Risk Assessment Technology and its Application to Tanker Based Floating Production Storage and Offloading (FPSO) Systems
Authors: Nesje Jon D. , Aggarwal Rajiv K. , Petrauskas Chuck , Vinnem Jan E. , Keolanui Gus L. , Hoffman Joe , McDonnell Robert 
Published: October 2008

This paper is prepared based on work performed in a Joint Industry Project (JIP) on "Risk and Reliability of a FPSO System in Deepwater Gulf of Mexico". The background and JIP objectives and the overall issues are discussed in detail in a companion paper [1].

The key elements of the risk assessment technology are presented and the methodology applied in the JIP is described. The qualitative and quantitative methods that are being used to assess FPSO risks are presented. The application of risk assessment technology from concept development stage of a project to its detailed engineering and operation phases is identified. The current developments in risk assessment technology and improvements are identified.

The risks addressed cover those originating from subsea releases from risers and flowlines, leaks from process systems possibly causing fires and explosions, crude oil storage tanks and engine rooms, offloading to shuttle tankers, collisions with different types of vessels, and escape and evacuation operations. The major issues for certain hazardous incidents and the evaluation of risks from their escalation are presented. Numerical results are provided in a very limited way. A companion paper [2] presents details of the quantitative evaluation of the risks to the FPSO due to collisions from other vessels.

Introduction and Background

Risk assessment techniques have proved to be a useful tool to help in decisions and management of risks in different industries. Probabilistic Risk Assessment (PRA) has been used to quantify and minimize the risk of core damage in nuclear power plants. In the chemical industries, particularly in Europe after the Flixborough and Seveso disasters in 1974 and 1976 respectively, Quantitative Risk Assessment (QRA) has been used extensively, mainly to identify and quantify the risks to neighbors/third party.

Risk assessment in the offshore industry dates back to the mid 1970s when the Norwegian Petroleum Directorate (NPD) issued regulations requiring risk evaluation for offshore drilling and production platform, when provided with living quarters. Later, in 1981, NPD's Guidelines for Safety Evaluation of Platform Conceptual Design drew a distinction between survivable "Design Accidental Events" and uncontainable "Residual Accidental Events", and set a probability limit on the totality of the latter events. In effect, this was the first regulatory requirement for proper QRA, as it is known today. In response to the NPD requirements, operators carried out series of so-called "CSE"-studies(Concept Safety Evaluations) in parallel with design development, and there were several noticeable effects on design.

Today, the NPD regulations require the operators to perform risk assessments of all projects and major modifications and to submit a Plan for Development and Operation (PDO) before giving consent to the development. The risk assessments are to cover risk to personnel as well as risk to the environment. In the PDO there is a section on risk assessment, normally including results of some early coarse risk assessments. The NPD also requires the operators to define their own risk acceptance criteria against which results from risk analyses are to be compared. There is, however, no requirement that the risk assessments are issued to the NPD, but NPD can get access to the risk assessments if they so wish. In practice, NPD has the risk assessments for all major facilities on the Norwegian Continental Shelf.