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How Oil Tankers Work


Oil Tanker Mishaps, Tougher Laws
A sea otter relaxes near Alaska's Prince William Sound in 2004. The local ecosystem is still recovering from the Exxon Valdez tanker spill in 1989.
A sea otter relaxes near Alaska's Prince William Sound in 2004. The local ecosystem is still recovering from the Exxon Valdez tanker spill in 1989.
David McNew/Getty Images

On March 24, 1989, the world watched in horror as one of history's most environmentally destructive oil spills marred Alaska's Prince William Sound. The accident -- caused when Exxon's tanker Valdez ran aground -- would make the ship's name synonymous with man-made catastrophe. The Valdez spill would become a case study in how operator fatigue, environmental factors and faulty decision-making can mix for disastrous results.

The tanker ran aground just after midnight on the sound's Bligh Reef and gushed out nearly 11 million gallons (41.6 million liters) of oil. The slick killed countless birds, sea otters and other marine life. Viscous, foul-smelling oil coated the once-pristine shoreline and spread out to cover 120 square miles (310.8 square kilometers) of ocean around the tanker [source: Mauer].

If anything good came from the Valdez spill and others like it, it's that global standards for design, safety and maintenance have since become more stringent. The biggest recent change to hit the supertanker industry is the transition from single-hull to double-hull construction. Double hulls aren't as prone to breaches that result in oil spills, although they're not totally impenetrable. Some observers say that the protection provided by double hulls is exaggerated somewhat. Nonetheless, authorities demand that the transition to a global double-hulled oil tanker fleet be completed sooner rather than later.

The United States and various international bodies have established deadlines for implementation of the double-hull design. In 2007, the European Union (EU) made it mandatory for ships carrying heavy oils to be double-hulled to use ports in EU nations or to drop anchor in their waters. The United States passed a law in 1990 to phase out single-hull tankers by 2015. The deadline was later moved up to 2010. The International Maritime Organization (IMO), a United Nations agency that regulates global shipping, also has called for the eradication of single hulls by 2010.

Oil spills represent one threat to the environment, but explosions and the fires that result can pose a real danger to crew members aboard oil tankers. Even in an empty cargo compartment, a single spark can turn fumes into an inferno. That's why tankers of 20,000 DWT (22,046 tons) and above have inert gas systems installed that take gas from the ship's boiler flue, and pump it into empty oil tanks and partially filled tanks. This inert gas makes the air within those spaces nearly impossible to ignite [source: International Maritime Organization]. The IMO also requires inert gas systems on all new oil tankers.

Oil tankers feature thoroughly designed safety and security systems to guard against accidents. But how do tanker crews deal with those who wish to do intentional harm -- like pirates?