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Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
1
118 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Risk analysis
Oil and chemical pollution in Danish waters
Jørgen Kampmann, COWI
Carsten Jürgensen, COWI
218 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Background
The auditors of public accounts appointed by the Danish Parliament (Folketinget) recommended that a new risk analysis of oil and chemical spills be prepared.
The Ministry of Defence Denmark intends to prepare a plan for development of the emergency forces in Danish water on the basis of a risk analysis
EU request for tenders for such risk analysis was won by COWI
Work started April 2006 and was completed March 2007
The resulting reports (in Danish with English summary) will be published in relation to a symposium on marine environment in Copenhagen 21. May 2007
318 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Main requirements to the risk analysis
The risk analysis shall be a planning tool:
– Magnitude of risk and distribution on different parts of Danish waters, different types of spills etc. shall be described
– Risk analysis model to be constructed such that in the future, it will be possible to model the effects of different locations andconfigurations of the emergency services
The actual configuration of the emergency services is not to be considered. Instead an assumed generic model of the emergency response is used
The development until 2020 shall be modelled:
– today (1. July 2005 to 30. June 2006)
– 2010
– 2015
– 2020
418 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Illustration of risk of oil and chemical pollution
Frequency of spills
Consequence of spills
RiskSpill of oil and
chemicalsActivities in
Danish waters
Emergency response to spills
Risk reduction measures
518 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Relationship between spill effect and damage to the marine environment
Spill of oil and chemicals
Spreading and spill effect
Vulnerability Index
Damage to environment = spill effect X vulnerability index
618 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Approach for the risk analysis
Risk reduction measures
Ship traffic and other ship activities
Types and quantities of oil and chemicals
Identification of sources of
spills
Spill scenarios:- cause- type of spill- magnitude- location
Spill effect
Vulne-rability
Emergency response to spills
Spill frequency
Risk of spill effect
Risk of damage to
environment
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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718 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Approach for the risk analysis Modelling of the future
Prognosis for ship traffic
Future risk reduction
Identification of sources of spills
Spill scenarios:- cause- type of spill- magnitude- location
Spill effect
VulnerabilityEmergency
response to spills
Risk reduction measures
Ship traffic and other
ship activities
Types and quantities of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
Risk reduction measures
Ship traffic and other
ship activities
Types and quantities of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
818 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Ship traffic today = 1. July 2005 - 30. June 2006
AIS-data =>Intensity of ship traffic
918 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Ship traffic:Route net
AIS-signals are allocated to legs of the route net
Ship size and type found from Lloyd's
1018 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Ship traffic todayExample: All tankers
1118 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Transport of oil and chemicals in Danish waters
Classification of oil and chemicals
Description of the quantities onboard the ships:
– Cargo in bulk: Tankers, bulk carriers
– Cargo in packaged form: Container, general cargo, RO-RO, ferries
Sources:
– Reporting to SHIPPOS. Information on cargo incl. ballast for
Ships ≥ 20.000 GT
Ships with draught ≥ 11 m
Loaded oil, gas and chemical tankers ≥ 1.600 GT
Data from 1. May. to 21. Aug. 2006 used.
