casualty analysis of large tankers

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ORIGINAL ARTICLE

J Mar Sci Technol (2007) 12:240250DOI 10.1007/s00773-007-0255-8

E. Eliopoulou A. Papanikolaou (*)National Technical University of Athens, Ship Design Laboratory, 9, Heroon Polytechniou 15 733 Athens-Zografou, Greecee-mail: [email protected]

Casualty analysis of large tankers

Eleftheria Eliopoulou Apostolos Papanikolaou

and Control (POP&C1), casualty data for the Aframax class of tankers were systematically analyzed and post-processed as necessary for the application of a risk-based methodology regarding pollution prevention and control resulting from tanker accidents.

Further studies beyond those of the POP&C project were conducted independently by the Ship Design Labo-ratory of the National Technical University of Athens (NTUA), addressing Suezmax, Very Large Crude Car-riers (VLCC), and Ultra Large Crude Carriers (ULCC) tankers, and thus practically all classes of large tankers are included in the overall results presented herein. The results show remarkable trends for tanker accidents in the study period (19782003) and enable the identifi ca-tion of accident and pollution rates, which are necessary for the implementation of risk-based methodologies in tanker design and operation. Also identifi ed are the heavily polluted worldwide geographical areas as a result of tanker accidents. An effort has been made to link observed trends to historical developments in tanker design and operation (introduction of the double-hull concept), to the age of the tanker fl eet at risk, and to the effects of relevant international regulations introduced, particularly the International Convention for the Pre-vention of Pollution from Ships (MARPOL) and the US Oil Pollution Act OPA90.

2 Approach

2.1 Tanker casualty databases

Raw accident data are nowadays available from the well-established Lloyds Marine Information Services Ltd (LMIS). Much of the accident information con-

Abstract This article presents detailed results of a com-prehensive analysis of recorded accidents of large oil tankers (deadweight greater than 80 000 tonnes) occur-ring between 1978 and 2003. The analysis encompasses a thorough review of available raw accident data and their postprocessing in a way to produce appropriate statistics useful for the implementation of risk-based assessment methodologies. The processing of the cap-tured data led to the identifi cation of signifi cant qualita-tive historical trends of tanker accidents and of quantitative characteristics of large tanker accidents, such as overall accident rates per ship-year. Data were also analyzed for all major accident categories sepa-rately, taking into account tanker ship size/type, the degree of accident severity, and the oil spill tonne rates per ship-year; this led to the identifi cation of heavily polluted worldwide geographical areas as a result of large tanker accidents.

Key words Analysis of tanker accidents Tanker pollution Risk assessment

1 Introduction

The prime objective of the present study was the identi-fi cation and quantifi cation of the main hazards that may lead to a tankers loss of watertight integrity and may consequently cause environmental damage. Within the framework of EU-funded project Pollution Prevention

Received: June 1, 2006 / Accepted: June 26, 2007 JASNAOE 2007

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J Mar Sci Technol (2007) 12:240250 241

tained in the LMIS database is, however, in textual format. Consequently, it is diffi cult to extract and analyze this information systematically without further postpro-cessing. In addition, the LMIS accident categorization is insuffi cient for the implementation of a rational risk-based methodology, as necessary for the evaluation a ships loss of watertight integrity and the ensuing envi-ronmental damage, as proposed by the POP&C project (Papanikolaou et al.2).

Therefore, a new rational database was fi rst devel-oped to enable the full exploitation of existing accident information for Aframax tankers. The ultimate purpose of this new database was to facilitate the population of the POP&C Risk Contribution Fault Trees (FTs) and Event Trees (ETs) by a team of POP&C experts, consid-ering the main six identifi ed categories of accidents/hazards, namely collision, contact, grounding, nonacci-dental structural failure, fi re, and explosion accidents, which can potentially lead to loss of watertight integrity (LOWI) of a tankers hull. A detailed description of the POP&C casualty database is presented by Papanikolaou et al.3

Based on the same concept, two additional databases were developed by the Ship Design Laboratory of NTUA, namely one for Suezmax tankers and another containing the largest tanker sizes, namely VLCC and ULCC tankers. These databases were populated accord-ing to the POP&C procedure by diploma thesis students of NTUA under the supervision of the authors (Kanellakis4 and Bourikas5).

2.2 Sample of data

The analysis presented herein focuses only on accidents that could potentially lead to a ships loss of watertight integrity (LOWI). The period of occurrence of accidents studied was 26 years, from 1978 to the end of 2003. The presented studies refer to tankers of the following DWT size segments:

Aframax tankers: 80 000119 999 tonnes Suezmax tankers: 120 000199 999 tonnes VLCC tankers: 200 000320 000 tonnes ULCC tankers: greater than 320 000 tonnes.

