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1 INTRODUCTION C urrent law [P.L. 101-380, the Oil Pollution Act of 1990 (OPA 90)] re- quires that all tankers calling on U.S. ports in the future be fitted with a double hull to reduce the risk of oil spills from accidents. The law also specifies a schedule for phasing out single-hull ships.1 A similar pro- vision is contained in an international agreement under Regulation I/13F of the International Convention for the Prevention of Pollution from Ships (MARPOL) 73/782 (IMO 1996) of the International Maritime Organization (IMO), a specialized agency of the United Nations. In response to OPA 90 and MARPOL provisions, the world tanker fleet is changing to double-hull designs. However, international standards authorize, and in fact have allowed approval of, some alternative designs that are considered at least the equivalent of a double-hull design in preventing the outflow of oil in an accident. OPA 90 also allows for the evaluation of alternative designs that the United States Coast Guard (USCG) can determine to be at least equivalent to double-hull designs with regard to effectiveness in pre- venting the spillage of oil following a contact accident.3 However, in a report required by Congress, USCG (1992) set forth its determination that only the double-hull design meets the requirements of U.S. law. The basis for this conclusion is USCG's interpretation of the Clean Water Act, ac- cording to which USCG looks primarily at the probability of zero outflow in the event of an accident. Since the passage of OPA 90, several ship designers and other proponents of alternative tanker designs have approached the U.S. Con- gress with proposed designs they believe offer performance that is equiv- alent to or better than the double hull. Moreover, some members of the 1See NRC (1998) for a discussion of the schedule for phasing out single-hull tankers. 2So called because it was developed in 1973 and modified by the Protocol of 1978. 3OPA 90 also directed the Secretary of Transportation to prepare a study on other possible structural or op- erational requirements that might be at least as effective as double hulls in protecting the marine environment and to report back to Congress with any recommendations for legislative action. That report was completed in 1992 (USCG 1992). 13

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ENVIRONMENTAL PERFORMANCE OF TANKER DESIGNS 14 design community favor regulations that would call for performance cri- teria for designs instead of prescriptive criteria. These proponents be- lieve that if a method of evaluating equivalence to double hulls can be developed, a better design can be invented, whereas such inventiveness may be constrained if only a single prescriptive design, such as the double hull, remains a fixed requirement. There are also those who believe U.S. regulations should be more consistent with international law, especially in an area so closely connected to international trade. STUDY PURPOSE In the above context, Congress requested that the present study be un- dertaken by a committee under the auspices of the Marine Board of the National Research Council's (NRC) Transportation Research Board (TRB) to determine whether a methodology could be established for measuring the equivalency of alternatives to double-hull designs with regard to en- vironmental performance. Congress made this request through the USCG Authorization Act of 1998 but specified that the investigation be con- ducted independently of past USCG policy on double-hull equivalency (see Appendix B). Specifically, the committee was charged to accomplish the following: Develop a rationally based approach for assessing the environ- mental performance of alternative tanker designs relative to the double- hull standard. This element of the committee's charge is the primary focus of the study and this report. The committee began its work by con- sidering the limitations of existing methodologies, as well as investigating the state of the art of assessment techniques to identify those most ap- propriate for this application. The committee then developed a method- ology, prepared the analyses necessary for its application, and performed testing to demonstrate its use. Refine the IMO tanker damage extent functions and propose a method for adjusting the probability density functions to reflect the crashworthiness of tank vessel structures. The committee investigated the available data and methods for using those data to determine vessel crashworthiness. However, the available data could not be used for this purpose, and the committee's methodology employs a different tech- nique that does not require historical data. Develop a generalized spill cost database and use this database in formulating a rationally based approach for the calculation of an envi- ronmental index. The committee collected and analyzed available spill

