OPTIMIZATION OF DISPERSANT APPLICATION, ESPECIALLY BY SHIP

Abstract

ABSTRACT A lot of information has been made available for 10 years on the use of dispersants through offshore and meso-scale trials. A state-of-the-art review shows that among the key factors that have been identified, the contact between dispersant and oil is of utmost importance. A better knowledge of this parameter should be taken into account in defining operational procedures, especially when applying dispersants by ship, which is considered to be complementary to aerial spraying. Upon request of the French Navy, a series of meso-scale trials was carried out off Brittany in June 1987, according to the methodology previously used in 1984. Three dispersants were sprayed from a boat. It was concluded that a high level of energy at the sea surface mitigates discrepancies in dispersants’ efficiencies as measured in laboratory tests. Better results were obtained in the case of relatively thick oil slicks. The low efficiency that was measured when treating downwind was attributed to the already-observed herding effect. These complementary results reinforce the actions that have been recently developed to optimize dispersant application by ship:Shipboard equipment for neat dispersant spraying is described. Its main feature is an original nozzle assembly that allows the dispersant to be applied effectively onto the oil at a flow rate that can be widely and very quickly changed according to the estimated oil thickness.An operational treatment procedure is discussed, showing how to map, mark out, prospect and treat oil slicks according to the slick shape, estimated oil thickness, and wind direction.