978-1-4577-1884-7/11/$26.00 ©2011 IEEE. Operational Risk Assessment Framework of Mobile Mooring System Silvianita PhD Student, Department of Civil Engineering, Faculty of Engineering Universiti Teknologi PETRONAS, Perak, Malaysia Department of Ocean Engineering Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia vian_nita@yahoo.com Mohd. Faris Khamidi Senior Lecturer in Department of Civil Engineering, Faculty of Engineering Universiti Teknologi PETRONAS, Perak, Malaysia Kurian V. John Professor in Department of Civil Engineering, Faculty of Engineering Universiti Teknologi PETRONAS, Perak, Malaysia Abstract—Numerous accidents have happened in all types of moored units, permanent and mobile. The problems related to mooring system failures are collision, abrasion, anchors etc. These problems have impact on people, environment, assets and reputation of the company. The objective of this paper are to determine the frequency of failure, to categorize severity of failure of mooring system and to rank the particular hazards by dividing the dimensions of frequency and severity into risk matrix. This work proposes HAZOP (Hazard and Operability) analysis to evaluate risks related to accidents in mobile mooring system. In qualitative assessment the accident risk level and acceptance criteria were established through a scoring system. The result of this methodology can be used to prevent future damage and aid to set a priority of maintenance based on hazards ranking. Keywords- Assessment. Hazards, Mooring, Operational, Risk. I. INTRODUCTION In offshore installations, the numbers of accidents have increased significantly. For example the numbers of accidents for semi submersible in 1980-1989 were 377 accidents. During 1990-2005, the numbers of accidents for semi submersible increased and became 1495. In 2000/01 alone, about 700 accidents have happened for all types of installation. Out of these, about 180 accidents were related to positioning, dropping objects and weather condition. This represents 25% of all dangerous occurrences [1]. The mooring system failures are related to mooring lines, mooring devices, winching equipment or fairleads and anchors. In the Gulf of Mexico (GoM) various moored Mobile Offshore Drilling Units (MODUs) had complete mooring system failures during Ivan, Katrina and Rita hurricanes. Since then the standards regarding mooring of MODUs have been revised. For example, the selection of the design return period is no longer prescriptive but based on performing a suitable risk assessment [2]. Risk assessment can be used to understand the risk causes and their impact of mooring failures. Therefore this paper discusses a framework of risk assessment for mobile mooring using HAZOP approach to assess the frequency of failures and to evaluate the potential impact of specific failures. The objectives of this paper are: (1) to determine the frequency of failure; (2) to categorize severity of failure of mooring system; (3) to rank the particular hazards by incorporating the dimensions of frequency and severity into risk matrix. MODUs can be semi submersibles, ship shaped vessels and barges [3]. Semi submersibles have been used for various different functions such as drilling, diving support, fire fighting, crane operations, pipe laying and accommodation. They have been used for several years as pipe lay vessels and the stability standards are not different from those applied to drilling units [4]. The platform used for this case study is a semi submersible column stabilized pipe lay barge fitted with 12 point mooring system to aid controlled movement during pipe lay operations. The vessel has a hull with four columns and two pontoons as illustrated in Fig. 1. Figure 1. A semi submersible column stabilized pipe lay barge In each of the four corners of the semi submersibles there are three winches with two positioned in the pontoons and one in the column above. The vessels need the assistance of an anchor handling tug (AHT) in order to moor the vessel in a working pipe lay configuration. The vessel has no dynamic