A Framework of Dynamic Risk Assessment and its Evolution Forecast of Hazardous Chemicals Accidents Shuxia LI School of Business, East China University of Science & Technology; Department of Industrial and Operations Engineering, University of Michigan Shanghai, 200237, China; Ann Arbor, MI48109, USA Jie LI School of Business, East China University of Science & Technology Shanghai, 200237 and Hongbo SHAN * College of Mechanical Engineering, Donghua University Shanghai, 201620 ABSTRACT Once hazardous chemicals accidents occur, the damage to the society is often enormous, as well as the threat to our living environment. risk and its dynamic evolution process should be scientifically assessed and predicted to effectively control and prevent the enlargement of accident risk. A framework for dynamically assessing and predicting evolutionary environmental risk and prediction of hazardous chemicals accidents is presented. Considering the intrinsic complexity, strong mobility and high uncertainty of hazardous chemicals accidents, the challenge of key environmental risk factors analysis and uncertain environmental risk modeling in term of environmental vulnerability, exposure intensity and uncertainty are presented firstly. Then, the need and associated problems of dynamic assessment of environmental risk from the viewpoint of natural and controlled diffusion is proposed. And three-level risk evaluation scheme, namely, unit level, space level and system level is put forward, which depends on different affecting space and evolution mechanism. Furthermore, environmental risk evolution track and prediction model under this framework are discussed. This study will provide useful decision support and theoretic and methodological guidance for environmental control and emergency planning of hazardous chemicals accidents. Keywords: Hazardous Chemicals, Risk, Risk Model, Risk Assessment, Risk Evolution Prediction. 1. INTRODUCTION According to European Chemicals Bureau, the current European Inventory of Existing Commercial Chemical Substances (EINECS) contains 100,204 substances, including nearly 2500 high production volume chemicals. The production and * Corresponding author, hbshan@dhu.edu.cn. development of chemicals have vastly improved the status of modernists. However, the hazardous property of chemicals pose threat to human s living environment, especially the accidents that occur during the production, administration, storage, use and handling of hazardous chemicals. Although efforts have been made to address the security issues in each phase in the whole lifecycle of chemical producing, chemical accidents still occur frequently. With the high speed economic development, China is experiencing high chemical accidents occurrence, which due to China s manufacturingoriented economic development model. During 2000~2006, 11,706 chemical accidents causing environmental pollution and destroy in China were reported, among which the amount of accidents in 2006 reached 842 [1]. When the chemical accidents occur, much attention should be paid to the emergency response and cutting losses. Besides, the control of environmental hazard urgently needs more attention. risk and its dynamic evolution process should be probably assessed and predicted to prevent the enlargement of accident risk, thus keep hazardous chemicals from entering into the environment, which does harm to people s health and the whole environment. It is no doubt that dynamic environmental risk assessment and evolution prediction of hazardous chemicals accidents is the basis of safety transportation decision and the key of accident warning and emergency rescue. More importantly, it is the significant means to minimizing the risk and losses, and protection our environment. 2. THE STATUS OF CURRENT RESEARCHES Current researches of risk assessment and prediction on accidents caused by hazardous chemicals mainly focus on such aspects as the description, assessment method, dynamic analysis and diffusion simulation of the environmental risk. However, current literatures put more attention to the polluting features of the chemicals themselves, and researches focusing on the range of pollution or the hazard assessment to the environment including the eco system are insufficient. Moreover, key points
of most of the researches are toxicity of chemical pollutants, rather than the risk of the accidents caused by hazardous chemicals with high polluting power and randomness [2][3][4][5][6][7]. In China, the risk management of hazardous chemical accidents is still leaning on the quantitative assessment, pre-warning and the formulation of contingency plan on personal risk, social risk and ecological security. The quantitative assessments of the environmental risk are conducted primarily at municipal and regional level, being imperfect in systematic methods [8][9][10][11][12][13][14][15]. The former two (the aspects of the description and the assessment method of the environmental risk) are more systematic no matter in theory or practice than the other two aspects, and they do give hints for us to conduct researches relevant with environmental risk assessment in China. For example, Bryant assessed the danger of chemical accidents on human beings and the environment with GIS techniques and established further a risk index model [16]. Additionally, with the support of the database of properties of the chemicals and environmental resource information, the model conducts analysis on features