Slide 1
© 2003 By Default!
Different aspects
of
oil spill dispersants
Alun Lewis
Oil Spill Consultant
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Slide 2
© 2003 By Default!
Purpose of Workshop
“To develop decision trees and guidance
for dispersant use
in the Netherlands EEZ of the North Sea”

Having a national policy regarding dispersant use
does not imply that dispersant use will be
automatically allowed in all (or perhaps any) areas
of the Netherlands EEZ

The guidance will provide the framework for
rational decisions to be made
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Slide 3
© 2003 By Default!
Important points

Dispersants are used to remove oil from the
surface of the sea
– If dispersed in deeper water, the spilled oil will not drift
into shallow water where most damage is caused
– Coastal habitats will not be polluted with oil

Successful use of dispersants inevitably means that
oil is transferred into water column
– Damage caused by dispersed oil is not inevitable
– Dispersion followed by adequate dilution causes
relatively little effect
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Slide 4
© 2003 By Default!
Three main questions about dispersants
1.
Will dispersants work?
–
2.
Will dispersing the oil do more good than harm?
–
3.
Sometimes, but not every time and not under all
circumstances
Any oil spill response that causes more damage than
the spilled oil is pointless. If dispersion of oil would
cause more harm than good, don’t do it!
How should dispersants be used?
–
–
Dispersant “approval”
Strategic and operational issues
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Slide 5
© 2003 By Default!
1. Will dispersants work?

Dispersion of spilled oil is a natural process caused
by wave action
– Low viscosity oils in very rough sea conditions naturally
disperse (e.g. the Braer incident in 1993)
– But natural dispersion stops when an oil ‘weathers’

Adding dispersant enhances this natural process
– Higher viscosity oils in calmer sea conditions will
disperse when dispersant is added

There are limits to dispersant capabilities
– High viscosity oils cannot be dispersed
– Limiting viscosity depends on sea-state
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Emulsification
Water depth (m)
0
1
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3
Natural dispersion
4
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Workshop on the use of oil spil
dispersants in the North Sea
Emulsification
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Emulsification
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Emulsification
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dispersants in the North Sea
Emulsification
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dispersants in the North Sea
Emulsification
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dispersants in the North Sea
Emulsification
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After many hours…
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Slide 26
© 2003 By Default!
The effect of dispersants

The active ingredients in dispersants (the surfactants)
greatly reduce the high interfacial tension between oil and
water

Surfactants act as a bridge between the oil and water
– The chemical barrier between oil and water is almost
totally removed

Mixing of the dispersant-treated oil and water by waves
causes very small oil droplets to be formed
– These will not float out anywhere near as fast
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Chemically enhanced dispersion
Water depth (m)
0
1
Spray dispersant onto spilled oil
2
3
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Workshop on the use of oil spil
dispersants in the North Sea
Dispersant enhanced dispersion
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Dispersant enhanced dispersion
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Dispersant enhanced dispersion
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Dispersant enhanced dispersion
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Dispersant enhanced dispersion
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Dispersant enhanced dispersion
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Dispersant enhanced dispersion
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dispersants in the North Sea
Dispersant enhanced dispersion
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dispersants in the North Sea
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Slide 44
© 2003 By Default!
Dispersion of small oil droplets

Small dispersed oil droplets will be rapidly diluted
by the water motion that exists under waves
–
They are kept in top few metres by water motion under
all waves (not just breaking waves)
– As they rise up due to limited buoyancy, they are then
pushed back down again into the water
– Normally penetrate only the top 10 metres of water, but
can go deeper in rougher seas
– Small dispersed oil droplets do not sink to the bottom
– Dispersed oil is rapidly biodegraded to a large extent by
natural micro-organisms in the sea
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Slide 45
© 2003 By Default!
1. Will dispersants work?

