Olga Aneziris

Probabilistic safety analysis in chemical installations

Abstract A set of procedures and corresponding methodologies for probabilistic safety assessment (PSA) in chemical installations is presented. State-of-the-art methodology for PSA in nuclear power plants is tested for suitability and applicability to chemical installations and applied on a refrigerated ammonia storage facility. The procedural steps comprise hazard identification, accident sequence modelling, data acquisition and parameter estimation, accident sequence quantification, hazardous substance release categories assessment, consequence assessment and integration of results. The results of the application indicate that the methodology applied is adequate from the procedural and completeness point of view and that no major aspect of PSA of a chemical installation is overlooked. A need for integrated computerized tools has, however, been identified.

Occupational risk of building construction

Abstract This paper presents the quantification of occupational risk of a building construction project. Risk assessment is based on the Occupational Risk Model (ORCA) developed under the Workgroup Occupational Risk Model project (WORM), in the Netherlands, for quantifying occupational risk. This model assesses occupational risk of a worker, by taking into account his various tasks, activities and their hazards. Risk is evaluated for three types of consequences: recoverable injury, permanent injury and death. The occupational risk model is based on a set of 63 bowties, which assess risk owing to different hazards such as fall from ladder, scaffold, roofs, falling object, struck by moving vehicle, contact by moving parts, etc. ORCA calculates the risk profile of a building construction site, consisting of thirty-eight workers in different job positions, such as operators of excavators, loaders, compaction equipment, workers in excavation and framing phases, etc. All risk profiles of workers have been quantified and jobs have been ranked according to their risk. Workers installing timber formworks have the highest fatality risk (1.57×10 −3 /yr), followed by the workers installing reinforcement (1.52×10 −3 /yr).

Technical modeling in integrated risk assessment of chemical installations

Abstract This paper presents the technical model of an Integrated Quantitative Risk Assessment method, taking into account management as well as technical design and producing risk level measures. The basic steps of the technical model consist in developing a Master Logic Diagram (MLD) delineating the major immediate causes of Loss of Containment and associated quantitative models for assessing their frequency. Appropriate management models quantify the parameters of the technical model on the basis of the safety management system of the installation. The methodology is exemplified through its application on the risk assessment of a LPG scrubbing tower of an oil refinery. A detailed technical model simulating the response of the system to various initiating events is developed, along with a detailed model simulating the influence of the plant-specific management and organizational practices. The overall effect is quantified through the frequency of release of LPG as a result of a Loss of Containment in scrubbing towers of the refinery.

On the quantification of the effects of organizational and management factors in chemical installations

Abstract The quantitative effects of organizational and management factors in chemical installations are assessed through a linking of the results of a safety management audit with the basic events of a quantified risk assessment (QRA). A safety management audit establishes the relative position of the organizational and management aspects of a particular chemical installation with respect to an ideal management scheme, and for a number of failure causes and failure prevention combinations. A quantitative risk analysis including detailed system analysis offers a plant-specific decomposition of the plant-damage-state frequencies into events like hardware failures, maintenance-related failures, operation-related failures and so on. The basic events incorporated in the QRA are then categorized into classes similar to those explored by the management audit and are quantitatively linked to the audit results. Knowledge of these quantitative links would allow for the reflection of the deficiencies or strengths that might exist in the safety management system on the quantitative risk indices. A case study of an ammonia storage facility that has been audited demonstrates that the sensitivity of the risk indices to the value of the quantitative links is extremely high and that hence great care should be exercised in assessing these links.

Uncertainty assessment in the quantification of risk rates of occupational accidents

Occupational risk rates per hour of exposure have been quantified for 63 occupational accident types for the Dutch working population. Data were obtained from the analysis of more than 9,000 accidents that occurred over a period of six years in the Netherlands and resulted in three types of reportable consequences under Dutch law: (a) fatal injury, (b) permanent injury, and (c) serious recoverable injury requiring at least one day of hospitalization. A Bayesian uncertainty assessment on the value of the risk rates has been performed. Annual risks for each of the 63 occupational accident types have been calculated, including the variability in the annual exposure of the working population to the corresponding hazards. The suitability of three risk measures-individual risk rates, individual annual risk, and number of accidents-is examined and discussed.

