The grounding of the oil tanker Sea Empress off the coast of South Wales provoked in the UK what, by now, must be regarded as the usual media and public reaction and the invocation of the all too familiar description - an `environmental disaster' - which is now routinely applied to such anthropogenic events. Similarly, that description has been given to the sinking of the Prestige, a 26 year old tanker 145 miles off the Atlantic coast of Galicia in Spain after its hull gave way during a storm on 13 November 2002. While it is inevitable in an industrial society that accidents will occur from time to time, each and every individual accident affecting the environment does not necessarily constitute a disaster. Whether or not an accident constitutes a disaster will depend on a variety of factors such as the loss of life involved, whether whole species are endangered as a result, the size of the area affected and the permanence of any residual contamination after clean-up operations. In effect, many so called environmental disasters, it is subsequently realised, constitute no such thing - when no loss of human life has occurred, species recover and residual pollution becomes difficult to find. The Prestige may be the latest to fall into this category following the hull's sinking on 19 November 2002 with most of its 70,000 heavy fuel oil cargo still retained in its tanks.

Oil spills at sea, on beaches and oiled or dead birds and mammals are visible, however, to the cameras of the media and the naked eye of the holidaying public in a way that holes in the ozone layer, soil erosion and the loss of tropical forests will never be. Thus the Prestige is but one of a series of major accidental oil spills alongside the Torrey Canyon, Exxon Valdez, Braer, Amoco Cadiz, Sea Empress the Mega Borg and many others which will probably remain, unfairly but firmly embedded in the public's imagination as being largely responsible and certainly signifying, in a big way, the destruction of local marine environments and the degradation of the overall quality of the world's environment generally attributed to pollution in the widest sense. Black oil will always be more visible to the public eye, especially on holiday beaches than trace concentrations of hazardous chemicals discharged into the environment whether accidentally, deliberately or unknowingly.

Nevertheless, when oil spills do occur as a result of accidents, a single incident has the potential to affect very large areas of sea and lengths of coast. While some individual oil spills may cause little permanent damage, the cumulative effect of such incidents on the marine environment is of greater significance than any individual incident and will result in growing pressure for improved environmental management and performance from the world's oil industry. The grounding of the Sea Empress and the loss of 85,000 tonnes of oil in one of the UK's most important marine environments may yet be found to fall into the category of accidents which causes little or no long term lasting damage to the South Wales coastal environment despite the undoubted immediate harm to marine life and the local fishing industry. The Sea Empress incident emphasises the ever present potential for large scale pollution of the marine environment. The Sea Empress spilled about 70,000 tonnes of oil - about as much as the Braer, and almost twice as much as the infamous Exxon Valdez.

When the Exxon Valdez ran aground in Prince William Sound on the south coast of Alaska in 1989 ten million gallons of oil poured into the sea and the oil eventually formed a slick covering 3,000 square miles and 300 miles of shoreline. When stormy seas forced the Braer oil tanker aground off Shetland in 1993, the tanker, carrying over 615,000 barrels of light crude oil, broke up discharging its cargo into the sea within a few days. Attempts to deal with pollution from the Braer were hampered by force 10 winds, but eventually the stormy seas dispersed most of the oil and the widely predicted disaster failed to materialise.

Exxon, however, had to spent $2 billion in its Alaskan clean-up operations and was subsequently ordered to pay $287 million in damages - mostly to 14,000 commercial fishermen and landowners - together with $5 billion in punitive damages. Since the Exxon Valdez incident, governments and the oil industry have introduced many new control measures. The US imposed unlimited liability on tanker operators within its coastal waters, the International Maritime Organisation ruled that new tankers built after 1993 should be double hulled and the industry began sponsoring research into new clean-up techniques. Following the Braer incident and the subsequent Donaldson inquiry, the UK government introduced a large number of new regulatory controls on tanker operators. These included a ban on the passage of oil tankers through the Minches channel. Similarly, a number of other governments, particularly in south east Asia, introduced new controls on the passage of ships, their manoeuvrability and on the recovery of spilt crude oil.

There has since been much discussion about the relative merits or otherwise of double hulled vessels, the permanence of environmental damage caused by oil spills and the need for further controls on oil tanker operations.

The Donaldson inquiry acknowledged that a double hull would not have prevented the Braer spillage and , while another tanker, the double hulled Borga, had run aground off Milford Haven last year and been refloated without loss of oil, many oil industry shipping experts are of the view that the use of double hulls introduces new risks - such as explosion hazards, for example.

While the area affected by the Exxon Valdez spillage was huge and the costs and damages incurred very high, there is some doubt, six years after the incident, as to the longevity of any effects. While traces of oil can be found in sediments in Prince William Sound, the US Geological Survey has reported that much of the residual oil does not originate from the Exxon Valdez supporting Exxon's own findings - that much of the residue is attributable to the routine import of oil from California - before the Alaska discovery - and to the 1964 earthquake.

Following the Braer incident the Norwegian classification society, Det Norske Veritas, suggested that the time had come for safety cases to be made and approved for oil tankers in the same way that they were required for oil rigs. Perhaps the real lesson to be learnt from a succession of accidents, is that the routine movement of very large tankers should, if possible, be restricted to a minimum number of the safest possible routes and ports which should be located away from very sensitive areas. The sea, with its associated tidal currents and winds will never totally be controlled by man and accidents will remain an ever present risk, however many precautions are taken. Accidents, though, contribute only a small fraction of all the oil discharged into the marine environment and unseen routine discharges may thus merit the greatest long term attention - provided of course, that large scale accidents don't become too frequent.

©Peter Doyle BSc MSc. Based on an article first published in WASTE & ENVIRONMENT TODAY 1996