This type of fuel oil “does not float on the surface” and “there is no proven technology in the world to eliminate it in water”, according to the same source. “That’s why the main method is coastal collection.”
“Mazout+ (M100, editor’s note) is a trade name for a particular type of +heavy fuel oil+ (Heavy fuel oil, HFO in English, editor’s note) produced in Russia and Kazakhstan,” explains Rob James, prime minister, to AFP. vice-president Europe/Asia at Lamor, an oil and chemical pollution control company.
Heavy fuel oils are low-cost residual fuels from the distillation of crude oil in refineries, “generally used as fuel for large ships and industrial boilers”, it says.
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Heavy or light oil, what’s the difference?
There are two types of oil: heavy fuel oils with almost tarry consistencies, and so-called “light” oils including diesel, gasoline or kerosene.
The first, very polluting, are characterized by high viscosity and density. They can be as heavy or heavier than water, sink or be suspended, and persist longer in the aquatic environment.
The latter, with low viscosity and density, degrade quickly.
Thus, “a heavy fuel oil can remain in the environment for years, while a lighter fuel, such as diesel, can completely evaporate and disperse in a few days or weeks”, summarizes Thomas Azwell to AFP , researcher at the University of Berkeley.
Due to its characteristics, “heavy fuel oil (HFO) does not evaporate and dispersants have little effect on it”. It is described “as ‘persistent’, because the climatic and biological processes which can naturally reduce the impact of a crude oil spill have little impact on heavy fuel oil”, underlines Mr James.
“Any heavy fuel oil generally presents more difficulty to clean up than a spill of crude oil or other refined petroleum products,” he adds. Cleaning requires “a mechanical or manual process which takes time and labor resources”, like the sinking of the Erika in December 1999 in Brittany (in western France) which had let 20,000 tonnes of heavy fuel oil escape.
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How does an oil spill evolve?
The type of oil as well as weather and sea conditions are determining factors.
Once spilled, petroleum products can undergo eight main chemical and physical modification processes including: surface propagation, evaporation, accentuated by strong winds and high temperatures, dispersion into droplets under the effect of waves, emulsification, which increases the volume of the oil as it absorbs water, sedimentation which sees the oil interact with sediment and sink.
“Spreading, evaporation, dispersion and emulsification are important in the early stages of the spill, while photo-oxidation, sedimentation and biodegradation are long-term processes that determine the final fate of the oil” , indicates a technical note from the International Federation of Oil Shipowners Against Pollution (ITOPF).
According to ITOPF, “a small number of residual oils are dense enough to sink in the event of a spill. However, most oils float and only sink if mixed with denser sediments.”
