A methodology for Environmental Risk Analysis (MIRA) in the Norwegian offshore oil and gas industry has been developed, funded mainly by OLF. Previously OLF has prepared Guidelines for how to establish Risk Acceptance Criteria for the environment. According to the OLF Guidelines, the risk to the environment may be quantified using categories for consequence and frequency, shown in a matrix. A recent SPE paper has proposed an alternative way to establish the values of acceptability of environmental damage. This, new approach is taken as the starting point for the present discussion, the proposed approach being the first known logical approach to acceptance limits for risk to the environment. The suggested approach is a consistent and systematic work, but is shown to divert in some respects from established practice for management of risk in general, most extensively applied for risk to personnel. Modifications to the proposed approach are suggested in order to improve it, and thereby arrive at an approach which is consistent with current risk management principles. The alternative development of risk acceptance criteria is discussed with respect to risk aversion and use of an ALARP approach. The approach is further compared with results from some recent studies, in order to illustrate how easily acceptability may be achieved.


Risk analysis of offshore operations has been carried out for platforms in the Norwegian Sector of the North Sea, since just before 1980. The first studies were mainly associated with risk to personnel, through the analysis of risk for the so-called 'Main Safety Functions' and later through the so-called "FAR" values. In 1990, the Norwegian Petroleum Directorate (NPD) and the Norwegian State Pollution Control Authority (SFT) issued the risk analysis regulations (Ref. 1), requiring that the risk to the environment resulting from oil spill be quantified in the same way as the risk to personnel. Such estimation of risk was carried out relatively simplistically in the first years. In 1994 the OLF Guidelines for Risk Acceptance Criteria for the environment were published (Ref 2). During 1995 an OLF/DNV/Norsk Hydro sponsored development of the MIRA methodology has been carried out by DNV and Norsk Hydro (Ref. 3). A somewhat different methodology is presented in a recent SPE paper by Klovning and Nilsen (Ref 4).

The experience basis for the formulation of risk acceptance criteria for the environment comes from the use of risk acceptance criteria for personnel. It is therefore useful to consider how these criteria have been established and used, to be able to adopt a practice built on experience from risk to personnel.

The purpose of the paper is to present a new approach to definition of risk acceptance criteria for the environment. This paper presents a brief overview of the present approaches including the values of the risk acceptance criteria that are being used. An example study from a wildcat drilling project performed by Elf Norge in 1995 is presented, in order to illustrate current approaches.

A discussion of the purpose and role of risk acceptance criteria for the environment is thereafter presented, seen both in a regulatory and company risk management context. This is followed by a proposal for an alternative development of risk acceptance criteria for the environment, which aims at reaching a compromise between what is acceptable by the society and what is achievable for the industry. A brief review of the statistics relating to oil spills and environmental damage is presented as the starting point for the development of the proposed risk acceptance criteria. The results of three case studies, including the Elf Norge wildcat drilling project are compared to the proposed risk acceptance criteria, in order to illustrate how the values relate to typical results from recent studies.

The main effort in environmental risk analysis is currently placed on environmental damage from oil spills. Sometimes also the environmental effects from accidental releases of hydrocarbon gas are considered, however, that is outside the scope of the discussion in this paper.

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