Consider this question first
–

If a dispersant does not work there is no point
considering the potential consequences (positive and
negative) of dispersing the oil
Decision-tree based on:
–
–
–
–
Should dispersants be used on the spilled oil?
Can the spilled oil be dispersed?
For how long will it be dispersible?
Are the sea conditions suitable for dispersion?
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Slide 46
© 2003 By Default!
2. Is the spilled oil of a type that is
dispersible?
YES OR NO
3. Is the oil likely to be within the time “window
of opportunity’ for dispersant use?
YES
OR NO
4. Are the sea conditions suitable for
dispersion?
YES OR NO
USE DISPERSANT
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DO NOT USE DISPERSANT
1. Should dispersants be used on the
type of spilled oil?
YES OR NO
Slide 47
© 2003 By Default!
Oil type
DISPERSE?
WHY?
Gasoline
NO
Dispersants would work,
Kerosene (Jet fuel)
NO
but would force toxic
Marine Gas Oil
NO
components of oil into
Marine Diesel Oil
NO
water column
Crude oil (paraffinic)
YES
Until the time
Crude oil (naphthenic)
YES
“Window of opportunity”
Crude oil (asphaltic)
YES
runs out
MAYBE
Pour Point?
Crude oil (waxy)
Hydraulic oil
NO
Lube oil
NO
IFO-30
YES
Until the time
IFO-80
YES
“Window of opportunity”
IFO-180
YES
runs out
IFO-380
MAYBE
Only at high sea
temperature or rough sea
IFO-500
NO
Viscosity too high
IFO-700
NO
Viscosity too high
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Slide 48
© 2003 By Default!
Is the spilled oil dispersible?
Oil type
DISPERSIBLE
FOR HOW LONG?
Crude oil (paraffinic)
YES
Until the time
Crude oil (naphthenic)
YES
“Window of opportunity”
Crude oil (asphaltic)
YES
runs out
MAYBE
Pour Point?
IFO-30
YES
Until the time
IFO-80
YES
“Window of opportunity”
IFO-180
YES
runs out
IFO-380
MAYBE
Only at high temperature
or rough sea
Crude oil (waxy)
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Slide 49
© 2003 By Default!
Oil “weathering” and the “window of
opportunity” for dispersant use

Crude oils and residual fuel oils are not pure chemicals
– Consist of an almost infinitely variable mixture of
hydrocarbons

Each individual crude oil and fuel oil will ‘weather’ at a
specific rate that depends on:
– Temperature (mainly sea temperature)
• High temperature causes rapid evaporation of volatile
components and therefore rapid viscosity increase
– Wind speed and sea state
• High wind speed and rough seas cause high rate of
natural dispersion, but also rapid emulsification
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Slide 50
© 2003 By Default!
The problem of “knowns and unknowns”
After Donald Rumsfeld

Does the “window of opportunity” for dispersant use have to
be determined precisely for every single oil that is
transported through the Netherlands EEZ of the North Sea?
– No
• A great deal of information is already available and
can be used
– Oil spill response is often about informed judgements,
not scientific precision
• EMSA recently sponsored the development of a
simple tool that gives an indication of the window of
opportunity based on available information
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Slide 51
© 2003 By Default!
Viscosity limits for dispersion

There are no accurate general oil viscosity limits for
dispersion. However, with a good dispersant:
Dispersion usually possible up to 5,000 cSt
Dispersion sometimes possible between
5,000 and 10,000 cSt
Dispersion unlikely when viscosity
above 10,000 – 20,000 cSt
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Slide 52
© 2003 By Default!
Sea conditions & wind speed for
dispersion

Dispersants require some breaking wave action to
work well
– Wind speed of at least 7 knots (Beaufort Force 2 to 3) for
rapid dispersion of oil
– If sea is very calm and dispersant is applied there will be
no rapid dispersion, but this will happen when and if the
sea gets rougher

Conditions can be too rough for effective dispersant
spraying
– Spilled oil becomes submerged by waves for a lot of the
time
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Slide 53
© 2003 By Default!
Beaufort Force 2 – Light breeze – 4 to 6 knot wind
No breaking waves:
Dispersant can be
sprayed, but will not
cause rapid
dispersion of spilled
oil
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Slide 54
© 2003 By Default!
Beaufort Force 7 – Near Gale - 28 to 33 knot wind
Starting to get too rough,
but if the crew can do it,
dispersant spraying still
possible
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Slide 55
© 2003 By Default!
Conditions suitable for dispersion
50
TOO ROUGH
Mean wind speed (knots)
45
40
35
30
25
20
15
10
5
0
0
1
2
3
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4
5
6
Beaufort Force
7
8
9
10
Slide 56
© 2003 By Default!
Information needed for the Netherlands
EEZ of the North Sea

Crude oil and residual fuel oil types transported
– “Safety at Sea” project has already identified major
imports, exports and trades in crude oils and Heavy Fuel
Oils