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INTRODUCTION 15 cost data. However, the data were inadequate for the purpose, and the committee therefore carried out this portion of its charge using a modeling approach. Apply the proposed methodology to double-hull tankers and alter- native designs. The committee performed a test application of the pro- posed methodology. Ensure that the methodology proposed is applicable to conditions prevailing in U.S. waters. The committee selected characteristics and lo- cations for developing and testing its methodology that reflect conditions in U.S. waters. BACKGROUND During the past two decades, significant efforts to improve safety and protect the environment have resulted in a downward trend in the total amounts of oil spilled as a result of tanker accidents worldwide. Since the early 1990s, these reductions have been especially significant in U.S. waters. Even so, the threat of tanker spills continues to evoke public concern, and the occasional large spill can result in major environmental damage. Measures to improve the environmental performance of tankers are many and varied. The first line of defense against pollution is pre- vention of accidents through such safe ship operational measures as crew training, competence assurance, navigational aids, and traffic management. Because such measures include human factors as well as elements sus- ceptible to mechanical failure, a second line of defense comprises design and construction approaches that can prevent or minimize oil spills in the event of a contact accident (e.g., collision or grounding). Accordingly, since the early 1970s, researchers and engineers have developed tanker designs aimed at preventing or limiting oil outflow after a collision or grounding accident. Double bottoms, double sides, double hulls, and a myriad of other structural arrangements have been proposed and used, and studies have provided evidence to show their effectiveness. By the 1990s, however, a consensus had emerged among regulators--especially in the United States--that a double-hull standard would offer the best protection against oil spills following collision and grounding accidents. Since then, the U.S. regulations requiring double hulls for tankers oper- ating in U.S. waters (discussed below) have resulted in a gradual change in the world tanker fleet, about 39 percent of which now comprises tankers with double hulls (see Table 1-1). That percentage is expected to continue to grow as new ships under construction enter the fleet and old ones are scrapped.

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ENVIRONMENTAL PERFORMANCE OF TANKER DESIGNS 16 TABLE 1-1 Distribution of World Tanker Fleet by Size and Proportion Double-Hull DWT Proportion Size of Fleet DWT of Double- of Double-Hull (thousands Number of of Fleet Number of Hull Ships Ships in of DWT) Ships in Fleet (millions) Double-Hull Ships (millions) Fleeta (%) 10­60 1,901 57.8 658 20.0 35 60­80 257 17.4 90 6.3 36 80­120 592 56.4 268 26.4 47 120­200 324 46.7 143 20.7 44 200+ 450 131.1 155 45.6 35 Total 3,524 309.2 1,314 119.0 39 NOTE: Figures shown are as of early 2001. DWT = deadweight tons. aShare is based on DWT percentage. SOURCE: Personal communication, D. Rauta, INTERTANKO, March 8, 2001. As noted, despite this trend toward double-hull tankers, many re- searchers and organizations have continued to propose alternative design approaches for achieving similar or better performance in preventing oil outflow following tanker accidents. It has been difficult to evaluate these alternative designs, however, because there has been no rigorous and generally accepted method for comparing them against the double-hull standard, and USCG has not recognized the IMO guidelines, which provide a methodology for assessing equivalency. When NRC (1991) issued a report comparing alternative designs with double hulls, it noted that there were no accepted criteria for measuring equivalency but concluded nonetheless that no alternative proposed to date was superior to the double hull for all accident scenarios. USCG has issued regulations to implement the double- hull approach but has been criticized for not having a method of evalu- ating whether new approaches might offer equal or better protection. As context for the discussion in the following chapters, the re- mainder of this section presents a review of relevant trends in oil tanker transportation in U.S. waters, the U.S. flag tanker fleet, tanker accidents and oil spills, and new tanker design and construction. A brief summary of the salient regulatory changes and the industry response to those changes is also provided. Relevant Trends Oil Tanker Transportation in U.S. Waters Total world trade of oil by tanker is near its highest level since the early 1980s. Within this overall trend, tanker trade to the United States is growing, while that to some other regions of the world is declining. U.S. oil consumption has been increasing at the same time that domestic oil