– HazMat. Ships with dangerous or polluting cargo to/from Danish harbours
1218 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Classification of oil and chemicals
Behaviour when spilled to the sea:
– Evaporating
– Floating
– Malfloating
– Soluble
– Sinking
Reacting: According to the result of the reaction
Hazard to the environment: MARPOL Annex II, A, B, C, D or "other"
Hazard to the personnel of the emergency services:
– Health
– Fire
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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1318 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Classification Hazard to environment, health and fire hazard
General
Hazard toenvironment:
Health andfire hazard:
Not hazardous
Less hazardous
Most hazardous
Other
MARPOL Annex II: C and D. Oil
MARPOL Annex II: A and B
More hazardous than crude oil
1418 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Classification of chemicals
14/ BentonitNot relevant
13/ MolassesNot relevant
12/ TarNot relevant
Sinking
11/ MethanolNot relevant
10/ MTBENot relevant
9/ AcrylonitrilNot relevantB
8/ Acetone cyanohydrinNot relevantASoluble andreacting and then soluble
7/ Toluene
5/ BenzeneFloating
1Not relevantEvaporating
Cargo group number/example chemical
FireHealthEnvir-onment
Behaviour when spilled to sea
1518 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Classification of oil
22/ gasolineFloating
21/ dieselFloating
20/ fuel oilFloating/malfloating
19/ crude oilFloating
18/ vegetable oilFloating
Cargo group number/example chemical
FireHealthEnvir-onment
Behaviour when spilled to sea
1618 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Quantities of oil and chemicals transported in bulk
SHIPPOS gives:
– Cargo group or ballast for reporting ships
– Distribution of reporting ships on Great Belt and the Sound
Extrapolation to all ship sizes and waters
Result, cargo in bulk i Great Belt and the Sound mill. tons/yr:
Chemicals harmful to environment:
Floating, yellow: 0.5
Soluble, red: 0.2
Soluble, yellow: 10
Sinking: 0,1
Oil: 190
Chemicals harmful to environment 11
Chemicals not harmfulto environment 21
Other (e.g. coal) 90
1718 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Identification of sources of spillsand spill scenarios
Prognosis for ship traffic
Future risk reduction
Identification of sources of
spills
Spill scenarios:- cause- type of spill- magnitude- location
Spill effect
VulnerabilityEmergency
response to spills
Risk reduction measures
Ship traffic and other
ship activities
Types and amounts of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
1818 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Identification and scenarios for spill of oil and chemicals
Accidents at sea (accidents with damage to ship > 300 GT):
– Spill of cargo from ships with cargo in bulk
– Spill of bunkers (oil for use onboard) from all types of ship
Spill during transfer of oil at sea due to errors or equipment failure
– STS operations, Kalundborg and Frederikshavn
– Bunkering at sea, Copenhagen, Great Belt, Ålbæk bight
Deliberate or inadvertent spills, eg.
– tank cleaning or emptying of waste oil tanks
– faulty cooling systems
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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1918 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Spill scenariosSpill sizes
0.3 tons (representing spills < 1 ton)
3 tons (representing spills between 1 and 10 tons)
30 tons (representing spills between 10 and 100 tons)
300 tons (representing spills between 100 and 1,000 tons)
3,000 tons (representing spills between 1,000 and 10,000 tons)
30,000 tons (representing spills > 10,000 tons)
For accidents at sea spill size 0.3 tons is not considered.
2018 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Spill frequency
Prognosis for ship traffic
Future risk reduction
Identification of sources of spills
Spill scenarios:- cause- type of spill- magnitude- location
Spill effect
VulnerabilityEmergency
response to spills
Risk reduction measures
Ship traffic and other
ship activities
Types and amounts of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
2118 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Spill of oil and chemicals Main results
350180Deliberate or inadvertent
21.4Transfer of oil at sea
2,2000.9Accidents at sea
Quantity
tons/yr
Frequency
Spill/yr
Type
2218 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Spill from accidents at seadistribution on spill size
1,6005109970.4Quantity, tons/yr
0.0450.150.320.220.12Frequency, spill/yr
30,0003,000300303
Spill size, tonsOil and chemicals harmful to environment
2318 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Spill quantities, accidents at sea distribution on types of spill, tons/yr
1001,900Total
4
2
100
1
Chemicals harmful to environment
Floating, yellow
Soluble, red
Soluble, yellow
Sinking
1,500
370
Oil
Cargo
Bunkers
2418 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Modelling of accidents at sea
General
Collisions
Grounding
Frequency of accident at sea
Frequency of spill given accident
Distribution on size in case of spill
Theoretical model
Modelling of damage to the ship that is hit
Based on Danish statistic
Based on literature
Based on literature
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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2518 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Spill from collisions and groundings
largest dot: 0.01 - 0.1 per yr
2618 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Effect of spillsEmergency response and combat
Prognosis for ship traffic
Future risk reduction
Identification of sources of spills
Spill scenarios:- cause- type of spill- magnitude- location
Spill effect
VulnerabilityEmergency response to
spills
Risk reduction measures
Ship traffic and other
ship activities
Types and amounts of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
2718 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Effect of spills
Types of spreading:
– Oil and floating chemicals
– Soluble chemicals
– Sinking chemicals
Modelling of a spill event (oil example):
– How and where does the oil spread?
