According to the text, “in situ burning" (line 29) is

                                                        Cleaning up a spill 
                                                       Written by Laura Hill

Water and oil don’t mix. We see this every day; just try washing olive oil off your hands without soap or washing your face in the morning with only water. It just doesn’t work!
When an oil spill occurs in the ocean, like the catastrophe in the Gulf of Mexico, what do scientists do to clean up the toxic mess? There are a number of options for an oil spill cleanup and most efforts use a combination of many techniques. The fact that oil and water don’t mix is a blessing and a curse. If oil mixed with water, it would be difficult to divide the two.
Crude oil is less dense than water; it spreads out to make a very thin layer (about one millimetre thick) that floats on top of the water. This is good because we can tell what is water and what is oil. It is also bad, because it means the oil can spread really quickly and cover a very large area, which becomes difficult to manage. Combined with wind, ocean currents and waves, oil spill cleanup starts to get really tricky.
Chemical dispersants can be used to break up big oil slicks into small oil droplets. They work like soaps by emulsifying the hydrophobic (waterrepelling) oil in the water. These small droplets can degrade in the ecosystem quicker than the big oil slick. But unfortunately, this means that marine life of all sizes ingest these toxic, broken-down particles and chemicals.
If the oil is thick enough, it could be set fire, a process called “in situ burning”. Because the oil is highly flammable and floats on top of the water, it is very easy to set it alight. It’s not environmentallyfriendly though; the combustion of oil releases thick smoke that contains greenhouse gases and other dangerous air pollutants.
Some techniques can contain and recapture spilled oil without changing its chemical composition. Booms float on top of the water and act as barriers to the movement of oil. Once the oil is controlled, it can be gathered using sorbents. “Sorbent” is a fancy word for sponge. These sponges absorb the oil and allow it to be collected by siphoning it off the water.
However, weather and sea conditions can prevent and obstruct the use of booms, sorbents and in situ burning. Imagine trying to perform these operations on the open sea with wind, waves and water currents moving the oil (and your boat!) around on the water.
What about the plants and animals? It’s easy to forget about the organisms in the sea that are under water. Out of sight, out of mind! There is not much we can do to help them. But when oil reaches the shore it impacts sensitive coastal environments including the many fish, bird, amphibian, reptilian, and crustaceanspecies that live there. We have easy access to these areas and there are some things we can do to clean up. For the plants, it is often a matter of setting them on fire, or leaving them to degrade the oil naturally. Sometimes, we can spray the oil with nutrients (phosphorus and nitrogen) that can encourage the growth of specialized microorganisms. For species that can tolerate our soaps, manpower is needed to wash every affected animal. Yet, if the animal has tried to lick itself clean, it can die from ingesting the toxic oil.
Unfortunately, there can be many negative economic and social impacts, in addition to the environmental impacts of oil spills and, as you’ve just read, the clean up techniques are far from perfect. Prevention is the very best cleanup technique we have. http://www.curiocity.ca/everyday-science/environme... -cleaning-up-a-spill.html, retrieved on Dec 10, 2010