Because the relevant VLCC and ULCC fl eet at risk data were available only as the sum of the two categories, the subsequent analysis considers VLCC-ULCC as one common category.

Furthermore, only the main subtypes of the above oil tanker categories were considered in the further investi-gation, namely oil tankers, crude tankers, shuttle tankers, product carriers, and chemical/oil tankers. It is noted that Ore Bulk Oil carriers (OBOs), ore/oilers, and pure

chemical tankers were excluded from the present analy-sis because these tanker subtypes have special design/layout and operational features that are not representa-tive of the whole class of tankers. An overview of ana-lyzed accident records is given in Table 1.

2.3 Fleet at risk information

The annual fl eet at risk information used in the present analysis is given in Appendix A. The raw data for the Aframax fl eet at risk for the studied period and their technical characteristics were provided by Lloyds Regis-ter in the framework of the EU-funded POP&C project. These data were further analyzed in order to cure some inconsistencies in the originally disposed fl eet at risk data (Papanikolaou et al.6). Suezmax and VLCC-ULCC fl eet at risk data were provided to the authors by Inter-tanko (stemming originally from Clarksons database).

3 Accidents potentially leading to LOWI

For the six LOWI accident categories identifi ed above, the accident rates per ship-year were calculated by divid-ing the total yearly number of accidents by the number of ships operational in that year (annual fl eet at risk). It is remarkable to note that the yearly frequency of acci-dents for all studied tanker categories progressively and signifi cantly decreased, particularly in the post-1990 period (Fig. 1). In this graph, the 3-year moving average is also shown to enable a better assessment of the observed trends.

Taking into account accidents with serious conse-quences only, including ship total losses, it appears that Aframax and Suezmax tankers exhibit similar behavior, showing a considerable reduction of accident frequen-cies in the post-1990 period, whereas the reduction for VLCC-ULCC tankers is less pronounced, but still signifi cant.

When considering accidents that caused pollution, regardless of the quantity of oil spilt, it is evident that

Table 1. Number of accidents according to tanker size

Aframax Suezmax VLCC-ULCC

Collision 232 135 150Contact 125 55 60Grounding 194 70 71Fire 79 48 81Explosion 39 26 44Structural failure 120 105 161

Total 789 439 567

VLCC, Very Large Crude Carriers; ULCC, Ultra Large Crude Carriers

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242 J Mar Sci Technol (2007) 12:240250

the rates of accidents causing pollution also reduced in the studied period, but not to the same extent as for the rate of overall accidents, see Table 2. However, caution is necessary when using these data for future assess-ments. A related confi dence analysis, presented in Appendix B, Table B1, reveals that in some cases, the 95% confi dence intervals with respect to the noted average values are quite wide.

It should be noted also that a series of IMO regula-tions concerning the prevention of incidents and acci-dents has apparently contributed to the observed declining trends of accident rates, particularly in the post-1990 period, marked by the introduction of the Oil Pollution Act OPA 90 in the USA. Figure 2 (Mikelis et al.7) presents the navigational accident rates of Aframax tankers along with some key relevant regula-tions that could be responsible for the declining trends of particular accident rates. Note that relevant regula-tions are herein presented according to their year of implementation and it can be expected that their effect

Accident Rate per Shipyear

0.00E+00

2.00E-02

4.00E-02

6.00E-02

8.00E-02

1.00E-01

1.20E-01

1.40E-01

1.60E-01

1.80E-01

2.00E-01

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

AFRAMAX SUEZMAX VLCC & ULCC

3 per. Mov. Avg. (AFRAMAX) 3 per. Mov. Avg. (SUEZMAX) 3 per. Mov. Avg. (VLCC & ULCC)3-year moving average (AFRAMAX) 3-year moving average (SUEZMAX) 3-year moving average (VLCC & ULCC)

Fig. 1. Accident rate per ship-year. VLCC, Very Large Crude Carriers; ULCC, Ultra Large Crude Carriers

Table 2. Average accident rates per ship-year

Pre-1990 Post-1990

Aframax All accidents 1.11E-01 3.72E-02 Accidents with serious

consequences or total losses2.27E-02 7.18E-03

Accidents leading to pollution 6.45E-03 4.29E-03Suezmax All accidents 9.95E-02 3.31E-02 Accidents with serious


Accidents leading to pollution 6.43E-03 2.46E-03VLCC-ULCC All accidents 6.04E-02 2.70E-02 Accidents with serious


