On 29 January 1975 at 12:30 pm, the oil tanker Jakob Maersk hit a sandbank while trying to enter the harbour. A few seconds later, there was an explosion in the engine room. The oil tanker caught fire and broke into three parts. The central and the stern parts sank while the bow part remained afloat. It ran aground on the beach a few days later. The explosions destroyed all the main tanks of the oil tanker and significant quantities of crude oil leaked from the wreck. A certain amount was partially burnt by the fire, another part of the oil was dispersed at sea or washed up on the coast.

On the days when the fire was at its worst, the flames were 100
metres high. The sky above Porto was darkened by a thick black smoke
for several days. 7 out of the 17 crew members died during the disaster,
as most of them were in the engine room during the explosion. Several
inhabitants living in this area were sent to hospital because of
the smoke.
A
follow-up operation was set up with aerial suveillance patrols.
The explosions and the fire raged on the wreck for the two first
days, preventing any oil recovery attempt at sea. Collaboration
between the Ministry of fisheries, the Army, the Navy, the ship
owners, Shell and a large part of the local population allowed rapid
action to be taken to limit the damage. A floating boom was installed
in the harbour entrance to prevent oil slicks from entering the
harbour. A straw barrier surrounding the wreck retained the oil
sufficiently until boats had spread dispersants. The most affected
beach was the shore immediately adjacent to the Jakob Maersk.

Name: Jakob Maersk
Date: 29 January 1975
Location: Portugal
Accident area: Entrance to Leixoes harbour, Porto (Portugal)
Ship type: Oil tanker
Date built: 1966
Flag: Danish
Type of pollutant: Iranian crude oil + heavy fluel oi (lBunker C)
Quantity spilled: 84,000 tonnes
Cause of spill: grounding
Clean-up
operations began with the removal of the upper sand layer. Dispersants
were also spread on the sand. Wave action facilitated the elimination
of oil from the rocks. It was estimated that the fire around the
ship burned between 40,000 and 50,000 tonnes of oil, that 25,000
tonnes drifted at sea and nearly 15,000 tonnes were washed up on
the beach. Hydrocarbon traces were found on beaches situated 50
km from the wreck.
The majority of the ecological damage was observed
on the foreshore. In rocky areas, seaweed (Fucus sp.) and molluscs
(mussels) were found dead. But growth was resumed a few months later
and mussels populations recovered from the accident. No harmful
effect was observed on fish populations but the taste of fishery
products was altered temporarily. Very few birds were affected,
at least in the coastal zone. In the course of the first week, only
half a dozen oiled birds were found in north Porto.
The cost of the catastrophe was estimated at 2.8 million dollars
by OECD (Organisation for Economic Co-operation and Development).
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Last update: April 2006