of the local pollution of spilling chemicals on land to the human health, underground water, surface water and soil resource, and provides relevant decision support for different decision makers. Taking the dynamic complexity of accident into account, Goh, Brown et al. proposed to conduct assessment of accident risk from the angle of systematic consideration, utilizing the method of causation circuit and basing on the mutual actions of roles of different spatial and temporal dimensions [17]. Zhang, Wu et al. used four kinds of event trees to set up models for most release accidents of chemical factories in design stage and conducted assessment of accident risk through uncertainty analysis, model transformation and mathematical computation [18]. Fortunately, more attention has been paid on the latter two fields, namely, the dynamic analysis and diffusion simulation of the environmental risks. However, the researches on them are usually conducted independently. For example, relative researches have been conducted aiming at the toxic gas in static facilities and in transport process, and considering factors such as release level, wind direction atmospheric stability, temperature, time and region, which include establishing random dynamic diffusion model and developing risk assessment software pack that capable of computing safe distance and personal and social risk [19]. Also, I and Cheng proposed a method to combine calculable fluid dynamics and 3D simulation, which is different from the traditional diffusion modeling and consequence analysis method that need complex computation and tend to exaggerate the risk [20]. With the support of relevant chemical and geographic databases and GIS technique, Bryant conducted dynamic computation and demonstration on environmental risk under different conditions using the overall consideration of the pollution property and transferability of the chemicals themselves [16]. All above shows that researchers have offered various useful modules and methods for reference. However, current researches have not identified enough the critical risk factors of hazardous chemical accidents. Compared with the researches of dynamic risk assessment with the purpose of the precaution against hazardous chemical accidents, the researches of dynamic assessment of environmental risk after accidents occur are relatively less, not to mention the researches on uncertainty risk with the combined methods of risk assessment and evolution prediction. Apparently, one of the reasons is that after hazardous chemical accidents occur, the intervention of human emergency rescues are uncertain, and are difficult to be included into risk assessment. On the other hand, environmental system is a complex one, how risk develops and evolves under the mutual action of other subjects is yet to be discussed thoroughly. It can be seen that effective environmental risk assessment should integrate evolution analysis and risk assessment together to focus on the dynamic of the environmental risk. So, it is of great significance to conduct research on dynamic risk assessment and evolution prediction of hazardous chemical accidents. Accordingly, centering on the issue of the environmental risk assessment and evolution prediction of hazardous chemical accidents, this paper gives a multiple-factory analysis on environmental risks first. Then, multiple-dimension environmental risk assessment system is established, and the dynamic evolution rule of environmental risk of hazardous chemical accidents and its dynamic assessment method are investigated as well. In this way, the systematic framework of environmental risk assessment and evolution prediction of hazardous chemical accidents is formulated at last. This framework and the proposed relative methods will provide detailed model construction and analysis process of risk conditions to different decision-makers and support them with the key elements they really care. 3. THE FRAMEWORK OF ENVIRONMENTAL RISK ASSESSMENT AND ITS EVOLUTION PREDICTION OF HAZARDOUS CHEMICAL ACCIDENTS To establish the system of environmental risk assessment and evolution prediction of hazardous chemical accidents, the following aspects should be considered: 1) The model construction of environmental risk of hazardous chemical accidents; 2) The dynamic environmental risk assessment of hazardous chemical accidents; 3) The model of environmental risk evolution prediction of hazardous chemical accidents. There exists a problem that the environmental risks are difficult to be integrated in a quantitative assessment model because the data of environmental disaster in hazardous chemical accidents is hard to acquire, and environmental risk factors are multiple. As a result, researchers tend to get conservative assessment results and couldn t provide the decision-makers with the adequate risk evaluation, which cause great difficulty in communication inconvenience. Along with the perfection of relevant systems of accident report and the execution of environmental protection strategy, it is necessary and feasible to integrate the hazardous chemicals, the population surrounding, relevant ecological environment and facilities as a whole system to establish multiple-dimension environmental risk assessment system of hazardous chemical accidents and conduct process-oriented environmental risk assessment from the viewpoint of risk evolution analysis. Figure 1 is a rudimentary design of the framework of this system.