Accidents leading to pollution 3.99E-03 2.13E-03

Fig. 2. Navigational accident rate for Aframax tankers with sig-nifi cant regulations shown in boxes. The numbers in the boxes represent the year of adoption of the particular regulation, whereas the position of the boxes in the graph corresponds to the year of implementation of relevant regulations. COLREG, Convention of the International Regulations for Preventing Collisions at Sea; SOLAS, International Convention for the Safety of Life at Sea;

MOU, Memorandum of Understanding; STCW, International Convention on Standards of Training, Certifi cation and Watch Keeping for Seafarers; ARPA, Automatic Radar Plotting Aid; VETTING, measure; OPA90, Oil Pollution Act; GMDSS, Global Maritime Distress and Safety System; ETS, European Telecom-munications Standard; ISM, International Safety Management Code; ILO C180, International Labour Organization

should be noticeable with some phase lag, depending on the nature of each regulation. It is also noted that the signifi cant MARPOL 73/78 convention is not indi-cated on this graph, though it is of importance, as it

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J Mar Sci Technol (2007) 12:240250 243

fell in the pre-1978 period not studied in the present work; the European ERIKA I, II, and III tanker safety packages and the more recent IMO-MEPC-50 provi-sions regarding the phase out of single-skin tankers are also not shown as they were implemented after 2003. The full version of this particular study on the infl uence of regulations on the safety record of the AFRAMAX tankers can be found at the POP&C project website (www.pop-c.org).

Figures 3 to 5 present the accident frequencies for each accident category separately; a downward trend is observed here as well. The introduction of the US regional agreement OPA 90 is indicated in these fi gures because it is believed that this particular regulation has had a striking impact on the safety level of tanker designs and consequently has signifi cantly contributed to the reduction of incidents in all accident categories.

3.1 Navigational accident rates

Focusing on the navigational accident rates (i.e., colli-sion, grounding, and contact accidents), all tanker sizes exhibit reduced rates in the post-1990 period. VLCC-ULCC tankers present the lowest rates in the studied period compared to the smaller tanker sizes considered, see Fig. 3. Regulations related to navigational and routing procedures apparently had a positive impact on the reduction of collision and grounding accidents. The International Convention on Standards of Training, Certifi cation and Watch Keeping for Seafarers (STCW), the International Safety Management Code (ISM), and the ILOs Seafarers Hours of Work and the Manning of Ships Convention improved seafarers responsibility and crisis management. The VETTING measure intro-duced voluntarily by the tanker operators has contrib-

Collision, Accident Rate per Shipyear

0.00E+00

1.00E-02

2.00E-02

3.00E-02

4.00E-02

5.00E-02

6.00E-02

7.00E-02

8.00E-02

9.00E-02

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003


Contact, Accident Rate per Shipyear

0.00E+00

5.00E-03

1.00E-02

1.50E-02

2.00E-02

2.50E-02

3.00E-02

3.50E-02

4.00E-02

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003


Grounding, Accident Rate per Shipyear

0.00E+00

1.00E-02

2.00E-02

3.00E-02

4.00E-02

5.00E-02

6.00E-02

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003


OPA 90

OPA 90

OPA 90

Fig. 3. Navigational accident rates per ship-year

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244 J Mar Sci Technol (2007) 12:240250

uted to increased operational standards and consequently has reduced the rate of accidents of all categories except for nonaccidental structural failures (no enhanced struc-tural surveying was required at that time).

3.2 Fire and explosion accident rates

A slight decreasing tendency can be observed in the yearly rates of fi re and explosion accidents throughout the studied period, see Fig. 4. Explosion accidents, however, exhibit considerably reduced rates compared to accidents in which fi re was the fi rst event. In addition to OPA 90 and the VETTING measure, the ISM Code and requirements regarding sensing devices (SOLAS 2000) apparently had an overall positive impact on the rate of fi re and explosion accidents.

3.3 Nonaccidental structural failure rates

The rates of accidents for Suezmax and VLCC-ULCC tankers exhibit a signifi cant peak in the period 19871991, see Fig. 5. Rates for all tanker categories were signifi cantly reduced in the post-1990 period. A separate investigation regarding the relation of nonaccidental structural failures to a ships age was conducted (Papa-nikolaou et al.6) for Aframax tankers. The study showed bell type behavior in this relation, whereby a higher frequency of nonaccidental structural failures was observed for middle-aged ships, namely those 1115 years old, than for more aged ships. Similar trends were found for Suezmax and VLCC-ULCC tankers. This interesting phenomenon might be attributed to a decreased maintenance effort on a ships hull structure

