General remedial measures

This section gives a brief review of the response options now generally available. These options are considered without regard to substance or hazard type.

Most of the response methods discussed in the following sections depend on specialist equipment, which needs to be available/ accessible at short notice. In particular in the case of non-persistent evaporators, and dissolvers the response time is so limited as to make such equipment needless, while the more persistent floaters and sinkers make such equipment deployment more worthwhile.

Stopping or reducing the release

Stopping or reducing the release can be the most effective response provided it can be applied safely as hazardous substances can be involved.

This method depends entirely on the nature and location of the release.

Some examples are :

• Turning a tap or valve can close off a leaking pipeline.
• Moving the substance to a different compartment in the same ship or to another ship can empty a leaking cargo tank.
• Foam plugging can close small holes. .
• Leaking packages can be placed in larger drums (over drumming).

Advantages of stopping or reducing the discharge are that:

• The greater part of the cargo can be prevented from entering the environment; that
• The seriousness of the incident can be reduced considerably; and that it
• May thus be limited to the extent of requiring no clean-up action.

Changing the position

Changing the position of a (potential) pollution source moves it to a place where a release will be less severe in its effects, can be more easily treated or left to disperse naturally. Such movement can reduce the effect of toxic products on populated areas. However, while such movement can be achieved by a ship’s own power or by towing, ignition of escaping flammable vapours must be avoided though it is unlikely that significant reduction in vapour pressure can be achieved by attempting to cool the cargo.

The advantages of changing the position of the source are:

• That the casualty poses less of a threat; and
• That more time is available for subsequent response.

The disadvantages are that:

• The substance remains in the environment if no recovery procedures are applied;
• That explosive mixtures may be formed during transport; and;
• That those involved in the relocation may be exposed to escaping vapours.

Controlled release

Under certain circumstances, it is appropriate to discharge part of the ship’s cargo to reduce the risk of losing the ship or cargo completely, a ship-to-ship transfer being the most favoured option where and when circumstances and conditions permit.

For instance, LNG carriers can jettison cargo via a stern discharge system, which extends from the loading manifold. Also the chlorine cylinders of the Sinbad were subjected to controlled release to prevent their inadvertent collection in fishing nets when later corroded to unknown extents.

Advantages of this method are that:

• The release rate can be adjusted to keep the hazards as low as possible.

Disadvantages of this method are that:

• The substance is still released into the environment; and that
• Care is needed to ensure safety of the personnel involved.

Localization of substance

Localization and diversion of drifting substances or packages facilitates their collection and limits their subsequent movement.

Containment equipment and techniques for floating substances include the following:

Booms

There are many types of booms for the containment of oil spills, though the basic design comprises a buoyant top collar and suspended curtain to reduce the escape of oil with the water which of necessity passes beneath the curtain when held to restrain oil movement on the water surface.

Chemical booms (herders)

Such substances spread to a very thin layer on the water surface, in such a way as to prevent the spread of oil in contact with it and thus to contain the oil at a greater layer thickness than would otherwise be the case.

Booms can only be applied at current speeds (less than 0,5 m/sec) relative to themselves. At higher relative speeds, the floating substance passes beneath the containment system rendering it ineffective. Herders move with the current and cannot be restrained, though they may be placed between slick and shore to prevent stranding or onshore to prevent post-stranding retention.

Remove substance / Controlled sinking

If there is an obstruction on the sea surface, which will impede shipping traffic, it should be removed.

Salvage from the seabed

Any "obstruction" which will impinge on underwater constructions (pipelines) or impede shipping traffic should be removed. This requires salvage technology which is discussed in more detail in chapter 7.

Reduction of source strength

Reduction of the evaporation rate of as volatile liquid slick may be attempted, though evaporation and atmospheric dilution to concentrations below toxicity and flammability limits is the preferable option whenever and wherever possible.

One way of treating relatively small discharges in this way is to apply spray foam to the slick

• to reduce evaporation rate and/or to dissolve the liquid in the water-based foam, As to obviating temperature increase from solar radiation, thin surface slicks are unlikely to have temperatures significantly in excess of surface seawater temperatures and water soluble substances are likely to dissolve in seawater without assistance from water-based foams.
• Another way is to reduces vapour emissions is making use of Imbiber Beads®. This is a product known that meets the strict definition of swelling absorbents for organic liquids. Because liquid contaminants are absorbed into the molecular structure of Imbiber Beads®, the effective surface area exposed to the atmosphere is significantly reduced compared to a puddle of spilled liquid or an adsorbent pad. The reduced surface area translates to a massive 600% reduction in the rate of release of toxic chemical vapours, thereby making it dramatically safer for surrounding personal, property and the environment.

There are many different types of foams, for different types of spills.

Advantages of foam application are that

• The amount of evaporation can be reduced; that
• Time may thus be bought for mounting a recovery procedure; and that
• People are protected from vapour exposure.

Disadvantages are that

• The spill remains in the environment; and that
• Foam has to be applied accurately.

Foam is unsuitable for:

• Toxic gases,
• Fires involving gases,
• Fires involving flowing liquids or leaks from pressure vessels,
• Materials that react with water, or
• Live electrical equipment