Oil spills are not to reach the shoreline
The concept of barriers is used to determine the required response in a way that best describes the operational conditions. The barrier concept corresponds to the various zones in which the oil must be tackled and is
in accordance with international standards, for example IPIECA.
- Barrier 1 is as close as possible to the source
- Barrier 2 is between the source and the shoreline
- Barrier 3 is areas close to the coast
- Barrier 4 is stranded oil that can be remobilized
- Barrier 5 is stranded oil
Although no measure is 100% effective on its own, combining them can achieve a high level of performance in optimal conditions. Determining the required response considers the performance of the systems thus also the barriers. In each barrier (except the first), the effectiveness of the preventative measures in the previous barrier are considered.
Barrier 1
Natural prerequisites and operational conditions
- It is assumed that the response operation will take place in the open sea, where the effectiveness of systems is affected by wind conditions, wave height, and currents. It is also assumed that there is no depth or navigational restrictions in use on the oil response systems.
The oil´s properties
- Close to the source, the oil is assumed to be relatively fresh. The remedial work must be carried out at a safe distance from the source (outside the zone where there is an explosion risk) and where the properties of the emulsion are suitable for such remedial work. This is considered to be at a distance of approx. 1 km from the spill site, equivalent to 2-hour old oil. For some oil types, the viscosity or risk of an explosion will call for the work to be carried out further from the source of the spill.
- The remedial work is carried out close to the source, where the oil slicks are thickest and where there is expected to be adequate “access” to the oil so that the systems can operate optimally.
Remote measurement
- In this zone, the oil will be within a limited geographical area, with a known spill site. The zone will expand continuously in the occurrence of an ongoing spill. The main task of remote measurement is to identify areas with the greatest quantities of oil in order to tackle as much of the oil as possible.
Barrier 2
Natural prerequisites and operational conditions
- The same natural prerequisites are assumed in barrier 2 as in barrier 1. As remedial measures in barrier 1 can never be 100% effective, the method for determining the required response takes account of the need to tackle oil in dispersed slicks along the drift trajectory. This may be oil that has drifted from the spill site before adequate capacity was achieved in barrier 1 or oil that has escaped barrier 1 as a result of loss from the boom or between the systems since they have to be a certain distance apart for safety and operational reasons.
- This means that systems able to “pursue” drifting oil may be more suitable. Oil slicks that drift a long way from the source are assumed to be more broken up than those closer to the source and in many cases have a lower film thickness. This leads to reduced access to the oil, and systems in barrier 2 therefore usually perform less optimally than in barrier 1.
The oil´s properties
- The oil is assumed to be on average 12 hours old, corresponding to a distance of approx. 11 km from the spill site with a drift rate of 0.5 knots. This means the oil has now undergone natural disintegration to a greater degree, and the properties of the emulsion may have changed in relation to when it was close to the spill source. Other values for the properties of the oil can be used, but must then be justified and included in the calculations.
Remote measurement
- In this zone, the oil is expected to be spread over a larger geographical area and appear as a relatively extensive slick, but with the majority of the oil concentrated within a small part of the area of the slicks. The main task of remote measurement is to survey the slicks and to indicate where in the slicks there is the most oil; here too, the goal is to tackle as much of the oil as possible.
Barrier 3
Natural prerequisites and operational conditions
- Local conditions, which will be of considerable importance in this zone, vary significantly along the coast and include tidal currents, various shore types, intertidal zones, shallows, skerries, and grounds. In this zone, we also sometimes find high concentrations and the presence of vulnerable resources and a number of assets linked to the use of the coastal zone.
- Navigational conditions restrict which system devices can be used.
The oil´s properties (from offshore sources)
- Oil from offshore sources will have drifted for several days before entering the coastal zone. Properties vary significantly between different oil types, localities, and times of year. One general feature, however, is that a fully developed emulsion has now formed and the slicks are clearly demarcated.
Remote measurement
- In this zone, the oil is expected to be spread over a large geographical area. The main task of remote measurement is to survey the position and estimated volume of the slicks so that this information can be used in operational calculations of oil drift, compared with the presence of vulnerable environmental resources and used as a basis for prioritizing
remedial measures.
Barrier 4
Natural prerequisites and operational conditions
- In this zone, remedial measures will be able to be carried out from both the seaward and landward sides. Local conditions and infrastructure will vary significantly along the Norwegian coast.
- Here too, navigational conditions restrict which system devices can be used.
The oil´s properties (from offshore sources)
- The properties of the oil will initially be the same as for barrier 3, but the incorporation of other materials (e.g. seaweed, flotsam, gravel...) may increase the volume and make the collection more difficult.
Barrier 5
Natural prerequisites and operational conditions
- Remedial measures in this zone will largely be carried out from the landward side. Local conditions and infrastructure will vary significantly along the Norwegian coast.
- Prioritization is based among other things on the degree of contamination, the potential for remobilization, and environmental vulnerability.
- Logistics and appropriate interim storage of oily waste is key.
The oil´s properties (from offshore sources)
- The properties of the oil will initially be the same as for barrier 4, but the incorporation of other materials (e.g. seaweed, flotsam, gravel...) significantly increases the volume of oily mass.
Remote measurement
- In this zone, the oil is expected to be spread over a large geographical area. The main task of remote measurement is to survey the position of the oil so that this information can be used to assess the potential for further drifting and recontamination, and as a basis for prioritizing remedial measures.