Uncertain Information Adequate and Accurate Acquisition of Information Resource Model Construction of Uncertain Risk Toxicity of Chemicals The vulnerability of the Ecological Environment intensity Probability Subjective Uncertainty of Human Beings Natural Diffusion The Diffusivity and Permeability of Chemicals Dynamic risk assessment based on Cell and Space Dynamic Risk Assessment Controlled Diffusion Human Emergency Rescue Activity System Dynamic risk assessment integrating human risk decision making Risk Evolution Prediction Risk Evolution Track Model Transform Factor Sensitivity Analysis Risk Evolution Prediction Model Level vulnerability Control Level Evolution Track Risk Manager Grounds for Preventive Decisions Visibility Transparency Figure 1. The framework of environmental risk assessment and its evolution prediction of hazardous chemical accidents The identification of uncertain factors The influence of uncertain factors is prominent to increase the difficulty of the assessment of environmental risk. The uncertainty lies in the following aspects: The uncertainty of source information acquisition. Many environmental disasters and risks are not immediately discovered after accidents occur. There is a process of continual evolution of risk. The environmental risk assessment system requires a high accuracy and adequacy information acquisition. Only comprehensive control information resource can strengthen the handling ability after accidents occur. More importantly, the environmental risk prediction ability will be increased to win precious time to control further development of the accidents and perform effective handling. Therefore, with the precondition of uncertain acquirable information, current risk assessment framework could not support dynamic assessment of environmental risk after accidents occur. The dynamic evolution characteristics of risk. After accidents occur, the environmental risk dynamically changes along with the advancement of time. Out of mutual actions of multiple factors such as human beings, the evolution features and rules of hazardous chemicals in environmental protection become complex and uncertain. The complexity of multi-media and changeable environment risk. The diversity and changeability of the environment including living beings brings intrinsic complexity to the environmental risk assessment. When disposing this aspect of uncertainty, issues of the public, the society and the morality must be considered comprehensively. And, the dynamic evolution process of the environmental risk under the interaction of multiple subjects, especially human beings, should be investigated in order to provide proper grounds for preventive strategy decision of risk managers. The environmental risk modeling of hazardous chemical accidents There are multiple types of chemicals that bring harms in hazardous chemical accidents, and they differ a lot in influencing scope and levels on human beings and environmental subjects. As a result, the identification and description of the environmental risk of hazardous chemical accidents is the foundation for its assessment and prediction. However, current risk assessment models have difficulty in addressing the uncertainty information of the environmental risk and consequently need additional considerations in handling the description of environmental risk. In this paper, several aspects are considered in risk modeling as the follows: The analysis of key environmental risk factors in the hazardous chemicals accidents. With the support of the
database of hazardous chemicals and their accidents, a method combining Delphi with AHP should be used to systematically analyze not only the environmental risk factors such as air, sediment, soil, surface water, groundwater, animals and plants, human beings and their weights, but also the vulnerability of several typical hazardous chemicals accidents. The model of environmental risk exposure in the hazardous chemicals accidents. Through the identification of uncertain factors and the information of geographic environment, the aftermath of different accidents should be analyzed to establish a model of environmental risk exposure. Giving the emergency and the randomness of the accidents, the model should include the different intensity of environmental risk exposure. The multi-dimension uncertain environmental risk model. Basing on the diversity of hazardous chemical accidents and the complexity of environmental subjects, the environmental risk model needs to consider uncertain risk information (especially the subjective uncertain information of human beings) including such factors as the intrinsic toxicity of the chemicals, the vulnerability of the ecological environment system, the exposure level, exposure probability and so on. Then, a multidimension uncertain environmental risk model of hazardous chemical accidents is built accordingly. The dynamic environmental risk assessment of hazardous chemical accidents Due to the intrinsic mobility of the chemicals (such as diffusivity and permeability, etc.) and the direct or indirect activities of emergency rescue activities and other affecting elements in the system (for example, the food chain), the environmental risk will differ along with time and space. So, to track the environmental risk of hazardous chemicals quickly, the dynamic transformation rule of the environmental risk of hazardous chemical accidents shall be described. Considering the two diffusion modes in different hazardous chemical accident conditions, researches need to be carried out from two aspects: the natural diffusion of hazardous chemicals in the environment and the controlled diffusion of them when there are human interventions (e.g. the emergency rescue activities). The environmental risk evolution forecast of hazardous chemical accidents. Because there are mutual interactions between human beings and ecological environment, high uncertainties of the environmental risk evolution track of hazardous chemical accidents are unavoidable. The prediction on future evolution trend of the environmental risk of hazardous chemical accidents should include contents of the following two aspects: The risk evolutionary track model of hazardous chemical accidents. The sensitive points of reached targeting at dynamic environmental assessment of hazardous chemical accidents can further describe quantitatively the critical evolutionary track of environmental risk of the hazardous chemical accidents. The prediction model of the dynamic evolution of the environmental risk of hazardous chemical accidents. The main input parameters referred here shall include exposure level, environmental probability, density of exposed people, control level and risk evolution track. Meanwhile, the process of the risk evolution track and the prediction model of the environmental risk should be given in a transparent and visible form. 4. CONCLUSION There are high uncertainties on each stage of the environmental risk assessment process of hazardous chemical accidents. While current assessment on environmental risk is just limited in the loss property caused by the hazardous chemicals themselves. There are few researches intensively enough on the range of pollution or the hazard assessment to the environment, especially the eco system. And, the real-time dynamic assessment of environmental risk after an accident occurs is seldom supported by the existing assessment system. Therefore, the influencing factors of environmental risk must be considered systematically to establish a dynamic risk assessment system, in which, the interactions between human beings and environment are considered and the dynamic uncertain evolution characteristics of environmental risk are properly discovered and modeled. In this way, the proposed framework can handle the uncertain risk information and take the emergency rescue activities of people involved and the evolution rule of the environmental risk into account, which will provide decision support for different risk management people. 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