Spraying
Updated 29 April 2015
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This publication is available at https://www.gov.uk/government/publications/how-to-use-oil-spill-treatment-products-and-equipment/spraying
1. Before you spray
The response to an oil spill incident should be planned. Contingency plans establish resources that require protection and the circumstances to use dispersants.
The local contingency plan will contain information that provides a clear understanding of the circumstances under which you need to seek MMO’s approval for dispersant use and of the information you need to provide.
A test spray should be carried out before full-scale operations.
2. When you should spray
Aim for a fast response, but consider:
- state of the sea – wave height and temperature
- weather conditions and remaining daylight
- potential for dilution
- whether the advantages of dispersant use as opposed to any other treatment method (or the option of leaving the oil to dissipate naturally) justify this treatment method
Seek advice if uncertain.
3. When you shouldn’t spray
Dispersants should not be used to treat spills of diesel, gas oil, or similar light oil types which are likely to evaporate from the sea surface naturally.
Dispersants should not be used to treat oils that have a viscosity greater than the maximum specified for the dispersant. Spraying in wind speeds greater than force 6 (22 to 27 knots), or where there is a risk of the dispersant being blown back onto the land, is not recommended.
Dispersants should not be used in a freshwater environment, on mudflats or on saltmarshes, unless this has been specifically recommended by the statutory nature conservation agency.
4. How to spray from onboard a vessel
Droplet size should be about that of an average raindrop.
No more than 20% of the dispersant (and considerably less if possible) should fall off-target.
Where possible, use a spotter plane to control larger spraying operations or ones where the surface oil has become fragmented.
Begin at the edge posing the greatest threat and prioritise spraying thick patches of oil rather than thin films or sheen.
If a large, thick patch is identified, it may be advantageous to spray right round the outer edge first in order to restrict the spread of oil. Otherwise use parallel and continuous runs.
Where practicable, and if wave action is not considered sufficiently strong to aid chemical dispersion, use mechanical means (surface breaker boards) to increase water agitation.
5. How to spray from shorelines
Dispersants can be used on some shorelines (particularly sandy beaches), but only as part of the final stages of clean-up. The maximum depth of oil that can be treated effectively by dispersants is 6mm. For heavy pollution, the bulk of the stranded oil must be mechanically removed before dispersant use.
Rocky shores will not normally benefit from dispersant use because the wave energy associated with this type of coastline provides a high natural cleaning rate. Where, some spraying of the rock face is considered necessary, care should be taken to ensure that the dispersant does not accumulate in rock pools.
Avoid using dispersants in cases where further stranding of oil is likely to occur on successive tides.
Apply the dispersant to coincide with the tidal washing of the treated area within 30 minutes of the treatment, or use hosed seawater to wash off the dispersant and treated oil.
Dispersants are often not the best method of dealing with shoreline pollution, therefore other options (cobble-washing, for example) should always be considered first. The statutory nature conservation agencies will be able to provide advice on the relative benefits and impacts of different clean-up techniques.