MARINE SPILLAGE—SOURCES AND HAZARDS 681
hazards and pollution problems. The responsible regula-
tory agencies were active in studying and regulating vari-
ous special hazardous cargoes long before oil pollution was
recognized as a major hazard. Accordingly, safety codes and
regulations have been formulated and effectively enforced
for a long period of time. Regulations of the U.S. Coast
Guard, for example, which apply to various hazardous car-
goes, as well as liquefied petroleum and natural gasses, are
covered in References (9), (10) and (11).
Hazardous cargo transportation is given special treat-
ment by the designer and the cognizant regulatory agencies
by consideration of the following:a) Materials—Where indicated by the corrosive or
otherwise restrictive nature of the cargo, special
materials, subject to rigorous testing require-
ments, are specified. Liquefied gas containment,
for example, requires special steels or other mate-
rials to avoid brittle fracture at low temperature.
Similar restrictions hold for piping and cargo
pumps.
b) Containment—As noted earlier, in all cases where
special hazards exist, it has generally been the
practice to require transport of cargoes inboard
of shell plating, that is, cargo is contained within
an inner hull formed by an inner bottom and
longitudinal bulkheads. Further restrictions in
some cases require that the cargo containment
be structurally independent of the ship’s main
hull structure. This is the case with pressure ves-
sels and rectangular tanks for carrying liquefied
gasses at low temperature and molten sulfur at
high temperature. The requirement for second-
ary containment, that is, the ability to contain the
cargo for indefinite periods of time in the event
of rupture of the primary tank, has long been
established as a basic requirement for the trans-
port of liquefied gases at low temperature.
c) Cargo handling—Elaborate safety precautions to
avoid spillage and sources of ignition are inher-
ent in established design practices and regulatory
requirements.The above brief discussion indicates a comparatively high
level of design for safety in the case of hazardous cargoes.
In the event of a low energy collision or stranding there is a
reasonable probability that the primary containment system
will remain intact.
For the liquefied gasses, the greatest tonnage category of
special hazardous cargoes, pollution hazards are limited, or
at least of short duration, since the cargoes are volatile and
would be dissipated in a short period of time in the event of
primary tank rupture. For the other cargoes, toxic materi-
als in particular, the pollution hazard remains. Cargoes are
shipped in relatively small quantities, however, and effective
containment is readily achieved with modern construction
methods.Dry Bulk CarriersFuel oil is likely to be carried primarily in deep tanks, and,
to a lesser extent, in selected double bottom and wing tanks.
Accordingly, fuel bunkers comprise a relatively small portion
of total tank space and do not represent an unusual in the
event of collision or grounding.Combination Bulk CarriersWhen transporting oil cargoes, combination carriers func-
tion as tankers. The internal arrangement of ore/oil tankers,
Figure 3, resembles the arrangement of a tanker, with
respect to location of longitudinal bulkheads at least 20%
of the breadth from the side shell. Accordingly, the extent
of cargo oil pollution from side collision is comparable to
the case of the tanker, assuming comparable compartment
lengths.
The ore/bulk/oil, or OBO, carrier, however, is designed
with high capacity cargo holds in order to transport low
density dry bulk cargoes as well as oil. As a result, the
boundary of the center holds is well outboard the 20%
breadth penetration line, for either the single skin or
smooth skin side shell arrangement. In the event of a side
collision in way of a single compartment of a nine-hold
vessel about 1/9 the oil cargo will be exposed to the sea,
compared to about 1/20 the total cargo in the case of a
modern crude tanker. In the case of a low energy collision,
the OBO with double skin side shell will offer a somewhat
greater resistance to penetration than the more common
single skin arrangement.
The double bottom arrangement of combination carries
does provide for some grounding protection, particularly in
way of the center holds. The lower outboard sloping wing
tanks of some vessels, however, are regularly used as cargo
oil tanks.PREVENTIONImprovements in maritime safety standards have historically
followed some major disaster at sea. This was the case with
respect to loss of the TITANIC, the 1960 SOLAS conven-
tion with respect to the sinking of the ANDREA DORIA,
and now the accelerated IMO activity in the wake of the
1988 1989 casualties.
It must be emphasized that economic incentives are
the fundamental basis for the increased potential for pol-
lution due to collision and stranding. The trend to larger
tank vessels and toward simplification of the ship design,
all directed to substantial economies in construction and
operation, are not easily reversed. Yet this trend neces-
sarily increases the pollution hazard occurring from an
individual incident. In the light of the overwhelming short
term economic incentives, it is clear that all improvements
must necessarily come from the imposition of require-
ments from outside the industry; that is, from the delib-
erations of regulatory bodies at an international level andC013_003_r03.indd 681C013_003_r03.indd 681 11/18/2005 10:41:04 AM11/18/2005 10:41:04 AM