Category:Lost packaged goods

There are several salvage techniques for recovery of packages and sunken vessels from the sea floor It is not the substance in the package or ship that determines the best response option but factors such as water depth, strength of the package/ship and current speed. Again, as with sunken substances (sinkers), the major problem is detection of packages on the sea floor. Once found salvage companies have the ability and required skills to remove the packages, though salvage operators should always be prepared for the release of contents during operations.

In general, toxic substance packaging will withstand the marine environment for a while but corrosion and other degradation will eventually cause the contents to escape. Thus, depending on the degree of hazard, such packages should be recovered from the seafloor where possible.

Many liquid chemicals are transported in 200-litre steel drums. Using some typical data, the buoyancy of these drums can be calculated:

If we assume a seawater density of 1,024 kg/m3, liquids with densities less than 0.97 - 1.03 will stay afloat. Densities higher than that will cause drums to sink.

Table 37 gives examples of low-density liquid chemicals which are often carried in 200-litre steel drums, and which due to their density will cause the drums to float in water. Table 38 gives examples of high-density liquid chemicals, which due to their density will cause the drums to sink in water.

NB: Cans and drums filled with solid chemicals will always sink in water.

Table 37 Examples of low density liquid chemicals which due to their density will cause the drums to float Types of Chemicals Examples Hydrocarbons hexane, benzene, toluene, Alcohols methanol, ethanol, n-propanol, Ketones acetone, ketone, cyclohexanone Ethers diethyl ether, ethyl butyl ether Esters methyl acetate, ethyl acetate, Amines monoethylamine, diethylamine, ethylene diamine Aldehydes formaldehyde, acetaldehyde, butyaldehyde

Table 38 Examples of high density liquid chemicals which due to their density will cause the drums to sink in water Types of Chemicals Examples acids acetic acid, acrylic acid, formic acid bases sodium hydroxide solution, potassium hydroxide solution glycols ethylene glycol, diethylene glycol, propylene glycol chlorinated hydrocarbons carbon tetrachloride, tricholoroethylene, tetrachloroethylene miscellaneous carbon disulphide, toluene diisocyanate, tetramethyl lead

Containers are lost at sea at a regular basis. This is caused by container-ship accidents or loss of containers in bad weather.

The larger container ships are especially prone to the latter due to their high stacking loads and an increased vulnerability to the “parametric rolling” effect, though incorrect lashing, broken lashing equipment or incorrect stowage plans play an important part in the general loss of containers at sea.

From an environmental point of view, the threat posed depends on the hazard rating of individual containers.

All cargo is insured. A salvage operation normally takes place if the insurer, the P&I club, considers the benefits (value of recovered cargo) to outweigh the cost of recovery.

However, when the cargo is hazardous and pollution is threatened, salvage may be considered necessary regardless of cargo value. Again, when floating containers are a threat to navigation, salvage is required.

Lost containers present a number of hazards, either for the environment or to shipping. These are:

• Navigational hazards, when afloat, especially when partially submerged or floating just under the sea surface and difficult to spot by smaller vessels and yachts.
• Hazards to fragile marine environments on the seabed.
• Hazards to sub sea pipelines and cables.
• Hazards, to coastal environments and coastal economies
• Actual damage due to leakage in all of the above.

Buoyancy

Freight containers are often spotted when floating, partially submerged, or when already onshore. Thus, while they are not watertight, they can stay afloat for some time, whether they sink or stay afloat depending on a number of factors such as:

• The effects of poor maintenance.
• Inherent fragility to distortion on breaking free, subsequent wave action and the associated movement of loose contents.

A calculation can be made to determine if a container stays afloat or sinks. If the buoyancy forces equal or exceed the gravitational forces caused by the weight of the container, it should theoretically stay afloat. A forty-foot container has a volume of 77 m3. The density of seawater is 1,024 kg/m3, giving the container 79 tons of buoyancy force. Thus, with a forty-foot container having a maximum loading capacity of 34,8 tonnes, it should stay afloat. That it often sinks is due to the above damage or simply to the fact that it is not watertight.

There is no standardized method for salvaging containers. Every salvaging operation is different, examples of varying circumstances being:

• Water depth: deep-water salvage is extremely costly in requiring the use of divers (max. 700 m) or ROV's at greater depths.
• Seabed conditions: containers can become submerged in sand as time passes, adding to the cost of recovery
• Sensitive areas in the vicinity.
• Location of containers: If the location of the containers is known, as is usually the case with whole vessel salvage, there is no need to conduct sonar surveys to locate the containers, such surveys again adding to cost.
• Spread of containers: multiple loss and unknown spread requires locations to be determined by survey.
• Contents of container (e.g. whether valuable or hazardous)
• Strength of container: and duration of immersion, corrosion being time dependent while increasing the likelihood of breakup when lifting a out of the water.
• Presence of hazardous substances: containers containing hazardous substances require extra precautions by salvaging personnel in terms of PPE's to ensure their personal safety and to prevent, as far as possible, the hazardous substance from leaking into the sea.

Current salvaging techniques

The easiest and most commonly used method is simply to lift the container out of the water, though it will leak water and possibly hazardous material as it exits the sea. Such containers should be placed on a drip tray on board the salvaging vessel.

When a container is filled with cargo containing starch, such as rice or flour, it can become extremely heavy by soaking up water while its expansion can cause the container to lose its structural integrity and break when lifted out of the water.

When dealing with tank containers containing liquid, the process of 'intentional continuous release can sometimes be used. With this method, a hole is drilled at the top of the tank, and a hose is inserted through which compressed air is pumped. This way the (hazardous) liquid is diluted to non-hazardous concentrations. Otherwise, tank containers are lifted out of the water, as are freight containers.

It must be stressed that the practical application of any given method depends greatly on the total cost of the operation. The cost factor diminishes in importance only when dealing with very hazardous substances.