Effects of Double-Hull Requirements on Oil Spill Prevention: Interim Report (1996)

One goal of OPA 90 is to reduce the amount of oil spilled in U.S. waters by instituting preventive measures and to minimize the damage from oil spills by responding effectively to spills. Section 4115 of the act focuses on preventing oil spills by mandating changes in the design and operation of vessels. The committee will assess evidence of the impact of Section 4115. The key question is whether or not the marine environment has been better protected as a result of the implementation of Section 4115.

The principal requirements of Section 4115 are (1) that single-hull tankers must be replaced by double-hull tankers according to a schedule beginning in 1995 and running through 2015 and (2) that existing single-hull tankers must undergo structural and operational modifications in order to continue operating until retirement under the prescribed schedule. These changes are intended to reduce the probability of oil spills or reduce the amount of oil spilled during an event or accident.

The probability of an oil spill event (P_e) can be expressed as the product of two probability factors.

P_e = P_c × P

P_c is the probability of a casualty occurring, and P_s is the probability of a spill, in the event of a casualty. The double-hull requirement of OPA 90 addresses the second factor in the equation, the probability of a spill in the event of a casualty. The structural and operational modifications to existing single-hull vessels are also directed toward the second factor, although some elements in the proposed regulations stemming from Section 4115—such as ship bridge management, train-

ing, and maneuvering regulations—focus on the first factor, i.e., reducing the probability of a casualty.

The committee will determine if Section 4115 has had a measurable effect on the probability of oil spills. Data on vessel casualties and oil spill events, in U.S. waters and worldwide, are available from a variety of sources. The U.S. Coast Guard, the IMO, and private organizations are evaluating the effectiveness of double hulls and other structural and operational changes on implementation issues considered in assessing real and potential improvements in the protection of the marine environment.

The committee will:

• review the history and causes of oil spills

• examine the effectiveness of double-hull designs in reducing oil outflow

• identify and assess the effectiveness of structural and operational modifications to existing single-hull tankers in reducing oil outflow

Other factors that reduce the probability of casualties and spills include IMO regulations 13F and 13G, port state¹ actions, industry initiatives in vetting by charterers, and enhanced surveys. The consequences must also be evaluated by the committee because they influence the enforcement of regulations for preventing accidents and oil spills.

The committee is examining trends in oil spillage from tank vessel accidents that have occurred since 1985 in relation to tank vessel hull types and general types of casualties (e.g., collisions and groundings). Accident analyses will place particular emphasis on accidents in 1994 and 1995 to determine the extent to which measures taken since the passage of the act have reduced the incidence of oil spills in U.S. coastal waters (see the discussion under Outflow from Double-Hull Tank Vessels later in this chapter). In the past four years, there appears to have been a substantial reduction in the number and severity of serious accidents, such as collisions and groundings, which have resulted in the most significant oil spills. Figure 2-1 gives a graphic example of the data sets being evaluated by the committee.

Because relatively few double-hull tank vessels are currently in service, the apparent reduction in oil spillage from vessel accidents is probably due to factors other than hull design. Therefore, the committee will examine trends in the number of accidents, the types of casualties, and the volume of oil spilled, as well as in the types and ages of the vessels involved in recent marine casualties.

FIGURE 2-1 Oil spills from vessel accidents in U.S. waters (spills of 10,000 gallons or more). Note: Data include accidents involving both tank ships and oceangoing barges. Source: International Spill Statistics (1994).

Although it is unlikely that precise reasons can be given for the apparent reduction in oil spills, the committee will use a review of the post-OPA 90 safety record to evaluate and project the future effectiveness of the requirement for double-hull vessels.

The committee is examining oil spill statistics from the U.S. Coast Guard, the Minerals Management Service (U.S. Department of the Interior), the International Tanker Owners Pollution Federation, and two journals, Oil Spill Intelligence Report and Golob's Oil Pollution Bulletin.

Although there are inconsistencies among these sources in the level of detail and in methods of data collection, all of them report a decline in the number and severity of oil spill accidents in the past five years. During the course of this study, the committee will compile data from these five sources to ensure that all spills are accounted for and that discrepancies in the amount of oil spilled and the severity of specific incidents or casualties are reconciled. The resulting database will then be analyzed to determine if recent reductions in oil spills are indeed significant.

After studying the design and construction of new double-hull vessels, the committee will conduct an analysis, applicable to both tank ships and oceangoing tank barges, to ascertain the impact of design on oil outflow (see chapter 5). This analysis will be applied to spills that occurred in 1994 and 1995 to estimate what

might have occurred if the vessels involved in the accidents had been equipped with double hulls. If the accident involved a double-hulled vessel, the committee will analyze the amount of oil that would have been spilled if it had been a single-hull vessel.

