Oil Tankers Collide near Tobago

Date July 19, 1979

When two oil tankers collided in a rain squall off the island of Tobago in the Caribbean Sea, 370,000 tons of oil were spilled in the largest disaster of its kind up to that time.

Locale Caribbean Sea near Tobago

Key Figures

• Paschalis Chatzipetros (fl. late twentieth century), captain of the tanker Atlantic Empress
• Ioannis A. Zissakis (fl. late twentieth century), captain of the tanker Aegean Captain

Summary of Event

Powerful thunderstorms known as rain squalls are common in the Caribbean Sea, especially in the summer. At about 7:00 p.m. on July 19, 1979, some ten miles off the island of Tobago, two tanker ships classified as very large crude carriers (VLCCs) entered a squall from opposite directions. Visibility was very limited because of the storm, and radar was not effective in the squall. As a result, the tankers’ crews were unaware of each other until the tankers were less than one mile apart on a collision course. Despite last-minute efforts to maneuver, the bow of the Aegean Captain struck the side of the Atlantic Empress.

The Aegean Captain had loaded more than 200,000 tons of crude oil at the nearby islands of Curacao and Bonaire and was bound for Singapore. The ship was owned by a Liberian company and registered there, but it was managed by an office near Athens, Greece. Its officers and most of the crew were Greek. The eleven-year-old ship had been built by the Hitachi Shipbuilding and Engineering Company of Sakai, Japan, in 1968. The Aegean Captain measured 1,066 feet long and 155 feet in beam (width), and its keel lay 62 feet below the surface of the sea (this last measurement is called draft). It was powered by a steam turbine engine that drove its propeller through a reduction gear.

VLCCs are crude oil tankers that carry between 200,000 and 300,000 tons of cargo. These are huge ships that do not maneuver well. A typical VLCC takes nearly one and one-half miles to stop from full speed. Under calm conditions, such a ship has a turning circle of more than one-half mile in diameter. Ships are measured in long tons or metric tons. These units are nearly the same: A long ton is equivalent to 2,240 pounds, and a metric ton is the same as 1,000 kilograms or 2,200 pounds. A U.S. gallon of crude oil weighs slightly more than 7 pounds, so there are about 310 gallons of crude to the ton. Oil is often measured in barrels; 1 barrel contains 42 gallons.

The Atlantic Empress, also a VLCC, was carrying 270,000 tons of crude oil loaded at Jebel Dhanna in the United Arab Emirates on the Persian Gulf. The ship was headed for Beaumont, Texas. Also owned by a Liberian company, this tanker was registered in Greece. Odense Shipyard in Lindo, Denmark, had built the steam turbine-powered ship in 1974. The Atlantic Empress was somewhat larger than the Aegean Captain; it measured 1,139 feet long, 170 feet beam, and 73 feet draft.

Ship’s officers are grouped into three categories: mates, engineers, and radio officers. Each category is licensed for particular duties. Only mates are licensed to stand bridge watches, where they direct the navigation and maneuvering of the ship. At the time of the collision, the officer on watch on the Aegean Captain was the captain’s second in command, the chief mate. This officer had been licensed as a mate for five years and had served two years on the ship.

By contrast, the watch officer on the bridge of the Atlantic Empress was not a licensed mate; he was the radio officer. One of the licensed mates had been sent home from a British port without replacement in May of that year. The ship’s owner had instructed the captain to use the radio officer as a mate even though the radio officer lacked the legal qualifications for bridge watches. This person continued to perform his duties as radio officer and took on the additional responsibility of a bridge watch officer. As a result, he was standing watch approximately fifteen hours per day. From 4:00 a.m. to 8:00 a.m., he stood a bridge watch. He was on watch in the radio room from 8:00 a.m. to noon and from 1:00 p.m. to 4:00 p.m. Between 4:00 p.m. and 5:00 p.m., he was responsible for both the bridge and the radio room. Finally, from 5:00 p.m. until 8:00 p.m., he stood watch on the bridge. The radio officer was laboring under the stress of an exhausting schedule. In addition, the Board of Investigation of the Republic of Liberia found that he was “known to be a habitual drunkard.”