– How large quantities / for how long time?
2818 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals
Task: A model for spreading, which is applicable on 400,000 scenarios (80 points, 8 types, 5 spill sizes, 4 seasons, 12 wind directions, 3 wind speeds)
Simplified model based on
– Calculation by complex models for selected cases
– Analytical models
Parameters
– Slick radius based on volume, oil type and duration
– Fate incl. emulsification based on oil type and duration
– Drift direction and drift speed based on wind direction, wind speed and region
2918 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Model for oil on water
Påvirkning af kyst
Hydrografisk område 2
UdslipHydrografisk område 1
Processer:
Drift og spredning:
Henfald, emulgering mm:
Malflydning:
Bekæmpelse:
Region 2
Region 1
Impact on coast
Processes
Drift and spreading,
AND Fate, emulsification, etc.,
OR Submersed oil,
AND Combat.
Spill
3018 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Modelling of response
Main parameters:
– Capacities of pump-skimmer system
– Capacity of booms:
Length
Tow velocity
– Accident-combat time:
T1
T2
T3
– Maximum significantwave height
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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3118 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Modelling of combat
Input parameters for each area:
Application of assumedgeneric response:
– Realistic but not authentic
– Same parameters for all areas
0.7Non-dimensional
Reduction factor for health hazard class "red"
0.7non-dimensional
Reduction factor for fire hazard class "red"
0.5non-dimensional
Recovery efficiency for chemicals compared to oil
1.3mMax. significant wave height
Spring: 0.4Summer: 0.2Fall: 0.4Winter: 0.6
non-dimensional
Darkness coefficient (ratio of time where combat not is possible due to too little daylight)
Spring: 0.02Summer.: 0.01Fall.: 0.02Winter: 0.04
non-dimensional
Visibility coefficient (ratio of the time where combat not is possible due to fog and haze)
V1: 1V2: 1V3: 1
KnotTow speed at time T1, T2 and T3
T1 : 2T2 : 4T3 : 6
hourAlarm-combat time T1, T2 and T3
L1: 300*)L2: 600L3: 1200
mAccumulated. length of booms at time T1, T2 and T3
Cap1: 0*) Cap2: 50Cap3: 100
m3/hAccumulated capacity of pump-skimmer system at time T1, T2 and T3
Model-responseDimensionParameter
3218 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Modelling of soluble chemicals
Determination of the downstream distance where the mixing reduces the concentration to the no-effect-concentration. Basis:
– Spill volume and type (3 chemicals)
– Eco-toxicological limit value (no-effect-concentration)
– Applied model is widely used for assessments of spills from offshore platforms
Result: Affected area:
Flow
3318 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Risk of spill effect
Prognosis for ship traffic
Future risk reduction
Identification of sources of spills
Spill scenarios:- cause- type of spill- magnitude- location
Spill effect
VulnerabilityEmergency
response to spills
Risk reduction measures
Ship traffic and other
ship activities
Types and quantities of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
Risk reduction measures
Ship traffic and other
ship activities
Types and quantities of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
3418 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Risk of spill effects Oil and floating chemicals
Risk of spill effects = Effect of spills x frequency of spills
Representation of frequency: Events/year
Representation of effect of spills:
– On the coast: tons on coast
– On the sea surface: tons in grid element x duration
3518 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicalsRisk of spill effect on the sea
Effect: 10 t/km2 x 10 hours = 0.0114 t/km2 x year
Frequency: 0.01/year = 1/100 year
Risk: 0.0114 t/km2 x year x 0.01/year = 114 g/km2
10 hours 10 hours
100 yrs
time
3618 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals. Sea accidents.Risk of spill effect at present, no response
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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3718 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals. Sea accidents.Risk of spill effect at present, no response
Risk in Danish waters (all spill sizes):
• No emergency response: 8.0 tons
• Assumed generic response: 7.4 tons
Reduction: 7 %
