EHS Management

Understanding Risks with Sunken Vessels

Other Factors

The NOAA states that there are multiple general factors that must be considered in developing and implementing a plan to remove fuel or another potentially polluting substance from a sunken wreck.  For example:

•              Vessel construction/engineering.  The actual construction and engineering of the vessel in areas such as plate thickness, riveting, and welding may deviate from original plans, particularly for World War II-era vessels that were constructed on expedited schedules.  Poorly constructed rivets and welding in particular can cause problems during operations.

•              Wreck orientation.  The orientation of the wreck (upright, upside down, on port side, on starboard side) or portions of the wreck if it is broken is extremely important in planning the strategy for accessing tanks and oil pockets.

•              Depth.  Wrecks within RULET are all submerged, ranging in depth from 30 to approximately 15,500 ft.  Oil removal operations conducted on one wreck at a depth of over 11,000 ft as well as complex well capping at a depth of 5,000 ft at the Deepwater Horizon site demonstrated the capabilities of remotely operated vehicles (ROVs) at considerable depth.

•              Wreck condition.  The wreck may be in worse condition (more damaged, greater degree of corrosion) than anticipated, complicating operations.  There may also be less damage than anticipated meaning that there may be more oil on board than anticipated.

•              Safety factors.  The presence of munitions, unexploded ordnance, and hazardous materials can create safety issues for response personnel and the public.

•              Historical/cultural concerns.  With the operational goal of removing oil from the wreck, the fact that the wreck is a heritage site, on—or eligible to be on—the National Register of Historic Places, is a war grave, and/or contains noncombatant human remains creates particular needs for sensitive and respectful treatment of the wreck and any human remains or artifacts that may be found.

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                The NOAA emphasizes that each oil-removal operation brings unique challenges, and there is no one method or strategy.  Furthermore, there are no particular rules of thumb about whether or not a project is feasible.  Much like emergency oil spill response or fire fighting, most operations require custom solutions that can be addressed in preplanning to some extent, but may require adjustments and adaptations during actual operations.

                It is essential that each wreck receive as thorough an assessment as possible before any removal operation begins, states the NOAA. Wreck inspection can be conducted in a number of ways, including using remote sensing such as sonar technologies and ultrasonic thickness hull gauging, ROVs, autonomous underwater vehicles (AUVs), and divers. 

If the assessment indicates that removal is feasible, responders will typically make use of a combination of the following technologies:

•              Hot tapping.  The hot tap is an oil recovery device that can be used in shallow water to a depth of approximately 200 ft.  It is generally diver-operated, though some hot tap systems can be deployed with ROVs at greater depths.  The system creates a through fitting in a ship’s hull, which allows recovery of oil (or other fluids) without spillage. 

•              Viscosity lowering to aid in pumping.  For highly viscous oils, viscosity-lower techniques are required for effective pumping.  The most common method is heating.  This can be accomplished through direct heating of the individual oil tanks by using the ship’s tank heating coils and the injection of hot water or steam. In many cases, however, the ship’s heating coils are too corroded for use. Other methods of heating are the localized application of steam near the pump inlet or complete tank heating.  Either approach requires portable boilers on a surface work platform that can deliver steam to the wreck through hoses.

•              Pumping.  Low-viscosity oils can be removed from a wreck using a vacuum pump and long suction hoses handled by divers or surface crews through the use of an ROV.  Pumping of heavier oils has been accomplished using positive-displacement pumps fitted with annular water injection rings that lubricate discharge hoses to prevent clogging.

•              Alternative to removal—solidifiers.  Solidifiers increase the viscosity to such an extent that the oil would behave as a rubbery semisolid, reducing the risk of a liquid release.

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There is substantial uncertainty regarding the location of sunken vessels and the risks they pose.  Even with the uncertainties, the NOAA does not believe that U.S. coastlines are littered with “ticking time bombs of oil.”  Still, the NOAA asserts that it is necessary to put “reliable bounds” on the potential oil-pollution threats and start to plan accordingly.  Work being accomplished through RULET should provide a basis for future actions and decision making, says the NOAA

One major limitation on this work is funding.  For shipwrecks determined by the USCG to be a “substantial threat,” funding from the Oil Spill Liability Trust Fund (OSLTF) under the Oil Pollution Act is available for assessment and recovery.  However, in general, monitoring is needed to determine if a threat exists, and the OSLTF cannot be used for monitoring activities associated with potentially polluting wrecks.  The NOAA believes stakeholders need to be “creative” in addressing the risk.  For example, the NOAA states that it would be beneficial for the USCG to include a scenario involving a discharge from one of the priority wrecks for one of the National Preparedness for Response Exercise Program exercises to raise awareness and identify appropriate response resources and the availability of those resources for such an event.

NOAA’s Risk Assessment for Potentially Polluting Wrecks in U.S. Waters is at

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