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Oil Spills and the Marine Environment
Segregated Ballast Tanks
Some tankers
are now built with a number of tanks reserved exclusively for
ballast. These tanks are not filled with oil during a cargo voyage.
Because the use of segregated ballast tanks reduces the tanker's
carrying capacity, this practice is avoided wherever possible by
tanker operators.
Prevention of Contact of Ballast Water
with Oily Tank Walls
For some
time, people have considered the possibility of fitting each cargo
tank with a flexible rubber membrane that would be pressed up
against one tank wall when cargo was carried. Ballast water would
be pumped between the wall and the membrane, thus pressing the
membrane against another tank wall, when the tank was in ballast.
Oil would always touch one side of the membrane, and water the
other (). However, serious research on this concept did not begin
until 1972 (). The work done to date indicates potential
feasibility of the concept, and the U.S. Navy recently installed
such a membrane in one of their ships on a trial basis.
Slop
Burning
Porricelli ()
discusses the possibility of burning slop oil on tankers using the
load-on-top procedure. No further research in this area is known,
however, probably because slop oil is discharged ashore along with
the next cargo of oil, and burning is not practical for ordinary
oily ballast water.
PREVENTION OF SPILLS FROM TANKERS IN
PORT
Effect
of Port Facilities
The Georges
Bank Study () contains a relatively thorough statistical analysis
of spills into the oceans in the vicinity of the United States
coastline from all sources for 1971, as well as less complete
analyses of worldwide oil spills between 1957 and 1971. This study
estimates that 500,000 gallons were spilled from port transfer and
storage facilities in 1971. This amounts to one part spilled per
million parts handled. It was found that ten times this amount of
oil was spilled in the New England area. The report also contains
data on spills at the port of Milford Haven, Great Britain, for
1963-1969. The average spillage at Milford Haven during this
period, measured as a fraction of the total oil handled, was 1.8
parts per million (ppm). However, for the last two years reported,
the spillage was much smaller; in 1968 it was 0.5 ppm, and in 1969
it was 0.4 ppm. Milford Haven is a very large new port. In 1969,
with an average daily throughput of 745,000 barrels of oil, the
total quantity spilled was 4,050 gallons. The total average
spillage at Milford Haven between 1963 and 1969 is
unrepresentatively high because of some problems in 1967 when
73,000 gallons