Fire, Accident Rate per Shipyear

0.00E+00

5.00E-03

1.00E-02

1.50E-02

2.00E-02

2.50E-02

3.00E-02

3.50E-02

4.00E-02

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003


Explosion, Accident Rate per Shipyear

0.00E+00

2.00E-03

4.00E-03

6.00E-03

8.00E-03

1.00E-02

1.20E-02

1.40E-02

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003


OPA 90

OPA 90

Fig. 4. Fire and explosion accident rates

Non-Accidental Structural Failure, Accident Rate per Shipyear

0.00E+00

1.00E-02

2.00E-02

3.00E-02

4.00E-02

5.00E-02

6.00E-02

7.00E-02

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003


OPA 90

Fig. 5. Nonaccidental structural failure rates

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J Mar Sci Technol (2007) 12:240250 245

Table 3. Percentage of ships involved in accidents by age

Age

Suezmax VLCC-ULCC

1988 1989 1989 1990

05 years 0 0 5 5610 years 13 8 5 51115 years 67 67 80 611620 years 20 25 10 29>20 years 0 0 0 0

Table 4. Percentage of accidents with serious degree of severity including ship total losses

Accident category Aframax Suezmax VLCC-ULCC

Collision 13% 16% 14%Contact 15% 15% 15%Grounding 23% 36% 36%Fire 30% 28% 29%Explosion 54% 50% 57%Nonaccidental

structural failure 21% 19% 20%

Table 5. Frequencies of accidents with serious degree of severity including ship total losses


Collision 2.57E-03 3.05E-03 1.56E-03Contact 1.63E-03 1.16E-03 7.04E-04Grounding 3.69E-03 3.63E-03 1.95E-03Fire 1.97E-03 1.89E-03 1.80E-03Explosion 1.72E-03 1.89E-03 1.88E-03Nonaccidental

structural failure2.15E-03 2.90E-03 2.58E-03

when approaching the assumed design economic life of about 20 years and before the ship changes ownership for an extended economic life with a new operator.

In Fig. 5, the relatively high peaks for Suezmax tankers (years: 1988, 1989) and VLCC-ULCCs (years: 1989, 1990) are due to the observed relatively large number of accidents occurring in middle-aged ships, see Table 3. Regulations related to structural inspection and protec-tion, such as Enhanced Survey Program (ESP) surveys and condition assessment programs (CAPs), have had and are expected to have in the future a great impact and to generally decrease the rate of nonaccidental structural failures.

4 Severity of accidents

The degree of an accidents severity is herein defi ned according to LMIS coding, namely as nonserious, serious, and a ships total loss. The LMIS severity coding uses as a criterion a combination of an accidents conse-quences in terms of the ship as a platform, of the persons onboard, and of the marine environment.

Table 4 presents the percentage of accidents with a serious degree of severity, including ship total losses, for each major accident category. Reviewing these results, the following can be stated:

All three tanker categories considered have similar percentages of accident severity for collision and contact accidents (around 15%).

An increased accident severity percentage is indi-cated for grounding accidents for Suezmax and VLCC-ULCC (about 36%).

For fi re, explosion, and nonaccidental structural failure accidents, all tanker sizes appear to experience almost the same percentage of accidents with high severity. Explosion accidents are inherently related to a high percentage of severity, indicating that if an explosion accident happens, the consequences will be serious, leading even to the ships total loss with a high probability (more than 50%).

In summary, explosion accidents are the most severe type of accidents for all studied tanker sizes. For Aframax tankers, fi re appears to be the second most severe event, whereas for Suezmax tankers and VLCC-ULCCs, grounding accidents are the second most severe.

Table 5 outlines the frequencies of accidents with a serious degree of severity including ship total losses for all major accident categories and tanker sizes. The particular frequencies were calculated by dividing the total number of accidents with a serious degree of sever-ity and ship total losses for the entire studied period by the fl eet at risk over the same period. The 95% confi -dence intervals of these values are given in Appendix B, Table B2.

VLCC-ULCCs exhibit the lowest rates with respect to navigational accidents overall.

For groundings, Aframax and Suezmax tankers present considerably higher severity rates than VLCC-ULCCs.

All tanker sizes experience similar frequencies of highly severe fi res, explosions, and nonaccidental structural failures. It is noted, however, that although explosion accidents appear to be related to higher percentages in terms of severe consequences (Table 4), the corresponding frequency rates were not the highest.

5 Spill tonne rates

Table 6 presents the oil spill rates in tonnes per ship-year. Aframax tankers experienced higher spill rates in the

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246 J Mar Sci Technol (2007) 12:240250

post-1990 period, whereas Suezmax and VLCC/ULCC tanker ships exhibit signifi cantly lower values in the post-1990 period compared to the period before. These statistics are greatly affected by the possible occurrence of catastrophic accidents; in terms of Aframax tankers, there were two major accidents in the post-1990 period with serious environmental consequences, namely those involving the Braer (amount of spilt oil: 88 214 tonnes in 1993) and the Prestige (amount of spilt oil: 77 000 tonnes in 2002). In Fig. 6, the annual spill rate of each tanker size is presented, along with the most signifi cant acci-dents that led to environmental pollution of greater than 70 000 tonnes of spilt oil.

