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2007_6_Nr6_EEMJ

Robu et al.

Robu et al. /Environmental Engineering and Management Journal 6 (2007), 6, 573-592 environmental competent authority to request a risk assessment with the aim at evaluating the probability of harm and at finding the possible prejudiced entities. Not every site affected by a certain pollutant will exhibit the same risk or will need the same level of remediation. The risk assessment is defined by the World Bank as being a process for identification, analysis and control of the danger appeared due to the presence of a hazardous substance into a plant. The Report from 1992 of the British Royal Society explains the sense of the definition given in the Directive European Commission 93/67/EEC, enlightening the components of risk assessment, meaning the risk estimation and calculus. In consequence, the risk assessment involves an estimation (including the identification of the hazards, the magnitude of the effects and the probability of occurrence) and a calculus of the risk (including the quantification of the danger importance and consequences for humans and/or environment). Risk assessment aims at controlling the risks produced on a site by identification of: • Pollutant agents or the most important hazards; • Resources and receptors exposed to the risk; • Mechanisms of risk accomplishment; • Important risks that emerge on the site; • General measures needed for reduction of the risk to an accepted level. The risk depends on the nature of impact upon the receptors but also on the probability of the occurrence of this impact. Identification of the critical factors that influence the relationship source-pathreceptor involves the detailed characterization of the site from physical and chemical point of views. Generally, the quantitative risk assessment encloses five stages: • description of the aim; • identification of the hazard; • identification of the consequences; • estimation of the magnitude of the consequences; • estimation of the probabilities of the consequences. Concordant to Order to 184/1997, the risk is the probability that a negative effect to occur in a specified period of time and is often described by the relation: Risk = Danger x Exposure The risk assessment implies the identification of the hazard and of consequences that may appear as a result of occurrence of the events considered as risk sources. In function of the importance of the consequences one may decide if there is necessary or not to take remediation measures. Concordant to the Order no. 184/1997, the risk quantification is based on a simple system of classification, where the probability and severity of an event are descendent distributed, being assigned with an arbitrary score: Simplified model Probability Severity 3 = high 3 = major 2 = medium 2 = medium 1 = low 1 = insignificant This model is used not only for qualitative, but also for quantitative risk assessment. Thus, the risk may be calculated by multiplying the two factors (probability, severity) in order to obtain a comparative number, for example 3 (high probability) x 2 (medium severity) = 6 (high risk). This allows the comparison of different risks. The greater the results, the bigger the priority should be given to risk control. This basic technique may be developed for allowing more serious analysis by increasing the range of the scores for classification and by considering a bigger number of improved definitions for major severity, increased probability etc. When a big number of important pollutants are considered for assessment, an increased attention should be paid to a clearer manner of presentation. It is often necessary to summarize the information as a control list or matrix. 4. Quantitative risk analysis for port hydrocarbon logistics 4.1. Brief review Over the last few decades much experience has been gained in the field of risk analysis of standard chemical or petrochemical plants. Nowadays, this knowledge is being applied to a wide range of industrial activities involving hazardous materials handling, including ports (Crowl, 2002, Gavrilescu, 2003; Robu, 2005). Nevertheless, few works approached the application of QRA to navigational aspects and terminal operations are available, and this is to the role played by SEVESO II Directive. This method allows quantitative risk analysis (QRA) to be performed on marine hydrocarbon terminals sited in ports. A significant gap is identified in the technical literature on QRA for the handling of hazardous materials in harbors published prior to this work Ports are environments often overloaded with hazardous materials, both in bulk and containerized. The method described here is proposed within a Spanish project called FLEXRIS and applied to the premises of the port of Barcelona, one of the largest ports on the Mediterranean Sea (Ronza et.al., 2006). Several risk assessment reports, made available to the public, proved to be a valuable source of information. What these works lack is an attempt at standardizing the process of risk assessment of navigation and loading operations for a generic port/terminal. 580