Data for the analysis described above will be derived from a study to be conducted for the committee to determine the outflow parameters for a number of single- and double-hull tankers and barges in accordance with IMO methodology (IMO, 1994).² The outflow parameters will be used to compare the environmental performance of single-hull and double-hull vessels. The expected frequency of collisions and groundings will be estimated from a statistical analysis of actual casualty data in U.S. waters. The outflow functions will then be applied against the frequency of casualty data to estimate the amount of outflow if all vessels have double-hull arrangements. Additional information about the committee-sponsored study can be found in chapter 5.

The U.S. Coast Guard is developing regulations that comply with the OPA 90 requirements. A draft notice of proposed rules has been released and made available for public comment. The proposed changes would effectively require modifying all single-hull vessels that desire to continue trading in U.S. waters. Extensive public comments on that rule-making resulted in supplemental notices modifying the draft notice. Although the retirement schedule for single-hull tank vessels has been established by law, as provided in OPA 90 (Section 4115), ³ other U.S. Coast Guard regulations for single-hull tankers have not been completed. The U.S. Coast Guard has published a supplemental notice of proposed rules affecting the existing single-hull fleet (Federal Register, 1995). The proposed regulations address operational changes, bridge resource management training, work-time restrictions, enhanced surveys, maneuvering standards, and requirements for under-keel clearance.⁴

These regulations are intended to reduce potential casualties. Still to be developed and promulgated are regulations to reduce potential oil spillage through structural changes or vessel-loading practices. The effect of these regulations on

spills and industry economics cannot be determined until they have been finalized. The effects on different fleets will vary widely, depending on the age, design, and size of the vessels.

Provided that the Coast Guard regulations for single-hull tankers are issued in time to be considered, the committee will use studies by the U.S. Coast Guard and others to evaluate the effect of regulations on reducing outflow from the single-hull fleet.

The quality of the fleet serving U.S. ports appears to have improved as a result of the passage of OPA 90. The committee will investigate how new international regulations, increased port state activities, enhanced surveys by classification societies, and improved vetting by major charterers and the increased fear of liability have affected the safety of the fleet serving the United States. This investigation is described below.

Because international regulatory requirements are only now taking effect, as is the case with Section 4115 regulations, current spill rates are not expected to be directly linked to them. The international regulations can be expected to have an effect in the future, however, especially structural requirements (protectively located tanks) and operational requirements (hydrostatic balance and light loading). The structural and operational provisions for single-hull vessels apply to the world fleet. However, the United States has not yet accepted these provisions for existing tank vessels. The committee projections regarding potential oil pollution from future spills will take into account the requirements of both OPA 90 and IMO Regulations 13F and 13G.

The three initiatives described above are intented to reduce the number of substandard vessels currently being used, at least in countries actively pursuing the initiatives. The committee will investigate the activities of major port states, classification societies, and major charterers in identifying substandard vessels (and the owners and registry of vessels). The identity of these vessels, owners, and registries will be compared to the vessels that called on U.S. ports in 1990 and 1994 to evaluate the quality of the fleet. Data on vessel port-calls have been obtained from the Institute of Shipping Analysis in Göteborg, Sweden. Data on individual fleets, owners, and registries will be developed from published information from port states and the U.S. Coast Guard and through quality grading systems such as those developed by Clarkson Research and the Tanker Advisory Center.

Data are available to ascertain the number and volume of oil spills prior to and after the enactment of OPA 90. Consistency among these sources is limited, however, in terms of the range of spill volumes. Various sources define the lowest, or minimum, spill size as 500 gallons, 1,000 gallons, and 1,000 barrels.⁵ There is also some inconsistency among sources as to which vessels are included and the volume of particular spills. Nevertheless, a suitable database can be developed by cross-checking and comparing information from various sources.

Endeavoring to isolate the effect of Section 4115 of the act on real or apparent changes in oil pollution rates and volumes is complicated by two factors. First, safety-related activities of the maritime oil transportation industry and regulators have increased worldwide. Second, because the required phase out of single-hull vessels only started in 1995, Section 4115 of the act has had little effect thus far on the overall incidence of oil spills in U.S. marine waters. In addition, possible structural and operational regulations applicable to single-hull tank vessels have not yet been issued. Nonetheless, the committee believes that examining the long-term trend in the occurrence, magnitude, and nature of marine oil spills may be important in forecasting the future effects of the double-hull provisions of Section 4115 as soon as they are fully implemented. The committee believes that existing data sources are adequate in this respect and that the apparent decline in structure-related casualties in the past several years can be tested for statistical significance. To the extent that statistical results will allow, a comparative oil outflow evaluation of single- versus double-hull designs will be used to determine how full implementation of Section 4115 might alter future trends in oil spillage.