG-2: 396 m ERPG-2: 389 m

IDLH: 962 m IDLH: 950 m IDLH: 198 m IDLH: 194 m

ERPG-2: > 10 km ERPG-2: > 10 km ERPG-2: 4.3 km ERPG-2: 4.2 km

Plant C Phosgene ERPG-3: 6.7 km ERPG-3: 6.7 km ERPG-3: 1.8 km ERPG-3: 1.8 km

IDLH: 5 km IDLH: 5.1 km IDLH: 1.3 km IDLH: 1.3 km

Fig. 1. Plant A, Scenario I, 2 tons of chlorine, summer and winter, wind speed at 1.5 m/sec, atmospheric stability level F, southwestern and northeastern wind.

Fig. 2. Plant A, Scenario II, 2 tons of chlorine, summer and winter, wind speed at 9.5 m/sec, atmospheric stability level D, southwestern and northeastern wind.

Fig. 3. Plant B, Scenario I, 2 tons of epichlorohydrin, summer and winter, wind speed at 1.5 m/sec, atmospheric stability level F, southwestern and northeastern wind.

Fig. 4. Plant B, Scenario II, 2 tons of epichlorohydrin, summer and winter, wind speed at 9.5 m/sec, atmospheric stability level D, southwestern and northeastern wind.

Fig. 5. Plant C, Scenario I, 2 tons of phosgene, in summer and winter, with wind speed at 1.5 m/sec, atmospheric stability level F, southwestern and northeastern wind.

Fig. 6. Plant C, Scenario II, 2 tons of phosgene, in summer and winter, with wind speed at 9.5 m/sec, atmospheric stability level D, southwestern and northeastern wind level D, wind).

Fig. 7. ALOHA simulation graph (with wind speed at 7 m/sec, temperature at 21.4 °C, atmospheric stability level D, relative humidity at 83%).

Table 3 shows the results of toxic chemical release simulation for Plants A, B, and C in summer and winter. From the table, it should be evident that the dispersion of toxic vapor for Plant A in the summer of Scenario I was identical to what it would be in the winter; as for Scenario II, with the exception of IDLH dispersion in summer being greater than that in winter by 2 meters, the ERPG dispersion levels were similar. For Plant B, the ERPG-1 and IDLH dispersions in the summer of Scenario I showed discrepancies of 100 meters and 12 meters respectively compared to the winter; the ERPG-2 and IDLH dispersions in the summer of Scenario II showed discrepancies of 7 meters and 4 meters respectively compared to the winter. The dispersion of other ERPG and IDLH levels for the two scenarios and seasons were similar. As for Plant C, with the exception of IDLH dispersion in the summer of Scenario I and ERPG-2 in the summer of Scenario II having a discrepancy of 100 meters compared to their counterpart in the winter, the other ERPG and IDLH levels were consistent.

Looking at the results of simulation for Scenarios I and II, it should be apparent that given similar release conditions, the dispersion of toxic substances showed insubstantial discrepancies despite the fluctuation of temperature in different seasons. The only case of toxic vapor dispersion with a threat zone that exceeded 10 km in range in the simulation was the release of phosgene at Plant C. It is also the only case in the simulations that had the greatest dispersion distance, followed by the simulation of chlorine release at Plant A in Scenario I with a dispersion distance of roughly 8.1 km. Fig. 1 is an illustration of chlorine vapor dispersion at Plant A in the summer of Scenario I. From the figure, one can see that although the toxic vapor threat zone did not cover sensitive areas with a dense population, it could potentially affect surrounding residential areas and chemical complex with denser population with a change in wind direction in different seasons. From Fig. 1, it is evident that the threat zone of chlorine vapor released at Plant A in the winter of Scenario I has covered a large portion of the chemical complex. Refer to Fig. 2 for the results of dispersion simulation for Plant A in Scenario II; the threat zone only affected facilities that surround Plant A. Fig. 3 illustrate the result of dispersion simulation for Plant B in Scenario I; both figures revealed a situation that is similar to Plant A in the same scenario with the only difference being its smaller threat zone. However, the simulated threat zone could still affect the nearby residential area and the chemical complex with dense populations. Fig. 4 show the results of dispersion simulation for Plant B in Scenario II and based on the depictions, the threat zone would affect just the surrounding facilities. The results of dispersion simulation for Plant C in the summer and winter of Scenario I are as illustrated in Fig. 5. From both figures, it is evident that the threat zone of phosgene release has exceeded 10 km with a larger coverage over the sensitive areas. Fig. 6 show the results of dispersion simulation for Plant C in Scenario II. It is evident from these figures that in addition to affecting neighboring facilities, the threat zone would affect a portion of the surrounding residential areas.

In summary, based on the results of dispersion simulation for all three plants in both scenarios, the leak of phosgene at Plant C had the greatest threat zone, followed by the leak of chlorine at Plant A and the leak of epichlorohydrin at Plant B.

In a hypothetical scenario where phosgene is directly released into the atmosphere from an alkaline washing tower at normal temperature with a total release time of 60 minutes, wind speed at 7 m/sec, measurement elevation at 10 m, rural township terrain roughness, cloud cover at 10, temperature at 21.4 °C, atmospheric stability level D without thermal inversion, humidity at 83%, release height at 35 m in a heavy gas dispersion model. Assuming the source of release to be 500 m downwind and the concentration of phosgene reaching 0.3 ppm after an hour of release, one can deduce the disperse rate of phosgene in the atmosphere to be at 37 kg/hour, with an IDLH area of 185 m based on the results of the scenario simulation as shown in Fig. 7.

4. Conclusions

From the simulations performed using the ALOHA model, wind speed, atmospheric stability levels and total release time have been identified as the primary causes for the discrepancies in the dispersion of toxic vapor between Scenario I and Scenario II. Furthermore, from the results of dispersion in both seasons from both scenarios, with the exception of ERPG-1 level for epichlorohydrin dispersion in Scenario I and the IDLH and ERPG-2 levels for phosgene dispersion in Scenario II having a discrepancy of 100 meters in the two scenarios, the data for other simulations showed insignificant differences. From this, it would be safe to assume that the temperature had minor impact on the dispersion of the toxic substances in the scenario simulations. Results of the scenario simulations for all three plants revealed that the release of phosgene at Plant C had the greatest threat zone, followed by the release of chlorine at Plant A and the release of epichlorohydrin at Plant B. In a hypothetical scenario where the source of phosgene release happened to be 500 meters downwind with phosgene concentration reaching 0.3 ppm after an hour of release, one could deduce the rate of release to be at 37 kg/hr with an IDLH area of 185 m. These simulation results could be used as the basis for relevant effects analysis and risk assessments. If operators of petrochemical plants had performed the environmental survey at the initial stage of hazard and simulated the pattern of toxic vapor dispersion using the ALOHA model by plugging in various measurements, the statistics from the simulation would not only serve as a useful reference for the commanding officer of the rescue operation but also as a basis to notify residents in the affected areas to take necessary safety precautions to ensure the safety of their lives and properties.

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