Methods and procedures for environmental risk assessment 4.2. QRA – method description Only liquid hydrocarbons are considered in this method. Moreover, only bulk transportation and handling are included within the scope of the research project mentioned above. The analysis covers port waters (from port entrance to berths) plus (un) loading terminals. Accidents occurring during the external approach of the tankers to the port are not take into account, nor are land accidents, such as those that can take place during storage and land transportation (within and outside the confines of the port). Finally, possible sabotage related scenarios and accidents likely to occur during tanker maintenance operations are excluded from this analysis. Instead, navigation through port waters and discharge are specifically addressed (Ronza et.al, 2006). 4.2.1. Data collection The first step is to gather the relevant data that are used further during the analysis (Fig.1). This is a very important phase and ensuring that it is carried out properly can save great deal of time and avoid rough approximations. The data needed to be collected are (Ronza et.al., 2006): • The geographical location of the port; • A detailed map of the port; • Climate data; • Technical data on berths and (un)loading locations; • Physical and chemical data for the hydrocarbon products taken into account; • Traffic data (critical for the calculation of the frequency of accidents); • Duration of (un)loading operations; • Tanker hulls; • Data about the past accidents that above occurred in the port involving hydrocarbons. 4.2.2. Scenario From a general point of view, only two basic events can cause a loss of containment during aforementioned operations: hull failure and loading arm/hose failure. For every loss of containment, two fold possibilities are considered: • In the case of hull failure, a minor as well as a massive spill; • For loading arms, partial and total rupture. In a general application, the number of scenarios is as follows: Number of scenarios = 4n+2m n being the number of hydrocarbons products traded and m the number of products bunkered (usually m=2, diesel oil and fuel oil being the bunkered fuels). 4.2.3. Frequency estimation The approach was to estimate accident frequencies on the basis of both traffic data and general frequencies from literature. This method considered that the arm scenarios are of purely punctual natures, and hull ruptures are both punctual and linear. The authors (Ronza et.al., 2006) made remark that in fact the latter nay be caused be any of the following: • An external impact (ship – ship or ship – land) while the tanker is moving towards the berth or from the berth to the port entrance (linear option); • By an external impact (ship – land) during maneuvers near the (un)loading berth or a ship – ship collision while the tanker is (dis)charging (punctual operations). The dual nature must be taken into account because while the physical effects of the accident are practically the same, their consequences on people and installations may be different. Also, it is important to calculate separate the frequencies for punctual and linear scenarios. 4.2.4. Event tree analysis The next step is to draw proper event trees and assign numerical probabilities to each of their branches. It was drown only n event trees, n being the number of hydrocarbon products analyzed. The event tree from Fig. 2 was used by authors (Ronza et.al., 2006) in the application of the method to the Port of Barcelona. 4.2.5. Consequences analysis The phenomena or quantities used by authors in the consequences analysis, needed to be modeled are: • Liquid release; • Evaporation rates • Burning rates • Pool fire radiation • Jet fire radiation • Cloud dispersion • Oil spill evaluation. Individual risk was assessed using the vulnerability correlations ((Ronza et.al., 2006). An additional criterion was adopted that is currently widely accepted: in the case of flash fires, 100% lethality was assumed for the area occupied by the portion of gas cloud in which the concentration is greater that the lower flammability limit, while outside that zone, lethality is assumed to be zero. 4.2.6. Estimation of the individual risk The societal risk was estimated by building on the general procedures. The individual risk at a point (x, y) is expressed by the following equation: 2π 6 ∫ ∑ R ( x, y) = fRF ( x, y) p( θ ) p dθ (1) θ = 0 k = 1 kθ where θ represents the wind direction, k stands for stability class, f is the accident frequency, RF kθ (x,y) the lethality function estimated on the basis of the vulnerability criteria, p(θ) the probability that the wind will blow in the direction θ and p k is the probability of the class of stability k. k 581

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