Oil spill dispersant article

CASE STUDY 2
The Braer oil spill - an example of
natural dispersion of oil
In the morning of 5th January 1993 the tanker
Braer, en route from Norway to Canada and
laden with 84,700 tonnes of Gullfaks crude oil,
lost all power 15 km south of Shetland. By
midday she was aground in very rough seas
with wind speeds of Beaufort Force 10 and 11
and started to leak oil. Just over 100 tonnes
of dispersant was sprayed on the oil on the
next day (January 6th) from six DC-3 aircraft.
The weather then deteriorated and no further
signifi cant dispersant spraying was possible until
January 9th when a further 20 tonnes of dispersant
was sprayed. Large oil releases were
observed on the morning of January 9th, with
a massive release on the afternoon of January
11th when the ship broke into three sections.
By January 24th the wreck had been totally
broken up and it was judged that all the 84,700
tonnes of crude oil and several hundred tonnes
of Heavy Fuel Oil had been released. Gullfaks
crude oil does not readily form stable water-inoil
emulsions. The extremely rough seas caused
all of the oil to be naturally dispersed into the
water column. It was estimated that the dispersant
may have dispersed only 2 - 3% of the total
volume of oil released - nature dispersed the
rest.
The concentration of dispersed oil in water
around the wreck was very high; values as high
as 50 ppm (20,000 times background level) were
measured for several days as the oil escaped. Ten
days after the incident, the oil concentration was
measured to be 5 ppm. The water containing
the dispersed oil drifted northwards and the oil
concentration fell as dilution occurred, eventually
falling to background levels 60 -70 days after
the incident. Some oil became entrained in sediments
to the south of the Shetlands.
The waters around Shetland are rich fi shing
grounds and sea fisheries are a central feature of
Shetland’s economy. Shellfi sh and salmon farming
are large contributors to wealth and employment.
The potential impact of the Braer oil spill
was very high. Precautionary fi shing bans were
put in place and a long series of studies were
undertaken. The ban on fi shing for all species of
wild fi sh was lifted in April 1993. The bans on
the taking of shellfi sh persisted for longer. The
salmon farms had been badly affected, mainly by
the loss of the reputation for pure products.
Some tainting of the salmon fl esh was found, but
this declined with time and there was no further
recontamination from oil that might have been
trapped in sediments. However, it was decided
to destroy all the salmon so that a fresh start
could be made with the confi dence of consumers
restored.
Effects
An extensive series of studies were carried out
after the Braer oil spill by ESGOSS (the Ecological
Steering Group on the Oil Spill in Shetland)
(Scottish Offi ce 1994). They concluded that:
“The impact of the oil spill on the environment
and ecology of South Shetland had been minimal.
Adverse impacts did occur but were both
localised and minimal. The resilience of ecosystems
and species populations has already been
powerfully demonstrated and provides confi -
dence and reassurance for the future.”
Subsequent studies have shown no effects from
the spill, although fi shing for nethrops (Norwegian
lobster) is still restricted near oiled sediment
areas.
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