Remedial measures

In this section the response options mentioned in the decision trees are discussed more fully.

No direct action

Many factors have to be evaluated, before deciding that direct action is unnecessary.

This nil-response option is viable only if the spill presents no short term or long-term hazards for human beings or the marine environment, the determination of which requires:

• Substance identification
• Hazard identification
• Quantity and concentration
• Behaviour
• Position and trajectory
• Weather conditions

Issuance of warnings

The issuance of warnings and access restrictions is to prevent people from coming into contact with dangerous substances (mostly vapours and gases).

Types of warnings are:

• Stay indoors
• Close all openings (toxic hazard)
• Open all windows (explosion hazard)
• Stay out of the path of the vapour or gas
• Divert the course of a vessel
• Turn off ignition sources

A warning notifies people to stay out of the danger zone, and prepares them for possible evacuation.

It is however difficult to reach everyone with a warning, while care should be taken to avoid panic.

Restriction of access

Model calculations and sampling/analysis, particularly the latter, can indicate the size of the affected area, access to which can be restricted in the general warning. The contingency plans prepared by local authorities and commercial organizations such as those operating offshore facilities should be taken into account in drafting warnings and restriction orders. By placing such restrictions on an area, the authorities can effectively prohibit activities such as:

• Shipping
• Agriculture
• Air transport
• Offshore operations
• Recreational use
• Fishery activities

These activities could involve direct contact between people and contaminated air/water or indirect contact through food products from land and sea.

Evacuation affected areas

Depending on the hazards presented by the spill, it may be necessary to order evacuation of those thought to be in danger. Under such circumstances, consideration should be given to complete or partial evacuation of people and/or animals.. Evacuation is one of the most drastic responses to an accident and should only be contemplated as a last resort. To ensure that such operations are carried out smoothly, contingency plans should indicate how this could best be achieved.

The advantages of clear planning are that harmful contact between people and noxious substances can be avoided; and that Evacuation can be carried out relatively quickly to this end.

Disadvantages of evacuation are that: If the evacuation is not handled properly, panic can develop if planning is inadequate; and that poor execution can aggravate an already fraught situation.

Personal Protection

When skin contact with a dangerous substance is inevitable or likely, preventive countermeasures should be taken by wearing special whole-body protective clothing. While breathing apparatus can be used to protect the respiratory organs from toxic gases with this or in combination with other protective clothing. More information on such personal protection is to be found in Chapter 8.

Visualisation of vapour, gas and solute plumes

Both vapour/gas plumes in the air and plumes of dissolved substances in the water column can be made visible by specific reagents. When plumes are thus made visible the exact position, dimensions and track can be assessed more easily.

An example of this procedure is shown in Picture 58, in which a salvage ship sprayed ammonia towards a chlorine plume to form visibly white ammonium chloride.

The advantages of this response option are that

• The dimensions of the cloud can be seen to the extent of reagent dispersal; that those who have not heard the warning may see the plume and take avoiding action; and that;
• Other responses may be mounted more effectively while avoiding contact with the plume.

The disadvantages are that:

• The products present in the plume remain in the environment though at ever decreasing concentration; and that;
• The size of the plume can be underestimated when insufficient reagent has been added.

Controlled Combustion

Controlled combustion of a chemical spill implies that setting fire to it can break down the pollutant in question. However, combustion should only be attempted when the benefits clearly outweigh the risks. Changeable weather conditions and surface currents being among the factors likely to increase risk. Controlled combustion of liquids would best be performed at the source of the spill, though care is needed to avoid compromising the safety of those involved while gas ignition calls for even greater care and remoteness.

Igniting them at the point of discharge can often flare off the products escaping from leaking pipelines or valves. Personnel performing these duties should take positions upwind of the leakage point. A careful assessment of the site, wind and geographical conditions must therefore be carried out before undertaking such operations. The dimensions of the exit plume should at least be approximately known so that the extent of the damage caused by burning off the products can be estimated. Ideally, the substance should be highly flammable so that no additional combustion agents have to be added. Information must be available about the reaction products that will be formed to avoid unnecessary risks to operatives.

