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These systems tend to waste the dispersant and has limited encounter rate, although it is
found on most vessels, it should be used only if no other equipment is available.
Injection systems consist of two pumps: one for water and the other, similar to chemical
feeder pumps with variable flow rate, for the dispersant. The dispersant is applied through
nozzles mounted on spraying arms attached to the vessel's side. Fixed and portable designs
exist, and are preferably installed on the vessel's bow in order to benefit from the mixing energy
provided by the bow wave.
It should be emphasized that pre-dilution into sea water can reduce the efficiency of dispersant
especially when the oil is a bit viscous, i. e. weathered (>700 cSt). For this reason, the neat
dispersant application (developed below) is strongly recommended.
Figure 28: Application of dispersant pre-diluted into sea water
11.2.3 Systems for spraying neat dispersants
Systems for spraying neat concentrates are specifically designed for the application of
undiluted concentrate dispersants.
These units are usually bow mounted, have a pump with a variable flow rate and the
dispersant is discharged also through nozzles mounted on spraying arms. These are usually
longer as compared to stern mounted arms, having a greater oil encounter rate. Mixing energy
is provided by bow wave.
In order to increase the dispersant flow rate range some units are equipped with multiple
spraying assembly. By operating one or several spraying assembly, the flow rate can be
adjusted to cope with different situations encountered (ship speed, oil thickness and type…).
Different types of vessels may be used for spraying dispersants and, in addition to specially
built anti-pollution vessels; these include tug boats, supply vessels, trawlers or small fishing
vessels. The necessity to operate at low speeds at the same time retaining the necessary
manoeuvrability may be a limiting factor in the selection of vessels. Suitable vessels should
also have sufficient storage space for dispersant.
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Figure 29: Neat Concentrate dispersant spraying system for boat
11.3
Portable units for individual use
Light weight, cheap and easily available back pack units, normally used in agriculture, and
mainly designed for shoreline rock cleaning, may also be used for application of dispersants to
small spills near the shore. The application rates are limited.
There are designs where the tank and the pump are trailer mounted and connected to the
portable spraying gun by a flexible hose.
Both hydrocarbon based and concentrate dispersants can be used with this group of devices.
12.
LOGISTIC REQUIREMENTS FOR THE EFFICIENT USE OF DISPERSANTS
Regardless of the scale on which dispersants are applied, their use calls for well organized
logistic support. As oil is liable to chemical dispersion only during the first hours or days after
being spill at sea (window of opportunity for dispersion), at the time of the spill, the responder
should be able to implement the dispersion application without loss of time. Therefore, all the
logistics should be pre-planned. This aspect may appear particularly important when
dispersants are used for the treatment of massive spills relatively far offshore. Since
mechanical recovery of oil also requires significant logistic support, logistical constraints may
be a decisive factor in deciding whether to use one method or the other. The availability of the
necessary equipment, products and personnel will play a key role in taking decisions. However,
other factors such as the size of the spill and its location, time required for mobilizing
equipment and personnel and prevailing sea and weather conditions, will also strongly
influence the decision on which method to choose.
To ensure maximum efficiency of the dispersant treatment operation, particular attention needs
to be given to its logistic aspects:
Treatment of oil with dispersants requires the use of significant quantities of the
product. The dispersant quantity can be estimated at approximately 5 % of the
volume of oil which is planned to be treated when concentrate dispersants are
used. If conventional hydrocarbon-based products are used it can be up to
almost the same volume of oil (100%) to be dispersed. This explains why
nowadays conventional products are almost no longer used for the treatment.
Stockpiles of dispersants existing in most of the countries are usually planned to
be sufficient only for initial response. Pre-arrangements with manufacturers
and/or distributors are therefore recommended to provide additional quantities
of the product at an extremely short notice. International, regional, sub-regional
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and bilateral agreements with neighbouring countries should be considered in
advance in view of mutualising national stockpiles available in the region or in
remote countries. Particular attention should be given to custom pre-
arrangement to ensure smooth transboundary movement. Countries affected by
a spill requesting additional stockpiles and equipment can, in the framework of
the Protocol Concerning Cooperation in Preventing Pollution from Ships and, in
Cases of Emergency, Combating Pollution of the Mediterranean Sea, request
the assistance of REMPEC to facilitate the coordination of the regional
assistance.
