6.7        Salvage operations involving
             sunken packaged goods

6.7.1          General

Specialist resources must often be used in connection with activities described below.
 

Searches, especially over large sea bottom areas, are best done by using side scan sonar.
 

Selection of echoes is performed by interpretation of imageries from a sides can sonar.
 

Locating and positioning of echoes can be done by a system consisting of a hydroacoustic transmitter on board a search vessel and transponders which are set out on the bottom within the search area.
 

Sorting out insignificant echoes can to some extent be made by colour coded sector scanning sonars.
 

Identification of remaining ”hot” echoes could preferably be done by submersibles to ascertain which of the echoes originate from intended items.
 

Close inspection of found items should be done by submersibles or divers in order to find out their physical appearance, i.e. if they are leaking, how they should be salvaged, etc.
 

6.7.2        Locating packages on the seabed

When lost packages have sunk to the seabed it will normally be necessary to search for them over a large area. When targets are spotted, they should be inspected more closely, in order either to discard them as false, or to identify them as the lost packages.

Locating packages on the seabed may be very difficult and will depend on the situation. When organizing and performing a search for lost packages, the most important information is the position report and an indication of its accuracy. The water depth and the topography of the sea floor will highly influence the complexity of the search operation. Other important factors affecting the search are package type, size and shape, packing material, as well as sea currents and sea state.

Currents may also move packages from the known position or cover them with bottom sediments. Their position may also be affected by fishermen's trawling.

Precision navigation systems
On many occasions during search operations at sea, it is necessary to utilize specific navigational systems to be able to manoeuvre vessels in  a precise manner and make accurate map plots of the search area.

Whichever system is used to locate the lost packages, the prime requirement is that the system must be very accurate so that the echoes can be easily found again after the general large area plotting.

A prerequisite for a successful large area search is a well-equipped platform. The brain of the platform is a survey computer that can

Searching large bottom areas
An underwater search for sunken items usually starts with searches over large areas  by sonar systems (hull-mounted, towfish-mounted or ROV-mounted) sometimes in combination with magnetometers. A major factor in the success of modern side-scan sonar systems is that they are towed near the bottom rather than hull mounted. Proximity to the bottom allows much more detailed, higher resolution records. When a number unidentified echoes have been registered and positioned they have to be more closely inspected and identified by certain high-resolution sonars, underwater camera systems and/or divers.

Picture source: Swedish National Defence Research Institute
Figure 6 - 40 Large bottom area search by hull- and towfish-mounted sonars.

6.7.3

Underwater techniques using submersibles
for actions against sunken packages

General
By means of various submersibles it is possible to perform a variety of underwater work, e.g. inspection and identification of packages on the seabed. However, it is difficult to accomplish salvage of cargo from the seabed utilizing solely submersibles. Some submersibles have manipulator arms that can be used to touch and turn items. More sophisticated submersibles are equipped with gear that can grab and salvage single items. Some submersibles are even manned and may thus be more versatile.
 

Inspection and identification of sunken packages

If it is not judged to be safe to use divers in underwater operations, the use of submersibles equipped with TV cameras is recommended.

Conventional TV or low-light-level TV (LLLTV) cameras may be used, if necessary combined with a light source. Simple sleds carrying TV cameras may be towed or trailed by an umbilical cord.

If the identity of the contents is known (e.g. if the labelling is intact), the hazards can readily be assessed. If not, identification of the contents and assessment of the hazards should be obtained before recovery is attempted. If the presence of radioactive material is suspected, measurement of the radiation level should be carried out before any other actions.

It may be possible to use detection equipment (monitoring instruments) in the field to assist in these processes. A chemical laboratory may be necessary to identify samples where the use of detection equipment is insufficient.

