Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region
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- Injection systems
- Figure 28: Application of dispersant pre-diluted into sea water
- Figure 29: Neat Concentrate dispersant spraying system for boat
- Figure 30: Dropping zone, arranged on the coast to operate a helicopter equipped with a spraying bucket
- 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
- BIBLIOGRAPHY
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region Part II: Basic information on dispersants and their application – Page 31
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.
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…).
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.
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region Part II: Basic information on dispersants and their application – Page 32
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.
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
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region Part II: Basic information on dispersants and their application – Page 33
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.
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.
operation should be planned. Supplies of the most important spare parts need to be available at the base.
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.
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.
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region Part II: Basic information on dispersants and their application – Page 34
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).
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region Part II: Basic information on dispersants and their application – Page 35
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.
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.
8. Merlin, F. (1991), Selecting dispersants and periodic checking of their quality, CEDRE, Brest, France.
9. IMO / UNEP (1995), IMO / UNEP guidelines on oil spill dispersant application and environmental considerations, IMO, London, U.K.
10. IPIECA, 2001. Dispersants and their role in oil spill response – 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. 13. Energy Institute, 2004. Operational guidelines on the use of oil spill dispersants at sea. 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.
ITOPF, London.
18. Lewis, A, Merlin, F, Darling, P, Reed, M, 2006. Applicability of oil spill dispersants. Part 1 –
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 – State of art – WP2. Oil Spill Response at Sea –
SPREEX program. 21. MERRAC Technical Report No. 3. MERRAC
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