Encyclopedia of Environmental Science and Engineering, Volume I and II

672 MARINE SPILLAGE—SOURCES AND HAZARDS

crudes and refined products, transport of these commodities

may involve unique containment problems and associated

hazards.

Special products carriers may be classified in the following

manner, according to nature of cargo:

1) Liquefied natural gasses (LNG) and liquefied petro-

leum gasses (LPG).

(a) Low temperature—ambient pressure contain-

ment—The most exacting containment require-

ments are in this category, with cargo carried at

about −260F for liquefied natural gas (LNG). The

largest LNG carriers at this time have capacities of

about 130,000 cubic meters.

LPG transport includes the carriage of such gasses as

propane, butane and ethylene, with propane, carried

at about 
 50 F, the most common.

In a typical LNG or LPG carrier, cargo is car-

ried in an independent, insulated tank or membrane

liner. Double bottom and wing tank spaces are nor-

mally assigned to salt water ballast and fuel oil is

carried in a relatively small portion of the double

bottom and in deep tanks within the machinery

spaces. Geometry is similar to that of a container

ship and clean ballast operation is accomplished

with no difficulty.

(b) High pressure—ambient temperature—LPG may

be carried in pressure vessels, designed to the

A.S.M.E. Code for Unfired Pressure Vessels.

While this mode of containment has been gen-

erally superceded by low temperature transport

for international trade, a considerable amount of

LPG and similar cargoes is carried in this man-

ner on the inland waterways of the United States

and Europe and in smaller coastwise vessels and

barges. The limiting design condition is usually

for propane, in cylindrical tanks designed for 250

psig. In general, vessels carrying cargoes in pres-

sure vessels have sufficient cubic capacity to per-

mit clean ballast operation.

2) Miscellaneous liquefied gasses—Anhydrous ammo-

nia is carried in significant quantities in U.S. inland

and coastal waters. This commodity may be carried

at low temperature or under pressure, in containment

designed for the transport of propane.

Chlorine gas is commonly transported by barges

in U.S. waters, primarily in pressure vessel contain-

ment. Other commodities of importance are primarily

petro-chemicals, including butadiene, ethane, ethyl

chloride, prophylene and vinyl chloride.

3) High temperature commodities—The transport of

molten sulfur at about 275F in heated independent

insulated tanks has become the most common high

TABLE 1

Representative modern U.S. flat tank vessels

NAME EXXON CHARLESTON EXXON BAYTOWN ATIGUN PASS B.T. SAN DIEGO EXXON VALDEZ

Length, B.P., m 185.93 229.82 263.35 278.90 288.04

Breadth, mld, m 32.26 32.26 52.74 50.60 50.60

Depth, mld, m 18.29 18.29 22.86 23.78 26.83

Draft, keel, m 12.80 11.73 17.47 18.08 19.66

Displacement, tonnes 56,970 73,700 200,400 220,800 244,145

Deadweight, tonnes 42,800 58,645 176,160 191,100 214,860

Cargo capacity, m^3 59,200 62,660 184,300 209,980 240,890

Ballast capacity, m^3 18,500 32,000 57,400 59,600 69,600

Cargo Chem. and prods. Crude Crude Crude Crude

Number of cargo tanks 42 14 13 15 13

Propulsion machinery Dir. diesel Dir. diesel St. turbine St. turbine Dir. diesel

Horsepower, max

continuous

17,000 bhp 17,000 bhp 26,700 bhp 28,000 shp 32,240 bhp

Service speed, knots 16 15.8 16.5 14.25 16.25

Year delivered 1983 1984 1977 1978 1986

Notes:

1) Segregated ballast yes yes yes yes yes

2) Double bottom yes yes no yes no

3) Double hull no no no no no

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