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
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Page 8
Figure 5: Aerial dispersant application with a DC3 aircraft
from the UK authorities (source MPCU)
The possibility of balancing properly these advantages and disadvantages decreases in an
emergency situation, and accordingly the use of dispersants and its place in a general
response strategy for oil spills needs to be defined in advance. Where and under which
circumstances the use of dispersants will be given priority over other available combating
methods needs to be analysed and decided during the preparation of the contingency plan. By
evaluating different interests for each particular zone, geographical boundaries may be defined
within which dispersants may or may not be used. As a general rule, dispersants should not be
used in the areas with poor water circulation, near fish spawning areas, coral reefs, shellfish
beds, wetland areas, and industrial water intakes (Refer to Part III of these Guidelines).
Massive oil spills also often necessitate international co-operation. Application of dispersants
may be a part of the assistance offered to a country confronted with such a spill. In order to
facilitate inclusion of offered assistance in the national response activities, some countries or
groups of countries (Bonn Agreement countries) have agreed to mutually accept the
application of products approved for use by each country, in case of emergency. Part I
(“Regional Appoval”) of these Guide
lines provides guidance on regional cooperation.
When such a general policy has been adopted in advance, a final decision on the use of
dispersants in a spill situation will have to be taken only on the basis of given circumstances
(type of oil, conditions, availability of material and personnel, etc.). The preparation of decision
trees to help responsible officers greatly facilitates this process (Refer to the Annex of Part III of
these Guidelines).
Taking a decision on the use of dispersants is one of the priorities in each spill situation since
relatively shortly after the spillage most oils will no longer be amenable to chemical dispersion.
Once the decision to use dispersants has been taken, the strategy of their use becomes
decisive for the positive outcome of the operation. From a strategic viewpoint, some basic
principles in this regard can be defined:
dispersants should be applied to the spill as early as possible;
dispersant spraying operation should be terminated when the oil reaches the
state of weathering (viscosity, mousse formation) in which it is not readily
dispersed anymore;
if the oil is approaching a sensitive area, dispersants should be applied to the
part of the slick nearest to it.
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
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Page 9
In case of a massive oil pollution affecting an extensive area, it is possible and often necessary
to use a combination of spill response methods. In such situations dispersants can be used on
one part of the slick while oil is mechanically recovered on the other end of it.
On location dispersant should be applied according to specific operational rules such as:
dispersants should be applied to thick and medium thick parts of the slick and
not to the low thickness areas (sheen);
treatment should be methodical, in parallel and contiguous or slightly
overlapping runs;
it is important to treat the slick against the wind;
vessels are suitable for treatment of smaller spills near the shore, but aircrafts
permit a rapid response (less than 24 hours after the spillage), in particular
when large offshore spills are concerned;
regardless of whether dispersants are sprayed from vessels or aircraft, spotter
aircraft should be used for guiding them and assessing the results.
Figure 6: Spotter aircraft of the British Maritime Coastguard
Visual aerial observation, complemented with photography, video recording or using one of the
available remote sensing techniques should be used for evaluating the results of the
application of dispersants. Such reports and records can be also used for record keeping
purposes of the different phases of the operation.
Finally, from a practical viewpoint, countries which decide to consider the use of the chemical
dispersion in the response strategy need to pay particular attention to:
a) storage of sufficient quantities of selected and approved products;
b) procurement and maintenance of adequate spraying equipment;
c) training of personnel on all aspects of dispersants use, including organizing
practical exercises at regular intervals.