Transportation of dispersant from the sites of storage, production or from the
airport of arrival (only airlifting the supplies from one country to another is fast
enough to bring dispersants to affected country in time) to the spill site or base
of operations, needs to be properly planned and precisely executed.
If large quantities of dispersants are utilised, their transportation from the stores
to the operations‟ base in road tankers or liquid containers is more efficient as
compared to transportation in drums. High capacity pumps should be used for
reloading of spraying units.
Maintenance of spraying equipment as well as vessels or aircraft included in the
operation should be planned. Supplies of the most important spare parts need
to be available at the base.
Fuel for vessels and aircraft needs to be available at the base and refueling
operations executed promptly in order not to delay spraying operations.
Problems are often encountered when aerial spraying is used, since in most
places the fuel for piston-engined aircraft is in short supply. If local aircrafts are
used, necessary arrangements for fuel supply are made in advance through the
contingency planning process.
Figure 30: Dropping zone, arranged on the coast
to operate a helicopter equipped with a spraying bucket
Generally speaking, helicopters can land or change the spraying systems, even
without landing, almost anywhere. Landing sites for small aircraft can be
improvised if proper airfields are not available. However, larger aircrafts need
long runways and only appropriate airports can be considered as bases for the
refueling and reloading of dispersants.
Accommodation for crews needs to be provided near the base. When larger
vessels are used for spraying, this problem is eliminated since the crews are
accommodated on board.
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Appropriate communication links, in particular those between spotter aircraft
and spraying units, are essential. VHF appears to have advantages over other
systems.
Permanent contact needs to be established with national aviation authorities to
obtain clearance for planned operations without delay.
If requesting aircraft through international assistance is considered, flight
authorizations, compatibility of the infrastructure (e.g. runway specification),
availability of specified fuel needs to be checked in advance, preferably when
preparing the contingency plan
13.
STORAGE OF DISPERSANTS
13.1
Storage
Quantity of dispersants to be stored for emergency response needs to be assessed during the
preparation of contingency plans. It will be calculated on the basis of the quantity needed
to respond to the most likely size of spill during the period necessary to bring in
replacement stocks. The time needed for stock replenishment (either by the manufacturers or
from other sources) has also to be negotiated and determined in advance (cf. Chapter 12).
Except for continuous release, arrival of new quantities of dispersants more than 48 hours after
the start of spillage will be useless in most cases.
Dispersants are most often stored in 200-litre steel drums, usually in open space or preferably
in sheds. Although the possibility that the drums will corrode from the inside should not be
neglected, it is more likely that the corrosion will start from the outside.
Accordingly, regular control of stored drums is strongly recommended. Alternatively,
dispersants may be sold and stored in plastic drums, which are corrosion resistant, however
these should be protected from direct sunlight in order to avoid their deterioration.
Delivery and storage of dispersants in bulk containers is also possible. From the operational
point of view, taking into account the need for quick response and hence the need for
transporting large quantities of the product, this option is preferred to storage in drums. Storage
in road tank trailers is even more practical.
Countries that make use of specialized anti-pollution vessels may opt for storage in vessels'
integral tanks. For spraying from other vessels, when the need arises, dispersants can be
transferred from storage containers to flexible pillow tanks, which can be placed on board
practically any vessel.
Relatively high capacity portable pumps, made out of materials resistant to the components of
dispersants, need to be available for the transfer of products from storage containers to
spraying units.
13.2
Ageing
Dispersants are a complex mixture of various components, and with ageing their properties
may be subject to changes, i.e. their stability is not necessarily good. During the prolonged
storage, certain components may separate from the solution in layers or even crystallize.
Usually dispersant deterioration results from bad storage conditions, dispersant quality may be
altered (e.g. dispersant stock polluted by an external product or dispersant tank overheated
under the sun for long periods…). Most often, deterioratio
ns are reflected as a loss of
effectiveness of the product. Therefore, it is advisable to check periodically the quality of the
products (e.g. laboratory controls every 2 years).
