Purposeful Jettison of Petroleum Cargo (1994) / Chapter Skim
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Part I History and Technical Background
Part I History and Technical Background
Pages 23-56
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Proceedings of the Symposium on the Purposeful Jettison of Cargo PART 1: HISTORY AND TECHNICAL BACKGROUND
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Ships still depended to a degree on sail, propulsion machinery was not always reliable, and navigational aids were primitive. The Salvage Associations' records for IS92 any IS93 show its surveyors attending many groundings.
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Nevertheless, it is submitted that with dry bulk cargoes where it is not usually possible, as it is on a tanker, to shift the cargo around the ship to assist refloating, jettison must still be seen as an important option to facilitate refloating, to avoid a semipermanent wreck and in particular to avoid the risk of pollution from fuel oil onboard. It should be remembered that a bulk carrier, depending on size, could have anything up to 4,000 tons of fuel oil onboard, and that this is usually a more potent pollutant than crude oil.
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This tanker ran aground on the Nantucket Shoals in 1976 with 27,000 tons of No. 6 fuel oil onboard.
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A tanker can be ballasted down very readily, if the seabed is suitable and it is not being ballasted down onto further pinnacles - and problems. LIGHTENING OF TANKERS While there have been no recent cases of jettison of oil cargoes, there have been very many cases of tankers being lightened in order to refloat.
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The time frame in shipping casualties is often very short. Whereas the case with an aircraft emergency may be clearcut, the case with a ship carrying an oil cargo is less straightforward.
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Blowing out damaged tanks or jettison of some cargo or even fuel oil might, under extreme conditions, be the optimum solutions. CONCLUSION Because salvers have not resorted to jettisoning oil cargoes in recent years, it might be concluded that to prohibit such jettison is, like Rhodian law, merely to confirm what has become the practice.
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Better to jettison and accept that sometimes sacrifice is necessary for the common good and that this applies not only to preserving property but also, and perhaps more so, to preventing even greater pollution. Michael Ellis is the general manager of the Salvage Association in London, England Me served in the British Navy for nineteen years, and d uring that time he qualified as a barrister.
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Consultants Report to the Marine Spill Response Corporation, Washington, D.C. October 4, 1991.
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One of the useful classifications in relation to oil spill response and spill effects is to characterize oils on the basis of their "weight," as light, medium, or heavy oils. This classification is analogous to a characterization of low to medium to high viscosity.
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1987. Response to Marine Oil Spills.
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This relative inverse relationship is enhanced by waxes and asphaltenes in medium- to heavy-weight oils. The relationships between physical/chemical properties and possible adverse effects is summarized for light to heavy oils in Table I.5 PHYSICAL ENVIRONMENTAL CONDITIONS The physical environmental conditions of relevance to oil spill fate and effects and to spill response are sea state (a combination of wind, wave energy, and temperature)
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may be adversely affected by smothering Moderate to · Moderate to high viscosity · Adverse effects in marine heavy oils · Tend to form stable organisms result from chemical emulsions under high energy toxicity and smothering marine environments · Toxicity depends on light · Penetration depends on fraction substrate particle size · Toxic effects reduced in tropical · Weathered residue may climates due to rapid evapora sink and be absorbed by tion and weathering sediment · Low toxicity residue tends to · Immiscibility assists in smother plants or animals separation from water · Light fractions contaminate · Weather to tar balls interstitial waters Asphalt, #6 · Form tarry lumps at ambient · Immediate and delayed adverse fuel-oil, temperatures effects due to small aromatic Bunker C, · Resist spreading and may fractions and smothering waste sink · Most toxic effects due to · May soften and flow when incorporation in sediment exposed to sunlight · Absorption of radiated heat · Very difficult to recover from Paces thermal stress on the water environment · Easy ~ remove manually · Lower toxicity in marine plants from beach surface with than mobile animals conventional equipment SOURCE: Exxon Production Research Company.
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would at least initially be more susceptible to the influence of these environmental variables, However, it is difficult to be definitive since there is little quantitative information on the relationship of wave energy spectra with dispersion potential, as well as to the probability of formation of emulsions. Although it may be suggested in a speculative fashion that the wave dampening effects of oil slicks would be greater for large oil spills than for small ones, this is probably only plausible in the early stages of a spill when there has 36
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Oil Spill Response Manual. as yet been little spreading of the of} to thin the slick layer.
