|Diver Mike Lucia prepares to head below from the dive support vessel Sea Trader to the research vessel Ocean Leader, which sank in 170 feet of water off the coast of Veracruz, Mexico. (Photos courtesy Global Diving and Salvage)|
Before salvage operations can begin, many salvage companies now require that any potentially polluting liquids first be recovered from a sunken vessel.
Even in cases where it is decided not to raise a vessel, often it is still deemed necessary to remove any liquids that might be harmful if they were to escape into the environment.
“The Coast Guard and state regulators often require the removal of hydrocarbons from a vessel where there is a substantial risk to the environment,” said John Lane, a partner with Maritime Alliance Group, Inc. of Fords, N.J., an oil and hazardous spill management company.
Removing these liquids represents a daunting engineering challenge for salvors and increases the overall cost of the salvage effort for vessel owners. Advances in diving technology, the use of remotely operated devices, specially fitted emergency tank access ports on vessels and improvements in hot-tapping technology have all made liquid retrieval a more common practice in salvage.
The most widely employed technique for removing pollutants from the tanks of sunken vessels is hot tapping.
Lane explained how Titan used hot tapping to remove oil from the research vessel Ocean Leader, which sank in 170 feet of water near Veracruz, Mexico, on Dec. 1, 2006. The vessel was hot tapped for removal of the vessel’s fuel in May 2007.
Working from blueprints of the vessel, divers marked the tanks and the tapping locations. At each location, a 5/8-inch hole was drilled through the hull plating into the tank by a diver using a hydraulic drill. The hole was also threaded using the same tool. After removing the tool, the diver determined the nature of the contents of the tank — whether oil or water — and resealed the hole with a bolt.
Once the tanks containing the pollutants had been identified, a landing plate with a valve and a cam lock hose fitting was installed on the tank. A hot-tap device was then fitted to the cam lock fitting on the landing plate.
The hot-tap device is designed to drill through the plating without allowing the tank’s contents to escape. According to Lane, using a hydraulic drill, a 2.5-inch carbide-toothed hole saw was advanced through the open valve to the plating.
|The dive control van aboard Sea Trader with the gas rack used to manage different gas mixtures sent to the divers.|
“Once the plating is penetrated with the hole saw, the tool is backed out and the valve closed. This process reduces the amount of oil that escapes to just several ounces for each penetration,” he said.
Finally a 3-inch suction hose was attached to the cam fitting on the landing plates. Once secured, the diver opened the valve and transfer of the liquid to the recovery vessel began.
Current advances in hot-tapping technology include waterjet cutting devices as an alternative to carbide drills and saws. Colorado-based Easy Tapper manufactures a new generation of hot-tapping devices that employ waterjets exerting pressures of up to 60,000 psi. Abrasive compounds can also be injected into the device to expedite cutting.
Hot-tapping techniques become less practical when divers are subjected to depths over 100 feet for extended periods of time. To address this safety issue, SMIT Salvage B.V. of the Netherlands has developed an alternative. Together with its Norwegian partner Frank Mohn, SMIT has developed a diverless pollutant recovery system. Because it is diverless, this system is capable of removing pollutants from wrecks at great depths without the added cost and hazard of saturation diving. The system relies on a remotely operated hot-tapping device to drill the hole and install the valve. Once the tank is tapped, the system uses a remotely operated offloading system to pump the contents to the recovery vessel.
SMIT has successfully used its system to recover oil from sunken tankers off the Korean coast and in France. This technology was also used to recover 4,000 tons of styrene cargo from the chemical tanker Ievoli Sun after it sank in 311 feet of water in the English Channel near France. These innovations have earned SMIT and Mohn a Seatrade Award for countering marine pollution.
|Supervisor Gary Young performs system checks on a decompression chamber before diving operations begin.|
Another innovation from SMIT is a pre-installed oil recovery system. This system was developed in partnership with JLMD Ecologic Group, Paris. The FOR (Fast Oil Recovery) system is based on Archimedes’ principle that a substance in water is buoyed by a force equal to the water it displaces.
The system involves permanently installed pipes in the hold, connected to easy access points on the deck to which salvors can transfer connect hoses. Seawater is pumped into the tank via pipes leading to the bottom of the tank. The seawater displaces the more buoyant oil to the high point or top of the tank. There, hoses are connected and the oil is removed through fail-safe fittings. Multiple access points across the vessel ensure that the highest and lowest points of the tanks can be reached regardless of how the vessel is positioned on the sea floor.
Every access point is a stand-alone, the advantage being that if any one tank is breached or if the vessel breaks apart, the remaining tanks can be safely emptied. The system is ideally suited for newly built vessels but can also be retrofitted on existing vessels.
|Working at great depth requires the right equipment and careful preparation|
On Dec.1, 2006, the 220-foot research vessel Ocean Leader sank in a storm in 170 feet of water near Isla Lobos, Veracruz, Mexico. Because the sinking occurred in an environmentally sensitive area, recovering the oil aboard was the first priority.
Titan Salvage of Dania, Fla., was the salvor. The company’s diving partner in the project was Global Diving and Salvage of Seattle, Wash. Mauricio Garrido, director of business development for Titan Salvage, said that both companies have worked together on projects in the past. “It helps that all of our crews know each other and work well together. We use Global on deep dives like this one,” he said.
David DeVilbiss, Global’s project manager on the Ocean Leader salvage, said that once his company received the call from Titan to mobilize crews and equipment, Sea Trader was chartered to serve as the dive platform. The vessel was equipped with three decompression chambers. In addition to the diving equipment, Sea Trader also carried a remotely operated vehicle (ROV) with a video camera and control arms to perform simple tasks and sector scanning sonar to help locate the wreck.
Crews and equipment were mobilized from Galveston, Texas.
Because of the depths involved, 180 feet, diving on Ocean Leader required three different mixes of diving gases, DeVilbiss said. A mixture of helium and oxygen was used when the diver was on the bottom, a mix of nitrogen and oxygen for decompression as the diver returned to the surface, and finally, a surface mix of pure oxygen.
“First we use the ROV to locate the wreck and then a diver is sent below to establish a ‘downline’ to the wreck. The next step is to position the support vessel over the wreck,” DeVilbiss said.
Divers then begin to survey the wreck and mark frame numbers on the hull to orient themselves and determine the location of the tanks. At depths of 170 to 180 feet divers typically remained below for 40 to 80 minutes at a time. A diver working for 80 minutes would then have to spend 90 minutes returning to the surface in 10-foot increments and two hours in a decompression chamber once aboard the dive vessel.
Deep diving is an inherently risky business, but DeVilbiss said his company had taken every precaution to minimize risk to the divers. One of the difficulties they faced was that occasionally divers were not able to precisely maintain the various decompression depths because of vessel movement caused by a swift 3-knot current in the area. Another was the risk of manta rays striking the diver’s hose lines.
Should a gas hose be severed or tangled, auxiliary hoses containing breathing gases were available in a cage that the divers used when ascending and descending the downline. Another safety issue was the remote location of the dive site, 8 miles offshore and 30 miles from the nearest port. Arrangements were in place for sending a helicopter in case an injured diver needed to be evacuated. A doctor specializing in hyperbaric illness was also on call.
After the vessel was surveyed, the divers began verifying tank contents by drilling small access holes to see if the tank contained oil or water. The tank was then plugged. Once the tank had been located and its contents verified, hot-tapping operations could begin. A single hot tap can be accomplished in about two hours of bottom time.
Nearly 80,000 gallons of oil were recovered from Ocean Leader and reclaimed for use. The entire operation lasted 15 days, finishing a little ahead of schedule with only a day and a half of weather delays. John Snyder