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6 SAFER Safety issues attendant to the disposition of offshore platforms include concerns about the safety of vessels navigating in the vicinity of structures and the safety of platform removal operations. Navigational safety issues are an important cons ideration. If offshore platforms are a significant hazard to navigation (as demonstrated by the incidence of collisions of ships with platforms and as supported by estimates of probability), then safety concerns weigh in favor of completely removing offshore platforms from the ocean at the end of their useful life. On the other hand, if the platforms aid navigation or provide refuge for small boats' then some will argue that they should be maintained even after petroleum production has ceased. HAZARD TO SURFACE NAVIGATION Offshore platforms and merchant vessel traffic are in close proxi- mity in many areas ~ see Figure 12) . The hazard to surface navigation posed by offshore platforms has been a subject of keen interest to ship operators and owners, oil companies, state governments, and federal agencies. The Coast Guard is especially concerned about the threat to navigation safety of permitting offshore platforms to remain in place when they are no longer actively being used to produce oil and gas.* The agency feels that risks to navigation and the environment, which may be acceptable when the national interest in energy production is being served, may not be justified when produc- tion ceases. Furthermore, since the Coast Guard is responsible for marking obstructions to navigation, Coast Guard officials are con- cerned that when an offshore platform has been negligently maintained, when the platform operator's identity is ambiguous, or when the operator is no longer financially able or willing to maintain navigation aids on structures, the Coast Guard will inherit these responsibilities by default. In their view, these eventualities, and See Coast Guard response to Federal Regi ster (49FR44924, 13 November 1984~. Letter no. 16670. RIGS, 7 December 1984. 53
54 \ \ \ it\ \ \ \: I: at, - .. ~ \ \: ~~ ~ :\ . \ ~ i:: \ \ ~ . ~~ ~~ ~~ ~ ~ of\ \1,, ~ :. :\ - .. ~~ : i,. ~ ~ ~.~ ~ \ W: ~ a. W~ .. . . W..~,.'~:~-.~,~'.'''.2::'WN'.~"'.~:'~::\ ~ W\~ I:....:...'.,.:: ~~..-:,~,~\ I:: ::: 1 · ~4 Note to Figure: Extract from navigation chart 11340. Note designated shipping fairways to Lake Charles, La., Port Arthur, Tx., and Galveston, Tx. (and Houston ship channel). The shipping fairway is bracketed by a confusing array of offshore platforms. One platform, located at a branch in the fairway, has a radionavigation aid. Two platforms adjacent to the fairway were struck by large, deep draft ships in the 5-year period 1980-1984. FIGURE 12 Proximi ty of offshore platforms and merchant vessel traff ic .
55 TABLE 6 Hazard of Offshore Platforms to Surface Navigation in the Gulf of Mexi co Type of Data Amount Sourcea Number of platforms to 1983 Major structuresb Estimated average number of new platforms per year (through 1990) Major complexes Gulf of Mexico port calls (measure of ship traffic, S-year estimate) Galveston Collisions (1980-1984) Large, deep-draft ships Offshore industry support craft Fishing vessels Towboats or barges Unknown 4,078 Committee data 1,64S Minerals Management Service 205 Committee estimate 78 Cocci ttee est imata 52,000 Merchant traffic, draft 19 feet or greaterC 11 , 000 r ~ U.S. Coast Guard, 8th DIST. 27 CORR. No. 16613, 1/30/85 6 15 2 aThese data are comparable to those used in a study of ship collisions with offshore platforms containing a method, applied herein, for QSti- mating the probability of collision (Failure Analysis Associates, 1978~. bMajor structures are defined by the Minerals Management Service as those having at least two pieces of production equipment, six drill slots, a heliport, or permanent quarters. CData from Waterborne Commerce of the United States as published in Marine Salvage in the United States (NRC, 19821. the liabilities and accidents that will ensue, will be much more likely if obsolete platforms are allowed to remain in place. Most of this concern is centered in the Gulf of Mexico, where 99 percent of all offshore structures are situated. However, navigation safety is a major concern in other regions of offshore oil and gas activity as well, especially the Santa Barbara Channeled Data on the number of offshore platforms, collisions of vessels with platforms, and ship transits are available to describe the historical situation and estimate the probability of collision in the Gulf of Mexico. These data are presented in Table 6 and Figure 13. - ~In at least one instance, a ship handling simulator has been used to study the interactions of offshore petroleum structures and the navigation of large vessels (Nieri, 1981~.
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57 Because of the magnitude of potential consequences, the committee was interested in the probability of collision of deep-draft ships with offshore platforms. The committee employed a method of estimating the probability of collision that had been applied to the problem in a previous study (Failure Analysis Associates, 1978). The probability of collision outside established traffic lanes is 3.3 10-4 platform years, or one collision in 3,000 platform-years. Within 1 mile of an established traffic lane, the probability of a large vessel collision is 2.86 ~ 10-2, or 1 collision in 35 platform-years. A 1977 study for the Coast Guard estimated the probability of collision in the Santa Barbara Channel at 1 in 8,000 platform-years (Reese et al., 1977). Intuitively, the probability of collision increases as the number of offshore platforms increases. HAZARD TO SUBMERGED NAVIGATION The operating population of submarines is quite different from surface ships. Submarines are sophisticated ships with a wealth of electronic and visual navigation equipment at the beck and call of the operators. Submarine crews are highly trained and always operate with several men on watch. Further, the ever-present threat to submarines in confined waters has engendered an operating doctrine that puts the submarine on the defensive, prepared to react quickly to avoid collision. U.S. Navy operating doctrine generally requires that submarines submerge on sortie as soon as water depth permits. This, of course, is subject to modification if hazards to navigation are numerous ~ for example, where the combination of platform density and visibility increases the risk of collision to an unacceptable degree. Submarines operate in all areas of the world oceans. To suggest that submarines would rule out a particular area, such as the North Sea, as a wartime patrol zone is to underestimate the guile of the submarine commanding officer, or to oversimplify the realities of war planning. The committee, therefore, considers the entire North American littoral as a potential submarine operating area. In short, with few exceptions, areas where platforms exist, or where they may appear, including the Arctic, are potential submarine transit or operas i ng areas . The foregoing suggests that submerged submarines are less at risk to collision with a platform than the average merchant ship, and certainly less than the numerous small craft that ply platform waters. Surface warships are also likely to be less at risk than merchant ships, as the result of operating doctrine. The committee is not aware of any reports of submarine collisions, submerged or surfaced, with offshore platforms in more than 30 years. This is understandable since submarine operating doctrine generally to avoid operating in proximity to fixed structures. The worldwide population of submarines is known. There are about 1,000 of all types, nuclear and diesel. About 140 of these belong to the U. S . Navy. However, information on submarine traffic is not available.
