Risk assessment for the benzene
leakage from a sunken ship
(沈没船からのベンゼン流出のリスク評価)

Marine Environment Systems Laboratory
66768 M2 Yoo Jung-moSupervisor Prof. Shigeru TABETAA table of contents
1. Introduction
1.1. Hazard map of wrecks aroundJapan
1.2. An accident outline
1.3. Location
1.4. A field research in Taiwan Strait
1.5. The purpose of this research

3.3. Computational and boundary
conditions
3.4. Simulations of benzene spillbehavior
4. Risk assessment
4.1. Introduction

2. MEC Ocean Model

4.2. Methods

3. Benzene Model

4.3. Results of numerical simulation

3.1. Governing equation
3.2. Model verification

5. Conclusions

1. Introduction
1.1. Hazard map of wrecks around Japan

Target ship (Samho Brother)

There are about 1,200 wrecks(over 100 tons) around Japan .
In USA, 150,000 wrecks
are reported.

Fig. 1. Wreck data around Northeast Asia (Kuroda 2006)
Notes: 1. Red circle: Position , 2. Black number: Hazard rank

1.2. An accident outline
1. 10th Oct, 2005
Samho Brother (Chemical Tanker: 3,100 tons of Benzene, UN1114 )capsized off the coast of Taoyuan after collision with another ship.
2. 27th Oct, 2005
Military actions to burn off the benzene by firing missiles at the ship Failed  Benzene spilled from the vessel at unknown rate

Sea bedFig. 2. Before and after military actions

1.3. Location

Fig. 3. An accident position: 24.57N-120.48E(70 kilometers offshore and 75 meters depth)

1.4. A field research in Taiwan Strait• On 26th April, 2007, research teams fromJapan and Taiwan launched to measure
benzene  Failed or not leaking ?

(a)

(b)

(c)

Fig. 4. (a) Injured fish (b) Installing ADCP (c) Water sampler

1.5. The purpose of this research• Obtaining the useful data for the planning of the optimal observation• To support fundamental data for Risk Evaluation and Risk Management

Forecasting model for benzene spills transport and fate

2. MEC Ocean Model• Continuity equation• Momentum equations in the x and y directions• Hydrostatic pressure equation

3. Benzene Model
Calculating U, V, W
by MEC Ocean Model
Droplet size
Buoyant velocity
Equation of number density

Benzene Model

Reynolds NumberDissolution rate
CLB, CDBFig. 5. A flow chart ofsimulation

3.1. Equations• Dissolution rate

• Buoyant velocity• Equation of number density

3.1. Equations• Evaporation rate (Mackay, D. et al., 1983)(8)(9)• Benzene transport equation

where CLB and CDB are concentrations of the liquid and dissolved benzene, respectively

3.2. Model verification
These are the first and only known field experiments for subsurface oil jet/plumes (Rye et al., 1997).
NorthMethod
1. Comparing with time that the firstCurrent speed
10 cm/s

droplet reaches the surface
2. The position comparison of oil jet/plume at a depth of 3 meters after 1
2 min 30 sec
A result of Method 1.
Yapa’s model
636 sec
Field experiment
600 sec
Present model
618 sec
A result of Method 2.
Field experiment40m from an origin
Present model
50m (Fig. 6.)

Spilled positionon the bottom

50 m
YSouthConcentrationof oil (kg/m3)

Fig. 6. Result of the position
comparisonX3.3. Computational and boundary conditions
Parameters for computation
1. Grid size: 1000m
2. Time step: 5sec
3. Calculation time: 24days
4. Beginning of leaking: 3rd to 4th day
5. Number of grids: 20 * 40 * 17(11,21)

6. Water depth: 75m (Uniform)
7. Calculation area: 20km by 40km

40km

Table 1 Benzene release scenarios
Y20kmX

Fig. 7. A schematic view ofcalculation domain

33°Wind speed(m/s)

Leaking rate(kg/s)

Dropletsize (m)Duration period (day)

15 (Summer)

100.011210 (Winter)

100.011

3

5100.0051

4

10

100.005

1

55

10.0051610

10.005

1

75

10.01

1810

10.01

1

3.4. Simulations of benzene spill behavior• Changes of droplet size, buoyant velocity, and dissolution rate with 8 cases (Table 1)(a) Droplet size(b) Buoyant velocity(c) Dissolution rate

Fig. 8. Time history profile in an accident position at 3 m depth: grid point (11,21)

3.4. Simulations of benzene spill behavior• Changes of concentrations of the liquid and dissolved benzene

(a)

(b)

Fig. 9. Time history profiles of concentrations of the liquid and dissolved benzene inCase 1 (a) and concentrations of the dissolved benzene in Case 1(10kg/s) andCase 7(1kg/s) in an accident position at 3 m depth: grid point (11,21)

3.4. Simulations of benzene spill behavior• Results of Case 1 (leaking rate: 10kg/s, droplet size: 0.01m)
20km

40km

YX

0kg/m3After 2h0.00110kg/m30.014

After 24h

3.3E-7 kg/m3

1.6E-5After 21d

Fig. 10. Horizontal distributions of concentration of the dissolved benzene
at 3 m depth
Note: Color bar: Concentration of the dissolved benzene (kg/m3)