Typical sea temperature range
– Summer and winter temperatures at key locations

Statistical wind speed frequencies
– Wind roses at key locations
All of this information is available somewhere
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Slide 57
© 2003 By Default!
2. Will dispersing the oil
do more good
than harm?
If the dispersant would work, i.e. disperse the spilled oil,
will the use of dispersant reduce the overall damage that
would have been caused by the oil spill?
There is no generic answer of “Yes” or “No”
It all depends on the specific circumstances
of the oil spill
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Slide 58
© 2003 By Default!
Benefits and Risks of dispersant use

Dispersing the spilled oil into the water column can
be beneficial
– Spilled oil is removed from the sea surface and will not
drift ashore or into shallow water where it does most
damage

Dispersing the spilled oil into the water column may
pose a risk to some marine organisms
– Risk of harm is an effect of exposure and can be small if
dilution is sufficient

Does the potential benefit justify the potential risk?
– Net Environmental Benefit Analysis (NEBA)
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Slide 59
© 2003 By Default!
Over-simplification can lead to
incorrect conclusions

The decision to use, or not to use, dispersants is
sometimes seen as a simple balance between:
– The impact on resources most harmed by spilled oil on
the sea surface and the coast
• Seabirds, coastal species and habitats, tourist
beaches, etc.
– The impact on resources most harmed by dispersed oil
• Marine organisms, i.e. fish and shellfish

Use dispersants and the seabirds “win”
– but the fish “lose”

Do not use dispersants and the fish “win”
– but the birds “lose”
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Slide 60
© 2003 By Default!
Marine
organisms
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Seabirds
Coastal
species
Tourism
Slide 61
© 2003 By Default!
Seabirds
Coastal
species
Tourism
Marine
organisms
Use dispersants
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Slide 62
© 2003 By Default!
Marine
organisms
Seabirds
Coastal
species
Tourism
Do not use dispersants
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Slide 63
© 2003 By Default!
But it is often much more complicated than that

The ‘choice’ is often not simply between the effects
on the ‘resources’ of:
– Spilled oil on the sea surface
– Dispersed oil in the water column

Spilled oil does damage in various ways to various
organisms and resources
– Not all resources will be present, or in equal proportion, or are of
equal priority
– Response actions can only modify some of the impacts of spilled oil

Provided that there is adequate dilution, in many
circumstances dispersed oil will cause only limited and
temporary effects
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Slide 64
© 2003 By Default!
Damage caused by spilled oil

The damage caused by oil spills may be
caused by:
– Water-soluble crude oil components
• Exert toxic effects on marine organisms
– Spilled oil on the surface of the sea
• Contaminates the plumage of seabirds
– Spilled oil that drifts into shallow water and ashore
•
•
•
•
Smothers some coastal organisms,
Poisons some benthic organisms
Pollutes benthic and coastal habitats
Pollutes socio-economic resources such as fishermen’s
nets and tourist beaches
– Dispersed oil in the water column
• Ingested by some organisms, especially filter-feeder
shellfish
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Slide 65
© 2003 By Default!
“Toxic effects”

Lethal or sub-lethal
– Mortality (death) is a very unsubtle indicator of toxicity
– Sub-lethal effects can alter feeding or breeding behaviour

Acute or chronic
– Short-term, non-persistent or long-term and persistent

Reversible or irreversible
– ‘Tainting’ of fish flesh is reversible, carcinogenic effects are not

Effects on individuals or populations?
– Some individuals may be damaged / killed, but is the species
population affected?
Toxic effects are proportional to exposure
(Concentration and period of exposure)
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Slide 66
© 2003 By Default!
Physical effects of dispersant use

Water-soluble crude oil components
Maybe increased
(if used very soon after spill)

Spilled oil on the surface of the sea
Reduced

Spilled oil that drifts into shallow
water and ashore
Reduced

Dispersed oil in the water column
Increased
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Slide 67
© 2003 By Default!
Consequences of dispersant use

Water-soluble crude oil components
– Toxic effects on marine organisms

Spilled oil that drifts into shallow water
and ashore
–
–
–
–

(if used very soon after spill)
Spilled oil on the surface of the sea
– Contaminates the plumage of seabirds