The advantages of controlled combustion are that

• It provides a relatively simple way to deal with a continuous discharge; and that
• It removes the risk of uncontrolled explosions.

The disadvantages are that

• Care is needed to avoid endangering those involved; that
• The precise dimensions of the exit plume is usually unknown; and that
• Weather conditions can change rapidly.

Removal of ignition sources

It is essential to remove or disconnect all potential sources of ignition if flammable gases or vapours are likely to enter a particular area. Action of this type will significantly reduce the risk of explosion as defined by the LEL values. Possible sources of ignition are:

• Internal combustion engines
• Cigarettes
• Gas stoves
• Heaters
• Flares
• Hot surfaces
• Sparks

Vessels that are already in a hazardous area and cannot be moved, should take the precaution of turning off all engines, power supplies and generators. Restrictions may also have to be placed on the movements of the people on board.

The advantage of removing ignition sources from a danger zone is that the vapour/gas may disperse and the threat may thus pass without any explosion-taking place.

The disadvantages associated with removing ignition sources are that:

• The plume may drift ashore where many more potential sources of ignition are likely to be found and where the effect of an explosion would be more severe;that
• It is difficult to guarantee complete removal of all ignition sources; and that
• The released product remains in the environment, though progressively diluting.

Fire Extinguishing

Extinguishing includes all possible means of combating small or major fires. Extinguishers may be based on carbon dioxide, water or foam.

Cooling

Cooling of hot metal and contained cargo can be considered if temperatures reach values that are unacceptable with respect to the flashpoint or ignition temperature, thereby endangering the crew.

Simply turning off the heaters can cool a substance transported at elevated temperature. Other cargos should be cooled by water-spraying facilities on board the ship, though sometimes the only way to cool down a cargo is to let in ship with cargo sink.

Mechanical recovery floating substances

Mechanical recovery involves containment of the floating pollutant and its removal from the sea surface by mechanical means. This can be done with oil spill recovery systems such as:

Skimmers

All equipment intended to remove oil from the water surface can be called a skimmer, they’re being a range of types. Weir type skimmers collect the upper layer of the water column by means of weir-overflow following which the presence of water may facilitate pumping by reducing the viscosity. There are also skimmers that use the ‘stickiness’ of the oil to collect it on rotating brushes or disks which thus remove it from the water surface.

Sweeping systems

To enable the oil to be picked up from the surface, it should be concentrated to a greater layer thickness near the skimmer by sweeping.

A sweeping system usually makes use of flexible floating booms, though rigid-arm sweeping systems are also available.

Netting

Netting, through which the water flows while the oil is retained, can contain very viscous substances. The disadvantage is that water ceases to flow through when the mesh is blinded by the retained oil; and that all such recovery equipment has to be cleaned afterwards.

However, such oil spill response equipment, can be used for floating hazardous noxious substances also, provided the material of construction is compatible with the spilled substance. The physicochemical properties of HNS determine recovery equipment usage. Dispersion

A floater on the water surface will eventually form droplets and become dispersed through the upper layers of the water column. The formation of these droplets increases the contact area of substance/water, assisting oxidative and biological breakdown.

The extent, to which a floater disperses, depends on the surface tension, viscosity of the substance and the sea state.

In oil spill response, the addition of surfactant chemicals enhances the natural dispersion rate by is a lowering the surface tension and the viscosity of the oil which in turn lowers the energy needed to form droplets.

For floating HNS spills this could also be an option, though most HNS are of sufficiently low viscosity to disperse naturally at rates comparable to those of kerosene and diesel oil.

Again, natural dispersion can be enhanced by mechanical means such as by propelling boats through low viscosity slicks to agitate them into the water as droplets.

Gelling agents

Gelling a liquid means adding an agent to increase its viscosity to the point of solidifying. A floater, which has been treated in this way, can be recovered more easily. Once a substance has been gelled there is no more dispersion or spreading, unless the gelling is granular.

