Mid-scale ISB experiments were conducted in a large water-basin (20 m 2 x 1 m) in order to assess the applicability of chemical herding of weathered crude oil spills on water in association with in-situ burning (ISB). A silicone-based chemical herding agent, OP-40, was used to confine, or herd, three different crude oils (Siri, Grane and Oseberg blend) at various weathering degrees. The herding agent was capable of obtaining the minimum required oil slick thickness for ignition and subsequent flame spread in most of the experiments, but not for the strongly weathered oils. Also, the herding agent was capable of re-thickening the oil slick after flame extinction. The burning efficiency results indicate that the method can be viable for ISB with herders at a larger scale, and suggest that the burning efficiency scales with the amount of crude oil. Sinking behaviour of residues was also observed and quantified, as such a behaviour can pose a serious environmental threat in real scenarios.

The thickening effectiveness of two commercially available herding agents (OP40 and TS6535) was investigated parametrically in small-scale laboratory experiments with two different crude oils (ANS -Alaska North Slope and Grane). Both fresh and emulsified in cold water conditions were used in order to provide further information for in-situ burning operations in an Arctic context. Two application procedures for the herder, as well as variations in the duration of the tests, were other variations in the study. Both herding agents demonstrated the ability to obtain the minimum oil slick thickness (1-5 mm) required for successful in-situ burning. OP40 was more efficient for short periods than TS6535, whereas TS6535 remained active for long periods (up to 400 hours). Both herders were more efficient in pre-spill application than post-spill application of the herder. The herder monolayer was not affected during burning and was still active once the burning ceased. Nonetheless, some contradictory results were found over a range of parameters, but are still in line with previously reported findings. Further systematic studies study based on physical/chemical characteristics of the oils and herders are required to fully establish the physical dependencies.

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