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Countries which have established approval or acceptance procedures regularly require the
information on shelf-life from the manufacturer of the product (cf. Chapter 6, paragraph 6.5).
Regardless of the manufacturer's declaration, the most reliable method for discovering
changes in the original quality of the stored dispersant is to periodically test its effectiveness
and to compare the results with the results obtained, using the same method and the same
product when it was fresh. Such tests can be easily carried out and do not necessitate
expensive laboratory equipment.
13.3
Disposal of aged stockpiles
Stockpiles of dispersant should be periodically checked for their quality and good conservation.
Ideally, stockpiles should be controlled for their efficiency periodically (e.g. every 2 or 3 years),
using laboratory test procedure.
In order detect corrupted dispersant stockpiles, a first assessment could consist in a simple
control of physical characteristics of the product (e.g. visual appearance, density, viscosity,
homogeneity, absence of decantation or separation phase). Any change in these
characteristics may show an alteration of the stockpile and lead to further consideration for its
replacement.
Aged dispersant stockpiles should be disposed when their characteristics, in particular the
efficiency does not meet the technical requirements of the approval procedure (refer to chapter 9).
Aged dispersant stockpiles disposal should be carried out as any industrial waste, through
specialised service companies. Alternatively the dispersant supplier may be required to take
care of the aged dispersant disposal when replacing it by new stockpile. In such a case
additional clause in the contract with the dispersant supplier may be required to ensure this
service.
BIBLIOGRAPHY
1. ITOPF (1986), Response to marine oil spills, ITOPF, London, U.K.
2. CONCAWE (1986), Oil spill dispersants efficiency testing: review and practical experience,
Report No. 86/52, CONCAWE, The Hague, The Netherlands.
3. Bocard, C. (1987), Basic considerations on the use of dispersants / Selection of dispersants
(Technical paper for MEDEXPOL 87 training course), Marseille, France.
4. Bonn Agreement (1988), Position paper on dispersants, Bonn Agreement, London, U.K.
5. IMO (1988), Manual on oil pollution, Section IV: Combating oil spills, IMO, London, U.K.
6. CONCAWE (1988), A field guide to the application of dispersants to oil spills, Report no. 2/88,
CONCAWE, The Hague, The Netherlands.
7. Bonn Agreement (1991), Amended Chapter 20 of the Bonn Agreement Counter Pollution
Manual (working paper), Bonn Agreement, Paris, France.
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France.
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environmental considerations, IMO, London, U.K.
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Technical report series volume 5.
11. Maritime Safety Authority of New Zealand, 2001. Oil spill dispersants. Guidelines for use in
New Zealand. Maritime Safety Authority of New Zealand.
12. GAOCMAO, 2002. Guidelines for the use of oil spill dispersants in the Gulf.area. GAOCMAO.
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Energy Institute.
14. CEDRE, 2005. Using dispersants to treat oil slicks at sea. Airborne and ship borne treatment.
Response manual. CEDRE.
15. NOWPAP MERRAC, 2005. Guideline for the use of dispersant.
16. National Research Council, 2005. Oil spill dispersant. Efficacy and effects. National Academic
Press.
17. ITOPF, 2005. Technical Information Paper - The use of chemical dispersants to treat oil spills.
ITOPF, London.
18. Lewis, A, Merlin, F, Darling, P, Reed, M, 2006. Applicability of oil spill dispersants. Part 1
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Overview. EMSA.
19. EMSA, 2007. Inventory of national policies regarding the use of oil spill dispersants in the EU
member states. EMSA.
20. 2007: Merlin F.X., The use of dispersant
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State of art
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WP2. Oil Spill Response at Sea
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SPREEX program.
21. MERRAC Technical Report No. 3. MERRAC
__________
REMPEC
MARITIME HOUSE, LASCARIS WHARF, VALLETTA VLT 1921, MALTA
rempec@rempec.org - www.rempec.org
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