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From: (Bruce Hamilton)
Subject: Re: Question about Oil spills
Date: Tue, 09 Apr 1996 14:57:27 GMT (Carol Rizzo) wrote:
>Which is worse for the ocean; regular tanker oil or refined tanker oil?
>What impact does each have on the sea habbitat?

Unfortunately, it is not a simple issue. Firstly, crude oil can have very
different qualities - it can be a thick, semi-solid, black mass ( very heavy
crude ) to a light, golden-coloured volatile fluid ( such as a natural gas
condensate or a light crude ). When the oil spills, some of the volatile
material evaporates and the oil "weathers"( which can include oxidation of
reactive hydrocarbons ), leaving an even thicker mass which often forms black
tar globules when it is washed ashore. The oil slick itself ( whether a light
oil or heavy oil ) will trap unwary seabirds and other surface dwelling
species. When it reaches the shore it will devastate tidal communities,
regardless of whether it is from a refined produce or crude oil.

The finished products ( or "refined" products ) that are shipped by tanker can
range from a  gasoline ( that  will almost all evaporate, and can be a motor
gasoline for cars, or a aviation gasoline for planes ), to a kerosine ( much
slower evaporation, and can be a lighting kerosine used for illumination or
a aviation turbine kerosine used on civilian aircraft ( such as Boeings ) or
military aircraft ), to diesel ( will leave a slight residue and used on
trucks, buses, trains, and ships  ), to lubricating oil base grades ( vacuum
refined - virtually non-volatile, but representing a very small percentage of
refined product shipments ).

Residual fuel oils ( very cheap - often used as fuel in large merchant ships -
and are the thick black material left after all the above volatile fuels are
refined from the crude ) are particularly yucky. A similar material is found
after a crude oil has "weathered" and lost the volatile material. These tend to
have the most adverse environmentale effects, and can arise from either the
ship's own fuel tanks ( residual fuel oil ) or as a carried product ( crude oil

So you can see that it depends very much on the particular refined oil or
crude oil as to what adverse environmental effects there are. In general,
the heavier crudes and residual fuel oils are the worst, and can have fairly
long term adverse effects on wildlife. It is only very recently that the long
term behaviour and consequences of a spill have been closely monitored,
and some of the claims about how long environmental damage will remain after a
single large spill are still contentious. Because ships fuel oil tanks
are routinely cleaned,  many of the incidents are small as the ships illegally
dump the material, whereas the most publicity goes to incidents involving
large crude oil carriers such as the Exxon Valdez mainly because a single
large spill will have an immediate dramatic effect that is obvious on TV.

If you were to visit the Malayian western coast ( Straits of Malacca ) you
would find the once golden sands are now completely black around the
tidal mark from the continual arrival of oil residues from passing shipping
over the past few decades. This would perhaps result in much more
serious, long-term environmental damage than the single incidents such
as the Exxon Valdez ( as whole shore communities have now lost their
habitat ), but is not such good TV as a large tanker spewing oil.

Note that a requirement for tankers to be double skinned, and enforced
strict tank cleaning rules for all shipping, would dramatically reduce the
amount of annual oil pollution. Unfortunately the low price of crude oil
and residual fuels discourages such requirements, whereas the higher
price of refined distillate products ( gasoline, kerosine, diesel ) means
that more care is taken to avoid losses of them.

I suggest you visit some of the home pages of environmental groups
and oil companies to discover the differing perceptions of the problems
of the worldwide shipping of crude oil. The single incidents receive lots
of coverage, but the continual pollution caused by ships fuel tanks and
tank cleaning receives much less publicity, but is a very serious problem,
especially in areas of high maritine traffic that are adjacent to fragile
coastal environments such as marshes.

              Bruce Hamilton

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