Offshore oil spill clean up case study


Courtesy of Oil Pollution Environmental Control Ltd

In the event of a major incident occurring offshore, for example a tanker casualty running aground or breaking up for any reason, it is of paramount importance to deploy emergency response to protect and save human life. Once this has been done an assessment of the casualty should be made on whether it is possible to salvage the vessel and its contents and to assess the type and amount of oil that is being spilled.
All this is carried out by an incident room, which should be set up at the nearest port/land base, from which equipment and manpower can be deployed. This should be supported by a crisis management team and offshore/onshore teams to co-ordinate the spill response and salvage operations. Aerial recognisance should also be set up immediately, whether it be fixed wing or other aircraft, to monitor oil slicks as they develop.

If through wind and tide the slick is being blown out to sea then it is best for nature to take its course and allow natural dispersion to take place. If it is likely that the oil should make a landfall, all efforts should be made to recover as much oil at sea as is possible.

OPEC Force 7 utilises the well established adsorption characteristics of polypropylene mops and we have developed a surface trawl mop net which when deployed on the open sea gives a trapezoidal configuration and a swathe path of 15 metres and a net length of 60 metres with an adsorption capability of up to 12 tonnes. The cycle operation allows a deployment and retrieval cycle of 7 times per hour giving a recovery rate of 70 tonnes per hour.

This is a single ship deployment system without the need for containment booms. Due to national or international maritime rules, vessels used in oil recovery may not be classed to allow recovered oil to be stored in inboard tanks. Therefore it is important to also have towed temporary recovered oil storage tanks available to allow the operation to continue without the need for support vessels. The OPEC Flexitanks were developed and designed for this purpose and are supplied in standard sizes between 5 tonnes and 100 tonnes recovered oil storage capacity. These can be folded up and stored on deck when not in use and have in-built buoyancy to assist in deployment and retrieval.

With such a system there is the obvious advantage of using 1 vessel. The recovery costs are minimised since all vessels available can be used to the maximum effect, operating costs are much lower, manpower requirements are much lower, ongoing training and maintenance costs again are very much lower. Definite alternatives to be considered for future offshore cleaning operations at sea.

Oil recovery on land
It must be expected that whatever means are used not all of the oil will be recovered at sea and landfall will occur, in which case oil/debris containment booms should be deployed to minimise the area of pollution along the coast by deploying the boom in such a way as to deflect the oil to sacrificial beaches. These should have good access for equipment and manpower and be as far away as is possible from the natural habitat of marine creatures and docks and harbours.

In the event that polluting oil makes landfall, whether or not it be a sacrificial beach, OPEC have specialised equipment which can remove this oil along the shoreline. The Series 5000 has been specifically developed to deal with heavy oils and heavily weathered crude oil and can be used in boomed areas to recover large quantities of oil very quickly. The equipment will pick up oil with very little free water and incorporates an integral pump system to allow the transfer pumping of recovered oil to pits which can be subsequently emptied by gully suckers/tankers or directly to tankers. If the oil gets on to the beach, trenches can be dug and OPEC E-Series mop skimmer systems can be deployed to recover the oil gathering in the trenches. In some cases the mop skimmer can also be deployed over the surface of the beach area as required.

In the event of small pockets of oil being removed in rock pools etc., the Hand Mops can be used together with a versatile wringer which can be mounted on open topped 200 litre drums and will provide a contingency operation with very little disposal costs of contaminated adsorbent material.
We would not recommend the use of adsorbent fabric and adsorbent booms for this type of work since the ongoing disposal costs are high. (However there are exceptions, see A Method for Cleaning Foreshores). In one incident that occurred in Year 2000 it was reported that a spill of 20,000 tonnes has resulted in the removal of over 200,000 tonnes of contaminated material - a lot of which was adsorbent of one sort or another. With the proper use of specially designed equipment and properly deployed manpower, costs would be reduced dramatically.

The use of dispersants should be kept to a minimum; it should never be used as the main line of attack on an oil spill. Problems occur when trying to deal with weathered and emulsified oils which have been treated with dispersants. Mechanical removal methods must be the preferred method.

Dispersants used on an oil slick can cause the following problems:

  • Adding chemicals to an oil spill only further adds to the amount of environmentally damaging toxins present.
  • By dispersing the oil into the water column some will fall to the bottom and create pollution to bottom feeding marine life.
  • The oil that remains in the water column may well eventually make landfall and because it has been dispersed will pollute a much wider area.
  • Also the chemical structure of the oil will be altered and may make it more difficult to deal with.

High power jet sprays should also be avoided when cleaning rocky beaches:

  • Power jets temporarily push the oil from one area to another. The oil is blasted further down into the sand or pebbles. This does not reduce the amount of pollution that already exists in a pollution spill.
  • Power jets disturb the ecological surroundings, moss, seaweed's etc.
  • The detergeants used in power washing only add to the environmentally damaging toxins.

So what can you do when oil is sticking to rocky outcrops at the sea edge? One solution could be to apply the technology of 'bioremediation'. Biochemistry means powerful cleaning without the use of harsh man-made chemicals. In this instance OT8 Gel can be applied and simply left to 'eat' the hydrocarbons until there is nothing left apart from water and 'dirt' which would simply wash away through natural factors such as the wind, rain and wave action of the sea.

From the information given above here is a suggested contingency plan for dealing with an offshore oil spill.

  1. Coast Guard to deploy emergency response team in the effort to preserve human life.
  2. Marine engineers to assess the damage and try to salvage the vessel to reduce the amount of pollution discharged at sea.
  3. Assess the type and amount of oil that has been spilled.
  4. Monitor the oil spill from an incident room and aerial recognisance.
  5. Crisis management team to coordinate offshore and onshore teams for spill response.
  6. If there is a threat of oil coming ashore deploy offshore teams with mechanical pollution recovery equipment. Attempt to recover as much oil at sea as possible.
  7. Using data from the aerial recognisance, weather reports and admiral charts use onshore teams to deploy oil/debris containment booms to deflect the oil to a sacrificial beach.
  8. At the designated area for the sacrificial beach deploy mechanical oil recovery equipment and prepare trenches for the collection and temporary storage of the oil.
  9. Use hand mops for rock pools and hard to reach areas.
  10. Use bioremediation products, such as 'OT8' for the removal of oil from rocky outcrops.

A contingency plan is essential for all port and harbour officials and emergency response crisis teams. The management involved in a pollution response project should be aware of the expertise and equipment available to them in order to be as efficient and as effective as possible with the minimum amount of waste.

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