Naval Sea Systems Command's (NAVSEA) Supervisor of Salvage and Diving (SUPSALV), in a U.S. Coast Guard directed initiative, provided a key operational and technical role in removing 60,546 gallons of petroleum products from the sunken ex-USS Chehalis (AOG-48) , concluding, April 6.
Ex-USS Chehalis sank in Pago Pago Harbor, American Samoa, Oct. 7, 1949, as a result of a gasoline tank fire and multiple explosions on the ship. The fire caused the ship to sink and subsequently capsize in more than 160 feet of water.
The Coast Guard requested SUPSALV expertise to support American Samoa's request for assistance by conducting a ship diving survey, detailed planning for, and the safe removal of the petroleum products from ex-USS Chehalis that represented a potential threat to Pago Pago Harbor.
"What's unique about this Patapsco-class gasoline tanker that sank off the coast of American Samoa more than 60 years ago is that highly volatile gasoline remained in several of the ship's cargo tanks," said Kemp Skudin, SUPSALV's ex-USS Chehalis project lead. "We do not normally encounter gasoline in sunken wrecks. Gasoline is not usually a maritime fuel and normally would have been consumed by fire or lost since it has a much lower flash point compared to diesel fuel marine or black oil."
Typically, and in this case for ex-USS Chehalis' diesel bunkers, less volatile fuels are removed using the "hot tap" method, requiring the tank to be cut into in order to install a valve and attach a pumping system . This method causes heat that can be explosive when combustible fluids like gasoline are involved. Also, gasoline in motion can explode due to electrostatic discharge caused by pumping turbulence in hoses, or when falling into a storage tank. Since safe diving operations are the highest priority for Navy divers, SUPSALV had to develop an alternate means of removing the gasoline.
"We used a buoyed suction head fed into the cargo tanks through their hatches by divers and controlled by an air hose on the surface. This meant we did not have to hot tap into the gasoline tanks. To pump the gasoline we used an intrinsically-safe pneumatic pump on a small floating platform through internally and externally bounded suction and discharge hoses," said Skudin. "Our barge was rigged to load the tanks through the stripping lines. This limited the gasoline fall into the barge's tank to only a few inches, further reducing the potential for static electricity. As an added precaution, the Mobile Diving and Salvage Unit One Divers, working from USNS Sioux (T-ATF 171), were put in a separate moor from the pumping platform and ocean-going barge to which the gasoline was removed. "
The Navy's Salvage capability typically requires cooperation between uniformed fleet Navy Divers, Military Sealift Command, and SUPSALV civilian and contractor resources to accomplish complex or technically challenging salvage and pollution response evolutions. The Navy team involved in the ex-USS Chehalis offload was able to exercise the coordinated effort necessary to meet salvage mission challenges while demonstrating our commitment to preserving and protecting the environment.