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2007_6_Nr6_EEMJ

Robu et al.

Robu et al. /Environmental Engineering and Management Journal 6 (2007), 6, 573-592 The environmental risk management provides a formal set of processes that constitutes the fundament for environmental decision making and support the decision factor in the steps of incertitude level minimization. 3.2. Qualitative risk assessment 3.2.1. Control list Control list, generally, identifies known, predictable risks and refer to standards. The following techniques are used: • DSF – “Diagnosis Safety Form” is based on a questionnaire containing 50 questions concerning problems related to technical equipment, environment, production planning etc. • DCT – “Diagnostique et Conditions du Travail” contains a questionnaire similar to the above described one, but in this case the evaluation is performed in three stages: good, average and poor; • SQD – “Safety Diagnosis Questionnaire” has as purpose the identification of the critical situations concerning the incompatibilities between technical and organizational conditions, on a hand, and the safety requirements of the activities, on the other hand. • MORT – “Management Oversight and Risk Three” uses a questionnaire containing around 300 questions with optional answers. It is focused on human activities and was conceived with the aim at significantly enhance the performances regarding the system safety. 3.2.2. Integral inspections of the industrial units Within current interpretation, the integral inspections emerged as a necessity to develop the measurable characteristics of the safety systems performances. These inspections give useful information on the activities concerning design, construction, starting-up, operation, closing in, disassembly and storage of the plant components. The integral inspections take places on three levels, the operators, experts and authorities having specific tasks (Gavrilescu, 2003): • constant inspection of the plant and its components operation by the process managers and inspectors entrusted with special tasks; • initial and periodic inspections at pre-established intervals by independent experts, eventually from the exterior of the system; • announced inspection of the local authorities in order to issue the working license, as well as not announced inspections. In close relation with plant inspections is the audit that represents, in broad sense, an independent investigation of the activities in field and constitutes a part of the management system of plant safety. This involves a program containing systematic questions (clearly formulated and addressed to the person responsible for plant units), answers evaluation and action plan defining. 3.2.3. Ranking Ranking refers to identification of danger sources in designing phase or comparison of the plants situated on a working industrial platform. There are thus, quantified the potential risk sources by conferring corresponding levels of importance and establishing prevention measures. 3.2.4. Preliminary Hazard Analysis (PHA) PHA focuses on the regions were hazardous materials are concentrated, as well as on the main units, monitoring the places where it is possible to result uncontrolled hazardous substances leakages or energy losses. The main considered points are: • used substances in the process and potential danger; • system units; • interfaces between system components; • environment; • system operations; • endowments; • safety equipments. 3.2.5. “What if” Method This method is based on iteration of some series of questions that lead to identification of the unexpected events with eventual unfavorable consequences and is applied on specific activity fields (Gavrilescu, 2003). A. Analysis of the faults, effects and critical states This analysis may be done at both qualitative and quantitative levels and focuses on plant/system components. It is based mainly on elaboration of a table, which contains: • equipment position, name and description; • faulting ways; • consequences; • assignment of critical coefficients on a conventional scale previously established. The algorithm of the method involves the following steps: • defining of the system; • identification of the faulting way; • analysis of the faulting causes; • analysis of the faulting effects; • analysis of the compensation possibilities; • assessment of the risk associated to each faulting way; • proposals for remediation and prevention measures. In the first stage, the main and secondary functions, the role of the components, the working related interdictions and the acceptable working limits are established; there are also elaborated the flow sheets for clarifying the interconnections between the components. 576

Methods and procedures for environmental risk assessment In the second stage, the framing within one of the following 5 faulting ways is foreseen: • blocked at zero – breaking of a connection, short-circuit; • degradation – pipe cracking, plant mechanical weakening; • intermittent switching-out –electronic elements working accidentally; • undesired secondary effect. The third stage is developed concomitant to the identification of faulting ways. The material components (technological equipments- wear and deformation) and energetic fluxes inserted by the respective component are studied. The effects analyzed in the forth stage are classified in local (at the level of the component that is damaged) and general (at the level of the whole system). The analysis of the effect compensation possibilities consists in: • reduction of the fault occurrence possibility (safety devices, preventive maintenance); • diminution of the propagation effects in the system (components doubling, signaling devices); • reduction of the consequences (use of the protective means). In the sixth stage, the assessment of the risk associated to each fault way is done in relation to the severity (G) and probability (P). The qualitative analysis assigns scores on the scale 1 - 6: For severity level: Ignorable – does not involve working accidents or material damages; Marginal – admits corrective measure for preventing the working accidents or material damages Serious – needs urgent measures Major – serious working accidents or system damages Major - serious working accidents or system damages at the company level Major – serious working accidents or system damages exceeding the company level. For the probability level: Extremely rare - p 10 -2 . In the case when combination (G – P) has the following values: 4 – 5; 4 – 6; 5 – 4; 5 – 5; 5 – 6; 6 – 3; 6 – 4; 6 – 5; 6 – 6, the risk is considered as being unacceptable. Finally, remediation measures are proposed with the aim at minimizing the risk (risk management). For unacceptable risks primary, secondary and tertiary measures are proposed (referring to the la possibilities to control the accident consequences). B. Analysis of human errors The human errors defined as mistakes, lack of concordance between perception and objective reality confirmed by the practice are inevitable and not predictable. For this reason, it is very expensive to ensure the safety due to the difficulty to anticipate the multitude of the possibilities to affect the process/plant/system safety through negligence or fatigue. However, one may apply elaborated packages of prevention measures for diminishing the human contribution to the major accidents if the type of possible error is known. A classification of the human errors could be the following: • Errors appeared due to a moment of lack of attention; • Errors owed to an improper instruction/training; • Errors owed to weak mental and physic abilities of the operator; • Errors appeared due to wrong decisions; • Errors committed by managers. 3.2.6. HAZOP method The objectives of the HAZOP (hazard operability) methods are (Crawley, 2000): • Identification of the hazard locations, • Ascertainment of the project particularities that lead to identification of the probabilities of some undesired events occurrence, • Establishment of the necessary information for design from the perspective of ensuring the plant reliability, • Initiation and development of quantitative studies related to hazard and risk. Traditionally, the safety in chemical plant design is based on designing and exploitation codes, as well as on control lists achieved by using experience and knowledge of the experts and specialists from industry. Unfortunately, such approaching may solve only existing problems. Once the complexity of modern plants increased, these traditional methods lost their importance, being considered that their application in design phase is the most recommendable (Crawley, 2000). HAZOP was elaborated as an applied technique for systematic identification of the potential hazards and operation problems in the new plants. Through HAZOP, a critical examination of the plants or processes by an experimented team is done in order to identify all the possible deviation from a certain project alongside the undesired effects on safety, operation and environment that would appear. The possible deviations are found by using rigorous questionnaires, containing key-words, applied to the analyzed project. The success or the failure of the study depends on: accuracy of the project or of other data used for the study; technical skills or experience of the team; ability of the team to use the method as 577

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