Cost-based fire risk assessment in natural gas industry by means of fuzzy FTA and ETA

Fire is the most prevalent accident in natural gas facilities. In order to assess the risk of fire in a gas processing plant, a fault tree analysis (FTA) and event tree analysis (ETA) has been developed in this paper. By utilizing FTA and ETA, the paths leading to an outcome event would be visually demonstrated. The framework was applied to a case study of processing plant in South Pars gas complex. All major underlying causes of fire accident in a gas processing facility determined through a process hazard analysis (PHA). Fuzzy logic has been employed to derive likelihood of basic events in FTA from uncertain opinion of experts. The outcome events in event tree has been simulated by computer model to evaluate their severity. In the proposed methodology the calculated risk has the unit of cost per year which allows the decision makers to discern the benefit of their investment in safety measures and risk mitigation.     

An integrated methodology to manage risk factors of aging urban oil and gas pipelines

Aging urban oil and gas pipelines have a high failure probability due to their structural degradation and external interference. The operational safety of the aging urban oil and gas pipeline is challenged by different hazards. This paper proposes a novel methodology by integrating an index-based risk evaluation system and fuzzy TOPSIS model for risk management of aging urban oil and gas pipelines, and it is carried out by evaluating the priority of hazards affecting pipeline safety. Firstly, the hazard factors of aging urban oil and gas pipelines are identified to establish an index-based risk evaluation system. Subsequently, the fuzzy TOPSIS model is employed to evaluate the importance of these hazard factors and to decide which factors should be managed with priority. This work measures the importance of a hazard factor from three aspects, i.e. occurrence (O), severity (S) and detectability (D), and the weights of these three parameters are determined by a combination weight method. Eventually, the proposed methodology is tested by an industrial case to illustrate its effectiveness, and some safety strategies to reduce the operational risk of the pipeline are presented. The proposed methodology is a useful tool to implement more efficient risk management of aging urban oil and gas pipelines.     

How to treat expert judgment? With certainty it contains uncertainty!

To be acceptably safe one must identify the risks one is exposed to and decide what risk reducing measures are required. It is uncertain whether the threat really will materialize, but determining the size and probability of the risk is also full of uncertainty. When performing an analysis and preparing for decision making under uncertainty, quite frequently failure rate data, information on consequence severity or on a probability value, yes, even on the possibility that an event can or cannot occur, is lacking. In those cases, a possible way and sometimes the only way to proceed is to revert to expert judgment. Even in case historical data is available, an expert can be asked whether and to what extent such data still hold in the current situation.Anyhow, expert elicitation comes with an uncertainty depending on the expert's reliability, which becomes very visible when two or more experts give different answers or even conflicting answers. This is not a new problem, and very bright minds have thought how to tackle this in a rational and objective way. But so far, however, the topic has not been given much attention in daily process safety and risk assessment practice. Therefore, this paper has a review and applied character and will present various approaches with detailed explanation and examples.     

改进群组AHP-FCE法对路域的生态环境影响评价研究--以河南省栾川至卢氏高速公路为例

为了全面准确的评价公路建设对生态环境的影响程度,基于高速公路建设特点,从社会环境、生态环境、声环境、地表水环境、隧道对地下水环境影响及环境空气六方面构建评价指标体系,结合改进的群组AHP法,构建了改进的群组AHP-FCE相结合的评价模型,对河南省栾川至卢氏高速公路进行生态影响评价。结果表明,指标权重的比例分配更为合理客观,凸显了社会环境因素在评价中的作用,改进模型的评价结果更符合生态环境实际情况相符,表明该方法应用于生态环境评价方面具有较好的适用性和推广价值。     

Hospital site selection using fuzzy AHP and its derivatives

Environmental managers are commonly faced with sophisticated decisions, such as choosing the location of a new facility subject to multiple conflicting criteria. This paper considers the specific problem of creating a well-distributed network of hospitals that delivers its services to the target population with minimal time, pollution and cost. We develop a Multi-Criteria Decision Analysis process that combines Geographical Information System (GIS) analysis with the Fuzzy Analytical Hierarchy Process (FAHP), and use this process to determine the optimum site for a new hospital in the Tehran urban area. The GIS was used to calculate and classify governing criteria, while FAHP was used to evaluate the decision factors and their impacts on alternative sites. Three methods were used to estimate the total weights and priorities of the candidate sites: fuzzy extent analysis, center-of-area defuzzification, and the α-cut method. The three methods yield identical priorities for the five alternatives considered. Fuzzy extent analysis provides less discriminating power, but is simpler to implement and compute than the other two methods. The α-cut method is more complicated, but integrates the uncertainty and overall attitude of the decision-maker. The usefulness of the new hospital site is evaluated by computing an accessibility index for each pixel in the GIS, defined as the ratio of population density to travel time. With the addition of a new hospital at the optimum site, this index improved over about 6.5 percent of the geographical area.     