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INTRODUCTION 17 production has been decreasing; imports have thus been growing at a steady rate. Oil imports were at about 5 million barrels per day in the mid-1980s and are now above 10 million barrels per day. In 2000, the United States imported about 8.8 million barrels of crude oil and about 2.1 million barrels of product each day. These trends point to continuing growth in tanker traffic in U.S. waters (EIA 2000). The world tanker fleet is near record high levels and consists of more than 3,500 ships totaling about 300 million deadweight tons (DWT). It is not possible to isolate the portion of the world fleet that only carries petroleum to the United States, but looking at the fleet as a whole (Table 1-1) provides a reasonable picture of the proportion engaged in U.S. trade. Another illustration of the growing oil tanker trade in U.S. waters can be found in data on the number of U.S. port calls for tankers, which show a steady growth throughout the 1990s from about 3,300 annual port calls in 1990 to about 4,400 in 1998 (NRC 1998). The above data illustrate the growing importance of imported oil to the United States and the continuing increase in tanker traffic in U.S. waters. This trend will probably continue in the short term as U.S. oil pro- duction drops further and most sources of imports continue to be pre- dominantly in locations served by tankers.4 At the same time, the conversion of the world fleet to double-hull ships is continuing at a fairly steady rate, and these ships will make up a majority of tankers operating in U.S. waters within a few years.5 U.S. Flag Tanker Fleet The U.S. flag tanker fleet is not engaged in transporting oil imported to the United States, but rather consists of a small number of vessels either carrying refined products from one U.S. port to another or transporting crude oil from Alaska to refineries in the lower 48 states. U.S. law (Title 46, USC 388) requires that all vessels engaged in U.S. coastwise trade be built in this country and operated under U.S. flag. A few new tankers have been built for registry in the United States since the passage of OPA 90, but the fleet still consists mainly of older double-hull and single-hull vessels. The phase-out requirements of OPA 90 are in full force, but because of time- frame allowances, the demise of the U.S. flag single-hull tanker fleet is 4According to the U.S. Department of Energy (2000, p. 5), "U.S. crude oil production is projected to decline at an average rate of 0.7% from 1999 to 2020 to 5.1 million barrels per day. Advances in exploration and pro- duction technologies do not offset declining resources. . . . Percent net imports are projected to increase from 51% in 1999 to 64% in 2020." 5Proposed IMO amendments to MARPOL Regulation 13G would accelerate the replacement of the existing single-hull world tanker fleet by double-hull or equivalent designs as approved by IMO.

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ENVIRONMENTAL PERFORMANCE OF TANKER DESIGNS 18 TABLE 1-2 U.S. Flag Tanker Fleet, Numbers and Deadweight Size Fleet Double Hulls (thousands Numbers (millions Number of (millions Double Hull of DWT) in Fleet of DWT) Double-Hull Ships of DWT) Sharea (%) 10­60 59 2.3 18 0.7 31 60­80 6 0.4 0 0 0 80­120 8 0.7 0 0 0 120­200 18 2.7 3 0.4 14 200+ 4 1.0 0 0 0 Total 95 7.1 21 1.1 15 NOTE: Figures shown are as of mid-2000. They do not include four tankers that were converted from single-hull to double- hull and three double-hull fleet oilers that were operated by the Military Sealift Command. a Based on DWT. SOURCE: Personal communication, A. Landsburg, U.S. Maritime Administration, Dec. 15, 2000. yet to come. The future demand for U.S. flag tankers is less clear because other options are available for transportation of domestic oil. Table 1-2 shows the status of tankers in the U.S. flag fleet as of mid-2000, according to data supplied to the committee by the U.S. Mar- itime Administration. About 15 percent of the fleet is now double-hull, but it includes only six vessels (about 0.2 million DWT) that were built recently (in the 1990s) and four existing single-hull tankers converted to double-hull through the addition of new forebodies. Not shown in the table are 12 new double-hull tankers for the domestic trade that were under construction or contracted in U.S. shipyards as of the end of 2000.6 There has also been some recent construction of new double-hull tank barges, as well as modification of single-hull tank barges to double-hull. Thus, while there is little prospect for much future growth in the U.S. flag tanker fleet, new double-hull vessels are gradually replacing the older vessels in this small, specialized fleet. Tanker Accidents and Oil Spills The most recent data on oil spills in U.S. waters show a reduction in both the number of spills and the amount of oil spilled during the past decade at the same time that oil shipments and tanker traffic have been in- creasing. The worldwide trend also appears to be characterized by re- ductions in spill amounts, but complete data are not available, and the evidence here is less compelling. The committee commissioned a brief analysis of existing worldwide data on annual amounts spilled as a result 6 These include contracts for three Alaska Class oil tankers, with options for three more, with National Steel and Shipbuilding Co., San Diego, California, for BP Oil Shipping Co.; and contracts for four tankers, with op- tions for two more, with Avondale Shipyard, New Orleans, Louisiana, for Phillips Petroleum Co.