On the management of severe chemical accidents DECARA: A computer code for consequence analysis in chemical installations. Case study: Ammonia plant

Abstract A computer package is presented for the integrated risk assessment of accidental releases of hazardous substances. DECARA provides an integrated risk analysis including source-term strength evaluation, estimation of the hazardous cloud dispersion and quantification of health impacts. Multiple accidents, each with a certain probability of occurrence can be handled. Dispersion of heavier as well as lighter-than-air gases released instantaneously or continuously, can be simulated. Time-varying release rates are possible. Uncertainty analysis can be performed including both parameter and modelling uncertainty. The code calculates the unconditional fatality probability at any point around the site of release. Isorisk curves or maximum individual risk versus distance from the source can be generated. The computer package is portable and available for running in personal computers.

Accident sequence analysis for sites producing and storing explosives

This paper presents a QRA-based approach for assessing and evaluating the safety of installations handling explosive substances. Comprehensive generic lists of immediate causes and initiating events of detonation and deflagration of explosive substances as well as safety measures preventing these explosions are developed. Initiating events and corresponding measures are grouped under the more general categories of explosion due to shock wave, explosion due to mechanical energy, thermal energy, electrical energy, chemical energy, and electromagnetic radiation. Generic accident sequences are developed using Event Trees. This analysis is adapted to plant-specific conditions and potentially additional protective measures are rank-ordered in terms of the induced reduction in the frequency of explosion, by including also uncertainty. This approach has been applied to 14 plants in Greece with very satisfactory results.

Risk-informed selection of a highway trajectory in the neighborhood of an oil-refinery

A methodology for characterizing alternative trajectories of a new highway in the neighborhood of an oil-refinery with respect to the risk to public health is presented. The approach is based on a quantitative assessment of the risk that the storage facilities of flammable materials of the refinery pose to the users of the highway. Physical phenomena with a potential for detrimental consequences to public health such as BLEVE (Boiling Liquid Expanding Vapor Explosion), Unconfined Vapor Cloud Explosion, flash fire and pool fire are considered. Methodological and procedural steps for assessing the individual risk around the tank farm of the oil-refinery are presented. Based on the individual risk, group risk for each alternative highway trajectory is determined.

Quantitative occupational risk model: Single hazard

A model for the quantification of occupational risk of a worker exposed to a single hazard is presented. The model connects the working conditions and worker behaviour to the probability of an accident resulting into one of three types of consequence: recoverable injury, permanent injury and death. Working conditions and safety barriers in place to reduce the likelihood of an accident are included. Logical connections are modelled through an influence diagram. Quantification of the model is based on two sources of information: a) number of accidents observed over a period of time and b) assessment of exposure data of activities and working conditions over the same period of time and the same working population. Effectiveness of risk reducing measures affecting the working conditions, worker behaviour and/or safety barriers can be quantified through the effect of these measures on occupational risk.

Risk horoscopes: Predicting the number and type of serious occupational accidents in The Netherlands for sectors and jobs

Abstract The risk of a serious occupational accident per hour exposure was calculated in a project to develop an occupational risk model in the Netherlands (WebORCA). To obtain risk rates, the numbers of victims of serious occupational accidents investigated by the Dutch Labour inspectorate 1998–Feb 2004 were divided by the number of hours exposure for each of 64 different types of hazards, such as contact with moving parts of machines and falls from various types of height. The exposures to the occupational accident hazards were calculated from a survey of a panel of 30,000 from the Dutch working population. Sixty risk rates were then used to predict serious accidents for activity sectors and jobs in the Netherlands where exposures to the hazards for sectors or jobs could be estimated from the survey. Such predictions have been called “horoscopes” because the idea is to provide a quick look-up of predicted accidents for a particular sector or job. Predictions compared favourably with actual data. It is concluded that predictive data can help provide information about accidents in cases where there is a lack of data, such as for smaller sub groups of the working population.