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Response Tactics - Marine Oil Spills
(please note the Behaviour of Oil Section)
General Remarks
Oil Spills at Sea
Oil Spills in Lakes and Shallow Water
Oil Spills in Rivers
Oil Spills on the Shoreline
General Remarks:
Maintenance and Training
Health and SafetyIt is very difficult to generalize on marine oil spill situations. Each spill has its own set of characteristics: Location, close to shore or far off shore, degree of environmental sensitivity, shallow or deep water, waves, current, wind speed and direction, temperature, size of spill, type of oil, time after spill, debris, etc.
There are several factors which influence how succesfully the clean-up operation will be, and they are all incorporated in an appropriate contingency plan:
Availability and capability of properly maintenanced equipment and products (ships, skimmer systems, booms, pumps, storage, dispersants, absorbents, etc.).
Availability of manpower, well trained/not trained
What to protect first of all.
Communication
Information
Surveillance
Command
Strategy/PlanningRegarding the equipment and personnel involved in an oil spill combat operation, the most important factors for success are:
Maintenance and Training
Equipment for combating oil pollution should be treated as emergency equipment. These tools should be maintained and kept in a state of readiness in the same way as fire-fighters treat their gear. It is too late to inspect and repair oil spill combat equipment when the "alarm bell" of an environmental emergency rings!Training and exercising again and again is the only way to be sure to realize the full return on an investment in oil spill combat equipment.
Health and Safety:
Oil spill responders are dealing with several hazardous situations:Working at sea: Risk of drowning
Working with cranes
Working with pumps and skimmers with debris cutting knives
Working with heavy weight containment booms
Working in atmospheres containing toxic vapours
Working with various chemicals
Working in or close to explosive atmospheresIt is extremely important that an appropriate Health- and Safety Plan (HSP) has been prepared and that all involved personnel has received proper HSP education.
All safety instructions in the response equipment operating manuals must be obeyed!
Please note that for the sake of simplicity, the following oil pollution combating scenarios mainly use containment booms and free floating skimmers. We know that other techniques are available. They will gradually be integrated into this section, for instance by assistance from the manufacturers or the users.
Oil Spills at Sea (Mechanical Recovery):
Sweep configurations
Oil Recovery
Debris(Please note that for the sake of simplicity, the following oil pollution combating scenarios mainly use containment booms and free floating skimmers. We know that other techniques are available. They will gradually be integrated into this section, for instance by assistance from the manufacturers or the users)
Oil spill response at open sea is a challenging task, and is normaly only initiated if the oil pollution threatens a shoreline or important marine life. Our knowledge about the sea currents and the weather makes it possible to predict the most probable route which the spilt oil will follow. PC software is available for trajectory analysis. Surveillance is done by satellites or from aircrafts. Once it has been decided by the responsible authority to launch a response operation, the basic pattern should follow the instructions in the contingency plan for the area. The following describe some – but not all – of the tactics considerations which one should be aware of in the practical oil spill response at sea:
Sweep configurations
A free-floating skimmer is in most cases supposed to be within sight of the operator. The closer, the better control and recovery efficiency. Difficult debris can be observed and removed before disturbing the skimmer or the entire sweep. It is therefore recommended to use the skimmer(s) in conjunction with a Side Fitted Single Vessel Sweep (single or double sided) with the skimmer(s) placed in the apex of the sweep boom(s). "V" shaped sweeps are strongly recommended. Please see the boom section of this handbook.Excellent manoeuvrability makes these concepts suitable for small and medium size oil spills. They can rapidly attack the "windrows" of oil. Lane by lane.
For larger oil spills, the Side Fitted Single Vessel "V" Sweep configuration may be combined with a large "U" configuration with an open apex. The oil - which is concentrated by the large "U" - will be guided into a narrow stripe behind the U-sweep, and may immediately be contained and recovered by the Side Fitted Single Vessel Sweep following right after the "U".
