Risk Assessment Of Platform Decommissioning And Removal
Authors: Kierans Lonan , Vinnem Jan Erik , Bayly David , Decosemaeker Patrick , Stemland Espen , Eriksen Thomas 
Published: December 2007

This paper is based on recent analytical work involving quantified risk analyses of both decommissioning and removal activities. The main objectives have been to evaluate the effect of the activities on the occupational risk to personnel, identify the potential for risk reducing measures, support an ALARP demonstration, assess the variation of risk to personnel groups and assess the effectiveness of barriers. In addition the approach has allowed comparison of the level of occupational risk associated with different removal options. The paper presents the methodology and data used for quantifying occupational risk. The general approach for estimating the occupational risk combines exposure man-hours with injury and fatality rates related to a breakdown of the specific activities to be undertaken. Various approaches have been used for determining appropriate FAR values depending on the type of data available for specific activities.

Results have been produced which enable the risk from various activities to be ranked, the exposure of different groups to be assessed, comparison of different removal methods to be made and estimation of the impact of barrier "integrity".

Introduction

The Norwegian Continental Shelf is entering a new phase of decommissioning and removal of platforms. The application of quantitative risk assessment techniques to analyse the whole process in order to demonstrate that the risk is reduced to ALARP is a new challenge facing field operators, engineering contractors and HSE consultants.

TOTAL E&P Norge AS (TOTAL) requested Safetec Nordic AS (Safetec) to perform a series of studies relating to the decommissioning and removal of platforms in the Frigg field. The main studies included:Risk assessment of different decommissioning options for the field installations,Risk assessment of different disposal options for one particular platform,Risk assessment of the decommissioning of all platforms in the Frigg field,Risk assessment of the removal of all platforms in the Frigg field.

The first study was relatively coarse, and assessed risk to personnel for all phases of decommissioning of the field installations, according to the options chosen.

The second study developed a model to assess the potential occupational risk to persons either directly or indirectly associated with the removal of the topside only. The risk was measured in terms of potential for loss of life (i.e. fatalities) and in terms of potential to cause serious (i.e. major) injury to a person.

The third study assessed safety during the planned decommissioning phase. This study considered the risk from both major hazards and occupational incidents and was a key element in the decommissioning safety case (referred to as the HES Master Document) submitted to the UK and Norwegian authorities.

The latest modelling approach and data are currently being used for the evaluation of options for removal of all Frigg platforms.

Objectives

The objectives of these studies have in general been to assess all sources of risk to personnel during the relevant operations. This includes risk from major hazard scenarios and occupational accidents.

For the remainder of this paper emphasis is placed on the modelling of the occupational risk associated with removal only, although the approach used for decommissioning is broadly similar. The main objectives have been to:Evaluate occupational risk from removal activities,Identify the potential for risk reducing measures,Support an ALARP demonstration,Assess the variation of risk to personnel groups,Assess the effectiveness of barriers andAllow comparison of the level of risk associated with different removal options.