Further commenting on the pollution rates presented in Table 6, where the six LOWI accident categories have been evaluated, VLCC-ULCC ships clearly exhibit the highest spill rates per ship-year compared to the smaller tanker sizes. This should be expected because these vessels have comparatively large cargo tanks, therefore in the case of loss of the hulls watertight integrity in the cargo area, potentially a larger amount of oil can outfl ow. Appendix B, Table B3, presents the 95% confi dence intervals of the above spill rates. The calculated intervals are extremely wide and in most cases they numerically approach the average values. This is because of the inherent characteristic of pollution accidents in that there are only a small number of accidents leading to large amounts of pollution.Focusing on each accident category separately, the fi gures of spill rates vary between the studied tanker sizes, see Table 7:

Collision accidents. Suezmax tankers had similar spill rates in the pre- and post-1990 periods. A signifi cant reduction of rates is seen in the post-1990 period for VLCC-ULCC tankers.

Contact accidents. Comparable and signifi cantly lower values of spill rates were seen in the post-1990 period for all tanker sizes.

Grounding accidents. Aframax tankers experienced a sig-nifi cant increase of spill rates in the post-1990 period. For the larger ships, reduced rates were evident in the post-1990 period, with the VLCC-ULCC having the lowest values in this period.

Fire accidents. Almost zero spill rates for Aframax and Suezmax tankers imply that the majority of fi re

Table 6. Spillage rates (tonnes) per ship-year

Tanker size 19782003 Pre-1990 Post-1990

Aframax 31.16 27.52 34.81Suezmax 59.34 78.80 39.88VLCC-ULCC 114.17 143.86 84.48

Six accident categories, Spilled Tonne Rate per shipyear

0.00E+00

1.00E+02

2.00E+02

3.00E+02

4.00E+02

5.00E+02

6.00E+02

7.00E+02

8.00E+02

9.00E+02

1.00E+03

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003


ATLANTIC EMPRESS

CASTILLO DE BELLVER

KHARK 5

NOVA

ABT SUMMER

HAVER

INDEPENDENTA

SEAEMPRESS

IRENES SERENADE

BRAER

PRESTIGE

Fig. 6. Spill tonne rates per ship-year. The names of ships involved in major accidents are included in the boxes

Table 7. Spillage rates (tonnes) per ship-year, per category


Collision accidents Aframax 2.15 4.23 0.07 Suezmax 23.59 27.11 20.07 VLCC-ULCC 25.64 43.62 7.66Contact accidents Aframax 0.81 1.57 0.04 Suezmax 1.69 3.39 0.00 VLCC-ULCC 0.78 1.18 0.38Grounding accidents Aframax 13.07 5.28 20.86 Suezmax 27.39 34.97 19.81 VLCC-ULCC 18.74 37.25 0.24Fire accidents Aframax 0.06 0.13 0.00 Suezmax 0.00 0.00 0.00 VLCC-ULCC 30.77 32.42 29.12Explosion accidents Aframax 8.16 16.07 0.25 Suezmax 2.74 5.48 0.00 VLCC-ULCC 34.23 21.40 47.06Nonaccidental structural failures Aframax 6.92 0.24 13.60 Suezmax 3.92 7.85 0.00 VLCC-ULCC 4.01 7.99 0.02

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J Mar Sci Technol (2007) 12:240250 247

accidents occurred while the vessel was unloaded, as no oil pollution occurred during the accidents. In particular, looking into the details of relevant Aframax and Suezmax accidents, it seems that fi re often started in the engine room or the pump room or on the super-structure due to electrical faults or equipment heating. Furthermore, in other cases, the vessel was under repair and the ignition source was from hot works. In contrast, VLCC-ULCC tankers had high rates throughout the studied period. The average of 29.12 tonnes/ship-year post-1990 was accounting for by two accidents.

Explosion accidents. Signifi cantly reduced spill rates in the post-1990 period was evident for Aframax and Suezmax tankers, whereas VLCC-ULCC tankers showed a signifi cant increase in this period. The fi gure of 47.06 tonnes per ship-year in the post-1990 period was accounted for by a single accident.

Nonaccidental structural failures. Aframax tankers expe-rienced a signifi cant increase of spill rates in the post-1990 period, mainly because of the Prestige incident in 2002. In contrast, Suezmax and VLCC-ULCC tankers showed comparable behavior with negligible spill rates in the post-1990 period.