In order for this treatment to produce a continuous solid, wave energy is necessary to mix the chemicals with the spilled substance and this can result in production of granules only. Again, the quantity of gelling agent requires careful consideration.

Neutralization

Neutralizing spills of hazardous materials involves adding specific quantities of other reagents that will react with the spilled chemicals to form harmless secondary products. Before such operations can be safely carried out, the following information must be known:

• The amount of chemical discharged
• The location of the discharge
• Whether a suitable neutralizing agent is available for this substance
• The concentration at the point of discharge and various other locations

Neutralization is only applicable to acids and bases and should be performed with neutralizing agents that satisfy the following requirements:

• Available in sufficient quantities
• Dilution to the required concentrations
• Harmless to the environment

The physical state of the reagent should match that of the substance on release in order to maximise reaction between them.

A highly volatile liquid substance can only be thus neutralized when still in the liquid phase.

The main advantage of neutralizing a spill is that instead of a hazardous substance, relatively harmless reaction products are formed. For example hydrochloric acid is highly corrosive and gives off highly corrosive vapours, the latter requiring the protection of breathing apparatus. However when neutralised with sodium hydroxide, sodium chloride (common salt) and water are produced.

Neutralizing a spill has the following disadvantages:

• A great deal of information is required before such action can be contemplated
• The neutralization of bases is difficult because there are relatively few weak acids which can be used for this purpose
• Little experience has so far been gained with this method in the field
• It is no longer applicable once a vapour or gas has formed.

Acceleration of biological breakdown

Biological breakdown occurs naturally for organic substances, though micro organisms do not degrade inorganic substances.

The natural process may be accelerated by addition of nutrients or of micro organisms to a spill site, most conveniently onshore.

Adsorption

Adsorption is the uptake of the substance by an adsorbing surface. The movement of both the sorbent and the spillage can be controlled by of surface nets and booms if the adsorbed substance is lighter than water. If the substance is heavier than water both the sorbent and the spill will sink and might be recovered afterwards.

Adsorption material can be applied to spillage as sheets, mats, pillows and booms. .

The disadvantage is that the adsorbents have to be collected while the adsorbate may not be fully ‘contained’. Thus, for instance, a vaporising substance will evaporate faster if its surface area is increased by adsorption.

Absorption

Absorption is the uptake of a substance into the absorbing material. Different HNS spill absorption materials are available on the market.

Imbiber Beads®

Imbiber Beads® is a product known that meets the strict definition of swelling absorbents for organic liquids. The size of salt granules “engineered” to absorb a wide range of organic chemical contaminants, including:

• Transportation Fuels -such as Gasoline, Jet Fuels, Light Fuel Oil, Diesel Fuel, Crude Oil, etc.
• Aromatic Solvents -such as Benzene, Xylene, Toluene, Cumene, Ethyl benzene, Styrene, etc.
• Chlorinated Solvents -such as Percholorethene, Methyl Chloroform, Trichlorobenzene etc.
• Polar Compounds -such as Tetrahydrofuran, Methyl Ethylketone, Ethyl Acrylate, etc.

Imbiber Beads® possess a number of unique features including:

• Extremely high absorption capacity blanket has the absorption capacity of more than 50 surface-coating fibre adsorbent pads. Hence for a given volume of spilled contaminant, very much less Imbiber Beads® products are required
• Does not leach absorbed contaminant
• Once absorbed into Imbiber Beads®, the liquid contaminant becomes part of the molecular structure of the Imbiber Beads®. As such, there is absolutely no leaching of the contaminant, thereby safely containing the contaminant and preventing the liquid contaminant from further polluting the surrounding environment.
• Reduces vapour emissions of toxic contaminants by up to 600%
• 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 personnel, property and the environment.
• High affinity for oil & chemicals but completely ignores water (hydrophobic) Imbiber Beads® totally ignore water, but are engineered to have a high affinity for a broad range of the organic chemical spectrum. This performance characteristic makes Imbiber Beads® extremely suitable for soaking up and containing spills of organic contaminants that have spilled into canals, drains, rivers and reservoirs.