Very often, the importance of temporary storage capacity for the recovered oil is not taken seriously enough. It is important that all links in the "recovery chain" match up. Use for temporary storage:
Tanks onboard the recovery vessel
Barges or small tankers
Floating flexible towable storage bladders (TSB)
(Back)
Oil Recovery:
The recovery vessel’s forward movement will force the floating oil - trapped inside the sweep – to concentrate at the apex of the boom formation. Allow the oil layer to build up before starting the skimmer. An oil layer of at least 2.5 to 5 cm (1-2") is recommended. No type of skimmer will work efficiently in a real life situation without the presence of sufficient amounts of oil. But on the other hand the oil should continuously be pumped away as it enters the skimming zone. Otherwise it may escape under the boom. It is a question of obtaining a balance, and only the actual situation can indicate where this balance is. If you are in doubt, it is always better to start skimming too early than too late. In the first case, you may recover more water than necessary (dependent on type of skimmer), but in the second case you may lose the oil under the boom. If you recover too much water, it is not necessarily a big problem, as long as the type of skimmer pump used does not emulsify oil and water. Recovered water can easily be decanted from the storage tank, to be discharged in front of the sweep. In this way, any oil in the decanted water will be recovered again. (Back)
Debris
Debris is a universal problem in almost all oil spill situations. Therefore the skimmer should be able to handle a lot of the debris normally found at a spill site: Seaweed, kelp, plastic bags, aluminium cans, bottles, etc. But the bigger debris such as lumber, trees, big branches etc. must be manhandled. One way is to pull it away from the skimmer at the apex of the boom. But the best way is to deflect the bigger debris before it enters the sweep. Various techniques exist. One is to have personnel located in a MOB boat (rubber dinghy) in front of the sweep, using rakes to pull away the debris. The same may be done from a small vessel, which is preferable in bad weather. The deflection of debris may cause deflection of some oil too. But this is far better than losing all the oil contained in the boom, due to rupture or other complications caused by for instance a big tree floating in the water. (Back)
Oil Spills in Lakes and Shallow Water:
The response principle is as for open sea, but you use smaller units.
Oil Spills in Rivers
Small to medium size rivers
Fast flowing rivers
The combating of oil spills in large and slow rivers will in most cases follow what has been described for lakes and sea.For small to medium size rivers, there is a large variety of scenarios to consider. But the aim is to keep the recovery equipment fixed to the river bank or structures in the river, while the water with the spilled oil is doing the work. Always try to deflect the oil to the slow side (the inner bank at a curve) of the river, if possible.
Please observe that the speed of the river current may require that the booms are positioned in a very small angle relative to the direction of the current. This is due to the fact that the speed of the water perpendicular to any section of boom must be less than 0.7 knots. For more information please see the boom section under "Oil Spill Equipment".
The skimmer must be placed in a way which ensures the maximum flow of oil to it. In some situations it is possible to form a small circulation area close to the river bank, where the deflected and concentrated oil will rotate in a direction driven by the incoming oil, flowing along the boom. In this way the oil moves away from the critical entrainment zone at the apex, thus better avoiding loss of oil under the boom. Another very efficient way to ensure this, is to dig a small pond right next to the river. The river and the pond must be connected with one or two ditches. Use the boom to guide the oil into the pond. Both solutions work very well with the skimmer placed in the middle of the circulating oil.
It may not always be possible to drive a truck all the way to the river bank, as the ground is too soft or muddy. It may be necessary to man-carry the recovery equipment to the river. So low weight is of essence here! Air lifting by helicopter is another option.
Large debris must be deflected before it enters the boomed area. Rakes used from small boats will be quite useful. In some situations it is even possible to deflect large debris by means of a steel wire stretched across the river in or below the water surface, and placed in a small angle relative to the direction of the current. (Back)
Fast flowing rivers:
There exists a limited selection of equipment and techniques for oil spill response in fast flowing rivers. The realistic upper speed limit is 6 knots. The high speed current can make it impossible to get combat equipment dispatched and deployed in operating mode before the spill has passed. Therefore pre-positioned equipment is a must in fast flowing rivers. The oil must be deflected to the slow side of the river (the inner bank at a curve). Booms must be used at very small angles relative to the direction of the current. Skimmers must be used in conjunction with speed reducing sweeps, i. e. sweeps or ridgid constructions which lead the deflected oil into a system where the area of the upper oil/water cross section gradually is enlarged, thus reducing the speed. If the area of the cross section gradually is enlarged six times, you may reduce the speed of the top layer with the oil from 6 to 1 knots. (Back)
Oil Spills on the Shoreline:
Regular Sandy Beaches
Stony or Rocky Beaches
Gravel Beaches Subject to Tidewater
Unfortunately this kind of clean-up operation is not very unusual. It is threatening to the wild life environment and may result in the most costly recovery method. It should therefore be avoided by recovering as much as possible of the oil in open water. However, there are several ways of acting in the event of an oil spill on the shoreline, but they all depend on the actual situation:
Regular Sandy Beaches:
Small to medium size spill: Use beach cleaning machines or bulldozers on the beach if it will carry the weight of such vehicles. If there is no significant surf, you can wash and push the oil back into the sea, to be recovered by a small shallow water skimmer, operating in an area surrounded by a beach boom. Dig a hole under the skimmer if the water is too shallow. Use a Fastank or a ridgid open container for temporary storage.Larger spills/light to medium viscosity: Fence in the oil by means of a shoreline boom, and operate a shallow water skimmer from the beach. If possible, try to push or wash the oil on the beach back into the water in order to let the skimmer recover it. Severe surf will make this operation difficult, if not impossible.
