An oil
pollution control barrier, frequently called an oil boom, is a
device floated on the surface of the sea to prevent the passage of
an oil slick from one side of the barrier to the other. A pollution
control barrier looks like a vertical curtain piercing the surface
of the sea to a depth greater than the thickness of the oil slick.
To be effective, the barrier must follow the motions of the waves
so that its top never goes beneath the top of the slick and its
bottom never rises above the bottom of the slick. Typical barriers
have a vertical height varying from six inches to five feet, with
between 55 percent and 90 percent of this vertical height below the
sea surface and the remainder above the surface in calm water (see
Figure 3-1). For many years pollution control barriers have been
used to contain oil from leaking ships in harbors where the water
is typically very calm. There it is relatively simple to surround
the slick with a curtain ballasted at its bottom and buoyed up near
its top to keep it vertical and contain the oil between a ship and
barrier. This can be done with a fairly simple barrier. However,
when taken away from protected harbors into moderate currents and
waves, barriers designed for calm water break apart easily and are
unable to contain oil even if they do not break. The problems of
using a barrier in an unprotected area are caused by currents and
waves.
In a current,
a barrier is intended to hold the oil against the current. One
technological challenge is to make the barrier remain vertical at
the right height without rising or sinking. Another is related to
the hydrodynamics of containing the oil. Both of these problems
have been extensively researched (), (), () and ().
Ocean
engineers can now design barriers that will remain vertical in
moderate currents. Although a number of satisfactory barriers
exist, many barriers on the market still fall short. Of the
satisfactory calm-water barriers, the best in any circumstance is
usually the one that can be deployed soonest. Even with the
satisfactory calm-water barriers, containment is restricted by two
hydrodynamic effects. First, for any barrier depth in a specific
current speed, there is a limit to the amount of oil that can be
contained. The limit is passed when the pool of oil held by the
barrier is so deep that it flows beneath the