Fuzzy Application Procedure (FAP) for the risk assessment of occupational accidents

This paper concerns a procedure to quantify the risk of occupational accidents based on Fuzzy Logic approach, named Fuzzy Application Procedure (FAP). FAP was developed as a support tool, after the method based on fuzzy logic was developed and validated. The methodology and FAP support tool were found to be able to quantitatively assess the risk of occupational accidents for different industrial and site activities and to identify the most efficient intervention measures that can be taken to reduce risks. The application of FAP to two Italian industrial plant allowed the validation of the procedure. It can be seen how FAP should be considered easy to use for any type of company, with the only requirement of having a sufficient and homogeneous number of accidents recorded, so as to be able to correctly tune the reference parameters of the fuzzy methodology.     

A Conceptual Model for Defining and Assessing Land Management Units Using a Fuzzy Modeling Approach in GIS Environment

Appropriate land management decisions are important for current and future use of the land to ensure its sustainability. This requires that land management units (LMUs) be specified to enable the identification of specific parameters employed in decision making processes. This paper presents the development of a conceptual model, within geographic information systems (GIS), for defining and assessing LMUs from available biophysical information. The model consists of two main components (sub-models): land quality-based suitability analysis and soil erosion estimation. Using a fuzzy set methodology, the first sub-model was constructed to derive a land suitability index (LSI) for a cropping land utilization type. The LSI thus highlights the suitability grades of every pixel in the study area on a continuous basis. A sub-model of soil erosion was established based on the Revised Universal Soil Loss Equation (RUSLE) utilising the same spatial data bases employed for structuring the LSI. Using a soil loss tolerance principle, a fuzzy membership function of average annual soil loss (called soil loss index, SLI) was established, leading to compatibility between LSI and SLI for data integration. LMUs were then derived from various combinations of LSI and SLI. The methodology developed shows the significance of the model for refining available land suitability evaluation systems, which take no account of expected land degradation (from erosion) due to a nominated land use. It also provides a valuable guideline for cost-effective GIS applications in the identification and assessment of homogeneous land units, using available spatial information sets, at a finer scale.     

Identification of anthropogenic effects and seasonality on water quality in Daya Bay, South China Sea

Thirteen water quality parameters from 12 monitoring stations were collected to study the effects caused by climate and anthropogenic activities on water quality in 2003 in Daya Bay, South China Sea. The data matrix has been built according to the results, which were analyzed by fuzzy c-mean cluster (FCM) and cluster analysis (CA). This analysis has identified anthropogenic effects and seasonal characters of water quality. The dry and wet seasonality have been demonstrated with FCM and CA. The precipitation and the Southeast Asian monsoons, northeasterly from October to the next April and southwesterly from May to September have also an important influence on water quality in Daya Bay. In the spatial pattern, two groups have been classified with FCM and CA. Cluster I consisted of the sites S3, S8, S10 and S11 in the west and north coastal parts of Daya Bay. Cluster I is mainly related to anthropogenic activities such as fish-farming. Cluster II consisted of the rest of the stations in the center, east and south parts of Daya Bay. Cluster II is mainly related to seawater input from South China Sea. Thus, fuzzy c-mean cluster and cluster analysis can be an important tool for the successful characterization of regional-scale water quality.     

改进层次分析法与模糊综合评价的耦合模型在水质评价中的应用

对传统的层次分析法进行了改进,利用0.1～0.9五标度建立互补型的模糊判断矩阵,并把和行归一法或方根法与特征向量法结合使用,提出了改进的层次分析法与模糊综合评价的耦合模型,并将该模型应用于吴淞江(苏州段)水环境质量评价中.对评价结果的最大隶属度原则进行了改进,采用加权平均原则对评价结果综合评判与排序.     

两种模糊数学模型在土壤重金属综合污染评价中的应用与比较

依据土壤重金属污染程度的渐变性和模糊性 ,本文采用单因素决定和加权平均两种常见模糊数学模型对土壤重金属综合污染状况进行评价。研究表明 ,单因素决定模型适用于个别参评因子超标过大 ,评价出发点为希望体现单因素否决的情况 ;加权平均模型适用于各参评因子超标情况接近 ,评价出发点为希望体现各个参评因子对土壤重金属环境质量的综合影响的情况。