Maybe increased
Smothers some coastal organisms
Poisons some benthic organisms
Pollutes benthic and coastal habitats
Pollutes socio-economic resources such
as fishermen’s nets and tourist beaches
Reduced
Reduced
Reduced
Reduced
Reduced
Dispersed oil in the water column
– Ingested by some organisms, especially
filter-feeder shellfish
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Increased
Slide 68
© 2003 By Default!
Dispersant use and fisheries

Dispersant use is often of great concern to
fishermen
– The concern is that dispersing the oil into the water
column will inevitably harm the fish stocks
– The concern is both financial (short-term and long-term)
and ecological

Most importantly, oil spills pose a threat to public
health through contamination of the food chain
– Fishing bans introduced when oil spills happen
– The implications of dispersant use need to be taken into
account
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Slide 69
© 2003 By Default!
Marine ecological habitats and their
inhabitants

Pelagic – open water, upper layers
– Roundfish: Herring, mackerel, sardines, sprats, bass, mullet

Demersal – near the sea bed
– Flatfish: Dover sole, plaice, flounder, turbot, monkfish and rays

Benthic – on (and in) the seabed
– Flat fish; plaice, rays
– Crustaceans: Lobster, crabs, crawfish, Nethrops and shrimp
– Molluscs: Cockles, mussels, scallops, oysters, clams, whelks,
periwinkles, cuttlefish & squid
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Slide 70
© 2003 By Default!
Effects of oil spills on fish

There is no evidence to date that any oil spill has killed
sufficient numbers of adult fish, or early stages, in the
offshore open ocean to significantly affect the population

The potential for damage is greater in inshore waters
– Adult fish swim away from spilled oil (if they can)

Fish plankton can be affected
– But fish ‘over-produce’ larvae in huge numbers to
overcome predation

Oil-polluted sediments can have an adverse effect on
benthic species (bottom-dwellers, such as flatfish)

Oil spills do affect inshore shellfish beds
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Slide 71
© 2003 By Default!
Dispersants and fisheries

Do not use dispersants:
– In shallow water (less than ~ 10m) where dispersed oil at
high concentration will come into contact with the seabed
• However, dispersant use reduces the tendency of
dispersed oil to stick to sediment and persistent oil
pollution of sediments will be lessened if dispersants
are used
– Near inshore fish spawning areas and nurseries
– Near shellfish beds
– Near aquaculture facilities
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Slide 72
© 2003 By Default!
1. What resources are at risk of damage by spilled oil?
2. Are the resources more sensitive to:
(a) Dispersed oil
(b) Spilled oil on the surface
(c) Oil that drifts ashore
NO
YES
YES
UNKNOWN
OR
OR
OR
YES
NO
NO
3. Is the water deep enough for dispersion without
threatening benthic organisms?
YES OR
NO
4. Is the spilled oil far enough away from shore for
dispersion?
YES OR
NO
5. Is the spilled oil far enough away from resources
particularly sensitive to dispersed oil? YES OR
NO
USE DISPERSANT
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DO NOT USE DISPERSANT
KNOWN
Slide 73
© 2003 By Default!
Every question poses another question

What water depth is sufficient for dispersion?
– Dispersed oil is slightly buoyant so will tend to stay in
upper water layers, the well-mixed zone
– 10 metre penetration is typical in moderate sea states
• (Beaufort Force wind speed 3 to 7)
– Goes deeper in very rough seas
– Diluted as it enters deeper water

What distance is far enough away for dispersion?
– Depends on prevailing currents
– 0.5 nautical mile or 1 nautical mile are distances typically
used
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Slide 74
© 2003 By Default!
How to present all this information?


On marine charts as sensitivity maps
Include:
– Coastal sensitivity to oil pollution based on shoreline type
– Coastal ecology
• Habitat types and species population
• Seasonal variations
– Marine ecology sensitivity maps
• Commercial fisheries
• Sea bed types mapped by MESH will give an
indication of marine habitats and probable species
– 10 and 20 metre water depths
– Particularly sensitive resources
• ecological and socio-economic resources
RETURN TO THIS LATER
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Slide 75
© 2003 By Default!
3. How should dispersants
be used?
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Slide 76
© 2003 By Default!
Dispersant “approval” and the law

Dispersant “approval”
– There are two separate issues:
• Dispersant product approval (an “approved”
dispersant list)
• Dispersant use approval (when and where
dispersants can be used)