6 Geography of oil spills

Figure 7 shows the worldwide geographic locations of severe oil pollution caused by Aframax, Suezmax, and

VLCC-ULCC tankers over the period studied (19782003) along with the routes of major worldwide oil movements. Also, in Table 8, the geographic areas with total oil spills per Marsden Grid cell greater than 700 tonnes are identifi ed. The most severely affected areas worldwide (over 100 000 tonnes oil spilt) are: the Carib-bean Sea, the Bay of Biscay, Scapa Flow Bay, English Channel, southwest and South Africa, the Bosporus Straiteast Mediterranean, and the Strait of Malacca.

A comment is due on the arctic route (northern sea route) statistics, for which no pollution accidents were reported. This is a relatively new but increasingly exploited route driven by the recent large increase of Russian oil exports that also shortens transit distances between other existing and new trade centers. There are several possible reasons for the lack of pollution statis-tics here: increased navigational caution and support, the hostile environmental conditions, operation by relatively smaller tankers that are not included in the presented large tanker statistics, and possible under-reporting for political reasons.

7 Conclusions

Accident databases such as the one utilized herein are potentially important tools for assessing the performance of the maritime industry with respect to the safety of tankers and the protection of the maritime environment. They can be used as a rational basis for developments in

Fig. 7. World map of main oil transport routes (EMSA8) and marine pollution as a result of large tanker accidents between 1978 and 2003

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248 J Mar Sci Technol (2007) 12:240250

the international regulatory process and help to address the weakest links in the tanker safety and environmental protection chain. Additionally, they provide valuable information about the areas of tanker design, mainte-nance, operation, and crew training that may be in need of additional attention or of a new, risk-based approach.

The marine casualty databases that have evolved over the years were not designed with the application of risk assessment methods in mind, and therefore suffer from a number of serious limitations that make their usage in assessment studies problematic. Looking to the future, the increased application of risk assessment methods to ship design, operation, and regulations will lead to an increasing need for good quality, easily available marine casualty data. The methodology and analysis presented in this article might form a valuable basis for the way ahead.

The accident rates of large tankers signifi cantly decreased over the period 19782003. The rates of acci-dents leading to pollution as well as the rates of accidents

with a high degree of severity also reduced, but not to the same extent. Spill rates exhibit a declining trend throughout the studied period for Suezmax and VLCC-ULCC vessels. Concerning Aframax tankers, a slight increase was found in the post-1990 period mainly because of the Braer and Prestige incidents.

A series of regional and international regulatory mea-sures introduced in the past 30 years affecting tanker design, maintenance, operation, and the accelerated renewal of the world tanker fl eet has obviously con-tributed to the improvement of the safety level of tankers and of the safety culture in the tanker shipping industry, as refl ected in the present accident statistics.

When using results of the present statistical analysis for the forecasting of very serious ship accidents, particu-larly of accidents with catastrophic impact on the marine environment, one should be cautious. The limited number of such accidents and the complexity of the factors leading to them do not allow fi rm conclusions about the future, although trends appear optimistic. A confi dence analysis

Table 8. Total spill per Marsden grid for areas with pollution greater than 700 tonnes as a result of large tanker accidents from 1978 to 2003

Marsdengrid

Number ofaccidents

Number of accidentsinvolving oil pollution

Total tones spilled(19782003) Geographic area

43 41 4 315 647 Aruba Island, Caribbean Sea145 28 3 285 582 Bay of Biscay (La Coruna/Brest)371 1 1 260 000 St. Helena Island, South Atlantic Ocean442 11 1 252 000 Cape Town, South Africa181 36 4 196 719 Scapa Flow Bay, UK180 44 4 147 017 English Channel178 27 3 127 780 Bosporus Strait26 113 10 100 292 Strait of Malacca, Singapore Strait, Indian Ocean

142 63 6 94 722 Mediterranean Sea (Alexandria and Libya)103 133 3 87 409 Gulf of Oman (Al Fujairah)144 5 2 82 734 Skikda, Algeria109 46 3 40 570 Gibraltar231 13 4 36 433 British Columbia, Canada27 6 3 25 560 Strait of Malacca, Indian Ocean82 103 8 23 729 Gulf of Mexico, Corpus Christi/Aransas Bay

141 47 3 20 193 Suez (Bitter Lake, Port Said)376 14 4 18 153 Rio de Janeiro, Brazil432 3 1 17 983 Cervantes, Western Australia105 37 3 17 269 Jeddah, Suez, Red Sea (Saudi Arabia)110 6 1 11 000 95 Miles NNW of Lisbon441 11 1 10 161 Port Elizabeth, South Africa44 31 2 8 715 Maracaibo, Venezuela

