Allegra
Vegetable
oils, mainly from Asia and America, are being used increasingly
in Europe, especially in the food and cosmetics industries. It follows
that shipping patterns involving this kind of oil can only increase,
which means that potential occurrences of maritime casualties and
spills will also increase.
On 1 October 1997, in the Channel, just off the coast of Guernsey,
the Liberian tanker the Allegra was involved in a collision and
subsequently spilled 900 tonnes of palm oil. The oil solidified
quickly forming a slick measuring 800 by 400 metres. The slick continued
to spread and turned into an immense slick, 20 km long by 4 km wide.
The slick came ashore on the Channel islands and in the Cotentin
where it beached at high water mark. The spill was made up of 5
to 50 cm diameter margarine-like rubbery balls with a spongy yellow
core and a whitish crust.
The
slick drifted and as it did it was tracked by French Customs
and MPCU remote sensing aircraft using airborne SLAR (Sideways
Looking Airborne Radar) systems operating in the UV and IR bands.
The radar system was housed in pods under the fuselage. These
methods enabled the pilots to locate and track the slick for
the two days following the accident. Even though the spill had
no adverse effect on the marine environment, one can easily
imagine the effects the widescale landing of "margarine"
balls on the beach might have at the height of the summer season.
Research scientists at Cedre are currently seeking to know more
about the behaviour pattern of this kind of oil. The main difference
between palm and crude oil is that palm oil is solid at room
temperature. Three factors are being investigated: slick drift,
physical and chemical changes to the oil and its dispersion
pattern in the marine environment.
The
locations of the slick, as indicated by the remote sensing aircraft,
were compared to computer-generated predictions designed for oil
spills. However, computer modelling did not appear to be suited
to dealing with this kind of oil, due to its solid state. Oil samples
were collected both from the sea and from the beaches, in order
to investigate the way the product had been affected by the water,
however no change in the physical properties of this oil were observed.
Small scale testing was conducted at the Cedre in a bid to simulate
the Allegra spill. The oil solidified almost instantaneously into
very small particles, only a few millimetres in diameter, which
subsequently aggregated into "margarine" balls, 5 to 10
cm in diameter. Testing showed that the oil dispersed naturally
in the water column which may well explain why a large quantity
of the oil spilled seemed to have disappeared.
A post-spill research programme has subsequently elucidated the
fact that the physical state of the oil is of crucial importance
when a spill occurs. The drift of the slick, surface behaviour patterns
and response equipment and methods are radically different for solid
and liquid pollutants.
Name: Allegra
Date: 1 October 1997
Location: Channel
Accident area: western Channel
Cause of spill: collision
Quantity transported: 15,000 tonnes
Type of pollutant: palm oil
Quantity spilled: 900 tonnes
Ship type: vegetable oil and molasses tanker
Date built: 1986
Flag: Liberian
Aerial photo of palm nut oil on the water surface (source: Cedre)
The breach in the hull of the Allegra (source: Cedre)
Link
Last update: April 2006