When oil is accidentally released into a body of water, the most urgent priority is limiting the spill's spread to minimize the natural resources at risk and to facilitate cleanup and removal. Swift and skillful deployment of a containment boom is essential for achieving both of these goals.
Because oil is less dense than water, it rises to the surface, where floating fences called booms can corral it. In its simplest form, a boom consists of a length of rugged fabric with buoyant filler stitched into the side intended to float above the water, and a heavy chain or other ballast inserted into the bottom to weigh down the sub-surface skirt and make it sink. Boom material is brightly colored for ease of recovery and to help crews spot a break in the line. The freeboard (above surface) component is commonly designed to reduce splash-over, while the skirt is engineered to keep oil from escaping beneath the boom.
Under ideal conditions, a spill is quickly contained by booms strung end to end until they completely encircle the floating oil. Realistically, however, a number of factors, such as water current, wave height, wind velocity and oil viscosity steadily work to churn up the surface and hamper a boom's capacity to contain oil.  The result is that in heavy seas or during rough weather, some of the oil sloshes over and under the boom, making a single line inadequate. These cases require multiple concentric circles of oil boom extending over increasing diameters until the spatial extent of the leak is contained.
When a slick becomes too dispersed for circular containment or when it begins to approach land, a mobile retention boom, with or without a built-in recovery system or skimmer, can be deployed to assist the oil roundup.
A variety of booms designed to repel water (hydrophobic) and soak up oil (oleophilic) serve as a backup or replacement for physical containment booms. Unlike barrier-only booms, absorbent booms are lightweight, easy to deploy, and have the ability to simultaneously contain a spill and begin the recovery process. They also require timely retrieval or an anchor point to prevent sinking as the booms become heavy with oil.
Commercial absorbent booms are commonly made of an outer mesh with polypropylene filler and are engineered for easy deployment and maximum absorbency, as well as a long flotation period.
While booms made of natural sorbents  like hair, hay and even a 3,000-year-old Egyptian hibiscus plant called kenaf  reflect the largely low-tech measures still used to clean up oil spills, they are also environmentally safe and stimulate community involvement. 
Often functioning as the first and last line of defense in an oil spill, booms are meant to both contain and concentrate the oil close to the source, so it can be skimmed or vacuumed from the surface by other equipment, and then prevent the oil that manages to get through from washing up on beaches or marshes.
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Recovery: Skimmers and Separators