487 1 1 5 000 Punta Arenas, Strait of Magellan116 51 5 3 785 Delaware Bay, USA120 14 4 3 012 Los Angeles, USA232 2 1 2 797 Prince William Sound, Alaska132 34 3 2 166 Korea Strait (Ulsan, Bussan)Sea of Japan179 18 3 2 033 Mediterranean Sea (Gulf of Venice)81 18 1 1 770 Gulf of Mexico (Mississippi, Tampa)

131 41 2 1 337 Kobe, Japan217 6 3 1 164 Sullom Voe Terminal, Shetland Island, North Atlantic143 45 1 1 118 Mediterranean Sea (Malta and Sicily Channel)216 112 3 830 Hamburg Area157 12 1 770 Strait of Juan de Fuca, North America

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J Mar Sci Technol (2007) 12:240250 249

of the presented statistical data revealed useful uncertainty margins, which are of importance when deciding future regulatory and political measures.

The analysis of geographic locations of recorded accidents with high pollution showed that besides the Caribbean Sea, the southwest and south European and southwest and South African coasts were the most heavily polluted by large oil tanker accidents in the period studied. Regarding the pollution of European coastlines, it should be noted that one more casualty with catastrophic environmental consequences, not reg-istered herein because it fell in a smaller DWT tanker category, namely the accident involving the tanker Erika (37 000 DWT) 80 km off Brittany in 1999, led the Euro-pean Commission to act drastically in the matter by adopting a series of measures known as the ERIKA I and II packages, leading to an accelerated phase out of single-hull tankers operating in European waters (www.ec.europa.eu/transport/maritime/safety/2000_erika_en.htm). Similar measures were subsequently adopted by IMO-MEPC for worldwide tanker operations. It can be expected that these measures will signifi cantly contribute to a decrease in serious large tanker accidents, particu-larly of those leading to pollution of the marine environment.

Acknowledgments. Part of the study presented herein was fi nan-cially supported by the European Commission under the FP6 Sustainable Surface Transport Programme. The support was given under the STREP scheme, Contract No. TST3-CT-2004-506193. The European Community and the authors shall in no way be liable or responsible for the use of any such knowledge, informa-tion, or data, or of the consequences thereof. The authors would like to thank Dr. Nikos Mikelis (IMO, former Intertanko) for fruitful discussions and the provision of data for this study. The authors also thank their fi nal year students Messrs Kanellakis and Bourikas for the initial assessment and processing of part of the raw tanker accident data. Finally, the authors would like to thank the reviewers of this article for their valuable comments and sug-gestions that increased the value of the presented material.

References

1. POP&C (20042007) Pollution prevention and control. EU project, 6th Framework Programme, www.pop-c.org

2. Papanikolaou A, Eliopoulou E, Mikelis N, et al (2005) Casu-alty analysis of tankers. RINA Learning from Marine Incidents III, London, January 2526, 2006

3. Papanikolaou A, Eliopoulou E, Alissafaki A, et al (2005) Criti-cal review of Aframax tanker incidents. The Third Interna-tional ENSUS Conference, Newcastle upon Tyne, April 1315, 2005

4. Kanellakis G (2005) Casualty analysis of Suezmax tankers (in Greek). Diploma Thesis, Ship Design Laboratory-NTUA, Athens

5. Bourikas E (2005/2006) Casualty Analysis of VLCC-ULCC tankers (in Greek). Diploma Thesis, Ship Design Laboratory-NTUA, Athens

6. Papanikolaou A, Eliopoulou E, Mikelis N (2006) Impact of hull design on tanker pollution. The Ninth International Marine Design Conference, Ann Arbor, Michigan, May 1619

7. Mikelis N, Delautre S, Eliopoulou E (2005) Tanker safety record at all-time high. Lloyds List, September 29, 2005

8. EMSA (2004) Action plan for oil pollution preparedness and response. European Maritime Safety Agency, Brussels

Appendix A

Fleet at risk

YearAframaxtotal fl eet

Suezmaxtotal fl eet

VLCC-ULCCtotal fl eet

1978 372 268 7091979 358 267 7211980 383 263 7191981 412 264 6921982 416 252 6611983 401 247 5981984 382 243 5391985 375 245 4871986 368 235 4191987 380 229 4021988 383 232 3911989 397 236 3971990 414 248 4121991 438 255 4251992 460 268 4361993 463 287 4401994 470 288 4521995 467 283 4361996 481 281 4311997 487 278 4371998 518 288 4341999 552 296 4302000 552 288 4252001 559 292 4412002 568 276 4282003 596 287 428Ship-years 11 652 6896 12 790

Appendix B

Confi dence analysis

Due to the nature of the analyzed statistical data, a binomial confi dence analysis was considered necessary to establish the uncertainty margins of the obtained averaged values, see Tables B1 and B2. Concerning the spillage rates, the confi dence analysis was performed on the basis of mean values, see Table B3. The calculated 95% confi dence intervals, presented below, correspond to the 95% probability that certain values will be met. It is observed that in some cases the confi dence intervals are quite wide with respect to the average values. In those cases, caution is needed when using the particular values for decision-making purposes.

