Risk Analysis Team
Updated:October 14, 2009 17:07
MODELS USED IN THE RISK ASSESSMENT
The Risk Analysis Team brings collective modeling expertise to the Phase A study as described below:
♣ DNV brings the Marine Accident Risk Calculation System (MARCS) model. MARCS calculates its main outputs as accident frequencies and quantities of cargo and bunker fuel spilt at a particular location, and
♣ ERM brings their capabilities in spill trajectory modeling and fate analyses using the Chemical/Oil Spill Impact Module (COSIM) model.
Below is a summary of DNVs MARCS and ERMs COSIM models.
The MARCS model uses traffic data (vessel types and location), ship failure data (including both human error and mechanical failure frequencies), environmental data (such as wind speed and direction), and operational data (such as traffic separation schemes) to calculate accident frequencies. These frequencies are calculated for each vessel type and each accident type as a function of location within the study area. The accident frequencies are then used with event tree models of probable material lost into the sea to deliver risk results in terms of quantity of material released into the sea. These results can be developed separately for all the cargo types (e.g. crude oil, refined products, etc) included in the traffic data, and for bunker fuel oil. For more information, download the flyer on the MARCS model here.
ERM’s COSIM model is a plug-in component to ERM’s Generalized Environmental Modeling System for Surfacewaters (GEMSS), a numerical waterbody modeling package, capable of one, two-, or three-dimensional hydrodynamic analyses. GEMSS can be applied to any type of waterbody and can compute the circulation and transport of water and any constituents, including water quality parameters and the chemical or oil constituents of concern. The GEMSS-COSIM modeling system can produce time-varying mass balances to examine the fate of the released chemical constituents into the various phases and forms including the surface slick, shoreline, atmosphere, water column (dissolved or entrained), sediments, or removed via cleanup activities. The fate calculation includes the following processes: advection, spreading, evaporation, dispersion, dissolution, emulsification, photooxidation, sinking/sedimentation, biodegradation and encapsulation (when ice is present). For more information, download the flyer on the COSIM model here.
Several features set COSIM apart from more traditional two-dimensional surface-only spill models like the General NOAA Oil Modeling Environment or the Automated Data Inquiry for Oil Spills. COSIM has the flexibility to examine any location, whether coastal or inland, without being restricted to the shorelines built into the model. One of the strongest distinctions is its capability to examine in three dimensions water column and sediment concentrations of specific released contaminants. Unlike any other spill model, COSIM can perform simultaneous mass balances for a full suite of specific chemicals. This feature enables greater precision by applying chemical specific rates for solubility, evaporation, solids partitioning, and toxicological response estimates.
GEMSS and COSIM are in the public domain and have been used for similar studies worldwide. ERM’s Surfacewater Modeling Group has special expertise with the model because ERM staff contributes to the model development, customizes the source code and has completed many applications with the model.
Summary of Bowtie Methodology
The Bowtie method provides a graphical representation of a potential major risk, its causes and consequences and the controls that are, or will be in place. The Figure on the right illustrates the bowtie concept.
Example elements of a bowtie diagram could be:
• Top Event = loss of containment of fuel
• Threat = flange/gasket leak
• Consequence = injury/fatality due to fire
• Controls = use of appropriate gaskets, daily visual inspection etc
• Response control = vapor detection system
ERM and DNV Risk Assessment personnel have extensive experience in applying the Bowtie technique in both the project and operational environments, for a variety of facilities and activities and global locations. The following table summarizes the types of facilities and typical major accident hazards that have been assessed by ERM and DNV personnel using the Bowtie approach.
Bowtie Project Applications
| Types of Facilities/Activities Assessed by ERM Personnel | Typical Major Accident Hazards Assessed by ERM Personnel |
|---|---|
| • Fixed jacket production platforms • FPSOs • Bridge linked complexes • Wellhead platforms • Tank farms • Jackup drilling rigs • Semi-submersible drilling rigs • Onshore and offshore pipelines • Accommodation vessels • Onshore flowstations • Onshore gas gathering and processing plant • LNG production facilities • LNG jetty/marine operations • Well intervention activities • Simultaneous drilling, production and construction • Marine logistics activities • Fixed and rotary wing logistics activities • Lifting activities • Well testing |
• Loss of well control • Shallow gas blowout • Oil spill • Loss of containment from mud conditioning and circulating system • Gas accumulation in mud pits, mud pump rooms • Loss of containment (gas, liquids, LNG) from pipelines, risers, topsides, process equipment, tanks etc • Product loading/unloading (crude oil, LNG) • Toxic (H2S) gas • Loss of dynamic positioning/ drift off • Loss of power • Well completion, perforating, testing • Loss of stability • Loss of tow • Structural failure • Fire (machinery spaces, accommodation) • Ship impact • Helicopter impact/ditching • Dropped object/lifting activities • Logistics activities (road transport, marine transport, fixed and rotary wing aviation activities) •Simultaneous and Combined operations |