3818 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals. Sea accidents.Risk of spill effects at present, without 30,000 tons spills
No emergency response With assumed generic response
3918 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals. Sea accidents.Risk of spill effects at present, without 30,000 tons spills
No emergency response With assumed generic response
Risk in Danish waters (except 30,000 t):
• No emergency response: 3.8 tons
• Assumed generic response: 3.3 tons
Reduction: 13 %
4018 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Risk of spill effectsSoluble chemicals
Soluble chemicals
Risk of spill effects = Frequency of spills x effect of spill
Representation of frequency: Number of events/year
Representation of effect: Affected or not-affected (1 or 0)
Risk of spill effects: Number of events /year
4118 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Soluble chemicalsRisk of spill effects at present
Red: 1 - 3 times per 1,000 year
Light red: 0.3 - 1 times per 1,000 year
4218 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Risk of damage to marine environment
Prognosis for ship traffic
Future risk reduction
Identification of sources of spills
Spill scenarios:- cause- type of spill- magnitude- location
Spill effect
VulnerabilityEmergency
response to spills
Risk reduction measures
Ship traffic and other
ship activities
Types and amounts of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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4318 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Sensitivity index
13 different environmental parameters are included
The spatial distribution (abundance) for each parameter is mapped
Each parameter is weighted for its sensitivity towards 3 substance groups:
1. Oil and chemicals on sea surface
2. Soluble chemicals
3. Sinking chemicals
The cumulative sensitivity is integrated over all 12 parameters for each substance group (=> 3 maps)
The above is repeated for each season(=> 4 maps)
Result: 3 x 4 sensitivity maps
4418 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Vulnerability index
033002300440Nesting sea birds
440021104400Migrating sea birds
000400020004Wintering sea birds
444444444444Wadden Sea / marsh land
444444444444Protected areas
FallSpringSum-mer
WinterFallSpringSum-mer
WinterFallSpringSum-mer
Winter
Sinking chemicalsSoluble chemicalsOil on water surface
233134422331Spawning and Nursery Area
333322224444Marine Mammals
111144444444Rocky Shores
111111111231Sandy Beaches (Recreation)
111111112222City Areas
233233333342Shallow Areas (<10m)
000044443333Fish Farms
334234424444Archipelagos, Stone Reefs
4518 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Vulnerability map, Oil and floating chemicalsSpring
4618 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals, sea accidents,Risk of damage to environment, at present, no emergency response
4718 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals, sea accidents,Risk of damage to environment, at present, no emergency response
Risk of damage to the environment, Danish waters:
• No emergency response: 57 tons weighted
• With assumed generic response: 53 tons weighted
Reduction: 7 %
4818 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals, accidents at sea,Risk of damage to the environment, at present
Risk of spill effects Risk of damage
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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4918 apr 07
#Risk analysisOil and chemical pollution in Danish waters
The future
Prognosis for ship traffic
Future risk reduction
Identification of sources of spills
Spill scenarios:- cause- type of spill- magnitude- location
Spill effect
VulnerabilityEmergency
response to spills
Risk reduction measures
Ship traffic and other
ship activities
Types and quantities of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
Risk reduction measures
Ship traffic and other
ship activities
Types and quantities of
oil and chemicals
Spill frequency
Risk ofspill effect
Risk of damage to
environment
5018 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Prognosis for ship traffic
Principles
– Development of trade into and out of the Baltic Sea from Baltic Maritime Outlook
Prognosis for 2010 and 2020
Carried out for EU and national authorities
– Special assessment of oil export from Russia