6.7.4         Providing sunken gods with pingers and buoyant bags

Pingers
When sunken items have been found and identified it is necessary to mark them in order to facilitate for response personnel to find them afterwards. Acoustic transmitters (pingers”) can be used. They send ultrasonic pulses of certain frequencies which easily propagate long distances in water. With receiving (homing) systems the source can afterwards be located. The choice of frequency is of vital importance as low frequency (10 kHz) sound is transmitted longer but more difficult to locate exactly than a high frequency (40 kHz) sound.

Acoustic transmitters are normally very reliable but they should not be attached directly to the item on the seabed as masking effects may restrain the sound transmission in certain directions. The pinger should instead be attached firmly to the item by means of a 20 m long floating rope. Such a buoyant pinger reduces the risk of masking.

Buoyant bags
In some cases it may be beneficial to raise the item found on the seabed to the surface by attaching buoyant bags to it.

6.7.5

Underwater techniques using divers
for actions against sunken packages

General

Divers working with leaking packages should take particular care as the diver's suit may be torn and his skin may be exposed to the leaking substance. Therefore the divers should wear protective gear appropriate to the hazard involved to avoid skin contact with the surrounding water. The best solution is normally acquired by dry diving suits which are certified for the specific chemicals involved.

Packages up to the size of drums may be transferred by means of a transfer crane to a large container which is lifted to the surface when filled. Larger packages may be attached one by one to a line and lifted to the surface. These methods can be used for packages on the seabed or in a sunken ship. In the latter case the ships hull may need to be opened in order to reach the packages inside the ship, possibly causing the packages to float free.

Bounce diving
A bounce dive is a dive of relatively short duration and generally less than 10 minutes. Sometimes a bounce dive is characterized as a relatively deep dive with a short bottom time (with a long surface interval to eliminate gas bubble formation in blood and tissues).

In recreational diving the concept of bounce dives usually means going straight down and, immediately after reaching the bottom, coming straight back up, without stops. In commercial and military diving, any dive not involving decompression from saturation would usually be regarded as a bounce dive, even if it involved a long decompression.

"Bell bounce diving technique" means a diving procedure whereby a diving bell or diving submersible is used to transport divers who are under atmospheric pressure or pressures greater than atmospheric pressure to a work site and subsequently to transport the divers under pressures greater than atmospheric pressure from an underwater work site, but does not include saturation diving techniques.

Inspection of packages in shallow water and sometimes even recovery may be carried out by trained SCUBA (Self-Contained Underwater Breathing Apparatus) divers, i.e. air divers in light suits. If necessary, the divers should wear outer safety suits. In some situations, it may be convenient to use tethered divers. SCUBA divers normally work down to maximum 40 m.

Figure 6 - 45   A closed bell diving system

For deep water work "atmospheric diving" or “JIM diving” is an alternative to saturation diving. It can be utilized at depths beyond the range of conventional saturation diving. In atmospheric diving, a bulky, high-pressure resistant diving suit is used by the diver, who breathes air at normal pressure. An atmospheric diver needs no decompression time when resurfacing.

Figure 6 - 46
Underwater diving work in
an atmospheric diving suit

Picture source: Oceaneering

6.7.6       Methods for recovery of sunken goods.

It is often not advisable to drag or trawl the seabed for sunken dangerous goods. Such actions may often damage the packages so that their contents are scattered over the seabed. However, on occasions when the situation is completely under control as regards the packaging's construction, depth conditions, etc., trawling has sometimes been successful.

It is also possible to pick up sunken goods by means of bucket-like devices on grabbing-cranes. But it is advisable to supervise the seabed operation in order to hit the target and avoid to damage it. The supervision can be performed by means of TV-cameras or divers wearing protective suits.

Salvage of sunken drums

Method

Bottom package picker

Drums containing dangerous solids or drums containing certain liquid acids, bases, glycols, chlorinated hydrocarbons, organolead compounds, or organosulphur compounds.
 

Description

Figure 6 - 47
A so called ”bottom picker” equipped with a video camera
(ref.: Oy Kart Ab, Finland, and Finnish Environment Institute)
 

Recovered packages with potential contents of hazardous materials should by safety reasons always be transferred into salvage drums (cf. Figure 6 - 3) before further actions.
 

