230
A. NELSON-SMITH
enter Europoort it is sufficient to pump off 30000 tons, which takes
10 h. Before the large tanker could dock at Thames Haven or Tranmere (on the Mersey), she must be lightened by the full 70 000 tons
in order to reduce her draught to 45 ft (13.7 m) ; this takes 16 h (Anon.,
1968a). There is as yet no record of a serious spill during this procedure.
Kirby (1969) discusses possible sources and Shell refer to their experience of transhipnient in the Persian Gulf, pointing out that the Royal
Navy refuels warships at sea as a matter of routine. Wiebe (in discussion
following a paper by Edwards, 1968) advocates the off-shore unloading
of tankers exceeding 100000 tons as a safety measure, to avoid the
risks attending the navigation of these large vessels in constricted
waterways. Nevertheless, since most spillages occur during transfer
operations, the risk must necessarily be increased when multiplying the
number of these operations per voyage. It has already been noted that
many of the possible methods for containing and recovering oil spilt
during such operations cannot be carried out under open-sea conditions.
C. Coastal industry and other sources
A coastal refinery represents the most obvious risk for oil pollution,
considering the millions of gallons of crude oil and its fractions which
are processed or stored there. However, refineries are planned with
the possibility of spillage in mind, and, provided that the relevant
codes of practice (American Petroleum Institute, 1960, 1963 ; Institute of Petroleum, 1965) are properly observed, serious pollution
incidents occur only as a result of rare accidents. I n a refinery, crude
oil is purified and processed to produced a variety of fuels, lubricants
and solvents as well as feedstocks for petrochemical plants. During
these operations, continuous small-scale pollution occurs through
leaking connections and glands, spills, breakages, sampling operations
and the emptying of traps or settlement tanks. Larger volumes of oil
may be released during emergency or routine shut-down of plant,
cleaning and start-up operations. Water is used in some processes
and inevitably becomes contaminated with the product. All drainage
from the refinery site is carried to separators, usually of the API
gravity type, although process-water may need special treatment first.
The effluent may be held in a further settlement pond after passing
through the separator.
Most coastal refineries discharge to an estuary, creek or stream rather
than across the open coast, so quality standards will be demanded for
the effluent by some pollution-control authority, which may place the
maximum permissible oil content anywhere between 5 p.p.m. and 100
A. NELSON-SMITH
enter Europoort it is sufficient to pump off 30000 tons, which takes
10 h. Before the large tanker could dock at Thames Haven or Tranmere (on the Mersey), she must be lightened by the full 70 000 tons
in order to reduce her draught to 45 ft (13.7 m) ; this takes 16 h (Anon.,
1968a). There is as yet no record of a serious spill during this procedure.
Kirby (1969) discusses possible sources and Shell refer to their experience of transhipnient in the Persian Gulf, pointing out that the Royal
Navy refuels warships at sea as a matter of routine. Wiebe (in discussion
following a paper by Edwards, 1968) advocates the off-shore unloading
of tankers exceeding 100000 tons as a safety measure, to avoid the
risks attending the navigation of these large vessels in constricted
waterways. Nevertheless, since most spillages occur during transfer
operations, the risk must necessarily be increased when multiplying the
number of these operations per voyage. It has already been noted that
many of the possible methods for containing and recovering oil spilt
during such operations cannot be carried out under open-sea conditions.
C. Coastal industry and other sources
A coastal refinery represents the most obvious risk for oil pollution,
considering the millions of gallons of crude oil and its fractions which
are processed or stored there. However, refineries are planned with
the possibility of spillage in mind, and, provided that the relevant
codes of practice (American Petroleum Institute, 1960, 1963 ; Institute of Petroleum, 1965) are properly observed, serious pollution
incidents occur only as a result of rare accidents. I n a refinery, crude
oil is purified and processed to produced a variety of fuels, lubricants
and solvents as well as feedstocks for petrochemical plants. During
these operations, continuous small-scale pollution occurs through
leaking connections and glands, spills, breakages, sampling operations
and the emptying of traps or settlement tanks. Larger volumes of oil
may be released during emergency or routine shut-down of plant,
cleaning and start-up operations. Water is used in some processes
and inevitably becomes contaminated with the product. All drainage
from the refinery site is carried to separators, usually of the API
gravity type, although process-water may need special treatment first.
The effluent may be held in a further settlement pond after passing
through the separator.
Most coastal refineries discharge to an estuary, creek or stream rather
than across the open coast, so quality standards will be demanded for
the effluent by some pollution-control authority, which may place the
maximum permissible oil content anywhere between 5 p.p.m. and 100