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INTRODUCTION 19 200 150 100 50 0 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 FIGURE 1-1 Oil spills of more than 2,000 gallons resulting from tanker accidents worldwide (in millions of gallons), 1973­1999 (Etkin 2000). of tanker accidents for each year from 1973 through 1999; the results of this analysis are shown in Figure 1-1.7 For trends in spills in U.S. waters, the committee received data collected and published by USCG in October 2000, which are illustrated in Figures 1-2 and 1-3. Figure 1-2 shows a dramatic decrease in oil spills from tanker accidents in U.S. waters during the period 1973­1999. Figure 1-3 depicts spills from tanker accidents compared with those from other sources. These data reveal that tanker accidents (excluding barges) were responsible for about 10 percent of the oil spilled in U.S. waters during the 1990s compared with about 24 percent in the 1980s. These same data show a steady reduction in the amount of oil spilled in tanker accidents in U.S. waters in the 1990s compared with the previous two decades. Although the number of spill incidents and the amounts of oil spilled have shown a meaningful decreasing trend in recent years, sig- nificant and large spills worldwide continue to characterize the industry. In addition, history has shown that one very large accident can change the statistics in a major way. It should be noted that most of the large cat- astrophic tanker accidents are single rare events, and the amount of oil spilled during these events tends to overshadow all other spills. Table 1-3 gives the largest tanker accidents worldwide during the past 25 years, ranked by amount of oil spilled. The Exxon Valdez spill was by no means the largest (it is 26th on this list), even though its effect was most signif- icant in terms of U.S. perception and resulting policy changes. 7These data were prepared by Dagmar Etkin of Environmental Research Consulting and constitute a portion of the proprietary databases from that organization. NRC's Ocean Studies Board is currently working to de- velop more accurate estimates of worldwide oil spills, and the results are scheduled to be published in late 2001.

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ENVIRONMENTAL PERFORMANCE OF TANKER DESIGNS 20 14 12 10 8 6 4 2 0 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 FIGURE 1-2 Oil spills resulting from tankship accidents in U.S. waters (in millions of gallons), 1973­1999 (USCG 2000). The trend toward fewer tanker accidents and resulting spills has probably occurred because of many factors. While no attempt is made in this report to identify which causes have been most significant, a few comments are useful as context. Even though the world tanker fleet is gradually changing to double-hull construction, this change cannot as yet have contributed in a large way to a reduction in oil spills because of the difference in time frames. The available spill data, therefore, can- not be used to show the effectiveness of any specific tanker design al- ternative. Consequently, this committee has concluded that the only practical method available for evaluating the effectiveness of alternative tanker designs in reducing spills is to employ some form of predictive modeling. 25000000 20000000 Unknown All other nonvessels 15000000 Pipelines Facilities Gallons10000000 All other vessels Tankbarge 5000000 Tankship 0 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 FIGURE 1-3 Trends in oil spills resulting from marine accidents in U.S. waters: total volume of spills by source (in gallons), 1973­1999 (USCG 2000).