Just as the Atlantic Empress was entering the squall, the radio officer permitted the lookout to leave his post to get a cup of coffee. The captain came to the bridge and reprimanded the radio officer for allowing this but did not insist on the lookout’s immediate return. A few minutes later, the ships sighted each other at close range and attempted to avoid collision, but it was too late.

Oil tanks ruptured on both ships, and the escaping crude oil immediately caught fire. Crews from both ships attempted to fight the fire but failed. Soon after the collision, both crews attempted to abandon ship. On the Aegean Captain, the abandon-ship operation proceeded in a fairly smooth manner. One crewman fell overboard and was lost, but everyone else was saved. Evacuation of the Atlantic Empress, in contrast, was chaotic. The lifeboats and other safety equipment had not been properly maintained, and the crew had not held an abandon-ship drill for several months, despite a legal requirement for weekly drills. The crew panicked and botched the launching of the lifeboats; twenty-six of the forty-two people aboard the tanker were lost.

Every modern tanker is required to be equipped with an inert gas system (IGS), which uses boiler exhaust gas, which contains very little oxygen, to fill the empty space above the crude oil in the cargo tanks. The low oxygen content means that the crude oil vapors in the tank cannot ignite. The tankers in this collision were built before IGS was required, but the Aegean Captain had installed such a system; the Atlantic Empress had not. The presence of an IGS appears to have been one of the reasons the fire on the Aegean Captain was less severe than the fire on the Atlantic Empress.

Significance

One day after the collision, the captain of the Aegean Captain and some of his crew boarded the salvage tug Oceanic and returned to their ship. They were able to extinguish the fire, and the ship was then towed to Bullen Bay, Curacao, where its remaining crude oil cargo was unloaded. Since inspection revealed that the ship was beyond repair, it was sold for scrap to a Taiwanese company. It left Curacao under tow on October 13, 1979, and arrived in Taiwan on January 31, 1980.

As the Aegean Captain was towed from the collision site to Curacao, there was minor additional leakage. Chemical dispersants were used to break up this oil, and the oil did no harm. Initial reports estimated the size of the oil slick at the collision site to be 30 square miles in area, but later reports indicated that the size of the slick was closer to 10 square miles in area. By July 23, the slick was reported to be dispersing rapidly under the influence of natural forces such as wind and waves. Although equipment had been assembled to spray chemical dispersants on this slick, it dispersed so rapidly that the dispersants were never used. No oil washed up on the beautiful beaches of the numerous Caribbean islands nearby.

Fires on the Atlantic Empress could not be controlled. On July 21, tugs managed to take it in tow as it continued to burn. By July 29, the ship was more than 300 miles northeast of the collision site and well out into the Atlantic Ocean. At that point, a tremendous explosion occurred, and a huge fire erupted. The Atlantic Empress sank on August 2. Some of the crude oil that remained on board after the collision was consumed by the fire, but it is believed that most of the oil was still on board when the ship sank.

The Board of Investigation of the Republic of Liberia revoked the license of Captain Paschalis Chatzipetros, who survived the collision. The radio officer, who bore primary responsibility for the collision, did not survive.

Natural processes appear to have disposed of most of the oil spilled by this collision. In the early stages of a spill, the oil spreads in all directions, reducing the depth of the oil layer. This spreading is beneficial, because the natural processes work faster on thin layers. As the oil spreads, it also drifts. The whole slick moves in a direction determined by wind and current. If the drift is moving toward shore, rapid action may be necessary to prevent damage to beaches and living things at or near the shoreline. If the drift keeps the oil at sea, however, it is often best to let nature take its course.

