Controlled in situ burning (ISB) of oil slicks is a response technology that has been researched and employed at a variety of oil spills since the late 1950s, including limited use during the Exxon Valdez accident and extensive use during the Deepwater Horizon incident.
In situ burning is an oil spill response option particularly suited to remote, ice-covered waters. The key to effective in situ burning is thick oil slicks. If ice concentrations are high, this can limit oil spreading and keep slicks thick enough to burn. In drift ice conditions and open water, oil spills can rapidly spread to become too thin to ignite. Fire-resistant booms can collect and prevent slicks spreading and thinning in open water; however, even light ice conditions make using booms challenging.
A multi-year research project was initiated in 2004 and continues in 2015 to study oil-herding surfactants as an alternative to booms for thickening slicks in light ice conditions for in situ burning. Successful test programs were conducted in small and large test tanks and in field settings. Two herding agents (ThickSlick 6535 and SilTech OP-40) were placed on the U.S. Environmental Protection Agency National Oil and Hazardous Substances Pollution Contingency Plan (NCP) Product Schedule for consideration for use in U.S. waters, and were made commercially available as of June, 2012.
Herders at a Glance
- Herding agents were initially developed in the 1970’s as a method of thickening oil slicks prior to mechanical recovery.
- The use of herders to enable in situ burning has undergone more than 10 years of study.
- Field tests conducted off Norway in 2008 demonstrated that herders work in cold open water with ice nearby.
- Herders use surface active agents to thicken slicks without the need to collect the oil in a physical boom and do not require a physical boundary to work. They are effective in the open sea, with or without the presence of ice, as long as there are few breaking waves present.
- Herding agents cause oil slicks to contract, the same way a drop of dish soap in a wet, greasy pan forces the grease to the edges. As oil spills shrink in surface area, they get thicker growing from about a millimeter (0.04 inch) to 6 millimeters (0.24 inch) thick. This contraction makes it possible to ignite the slick and achieve an efficient burn. The thicker a spill is before it is burned, the more oil gets removed and the higher the overall response effectiveness.
- Herders are effective in fresh and marine waters
- Herders require very small quantities of a low toxicity surfactant
- Two herding agents (ThickSlick 6535 and SilTech OP-40) are now on the U.S. Environmental Protection Agency National Oil and Hazardous Substances Pollution Contingency Plan (NCP) Product Schedule for consideration for use in U.S. waters, and both are commercially available as of June, 2012.
- A helicopter delivery system for aerial herder application is in the process of being developed and tested through the Joint Industry Programme (see Field Research – HYPERLINK).
- Herders use about 30 times less product compared to treating a slick with dispersant. Herders are applied to the water around an oil slick, not on the oil itself. The use of herders on an oil slick does not detract from the effectiveness of subsequent or concurrent chemical dispersant application or mechanical recovery.
- Using herders to contract slicks on open water can improve the operational efficiency of dispersants applied by vessels as the slick area to treat is reduced.