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INTRODUCTION 21 TABLE 1-3 Thirty Largest Tanker Spills Since 1975 (Oil Spill Intelligence Report 1997) Spillage Vessel Year (Millions of Gallons) Location Atlantic Empress 1979 84 Caribbean Castillo de Bellver 1983 79 Atlantic Amoco Cadiz 1978 68 France--Atlantic Odyssey 1988 43 Canada--Atlantic Haven 1991 42 Mediterranean Irenes Serenade 1980 37 Mediterranean Hawaiian Patriot 1977 31 Hawaii--Pacific Independentza 1979 29 Bosporus Strait Urquiola 1976 28 Spain Braer 1993 25 Shetland Islands Jacob Maersk 1975 24 Portugal Aegean Sea 1992 22 Spain Sea Empress 1996 21 United Kingdom Nova 1985 21 Persian Gulf Khark 5 1989 20 Morocco--Atlantic Epic Coloctronis 1975 18 Caribbean Katina P 1992 16 Mozambique Assimi 1983 16 Gulf of Oman ABT Summer 1991 15 Angola--Atlantic Andros Patria 1978 15 Bay of Biscay British Ambassador 1975 14 Pacific Pericles GC 1983 14 Persian Gulf Tadotsu 1978 13 Strait of Malacca Juan A Lavalleja 1980 11 Algeria Thanassis A 1994 11 South China Sea Exxon Valdez 1989 11 Alaska--Prince William Sound Burmah Agate 1979 11 Texas--Gulf of Mexico Athenian Adventure 1988 11 Canada--Atlantic Borag 1975 10 East China Sea St. Peter 1975 10 Columbia--Pacific Using its existing data, USCG compiled for the committee an analysis of 1,660 tank vessel collision8 and grounding incidents in U.S. waters that occurred during the past 20 years. About half of these were collision and the other half grounding incidents. Most of the incidents did not result in any spillage of oil: only about 250 of the incidents in- volved oil spillage, and only a few resulted in large amounts of spill. 8For the purposes of this discussion, the term collision is defined as including both collisions (between two moving vessels) and allisions (between a moving vessel and a fixed object).

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ENVIRONMENTAL PERFORMANCE OF TANKER DESIGNS 22 Indeed, the three largest spills represented about 85 percent of the total amount spilled. In about 70 of the collision and grounding incidents in- volving oil spills recorded during this 20-year period, more than 100 gallons was spilled. These data also illustrate the current trend toward less oil being spilled as a result of tanker accidents in U.S. waters, as well as the scarcity of available recorded incidents in a form necessary for a rigorous statistical analysis. New Tanker Design and Construction As noted above, the world tanker fleet has gradually been changing to double-hull construction to comply with U.S. regulations that followed passage of OPA 90. Some of the first double-hull tankers built primarily in anticipation of both OPA 90 and IMO double-hull standards were char- acterized by single cargo tank configurations: there were no longitudinal bulkhead divisions in the cargo tanks. These designs raised questions for both the industry and regulators about whether such configurations had the potential to result in unexpectedly large oil outflows for some inci- dents. The designs also posed restrictions during cargo operations to which not all tanker operators were accustomed. This issue was sub- sequently addressed by IMO, classification societies, and USCG, and was examined in an NRC (1998) report. The latter included a recommendation to improve the double-hull standards, along with specific recommenda- tions relative to the reference vessels that are used as a basis for comparing alternative designs in the current IMO process. While the configuration issue has been largely resolved, it illustrates the fact that future developers of innovative designs should recognize the potential for unanticipated problems, and regulations need to have enough flexibility to address such problems adequately. Regulatory Changes and Industry Response In 1990, following the grounding of the Exxon Valdez in Prince William Sound in March 1989 and the spillage of more than 11 million gallons of crude oil into Alaskan waters, the U.S. Congress promulgated OPA 90. The intent of this law was to minimize oil pollution through improved tanker design, enhanced operational safety, and other actions designed to improve oil spill cleanup capabilities. Section 4115 of OPA 90 man- dated changes in ship design and construction to prevent or minimize spillage in accidents by establishing the double-hull requirement for tankers transporting oil in U.S. waters and calling on U.S. ports. The leg- islation required that all new tank vessels operating in U.S. waters be