Legislation and regulation of dispersant use
– Why is this needed?
– Depends on national laws and regulations controlling
the release of chemicals into the sea
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Slide 77
© 2003 By Default!
Dispersant “approval”

Two separate issues (often confused):
– Dispersant product approval
• Need to ensure that dispersant is of:
– Maximum permitted toxicity
– Minimum permitted effectiveness
– Dispersant use approval
• Need to ensure that the use of dispersant does not
cause more harm than good, i.e. make the oil spill
damage worse, rather than better
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Slide 78
© 2003 By Default!
Dispersant product approval

Not incident- or site-specific; is national

Toxicity testing
– Need not involve oil; aim is to ensure that the dispersant
is not too toxic for use
– Conduct a simple, standardised toxicity test (e.g.96 hour
LC50 procedure) on some marine species
– Not a simulation of dispersant use at sea

Effectiveness testing
– Use a ‘typical’ oil in an easy-to-repeat test
– Not a realistic simulation of dispersion at sea
– Set “pass mark”
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Slide 79
© 2003 By Default!
Dispersant use approval

Is incident- and site-specific

No toxicity testing involved
– Judgement of whether dispersed oil would cause a
hazard based on knowledge of:
• water depth
• water flow
• sensitivity to dispersed oil of resources near spill
location
– Use the marine charts containing relevant information to
define dispersant use and non-use zones
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Slide 80
© 2003 By Default!
Dispersant use zones used in France

Uses spill amount, distance and water depth to produce
maximum permitted dispersed oil concentration of 10 ppm
Spilled oil
(tonnes)
10
100
1000
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Distance from
shore
(nautical miles)
0.5
1.0
2.5
Water depth
(metres)
5
10
15
Slide 81
© 2003 By Default!
Land
Dispersant use
permitted on
Up to 10 tonnes oil
10 - 100 tonnes oil
100 - 1000 tonnes oil
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More than1000
tonnes oil
Slide 82
© 2003 By Default!
Dispersant use zones
Dispersant use permitted
Dispersant use permitted
only with specific prior permission
Dispersant use not permitted
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Slide 83
© 2003 By Default!
How to build up dispersant use / non-use zones
1. General limits set by water depth
–
Define water depth where dispersant use will not be
allowed under any circumstances red zone
• For example, less than 10 metres*
–
Define water depth where dispersant use will be
permitted without restriction green zone
• For example, 20 metres* or more
–
Zone in between is amber zone
*Water depths based on charts will be LAT (Lowest Astronomical Tide)
and real water will almost always be deeper
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Slide 84
© 2003 By Default!
How to build up dispersant use / non-use zones
2. Put coastal and marine sensitivities on chart
–
–
–
Shoreline types, habitats species populations
Establish priorities for protection
Decide what is more sensitive to:
• Spilled oil on the sea surface
• Dispersed oil
3. Modify size and position of zones to reflect
sensitivities and protection priorities
–
Try to eliminate amber zones where possible
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Slide 85
© 2003 By Default!
How to build up dispersant use / non-use zones
4. Consider water movement caused by ebb and
flood of tides
–
–
Restrict dispersant use to prevent dispersed oil coming
onto mudflats with the tide
Only allow spraying when tide is going out
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Slide 86
© 2003 By Default!
Conclusions

There are several sets of “decision trees” that could
form guidance for decisions about dispersant use in
the Netherlands EEZ of the North Sea

This information should not stand alone, but be part
of the Netherlands National Contingency Plan
(NCP)
– The essential part is a comprehensive sensitivity map /
chart of the Netherlands EEZ of the North Sea
– This enables rational decisions to be made about any oil
spill response (including dispersant use)
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Slide 87
© 2003 By Default!
The simple decision making process can then
be reduced to:
Will dispersants work?
– Consult subsidiary decision trees
YES
2.
3.
OR
NO
Will dispersing the oil do more good
than harm?
– Consult dispersant use / non-use
zones on charts
YES OR
NO
How should dispersants be used?
– Approved dispersants available?
YES
USE DISPERSANT
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OR
NO
DO NOT USE DISPERSANT
1.
Slide 88
© 2003 By Default!
But how could we actually use
dispersants?
See later:
STRATEGIC AND OPERATIONAL ASPECTS
OF THE APPLICATION
OF
DISPERSANT BY AIRCRAFT
Chris Francis
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