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Figure 5 shows the relative efficiency of various response techniques in relation to oil slick thickness, and Figure 6 demonstrates potential volume control rates for selected spill response techniques.7 In Situ Burning The effectiveness of ignition and combustion of of! floating on the sea surface is dependent on a mixture of variables, including wind, waves, rain, initial oil thickness, oil thickness reduction, formation of emulsions, evaporation and dispersion.8 However, the three main limiting factors for ignition and combustion of oil at sea are the oil thickness, oil thickness reduction, and the water content in the emulsion.
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1993. Marine Spill Response Corporation Oil Spill Response Strategy Seminar.
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An in-depth study of the operational feasibility of in situ burning as one of the suite of possible response tools is being carried out by the Marine Spill Response Corporation. Dispersants The application of dispersants has been used for removal of oil spills from the sea surface since the Torrey Canyon incident 25 years ago, when they were used for the first time in a major oil spill.
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physical oil and environmental variables as predicted for a North Sea oil are presented in Figure 7.12 The use of Emulsifiers in order to prevent formation of or reduce the amount of emulsion on the sea surface, followed by use of dispersants, is a relatively new response method under development in the United Kingdom. Application of Emulsifiers during mechanical cleanup operations may also reduce the water content in the recovered emulsions and extend the time in operation in the field by decreasing storage requirements.
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More oil on the sea surface also increases the probability that environmental conditions could become limiting to the response, increasing the time for weathering of the oil which is known to increase the difficulties of recovery operations, as described above. Quantification of the relationship, however, requires specific knowledge of spill response resources available, the time required for them to arrive on scene, characteristics of the spilled oil, and the environmental conditions of the spill.
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The sensitivity of a species or a population depends on its ecology. The zones of potential impact of oil spills are spatially limited to areas that contain oil, modified by the effect of dilution of toxic fractions of oil to a threshold where acute and chronic effects no longer occur.
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Tainting by biotransfer of higher trophic levels of the food chain is likely to be a temporary and localized phenomenon. Benthic Invertebrates The benthic invertebrate biota are an important component of the marine ecosystem, providing an energy base for fish, seabirds, and marine mammals.
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There is little evidence that standing stocks of fish have been much changed by oil spills. A more likely consequence is impact on harvest activities, either because the adult fish have left a contaminated area or because such fish have become or are perceived to be tainted through contact with oil.
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The results of both experimental data and information gathered from oil spills point out that a prediction of spill impact related to spill volume must take into consideration a wide range of variables. These include the characteristics of the spilled oil, physical environmental conditions, the effectiveness of oil containment and recovery measures, and the biological parameters of affected areas.
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HOW MODELS WORK Virtually all oil spill models that are available have to say something about the current, because anything dropped in the ocean is carried away or drifts off with the flow. This involves looking at oceanographic flow problems and hydrodynamics.
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In that case, the cells have to be quite small in order to resolve what you need to Took at, and this would require much larger computer resources. Another characteristic of oil spills that every mode!
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In theory, one could make a model of the ocean which would be similar to the weather service models; turn it on and it will tell you what is going to happen with the weather tomorrow. Atmospheric models are supported by the World Meteorological System's network of measurements at hundreds of places around the world every six hours.
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Once again, compare oil spills to smoke from a smoke stack. Thus there are aspects to currents and current flow that are very important, Yet we are not even close to being able to predict them with models.
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The Weather Service w~11 forecast to 24 hours; call them up on the back line and you can get 48; beat on the person doing the forecast and you might get 72. But they are not going to stand behind it and nobody believes it very much anyway.
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This would be a first attempt at trying to do what the Weather Service does, by keeping up a background model. Again, this is experimental and it is expensive.
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~ believe the decision to deploy a barge would have been made almost immediately, but it was several hundred miles away and towing a barge in the weather conditions that were prevailing would have taken a great deal of time. ~ assume that other suitable barges weren't available.
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from the sea surface so that it was very broadly spread throughout - diluted, basically - through nonaffected areas. Toward the end of January there was some significant resurfacing of oil.
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an idea what it is. If it is going to malinger for a month, you go back to climatology, which means that for a couple of days it wall be one way, a couple of days it wall be another way.
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