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INTRODUCTION 23 equipped with a double hull, with the exception that tank vessels of less than 5,000 gross tons could be equipped with a "double containment system" determined by the Secretary of Transportation to be as effective as a double hull [OPA 90, Sec. 4115(c)(2)]. These requirements apply to all tankers operating in U.S. waters, not just to U.S. flag vessels. OPA 90 had a worldwide impact on the international regulatory regime in the form of two additions to MARPOL 73/78. Regulation I/13F (MARPOL 13F) and Regulation I/13G (MARPOL 13G) for practical pur- poses mandated a worldwide transition to double-hull vessels or their equivalent. However, USCG has not accepted MARPOL Regulation I/13F for comparison of alternatives, in part because it is believed to place too little emphasis on zero outflow probability (i.e., the prevention of small spills) and in part because the IMO approach is regarded as conflicting with the intent of OPA 90 (see Box 1-1). The international tanker industry does not generally support the imposition of regulatory requirements for prescriptive ship design features BOX 1-1 U.S. Statement of Nonacceptance of MARPOL Regulation 13F "In 1992, the United States Embassy in London formally deposited a declaration with IMO stating that acceptance of MARPOL Regula- tions 13F and 13G would require the express approval of the U.S. Government to enter into force for the United States. The U.S. reservation against MARPOL 13F is based on conflicts with OPA 90, as follows: 1. Applicable vessel size: OPA 90 applies to all tank vessels regardless of size, whereas MARPOL 13F doesn't apply to tank vessels less than 600 GTs; 2. Applicability dates: OPA 90 applies to tank vessels con- tracted for construction after 30 June 1990 (or delivered after 31 December 1993) whereas MARPOL 13F applies to tank vessels contracted for construction after 5 July 1993 (or delivered after 5 July 1996); 3. Allowable designs: OPA 90 only allows double hull con- struction whereas MARPOL 13F also allows the mid-deck design, and provides for acceptance of other possible alternatives."

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ENVIRONMENTAL PERFORMANCE OF TANKER DESIGNS 24 such as double hulls. Nonetheless, since the passage of OPA 90, most of the industry has gradually come to accept double-hull tankers as the standard with which the world fleet will comply over time. Thus the industry as a whole (shipbuilders, owners, and operators) has neither lobbied in favor of alternatives to the double-hull tanker nor rallied to support research designed to measure the effectiveness of such alter- natives. The industry has no strong interest in promoting double-hull alternatives because it has already made significant investments in new double-hull tankers and gained public support in doing so. This is not to say that some in the industry would not support alternatives, but they would do so only if they (a) had political support and (b) did not incur liability for minor spills as the result of characteristics of the type proposed. Indeed, some industry members want to encourage the development of alternative designs, primarily because they consider double hulls to pose safety risks and to be more difficult to salvage when involved in major incidents. They continue to stress the need to evaluate alternatives that may offer superior effectiveness, to encourage research into new designs and advanced technology, and to press for the adoption of measurable per- formance standards based on desired environmental goals. Because the industry is fragmented in its response to the regulations and the politics of the issue dictates a low profile on any matter related to spilled oil, there is no consensus and no pressure on the industry to take a public position. There are primarily two organizations that speak on behalf of tanker owners and operators: the International Association of Inde- pendent Tanker Owners (INTERTANKO) and the Oil Companies Inter- national Marine Forum (OCIMF), the former representing independent tanker owners and the latter fleets owned or controlled by oil companies. Within those two groups are many different interests and values that may reflect political needs or public image, among other things. Both organi- zations are facilitators for consensus, not governors of policy. SCOPE AND APPROACH The focus of this report is on the committee's development and appli- cation of a computational methodology for comparing the environmental performance of alternative tanker designs. A description of how the methodology was developed is given, an initial example of its application is provided, its strengths and limitations are reviewed, and ways in which it can be further developed and implemented are discussed. The method- ology does not provide all of the information necessary for regulators (in this case, USCG) to approve a design, but it can serve as a tool for com-

