Nearly 3,800 platforms populate the U.S. federal outer continental shelf. Most of these are off the coast of Louisiana and Texas (MMS, 1995). The Minerals Management Service (MMS) of the U.S. Department of the Interior requires removal of platforms within one year after termination of the lease. Lease operators may remove platforms when the costs of operating and maintaining structures exceed revenues or when structures are obsolete or damaged. The options for disposing of offshore structures include complete removal with disposal ashore, placement in an approved ocean disposal site, conversion to a fishing reef, or removal for refurbishing and replacement elsewhere. In approved cases, maintenance in place is an alternative to removal. Removal must be to a depth that safeguards ocean shipping, that does not obstruct shrimp-trawling operations, or that allows for submarine passage and minimizes the threat of seabed obstructions.

The pace of platform removals continues to accelerate as aging platforms built in the boom years of the late 1960s and 1970s are taken out of service. More than 100 platforms have been removed from service in each of the last several years (181 were removed in 1993).

The most common procedure for removing fixed offshore structures is by cutting them into sections and removing them by lifting. The necessary submarine cutting is most often accomplished by submarine explosives, which can harm fish, turtles, and marine mammals. Damage from explosives can be mitigated by careful timing and operational procedures, but the extent of damage and the potential for mitigation have not been well documented. An alternative to explosives is cutting with jetting tools and torches or with mechanical cutting devices.

Many operators prefer using explosives because they cost less and are less risky. Experience has shown that, in most situations, severing and retrieving structures can be accomplished in one operation using explosives. Uncertainty is increased substantially if nonexplosive techniques prove to be inadequate or are unsuccessful during the removal process. Such failures may require active intervention, such as diver cutting. Diver interaction with a structure that has been damaged to an undetermined extent is inherently dangerous, time consuming, and expensive. The prevailing judgment of platform owners and operators is that explosive cutting is cheaper, safer, more flexible, and more reliable than available or reasonably prospective nonexplosive technologies for most platform removals.

Most of the problems with the explosive method are associated with the environmental impact, especially mortality of marine life in the region affected by the detonation. Although the presence of turtles and marine mammals around platforms is not well documented, the National Marine Fisheries Service of the U.S. Department of Commerce has identified explosive removals of offshore structures as a possible contributor to turtle and marine mammal mortality.

Fish kills associated with explosive removals are also of concern; however, only fragmentary data pertinent to fish kills are available. The range at which fish can be killed by explosives depends on several factors: the intensity of the explosive shock wave as determined by the type, configuration, and amount of explosive used; reflection and refraction of the shock wave, which varies with bottom material and water conditions (temperature, salinity, etc.); and the susceptibility of specific fish species to various shock waves.

The U.S. General Accounting Office (GAO) recently reviewed offshore structure removal operations and concluded that nonexplosive technologies merit further consideration and development because of concerns about the impact of explosive removal techniques on biological communities (GAO, 1994). The agency also concluded that the MMS has not adequately studied the costs and benefits of using nonexplosive technology that would reduce the risk of environmental damage from the removal of offshore structures. Moreover, the GAO concluded that certain actions by MMS may actually discourage the use of nonexplosive platform removal measures (e.g., an MMS proposal to relax limits on the use of explosives).

The MMS requested that the National Research Council (NRC) address the issues raised in the GAO report. A committee was convened to undertake a study of the technical issues and recommend alternatives for future MMS action. Specifically, the committee was asked to:

• review platform removal technology, including the costs of alternative techniques

• examine and appraise innovative technologies and techniques under development

• assess the occupational and environmental hazards of explosive and alternative removal techniques

• identify ways to mitigate the identified hazards

In the course of the study, the committee also learned about the requirements and concerns of other users of the marine environment (including shrimpers, fishers, recreational boaters, and people concerned about environmental damage), which should be taken into account in developing federal procedures for full or partial platform removal and for site clearance. The committee also assessed the adequacy of existing MMS regulations governing the removal of fixed offshore structures.

Based on its work, the committee prepared this report, which provides a comparative assessment of offshore structure removal technologies and existing and potential mitigation strategies for decreasing the damage to living marine resources. This report is intended to provide guidance to the MMS on the technical basis for development of offshore structure removal techniques and for updating pertinent federal rules and procedures. The report identifies alternatives for minimizing damage to the marine ecosystem from offshore structure removals.