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250 J Mar Sci Technol (2007) 12:240250

Table B2. Frequencies of accidents with serious or catastrophic consequences and associated confi dence intervals


Collision 2.57E-03 C.I. l.b.: 1.74E-03 3.05E-03 C.I. l.b.: 2.00E-03 1.56E-03 C.I. l.b.: 1.02E-03C.I. u.b:. 3.67E-03 C.I. u.b:. 4.83E-03 C.I. u.b:. 2.51E-03

Contact 1.63E-03 C.I. l.b.: 9.82E-04 1.16E-03 C.I. l.b.: 5.01E-04 7.04E-04 C.I. l.b.: 3.22E-04C.I. u.b:. 2.55E-03 C.I. u.b:. 2.28E-03 C.I. u.b:. 1.34E-03

Grounding 3.69E-03 C.I. l.b.: 2.82E-03 3.63E-03 C.I. l.b.: 2.35E-03 1.95E-03 C.I. l.b.: 1.33E-03C.I. u.b:. 5.16E-03 C.I. u.b:. 5.35E-03 C.I. u.b:. 2.98E-03

Fire 1.97E-03 C.I. l.b.: 1.32E-03 1.89E-03 C.I. l.b.: 1.00E-03 1.80E-03 C.I. l.b.: 1.14E-03C.I. u.b.: 3.06E-03 C.I. u.b:. 3.22E-03 C.I. u.b:. 2.70E-03

Explosion 1.72E-03 C.I. l.b.: 1.12E-03 1.89E-03 C.I. l.b.: 1.00E-03 1.88E-03 C.I. l.b.: 1.27E-03C.I. u.b.: 2.75E-03 C.I. u.b:. 3.22E-03 C.I. u.b:. 2.88E-03

Nonaccidental structural failure

2.15E-03 C.I. l.b:. 1.39E-03 2.90E-03 C.I. l.b.: 1.77E-03 2.58E-03 C.I. l.b.: 1.71E-03C.I. u.b:. 3.17E-03 C.I. u.b:. 4.48E-03 C.I. u.b:. 3.53E-03

C.I. l.b., confi dence interval lower bound; C.I. u.b., confi dence interval upper bound

Table B3. Spillage rates in tonnes per ship-year along with the 95% confi dence intervals determined for the mean values


Aframax 31.16 27.52 34.81C.I. 22 32 33Suezmax 59.34 78.80 39.88C.I. 44 77 44VLCC-ULCC 114.17 143.86 84.48C.I. 88 109 142

Pre-1990 Post-1990

Aframax All accidents 1.11E-01 3.72E-02 C.I. Lower bound 1.02E-01 3.08E-02 C.I. Upper bound 1.19E-01 3.98E-02 Accidents with serious consequences or total losses 2.27E-02 7.18E-03 C.I. Lower bound 1.87E-02 5.10E-03 C.I. Upper bound 2.71E-02 9.27E-03 Accidents leading to pollution 6.45E-03 4.29E-03 C.I. Lower bound 4.35E-03 2.82E-03 C.I. Upper bound 8.95E-03 6.12E-03Suezmax All accidents 9.95E-02 3.31E-02 C.I. Lower bound 8.87E-02 2.72E-02 C.I. Upper bound 1.10E-01 3.90E-02 Accidents with serious consequences or total losses 2.19E-02 8.36E-03 C.I. Lower bound 1.69E-02 5.53E-03 C.I. Upper bound 2.73E-02 1.17E-02 Accidents leading to pollution 6.43E-03 2.46E-03 C.I. Lower bound 4.03E-03 1.12E-03 C.I. Upper bound 9.92E-03 4.65E-03VLCC-ULCC All accidents 6.04E-02 2.70E-02 C.I. Lower bound 5.26E-02 2.30E-02 C.I. Upper bound 6.36E-02 3.17E-02 Accidents with serious consequences or total losses 1.37E-02 8.50E-03 C.I. Lower bound 9.64E-03 6.28E-03 C.I. Upper bound 1.48E-02 1.13E-02 Accidents leading to pollution 3.99E-03 2.13E-03 C.I. Lower bound 2.38E-03 1.10E-03 C.I. Upper bound 5.33E-03 3.71E-03

Table B1. Average accident rates per ship-year and associ-ated confi dence intervals (C.I.)

casualty analysis of large tankers

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