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Hydrocarbon leaks on offshore installations may result in severe consequences to personnel, to the environment and to assets. In order to prevent such leaks, it is crucial to understand their root causes. The objective of this paper is to study the circumstances of hydrocarbon leaks on the Norwegian continental shelf (NCS). In the study, all reported hydrocarbon leaks from process inventories on all offshore installations on the NCS, with an initial leak rate higher than 0.1 kg/s in the period 2008-2014, have been considered. This includes 78 hydrocarbon leaks, of which about 60 % have occurred during manual intervention on normally pressurized systems. The dominating activity when leaks occur is preventive maintenance. A significant fraction of the leaks occur during the preparation for maintenance; such a preparation is typically carried out during the night shift. About half of the leaks are associated with wellhead area and manifolds, separation and compression systems. A substantial fraction of the leaks can be associated with verification faults, dominated by the failure to comply with procedural requirements that are needed to carry out independent verification.

Summary The prevention of hydrocarbon (HC) leaks is of great importance because they are the most critical precursor events that may lead to major accidents, such as in the case of Piper Alpha. The number of HC leaks on offshore production installations on the Norwegian continental shelf (NCS) peaked just after the year 2000, with more than 40 leaks per year of an initial rate greater than 0.1 kg/s. The Norwegian Oil and Gas Association (Norwegian Oil and Gas) conducted a reduction project from 2003 to 2008, which resulted in only 10 HC leaks greater than 0.1 kg/s in 2007. The number of leaks increased in the years after 2007, and there were 15, on average, in the period 2008–2010, without any significant increase in the number of installations. Norwegian Oil and Gas started a new project early in 2011 to reduce the number of HC leaks yet further. The initiative will be completed at the end of 2013, but has already started to show promising results. A study undertaken as part of the project concluded that more than 50% of the leaks are associated with the failure of operational barriers during human intervention into the process systems. Human and organizational factors predominate with respect to circumstances and root causes. This paper presents the HC-leak-reduction project, the rationale behind it, and its main activities, which aim to reflect the operational challenges. The activities tie in closely with the results of the analysis of the leaks during the period 2008 through 2011. The single operational barrier that has failed most commonly is the verification of critical activities. The paper also discusses the risk-reduction principles in a barrier context, with an emphasis on operational barriers, as well as some of the challenges faced in the project.