58 Thus, the aforementioned analysis of collision probability cannot be meaningfully extended to the submarine problem. PLATFORMS AS AIDS TO NAVIGATION OR HAVENS Do offshore platforms help or hinder mariners? Do they augment aids to navigation to a degree that suggests they assist the mariner significantly? Do they provide a haven for small craft in bad weather? Or do they present a collision hazard that outweighs any positive answers to these questions? Navigation Aids Where ship traffic or platform density warrants, the Coast Guard has authority to establish navigation fairways or traffic separation schemes. These are charted routes that ships are expected, though not required, to follow in congested areas. There are several instances of these traff ic control schemes being instituted to improve naviga- tion safety in areas of offshore oil and gas production. ~ Several platforms located in strategic positions close to traffic control schemes are used by the Coast Guard for siting visual and radio navigation aids. The Coast Guard will not assume responsibility for maintaining an obsolete platform solely because the platform is being used as a site for a navigational aid. In presentations and letters to the commit- tee, the Coast Guard made it very clear that navigation aids were placed on platforms as a matter of convenience or, rarely, to ensure the electronic visibility of the offshore structure upon request of the operator of the structure. When an offshore petroleum field becomes obsolete and structures are removed, the necessity of traffic control in that area is lessened. Maintaining structures simply as sites for navigational aids is not cost-effective. Another concern, arguing for platform removal, is that a dense population of offshore platforms, which would be more likely if obso- lete platforms were not removed, reduces the Coast Guard's flexibility for realigning traffic control schemes to address future develop- ments. Tf structures are permitted to remain in place as offshore leases expire, and new structures are located in the area, there may be no areas into which traffic routing systems can be shifted to allow for other future uses of some offshore areas. Navigational safety concerns for small craft, less than SOO tons, are different. These include offshore petroleum industry support craft, tow boats and barges, fishing vessels, and recreational craft. U.S. Coast Guard District 11, letter no. 16711 dated 5 November 1984, to the committee. U.S. Coast Guard District 8 presentation to the coneni ttee on 7 January 1985 .
59 Traffic control schemes service large commercial vessels and ports, and may be incidental or irrelevant to small vessels. Small vessels also are likely to have less extensive navigational equipment on board (possibly just a compass and the human eye). They may travel on random tracks, including line of sight from platform to platform. For this class vessel, every navigational aid and offshore structure helps to get from point to point. Some small vessel operators would opt for leaving platforms in place. Platforms scattered generally throughout a sea area, as in the mid-Gulf of Mexico or the North Sea, are especially useful as navigational aids for small vessels because there may be no conventional aids nearby. Platforms as Havens Sometimes small craft are caught at sea when the weather turns. Occas tonally, they take refuge at or in the lee of offshore structures (even though insurance rules typically prohibit uninvited guests on offshore platforms). While the Coast Guard does not keep records of such incidents, isolated instances of mariners taking refuge on or in the lee of offshore structures are acknowledged by offshore platform operators, vessel operators, and the Coast Guard. Another view is that the very existence of offshore platforms far from land tempts some sport fishermen away from the protection and more benign conditions closer to shore. - HAZARD TO PERSONNEL IN DISMANTLING OFFSHORE PLATFORMS As discussed in an earlier chapter, the work involved in disman- tling and removing an offshore platform is comparable to the instal~a- tion of the platform. However, the risks to workers will be somewhat greater because of uncertainties as to the condition of the platform and the strains in the structural elements. Good planning and cautious operations will minimize risks. The total worker safety risks will vary directly with the number of individual worker actions, the time necessary to carry them out, and the water depth at which they occur. Thus, the safety risks will be greater for dismantling and removing a large complex structure in deep water that cannot be removed as a single unit and for full removal of such a structure as compared to partial removal. REFERENCES Failure Analysis Associates. 1978. Risk Assessment of Potential Ship Collisions With Offshore Platforms Outside of the Los Angeles--Long Beach Harbors. Contract study undertaken for Shell Oil Company. National Research Council. 1982. Marine Salvage in the United States. National Academy Press: Washington, D.C.
60 N1eri# David S. 1981. Coastal n~vlgetlon vs. energy resource recovery: The Santa Barbara Cannel Study. In Nevlgatlon: Journal of the Institute of Navixatlon 27~4). Reese, P. et "1. 1977. Draft Vessel Trefflc ^nalYsls--Polnt Conception LNG Termln~l. Ventura, Callf.: J. J. McMullen Associates.