3.4. Simulations of benzene spill behavior• Results of Case 1 (leaking rate: 10kg/s, droplet size: 0.01m)
40km

75m

0kg/m3After 2hZ0.0011

0kg/m3After 24h0.014

2.3e-8kg/m3

4.4e-4After 21dY
Fig. 11. Cross-sectional views of concentration of the dissolved benzene at 3 m depth
Note: Color bar: Concentration of the dissolved benzene (kg/m3)

3.4. Simulations of benzene spill behavior• Tidal effects on the subsurface benzene spills
Rank=1(dx=900m)
Rank=2(dx=300m)(12,22)

Rank=3(dx=100m)(7,10)

40km(4,5)(9,18)

20km

Fig. 12. A nested grid system

3.4. Simulations of benzene spill behavior• Tidal effects on the subsurface benzene spills
After 4h

After 6h

After 8hZY0kg/m30.060

After 10h

0kg/m30.07kg/m3

0.06

0After 12h

0kg/m3

0.075

kg/m30.06

After 14h

0kg/m30.06

Fig. 13. Cross-sectional views of the concentration of the dissolved benzene

4. Risk assessment
4.1. Introduction
In general seven steps can be identified addressing the key questions in an EcologicalRisk Assessment (ERA) (Fairman R. et el., 1999)
Problem Formulation
Hazard Identification
Release Assessment
Exposure Assessment

Benzene Model

Consequence or Effect Assessment

Daphnia Magna

Risk Characterization and Estimation

PEC/PNEC

Risk Evaluation

4.2. Methods• The 4th step: Exposure Assessment
PEC

Benzene Model• The 5th step: Consequence or Effect Assessment
PNEC values with Assessessment Factors(AF) of 100(OECD) or 1000(EU)(Tabel 2)
Daphnia Magna is chosen for ecotoxicity tests.

Fig. 14. A photo of Daphnia Magna

Table 2 Defined PNEC values [9]24hr(acute)

21d(chronic)

100(AF)0.08(mg/l)

0.01(mg/l)

1000
(AF)

0.008
(mg/l)

0.001(mg/l)• The 6th step: Risk Characterization and Estimation

4.3. Results of numerical simulations
20km

24 hours simulations

YX
40km

(a) An assessment factorof 100, Case 1 (10kg/s)(b) An assessment factorof 1000, Case 1 (10kg/s)

Fig. 15. Horizontal distributions of the PEC/PNEC ratio
at 3 meters depth, 24 hours after benzene spills
Note: Color bar: PEC/PNEC ratio(c) An assessment factorof 100, Case 7 (1kg/s)
0PEC/PNEC

1

4.3. Results of numerical simulations
20km

21 days simulations

YX
40km

(a) An assessment factorof 100, Case 1 (10kg/s)(b) An assessment factorof 1000, Case 1 (10kg/s)

Fig. 16. Horizontal distributions of the PEC/PNEC ratio
at 3 meters depth, 21 days after benzene spills
Note: Color bar: PEC/PNEC ratio(c) An assessment factorof 1000, Case 7 (1kg/s)
0PEC/PNEC

1

4.3. Results of numerical simulations(a) With an assessment
factor of 100

Case 1Case 3

Case 5

Case 7(b) With an assessment factor of 1000

Case 1Case 3Case 5Fig. 17. Histogram of polluted areas which PEC/PNEC ratio is over 1
at 3 meters depth

Case 7

5. Conclusions• In order to simulate benzene diffusion in Taiwan Strait, Benzene
Model is developed.
• Comparing with observation data of oil jet/plume, the present modelagrees well.
• An important factor to determine buoyant velocity, dissolution rate,and Reynolds number is the initial droplet size.
• Leaking rate and spill duration time strongly affect the concentrationof the dissolved benzene in water.
• Through the results of the risk assessment, the casualties would betremendous.

References• Papers[1] 黒田 貴子, 流出油防除のための環境影響評価と沈船の潜在的危険度評価[2] MEC Ocean Model オペレーションマニュアルVersion 1.1」, 日本造船学会海洋環境研究委員会, 2003.
[3] G. Alendal et al. 2001, Two-phase, near-field modeling of purposefully released CO2 in the ocean,
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Env. Sci. Tech, 17, 211– 217[6] Rye, H. et al., 1996. Subsurface oil release field experiment–observations and modeling of subsurface plume behavior,Proc., 19th Arctic and Marine Oil Spill Program (AMOP) Tech.Seminar 2, Env. Canada, Otawa, 1417–1435[7] Rye, H. et al., 1997. Verification of subsurface oil spill models, Proc., Int. Oil Spill Conf., Env. Canada, Ottwa, 551–577[8] Yapa et al. 1999, Modeling underwater oil/gas jets and plumes[11] Fairman R.et el. 1999. Environmental Risk Assessment – Approaches, Experiences and Information Sources. Monitoring and Assessment Research centre, King’s College, London. Published by European Environment Agency – EEA Env
ironmental issue report No 4.

• Books[4] R. Clift, J.R. Grace, and M.E. Weber, Bubbles, Drops and Particles, pp. 111-124, Academic Press, New York, 1978.
[5] Lars Olander, Equations and formulas for air and air contaminants• Websites[9] http://www.chem.unep.ch/irptc/sids/OECDSIDS/89612.pdf[10] http://yuiko.t.u-tokyo.ac.jp/mecnest/

Thank you for your attention!!!