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INTRODUCTION 25 paring alternative tanker designs against a specific double-hull standard. When fully implemented and used in conjunction with other tools, this methodology will allow USCG to determine whether a specific alternative design should be approved. To use this methodology appropriately, USCG will have to develop a double-hull standard for each vessel size to be com- pared, thus creating reference ships similar to those used in the current IMO methodology. As a first step, the committee reviewed and updated the IMO tanker damage extent functions and their application to the crash- worthiness of tank vessel structures. The committee also investigated his- torical data on oil spill costs and the potential for using these data to calculate an environmental index. Finding that historical data do not pro- vide a basis for evaluating new design concepts, the committee developed its own models of tanker accidents, structural damage, oil outflow, and resulting environmental consequences. For this purpose, hypothetical spill scenarios at typical locations in U.S. coastal and harbor waters were used to represent the conditions prevailing in future situations in- volving tanker transport into U.S. oil ports and terminals. The results of the structural damage and outflow models were combined with those of the spill consequence models to provide a comparative index of per- formance that is described in this report. Models and model results are used for a number of steps in the methodology and are discussed throughout the report. Although models are essential tools, they are only estimates, and the reader should note that uncertainty is always present. When applying the recommended methodology, it is important to understand this uncertainty by examining the upper and lower bounds of numerical results. Moreover, the method- ology is limited to comparison of performance in collision and grounding accidents. It does not address such issues as safety, risk of fire and ex- plosion, operational considerations, or structural integrity during normal operations, all of which are important when evaluating alternative de- signs. The committee's methodology must therefore be used in con- junction with other evaluation measures and judgment. Consistent with its charge, the committee did not perform a com- plete risk assessment of a tanker design or use its methodology to determine overall risk levels for tankers; rather, the methodology was used only to measure relative effects of environmental consequences from collision or grounding accidents as compared with the double-hull design. The com- mittee also conducted some tests to demonstrate how the methodology might be applied. These tests were not intended to evaluate any specific

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ENVIRONMENTAL PERFORMANCE OF TANKER DESIGNS 26 design, but only to illustrate the applicability of the methodology. In ad- dition, in this report a description of how regulators might wish to apply the methodology along with other measures of overall risk is given, ap- propriate cautions regarding its limitations are noted, and the data re- quired for its full development and application are identified. ORGANIZATION OFTHIS REPORT Previous methods used to evaluate alternative tanker designs; alternatives proposed to date; and the various historical databases on spill costs, damage statistics, and collision and grounding are reviewed in Chapter 2. The methodology developed by the committee is detailed in Chapter 3. In Chapter 4, the application of the methodology is illustrated through a de- scription of its use to compare two alternative designs with double-hull designs of comparable size. The committee's conclusions and recommen- dations are given in Chapter 5. REFERENCES ABBREVIATIONS DOE U.S. Department of Energy EIA Energy Information Administration IMO International Maritime Organization NRC National Research Council USCG United States Coast Guard DOE. 2000. Annual Energy Outlook 2001--Key Energy Issues to 2020. Report DOE/EIA-0383 (2001). Dec. EIA. 2000. International Petroleum Monthly. U.S. Department of Energy, Dec. Etkin, D. 2000. Worldwide Tanker Oil Spills, 1973 ­2000. Environmental Research Consulting, Mass. IMO. 1996. Interim Guidelines for the Approval of Alternative Methods of Design and Construction of Oil Tankers Under Regulation 13F of Annex I of MARPOL 73/78. MARPOL 73/78 1994 and 1995 Amendments. London. NRC. 1991. Tanker Spills: Prevention by Design. National Academy Press, Wash- ington, D.C. NRC. 1998. Double Hull Tanker Legislation: An Assessment of the Oil Pollution Act of 1990. National Academy Press, Washington, D.C. Oil Spill Intelligence Report. 1997. Cutter Information Corporation, Washington, D.C. www.cutter.com/osir/biglist.htm. USCG. 1992. Report to Congress: Alternatives to Double Hull Tank Vessel Design, Oil Pollution Act of 1990. NTIS Publication PB93-128874INZ. USCG. 2000. Polluting Incident Compendium: Cumulative Data and Graphics for Oil Spills, 1973­1999. Washington, D.C.