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CONTAINMENT
Offshore installations are generally designed, constructed and operated to prevent oil, gas or condensate from reaching the environment. With the emphasis on the emissions and discharges which could not be designed away, this is often forgotten.
The Figure below shows how primary, secondary and tertiary containment measures are working together to prevent oil pollution, whereas similar and even more stringent measures are generally implemented to prevent the release of gas.
An oil spill can only occur, if all levels of containment would fail simultaneously.
Primary containment measures
Primary containment measures are those that are in immediate contact with the hydrocarbons and that are integrated into the design of the facilities and include:
- Closed system platform processes designed to safely contain reservoir fluids in vessels and pipework under all process conditions. This includes design considerations, materials selection, metal thicknesses etc.
- Pressure, temperature, flow control and shutdown systems to maintain safe operating conditions at all times.
- Isolation valves to minimize spill volumes.
- Design selection of environmentally critical equipment. This includes selection of technology for oil/water separation to optimize separation and minimize process upsets leading to unplanned emissions.
Secondary containment measures
Secondary containment measures relate to the operation of the facilities and include:
- Corrosion prevention and monitoring programmes.
- Preventative maintenance programmes for environmentally critical equipment, to ensure that vessels, flowlines, valves, fittings and equipment remain in a safe operating condition. This requirement extends to fuel transfer hoses, and temporary equipment, which have potential to be sources of hydrocarbon spillages.
- Consideration of all potential spill scenarios to ensure procedures and resources are in place for prevention, control and mitigation. This includes the utilization of Job step plans, pre-task risk assessment, work permit controls and operations manuals.
- Training of platform personnel to operate and maintain the above safeguards in good working order.
- Inspection, audit and review.
- Reporting and investigation of oil spill incidents and positive actions taken to prevent reoccurrence.
Implementation of environmental management systems, aimed at ensuring that oil spill risks are considered, quantified and minimized and mitigated in a consistent manner across offshore operations, forms a key aspect of secondary containment.
Tertiary containment measures
Tertiary containment measures are those that are not in immediate contact with the oil and that are integrated into the design of the facilities and include:
- Leak trays under equipment with a high potential for spills.
- Bunding of areas with a potential for spills.
- Closed and open drainage systems and associated oil water separation systems.
- Visual inspections to stop minor operational leaks.
- Availability of clean-up equipment to deal with spillages before they reach the marine environment.
Some offshore activities are carried out in areas where there are no leak trays or bunding. Such activities are typically carried out under strict permit control, with pre-job risk assessment. Such higher risk activities include the bunkering of diesel oil from a supply vessel, or the transfer of diesel to satellite platforms in helicopter under-slung fuel bags.
Risk sources 1 2 3 4
