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Behaviour of Oil
This section of the Response Handbook has been divided into two chapters:
Behaviour of oil which has been spilled at sea
Behaviour of oil which has been spilled on land
Behaviour of oil which has been spilled at sea:
This chapter is the most fundamental part of the Response Handbook, when it comes to marine oil spills.Most of the oil which spills into water is crude oil. The spills are either due to natural leaking from the underground, as is the case off the coast of California, or due to human action in connection with exploration, production, or transportation of crude oil.
The behaviour depends of the origin of the crude oil, as well as the environment which it is spilled into, e.i. water- and air temperature, wind and wave conditions. But in very general terms, the following will happen within hours:
- Spreading: The oil spreads rapidly over a large area and breaks up in windrows, which are long an narrow slicks with the same orientation as the wind.
- Evaporation: The spreading causes the lighter fractions of the oil to disappear rapidly, leaving back in the water only the heavier parts.
- Emulsification: Wave action mixes water into the oil, forming a heavy and sticky
water-in-oil emulsion, sometimes called chocolate mousse.So, if you arrive at the spill site 10 to 20 hours after the spill, expecting to find something like the motor oil from your car, you may get a big surprise. And as if the heavy, sticky emulsion wasn’t bad enough, you may in addition find it mixed with all types of floating debris, such as kelp, seaweed, wood, cans, rope, plastic, and more.
The described behaviour of the spilled oil sets the demands for a successful oil spill response:
- Minimal response time
- Efficient and fast concentration of the widely spread oil
- Skimmers and pumps which can handle high viscosity emulsion and debris
- Appropriate temporary storage capability
(Options: Dispersant spraying may be used in the very early stages after the spill, provided permission has been granted by the authorities. In-situ burning may be an option to skimming).
It is relevant to mention that in some cases very light oil has been spilled in large amounts without significant visual impact. This is due to the fact that nearly all of the oil has evaporated, and that the ocean has handled the rest by natural dispersion. Only in blow-out situations or if such light oil has been trapped in a harbour or in a bay, a fast response may be able to recover significant amounts of the oil. (Back to Top)
Behaviour of oil which has been spilled on land.
Where the very light oils seem to cause the least problems at sea, it is the opposite situation on land:Light oil tends to penetrate the top soil rapidly, thus seeping into the deeper ground bringing the groundwater at risk. Heavier oil only very slowly contaminates the soil, as its higher viscosity makes penetration difficult.
Depending on the viscosity, the spilled oil will more or less fast flow to the lower part of the landscape. Apart from this, spreading will not take place, so the evaporation of the lighter fractions of the oil will be limited. Further, there will be no emulsification with water. Therefore the spilled oil will not physically change very much, unless it is left on the ground for a longer period of time.
But the oil will mix with gravel, soil, and the present vegetation, which may result in difficulties during clean-up.
The described behaviour of the spilled oil sets the demands for a successful oil spill response:
- Minimal response time, especially for spills involving light oil
- Efficient and fast limitation of further spreading (dikes and ditches)
- Skimmers or pumps which can handle debris and soil contaminated oil
- Appropriate temporary storage capability
(Options: Certain biologically degradable detergents may successfully be used for fast flushing of the oil to the collection and recovery area. In-situ burning may - in a few special situations - be an option to recovery, pending permission).
Apart from the above mentioned differences from marine spills, it is important to note, that land oil spills very often involve so called product oils. These are oils which have been refined, and their performances (as for instance diesel-, hydraulic-, transmission-, or lubrication oils) have been improved by additives, of which some are extremely toxic and harmful to the environment.
(Back to Top)
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