Aimed for relatively small packages (sizes up to drums).
Applicable under calm weather conditions.

Salvage of sunken drums

Method

Use of Remotely Operated Vehicles (ROV:s) and racks to hold the drums.
 

Drums that may be damaged and leaking substances which are so dangerous that diver operations should be avoided.
 

Description

Remotely Operated Vehicles (ROV:s) equipped with manipulator arms transfer the drums into outer salvage drums and the thus obtained packages into racks taking e.g. up to 20 packages.

The filled racks are hoisted to salvage barges by means of pontoon cranes (cf. Annex 3, accident “Santa Clara”).

Picture source: US Coast Guard
 

A sophisticated and accomplished technique and equipment must be available in order to perform such an operation.

A careful decontamination of the equipment may be difficult and time-consuming to perform.

Salvage of packages from depths
down to 500-600 m

Method

Bell diving system with saturation divers

A demolished vessel on the seabed cannot be salvaged together with its cargo by pontoon cranes. On such an occasion the operation must be planned in consideration of the cargo’s distribution within and outside the wreck. Divers must probably be utilized in an appropriate manner to handle the goods manually before it can be salvaged.

Whether demolished or not packages may have to be recovered from inside or outside the sunken ship on the seabed.

Figure 6 - 50

Description

Figure 6 - 51
A closed bell diving system

Very expensive operations with costly breathing gases and complicated decontamination procedures for divers and equipment.

6.7.7        Miscellaneous methods

Although recovery of sunken packages is the most natural way of response, other techniques must be considered on some occasions.

If the water is very deep or the goods is scattered over large areas the option of no response may be the only reasonable alternative because of enormous costs that cannot be justified.

Intentional release of packaged chemicals may sometimes be suitable for substances whose hazard can be reduced by mixing with water and where, for some reason, recovery would be more hazardous. Prior to undertaking any intentional release, careful consideration needs to be given to the proximity of the release to any sensitive marine resources and to currents or other factors which may influence the rate of dilution or transport of the released material.

The release may be performed by puncturing the package, by remote control if necessary, and monitoring the mixing and dispersion. Puncturing can be made by a cutting tool, a sledge or even gunfire. One case is documented where a large amount of small containers were punctured by firemen's axes before dumping into the sea (cf. Annex 3, accident Rio Neuquen) (Ref. 47).

Momentary river releases of acids and bases have earlier turned out to be devastating for the aquatic life. The spill moves downstream like a “cloud” in the river water and kills all organisms in the river down to the river outlet (Ref. 45 in Norwegian, and Ref. 46).

Intentional continuous release
from a sunken container

Method
Pumping substance into the surrounding water.

Description
Figure 6 - 52 shows how an air lift system can be used for controlled underwater discharge of a water-soluble chemical. This method has been used once with success for emptying a sunken barge with sulphuric acid in the Upper Mississippi River. (Annex 3, accident “Sunken barge”) (Ref. 38).

Figure 6 - 52   Use of an airlift dredge for controlled discharge of a liquid chemical into the surrounding water.

Intentional momentary release of gas
from a sunken container

Method

Breaking containers by explosives.

Corroded metal containers of a sparingly soluble hazardous gas, which might rupture during normal recovery operations.
 

Figure 6 - 53 shows an example of using explosives after an accident off the coast of the Netherlands. (Annex 3, accident Sindbad) (Ref. 44).

Sunken steel cylinders containing chlorine were broken by explosives and the gas escaped through the water column into the air.

Figure 6 - 53

The rising chlorine gas cloud was strictly supervised by fully protected personnel. An exclusion zone was established  (Figure 6 - 54) and patrolled by ships, helicopters and aircraft.

Figure 6 - 54
 

Very careful planning is necessary as regards safety for divers and crews of participating craft, as well as for seafarers and populated areas.