Dangers of oil extraction

The 1988 Piper Alpha disaster led to improved safety

By Corinne Podger

The explosions at the world's largest oil rig, and the fears of a major oil spill off the coast of Brazil, have highlighted the dangers of extracting oil from deep sea reserves.

Oil spills from rigs are much bigger than from tankers

As the world's land-based and shallow-water oil reserves have been tapped and exploited, the search for fresh reserves has identified many new sites beneath the ocean floor.

Deep sea rigs have become a major source of oil, and the world's oceans are now home to thousands of these structures.

Some are solidly anchored to the seabed; others float on the surface, connected by a thick pipe like an umbilical cord to the ocean floor and the oil below.

Peppered with accidents

Rig technology has developed now to the point where it is possible to drill several kilometres beneath the sea bed.

But the rig industry's history has been peppered with accidents, and the spills involved can be many times the size of a tanker accident.

In 1979 nearly a 150 million gallons of oil poured into the sea off the Mexican coast when a platform blew out. That is 10 times the size of the oil spill from the 1989 Exxon Valdese tanker disaster, off the coast of Alaska.

Tanker ships which collect the oil brought up by the rigs have been known to crash into them, and spills can also happen while oil is being transferred from rig to tanker.

While the oil giants like Brazil's Petrobras are working to improve the technology, extracting oil from the sea bed continues to be a difficult and dangerous job.