A spill gun was developed allowing for Imbiber Beads® to be carried in a water stream up to 30 meters and delivered onto the spilled hazardous noxious substance.

On contact with the HNS, the Imbiber Beads® absorbs, captures and contains the HNS within its molecular structure, rendering the recovery operation much safer to personnel, the marine environment and surrounding areas. Standard fire fighting equipment was used as delivery system for remote application of Imbiber Beads®.

Trials to prove the ability to fire bulk Imbiber Beads® in a fire water stream on to a volatile, floating, non-miscible HNS spill to render it visible, to immobilise it, to eliminate free liquid, to reduce vapour emission such that it is made much safer so that traditional booming and skimming can be used for clean-up.

These tests have demonstrated a simple delivery system for Imbiber Beads® on to colourless volatile spills on water. They allow standard equipment to be used and provide a solution for an HNS spill response for the specific range of HNS liquids with which they are effective.

The vapour cloud can be reduced, the spill is rendered opaque, therefore visible, and the free liquid is eliminated, thus significantly reducing the hazard. Thus traditional booms and skimmers can then be deployed to clean up the immobilised spill, which is now visible.

It is possible to use Imbiber Beads® inshore, for example in harbour or port approach for specific circumstances. This will allow fire monitors and stocks of Imbiber Beads® to be established in case of an incident, allowing rapid response and a huge reduction in the risks associated with HNS spills.

Data from MDPC in Japan showing the very great reduction in vapour emission from a range of volatile floating HNS liquids, which led to Imbiber Beads® being chosen as the preferred product to use with such spills in Japanese waters.

MDPC further explored and developed a system to 'broadcast' Imbiber Beads® onto HNS spills at sea from recovery vessels.

Coagulation/Flocculation

Coagulation and flocculation are in a sense related to the action of absorbers. Coagulants act to coagulate and then precipitate colloids. Flocculants precipitate themselves and, in doing so, carry the other substance with them. The substance is taken out of the water column and further spreading is prevented. It should be noted that this method could only be used on substances that disperse, and not on dissolving substances.

Reverse Osmosis

Reverse osmosis is a filtration technique in which the solvent is forced through a membrane by pressure, while the membrane selectively prevents passage of the solute. Selectivity may depend on both membrane and solute. These devices are available in mobile units, making them suitable for use at spill locations. However, the soluble substance will continue to dilute naturally in seawater prior to the application of reverse osmosis unless prevented from doing so in some way.

Mechanical dilution in air compartment

Dilution by mechanical means can reduce the concentration in air, thus reducing the hazard to marine organisms.

Large mechanical fans can reduce the concentration of hazardous materials in air. Though the following aspects need consideration:

• The effectiveness of the fans
• The time to mobilize
• The safety in use

In comparison with other response methods, this approach should only be contemplated for small-localised volumes of air and not for populated areas. A further drawback is the low availability of such ventilation units. An alternative is the use of water sprinklers to dilute the presence of vapour or gas in air.

The advantage of mechanical dilution is its direct action in decreasing the concentrations of hazardous substances in air.

The disadvantages are:

• Expense
• Use only for small volumes of air
• Low availability
• Cannot compete with wind in open situations.

Mechanical dilution in water compartment

Dilution by mechanical means can reduce the concentration in the water, thus reducing the hazard to marine organisms living in the water compartment.

Similar techniques as used for mechanical dispersion can be applied such as bow waves, breaking boards etc.

Dredging

Dredging is the removal of underwater material. It can therefore recover released substances that are heavier than water. A choice can be made between hydraulic, mechanical and pneumatic dredgers. Conventional dredging has the disadvantage of disturbing bottom habitats, banks and water-flow characteristics, though the use of vacuum units may minimise such effects.

Burial of spillage

Immobilizing a substance by burial isolates it from the environment to that degree by its localisation. However, removal may be the better option and should be evaluated comparatively.

Rendering explosives harmless

Specialists from the navy in explosives can render explosives harmless.