A committee of 12 people was convened by the NRC Marine Board. Biographies of committee members appear in appendix A. Members of the committee include experts on offshore civil engineering, geotechnical engineering, marine construction, underwater blast effects and mitigation, technical assessment, biology, ecology, and management of living marine resources. Composition of the committee provided the scientific, technical, economic, policy, and practical expertise to assess current conditions and make recommendations for the future. The points of view of the offshore oil and gas industry and associated service industries were represented on the committee, as were the views of scientists involved in research on the specific living marine resources (sea turtles, marine mammals, and fish) that may be affected by explosives used to remove offshore structures.

The committee was assisted by liaison representatives from the MMS, which sponsored the study, and the National Marine Fisheries Service (NMFS), which is charged with ensuring compliance with regulations protecting living marine resources. The principle guiding the committee, consistent with NRC policy, was not to exclude any information because of possible bias, if the information was vital to the study, but to treat all points of view fairly.

The committee focused on the assessment of offshore structure removal technologies and associated hazards and the development of strategies to mitigate environmental damage. Disposal of platforms after removal, either on site, in deep water, or onshore, was outside the scope of this study. Although issues concerning the requalification of offshore structures for extended service and their reuse through statesponsored “rigs-to-reefs programs” were originally excluded from the scope of the study, the committee found it necessary, for a full understanding of the complexity of the issues, to include a limited examination of the latter program and to present findings concerning the role of these programs in the Gulf of Mexico ecosystem. Although the assessment may provide valuable insights concerning removal of offshore structures from state as well as federal waters, an assessment of state rules was beyond the scope of the study. This report addresses technical and regulatory issues relating to the safe removal of offshore structures and minimizing harm to living marine resources.

The committee initiated the study with briefings from MMS and NMFS representatives involved in overseeing offshore removal activities. Experts from government, industry, and the research and environmental communities were invited to present information and insights on present and alternative methods of removal; the costs, reliability, safety, and measures for mitigating damage to the environment; and on regulatory issues, including possible changes in existing regulations. The committee reviewed available scientific literature on the effects of removals on living marine resources and invited representatives of other users of the marine environment, including the fishing, shrimping, boating, and recreation communities, to present their concerns about the effects of explosive removals on their activities and on the Gulf of Mexico ecosystem. The committee also heard presentations and obtained information from private companies about new technologies for nonexplosive removals and devices to mitigate the damage from explosions to marine animals.

A notice was issued in the Federal Register offering interested parties the opportunity to contribute information on all the major issues in the study. A copy of the notice and a list of those who responded can be found in Appendix B. This information was used by the committee in its analysis.

The report is not intended as a sourcebook on removal technology but as an assessment of the current status of explosive, nonexplosive, and mitigation techniques. The objective of this assessment is to formulate a strategy to ensure that as little harm is inflicted on the environment and on living marine resources as is compatible with safe, cost-effective operations.

The report represents a synthesis of information gathered by the committee through briefings, review of the literature,

technical presentations, analysis, and review of additional information gathered from interviews and articles.

• The Executive Summary is a synopsis of the report.

• Chapter 1 is an overview of the status of platforms at the present time and the regulations governing removals.

• Chapter 2 is an assessment of alternative cutting techniques.

• Chapter 3 is a discussion of technical considerations relevant to the selection of particular removal methods.

• Chapter 4 presents the environmental effects of current removal technologies.

• Chapter 5 is a comparative summary of the costs and benefits of alternative approaches to removals.

• Chapter 6 presents the major conclusions and recommendations that follow from the findings of the investigation.

• Appendices provide the reader with additional background information, a list of individuals who made presentations to the committee, the respondents to the Federal Register notice, and biographies of committee members.

This report is intended as a guide to the Minerals Management Service for making decisions about regulations governing the removal of offshore structures and about strategies for encouraging the use of techniques that will decrease damage to the environment and to living marine resources.

The committee wishes to thank the federal liaisons, Charles Smith and Mary Ann Turner of the Minerals Management Service and Gregg Gitschlag of the National Marine Fisheries Service, for invaluable information on agency activities and perspectives on the issues under examination in this study. Other staff members of both agencies also made timely and enthusiastic contributions of time and information to the committee. Special thanks are also extended to individuals who spoke to the committee on behalf of professional and public interest groups (see appendix C). These presentations enabled the committee to gasp the broader context in which the technical issues are embedded.

GAO (U.S. General Accounting Office). Offshore Oil and Gas Resources: Interior Can Improve Its Management of Lease Abandonment. Washington, D.C.: U.S. Government Printing Office.

MMS (Minerals Management Service). 1995. Offshore Statistics. First Quarter, 1995. Washington, D.C.: U.S. Department of the Interior.