• dynamic risk assessment
• environmental
• gnome
• impact
• offshore
• oil and gas
• risk assessment
• risk screening matrix
• trajectory model

Offshore installations need advanced systems for monitoring, assessing and managing risks for personnel and for the environment. This issue is a priority when the installation under examination is located in an area defined as sensitive. The commonly adopted procedure for quantitative risk assessment (QRA) has a static nature, it means that it does not take into account of eventual variation in the installation risk level, which may due to several factors. Furthermore, the performances assessment of safety barrier is not carried out with systematic methods. Several tools have been developed with the aim to investigate these two aspects.
The present work deals with the analysis of an offshore installation located in a sensitive area. The analysis consists of two parts, the first focused on risk concerning the personnel on board while the other on environmental risk. In both analyses, the purpose is to show how advanced risk analysis methods are needed for this type of installation.
The risk level at which the personnel on board is subjected is evaluated through an innovative tool, the Risk Barometer. This first part of this work was carried out in collaboration with the Norwegian research institute SINTEF, where the Risk Barometer has been developed.
The Risk Barometer consists of a step procedure in which the starting point is the review of the QRA of the installation and of other relevant information sources. The purpose is to identify possible hazards and define the associated safety barriers. The information should be sufficient in order to identify a series of parameters which result determinant on the risk level. Once the protection systems are determined, their relative importance should be assessed through a sensitivity analysis. In this way, performance indicators are selected referring to the barrier elements which result to be the more influential on the installation risk level. The aim of the tool is thus to measure the status of the most critical barriers rather than focusing on the less critical ones. Furthermore, by measuring the status of a limited number of very critical barrier elements, this may provide more information about the risk level than measuring the status of a large number of non-critical barrier elements. Real-time information concerning the barrier elements defined as critical are collected and made available. These are inserted in a model, developed by the user, able to relate the performance information with the installation risk level. Through the risk model, the performance information are translated in risk variation. These variations are shown in an adequate visualization format.
The Risk Barometer is a stand-alone tool, it means that it does not modify the quantitative risk assessment of the installation under examination, but it shows how its risk level changes over rime referring to the safety barrier performances.
The second section of this work refers to a preliminary environmental risk assessment related to a possible crude oil spill from the installation. The possible release scenarios are evaluated according to standard QRA procedures (API 581). Risk assessment requires considering both the severity of consequences of a potential oil spill and its frequency of occurrence. According to API 581, four release category are assessed and for these frequency and overall inventory are evaluated. The inventories are validated through DNV Phast ® software. Severity of each scenario is assessed on the basis of oil spilt quantity and involved area. This is estimated using the General NOAA Operational Modelling Environment (GNOME) software. GNOME is a Lagrangian model able to trace the movement of a pollutant released in a water body, considering the action of winds, ocean currents and diffusion process. The level of estimated risk is then compared with tolerability criteria, through a risk matrix, in which three different regions relating to three different risk level are identified. The risk level should be acceptable for operability, in the contrary case reducing measures should be adopted.
As it is shown in the present work, offshore installation located in sensitive areas are subjected to stringent tolerability criteria. This is the reason why, additional protective barriers are needed, sometimes even highly sophisticated, to decrease the risk to an acceptable level.