As much as one-half of an oil slick may evaporate into the atmosphere. Once in the atmosphere, most of the evaporated oil undergoes a process called photooxidation. Oil is composed primarily of carbon and hydrogen. Photooxidation converts the carbon to carbon dioxide and the hydrogen to water. The chemistry of this process is the same as that of combustion, but the process occurs slowly and without creating high temperatures. Although the water produced by photooxidation is harmless, the carbon dioxide contributes, to a small degree, to the greenhouse effect. Fortunately, many of the most toxic components of crude oil also evaporate most easily, thus the slick becomes much less toxic as a result of evaporation.

Dispersion is a natural process in which small droplets of oil break off from the slick and mix with the surrounding water. Human-made dispersant chemicals can be used to speed up the process of dispersion. Although dispersion does not eliminate the oil, other natural processes such as biodegradation work faster on dispersed oil than on the slick itself.

Biodegradation is the term for elimination of oil by bacteria, yeast, and fungi that “eat” the oil. These single-cell organisms are present in all surface water, fresh and salt. After an oil spill, these organisms tend to multiply rapidly. The addition of fertilizer to the water encourages this process. Fertilizer was not used off Tobago, but biodegradation was partly responsible for the rapid disappearance of the slick.

Sedimentation is a natural process in which oil attaches itself to solid particles of shell, clay, silt, and sand that are suspended in the water. These particles eventually fall to the seafloor and may remain there indefinitely.

Emulsification is an undesirable natural process. Oil and water can combine to form an emulsion called mousse. Mousse formation interferes with the desirable natural processes of evaporation, dispersion, biodegradation, and sedimentation. If emulsification is likely, chemical dispersants are used to disperse the oil before it can emulsify. When mousse has already formed, chemicals called demulsifiers can be used to promote separation of the oil and water.

There are many ways by which oil can reach the sea. Oil can escape into the ocean by natural means, but the majority of opportunities for oil spills are human-made. About 250,000 metric tons of oil per year enter the sea as a result of natural causes. In 1985, this figure amounted to nearly 8 percent of the total amount of oil entering the world’s oceans. About one-third of the oil comes from normal tanker operations, and another one-third comes from wastewater discharges from industries, cities, and towns. In an average year, tanker accidents are responsible for 400,000 tons, or about 12.5 percent of the total amount of oil escaping into the oceans.

Bibliography

American Bureau of Shipping. Record of the American Bureau of Shipping, 1979. New York: Author, 1979. This large volume provides a complete listing of every ship under the jurisdiction of the American Bureau of Shipping (ABS). This nongovernmental organization “classes” (inspects) ships to verify that they are reasonable insurance risks. U.S.-registered ships must be classed by the ABS, but the owners of many foreign-registered vessels choose to have the ABS class their ships. Tables in this book give basic statistics about each ship.

Cahill, Richard A. Disasters at Sea: Titanic to Exxon Valdez. Kings Point, N.Y.: American Merchant Marine Foundation, 1990. Captain Cahill, a graduate of the U.S. Merchant Marine Academy with forty years of experience at sea, brings the perspective of an expert to the analysis of the disaster. He probes issues, the importance of which other authors have failed to grasp. Deals with the events leading up to the collision, not with the cleanup.

Grove, Noel. “Sailing with the Supertankers.” National Geographic, July, 1978, 102-124. Article written to accompany an article about the Amoco Cadiz grounding provides very useful background information. Contains an excellent cutaway drawing of a large tanker as well as photographs of life on board. An artist’s rendering shows the major oil trade routes of the world.

Hooke, Norman. Modern Shipping Disasters, 1963-1987. London: Lloyd’s of London Press, 1989. An excellent general reference that provides a brief account of every merchant marine or naval ship lost between 1963 and 1987. Coverage of the Atlantic Empress collision is longer than most.

“Maneuvering into a Crash.” Technology Review 82 (November, 1979): 78-79. This brief, unsigned article discusses the maneuverability of large oil tankers. An excellent graphic shows how speed affects turning diameter. Although the graphic pertains to the Esso Benecia, maneuvering characteristics of the Aegean Captain and Atlantic Empress would be similar.