A skimmer head or pump with a self adjusting weir lip - mounted on a "Hiab" type hydraulic crane - a so called "Sweeper", is a very useful tool for this type of spill response. The skimmer- or pump head can always be placed in the best recovery position, remotely controlled from the beach, a vessel, or a barge. Fast to operate and safe for personnel. Pump the oil to a land-based storage or to a sea-based facility such as a barge or a towable storage bladder (TSB).
Larger spills/high viscosity: As just above, but due to the viscosity it may be necessary to dismantle the skimmer pump from the floats and use it for transfer of the spilled oil. Some times the oil emulsion in the water next to the beach will be so high viscous that a skimmer cannot sink into the oil. It will stay on top of it! Therefore a skimmer pump, mounted on a "Hiab" type hydraulic crane, a so called "Sweeper", also here is a useful tool. (Back)
Stony or Rocky Beaches:
Small to medium spill/light to high viscosity: Use absorbents for small amounts of oil and when gentle treatment is required. For larger amounts the best way to recover the oil from a rocky coast is to wash the oil back into the sea, using fire hoses or high pressure- or hot water cleaners, and let a small shallow water skimmer recover it there. Work in an area fenced-in by a shoreline boom. Use a Fastank or a ridgid open container for temporary storage.NOTE! It must always be considered whether it is environmentally feasible to pressure wash a coast line. If there are important living organisms at risk, and the spill is too big for using absorbents, a more gentle treatment with bio-degradable detergents or surface washing agents could be the option. No action at all may in some cases be the best solution. Therefore experts must be consulted before decision on how to clean a sensitve area is taken!
Large spill/light to medium viscosity: As above for small spills. However, you may want to use larger skimmers and pumps. Operate the skimmer from the shore, from a vessel, or from a barge, and store the oil in a land or sea-based temporary storage facility. A skimmer head or pump with a self adjusting weir lip - mounted on a "Hiab" type hydraulic crane - a so called "Sweeper", is a very useful tool for this type of spill response. The skimmer- or pump head can always be placed in the best recovery position, remotely controlled from the beach, a vessel, or a barge. Fast to operate and safe for personnel. Let nature finalize the cleaning process, or use a bio-degradable detergent or surface washing agent. Use absorbents whenever feasible.
Large spill/high viscosity: As just above, but dismantle the skimmer pump from the floats for transfer of the oil. Or use a skimmer which by means of a feeder can force heavy oil into the transfer pump. Some times the oil emulsion in the water next to the beach will be so high viscous that a skimmer cannot sink into the oil. It will stay on top of it! Therefore a skimmer pump, mounted on a "Hiab" type hydraulic crane, a so called "Sweeper", also here is a useful tool. Let nature finalize the cleaning process, or do the final cleaning using a bio-degradable detergent or surface washing agent. (Back)
Gravel Beaches Subject to Tidewater:
As it was the case after the Exxon Valdez spill in 1989, gravel beaches and tidewater cause special problems for the oil spill responders: When the tide goes down, the oil sinks with the water level deep into the gravel. And at every high tide the oil will be back at the surface. If you try to wash the top layer of gravel at low tide, as described in the paragraphs above, it may seem nice and clean until after the next high tide. Then new oil "from the deep" will cover the beach.A careful assessment of the pros & contras of cleaning must be performed prior to doing anything to these beaches. In the warmer parts of the World Mother Nature’s work may be the fastest and safest for the environment. But natural degradation may take many years under cold conditions. Therefore an expert evaluation could conclude that cleaning is preferable.
The application af fertilizers for speeding up the work of the "local" microorganisms have shown some results. More aggressive organisms may also be added. But the tidewater disturbs the bio-degradation deep in the gravel beach too much.
There are, however, bio-degradable chemicals available, which seem to be able to do the cleaning of the tidewater gravel beaches: They are avilable as a water dillutable "soap" or as a citrus oil based solvent.
The fastest working "soap" will stop the oil’s ability to stick to anything. However, only some of the oil particles will surface and may be recovered by a weir skimmer (adhesion does not work). The rest will remain in the water column as "powder", but due to its enormous surface it will be subject to relatively fast natural degradation. A slower working type of "soap" has the advantage of leaving most of the dispersed oil at the surface, an ability which is enhanced by the application of compressed air. The oil at the surface may be recovered using a weir skimmer with self-adjusting weir.
The soap types (mixed with water) must be sprayed on and into the beach at low tide. In this way they will reach the oil deep in the gravel and reduce or totally stop the oil’s ability to stick to the stones. The high tide will wash away the oil particles, some of which may be recovered and others leave the area totally dispersed.
The citrus oil based solvent must likewise be sprayed into the gravel at low tide. But quite differently from the "soaps", all of the oil that has been removed from the gravel will rapidly come to the water surface when the tide goes up. The oil is therefore faster and easier to recover, when compared to the soap washing method. (Back to Top)
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