Optimisation Of Fire and Explosion Protection On FPSO

Abstract

Introduction The present goal setting or prescriptive safety regimes in various parts of the world require that the design of equipment and structures of an offshore or onshore facility considers accidental loading in addition to the operation loads. Safety critical systems should function under accidental loading for a defined period of time to provide one or more of the following:–prevention of major hazard event,–control of the event, and–mitigation of the event. Requirements for safety critical systems are defined in the form of performance standards. According to Ref. 1, a "performance standard is a statement, which can be expressed in qualitative or quantitative terms, of the performance required of a system, item of equipment, person or procedure, and which is used as the basis for managing the hazard - e.g. planning, measuring, control or audit - through the lifecycle of the installation." There are high and low level performance standards. High level performance standards describe operating company's risk criteria. The confirmation that the high level performance standards are satisfied is provided by Quantitative risk Assessment (!RA). QRA uses "rule sets" to predict the effects of accidental loads on offshore facilities. In general, rule sets are based on past experience, statistics and simplistic response models, and require a great deal of human judgement. As such, they sometimes do not predict accurately enough the behaviour of systems affected by accidental loads, which often leads to over-conservatism and unnecessary costs due to severe design conditions. If the risk assessed by the QRA exceeds the high level performance standards the designer is required to provide adequate measures for the facility to resist accidental loads so that the risk can be brought withing the corporate risk criteria. These measures are expressed in the form of low/system level performance standards that describe the parameters the safety critical systems must achieve in terms of:–functionality–reliability and availability–survivability, and–dependency/interaction between systems. For risks of escalat ion of an incident, a conflict exists between over-conservative QRA rules sets that dictate the conservatism of performance standards, and the actual behaviour of equipment and structures. The thermal and strength reserves that already exist in equipment and structures would justify more realistic performance standards. This conflict normally leads to over-design and unnecessary high costs for operating companies. This Paper describes how this conflict can be avoided and summarizes typical findings of a recent study carried out for a FPSO