– Distribution of trade on types of ship based on SHIPPOS (bulk) and judgement (packaged goods)
– Increase in average size of ship estimated for different types of ship
Results for each type of ship and DWT class:
– Factor on number (greater factor for large ships than for small)
5118 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Development in oil export from Russia
mill. barrels/day = 50 mill. tons /yr
Increase:
2003 to 2010: 5,7 % /yr
2010 to 2020: 1,2 % /yr
Oil production and consumption in Russia and other FSUSources: MSR-consult & IEA, World Energy Outlook 2006
ConsumptionProductionExport surplus
5218 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Increase in traffic compared to today (1. July 05 -30. June 06) sailed nautical miles
25 %26 %
15 %14 %
26 %33 %
2020:All shipsTankers
16 %20 %
10 %12 %
17 %26 %
2015:All shipsTankers
9 %18 %
5 %12 %
10 %21 %
2010:All shipsTankers
All Danish waters
The SoundGreat Belt
5318 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Risk reduction
Risk reduction measures
– Proposal from the government's action plan from 2004
– Other measures such as general IMO and general development of ship design, primarily based on information from Danish Maritime Authority
Impact on frequency of accidents
≈ 0 %≈ 1.00"negligible"5
5 %0.95"small"4
20 %0.80"considerable"3
50 %0.50"large"2
80 %0.20"very large"1
Risk reductionEffect factorQualitative description
Category of measure
5418 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Most important measures
Pilot: Effect factor 0.5
Increased use of pilots due to
– systematic calls to all ships recommended to use pilots in Danish waters according to IMO recommendations
– a number of measures considered as "overall increased surveillance"
VTS Great Belt and VTS the Sound from 2010:Effect factor 0.5
ECDIS: Effect factor 0.5 for groundingsPercentage of ships with ECDIS increasing from 20 % today to 100 % in 2020
Double hull at cargo tanks: All tankers from 2010
Double hull at bunker tanks: New ships > 10,000 DWT from 2010
Risk analysis Oil and chemical spills in Danish WatersHELCOM Response Group 18. Apr. 2007
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5518 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Results for the future Changes compared to situation today, all Danish waters
+ 45 %+ 22 %+ 8 %Risk of damage to environment, oil and floating chemicals
+ 53 %+ 29 %+ 14 %Risk of spill effects, oil and floating chemicals
+ 41 %+ 21 %+ 9 %Spills, tons/yr
+ 4 %- 5 %- 11 %Spills, number/yr
202020152010
5618 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Risk of damage to environment, changes compared to situation today, selected parts of Danish waters
+ 45 %+ 22 %+ 8 %All Danish waters
+ 65 %+ 42 %+ 29 %12 Bornholm
+ 67 %+ 44 %+ 31 %4 Kattegat North
+ 66 %+ 42 %+ 27 %10 Kadetrenden
- 32 %- 38 %- 40 %8 The Sound
+ 1 %- 15 %- 24 %7 Great Belt
+ 77 %+ 47 %+ 30 %3 Skagerrak
202020152010Part of Danish waters
5718 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Oil and floating chemicals. Accidents at sea Risk of damage today and in 2020, no emergency response
today 2020
5818 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Summary, the model
Provides modelling of the pollution risk all the way from a description of the ship traffic to the impact on the environmentincluding the effect of the emergency response
Presents a picture of the distribution of the risk
– in the waters considered
– on the different spill sizes and spilled substances
Allows calculation of the effect of changes:
– Development of the ship traffic
– Introduction of risk reduction measures
– Development of the emergency response
5918 apr 07
#Risk analysisOil and chemical pollution in Danish waters
Summary, results for Danish waters(entrance to the Baltic Sea)
Harmful chemicals are small fractions of oils and chemicals transported and spilled
Major contributor to risk is very large spills of oil (class 30,000 t), which has not occurred yet
The most exposed area is the Great Belt
Assumed generic emergency response to spills gives 7 % reduction in spill effects for all spills, and 13 % when very large spills (class 30,000 t) are not consideredThis is in accordance with international experience
In the future the risk will increase due to increase in number and size of the ships despite the risk reduction measures, except for Great Belt and the Sound where VTS is introduced