A Tragic Mix of Oil and Water
How faulty plumbing sank the world's largest oil platform.
Illustration by John MacNeill
11:00 p.m., March 14, 2001, 75 miles east of Macae, Brazil: Another impressive day nears its end aboard the P-36, the world’s largest floating oil-production platform. Although in service less than a year, this 32,000-ton, 40-story behemoth already produces 6 percent of the nation’s oil, pumping 84,000 barrels of the stuff each day from the seabed nearly a mile below. Brazilian oil giant Petrobras considers the $485 million platform the jewel of its fleet.
11:30 p.m. A work crew begins emptying water from a drainage tank in the port aft column, one of four supports that connect the platform to two giant pontoons beneath the surface. Problems with pumps and valves, however, cause the expelled water to flow into an emergency drainage tank built into the wall of the starboard aft column. This tank is undergoing maintenance, and thus its relief vent is closed. Pressure builds as the liquid level rises. To make matters worse, an open valve in the oil production facility on the main deck begins forcing thousands of gallons of oil and water into the same tank.
12:22 a.m., March 15 The tank wall blows out with a resounding thud, rupturing a pipe that supplies seawater to the firefighting system. Oil and water begin gushing into the column’s central compartment. When the mixture reaches an opening in a ventilation duct 8 feet off the floor, it begins pouring into the pontoon below. The flooding is so rapid that the platform tilts 2 degrees within 5 minutes.
The huge flow of seawater through the firefighting pipes causes the fire alarm system to signal a serious fire. Eleven firefighters rush to the scene, but all they find is oil, water and a fine mist of petroleum vapor. The vapor escapes into the compartments above, where an ignition source triggers
a massive fuel-air explosion. Ten of the men are killed instantly. The 11th dies a week later in a Rio de Janiero hospital.
March 15-March 20 Petrobras summons hundreds of emergency experts from Holland, England and the United States to help in salvage efforts. Working around the clock, divers drill holes in the starboard buoyancy tanks and fill them with nitrogen gas to force out the
seawater. The flooding appears to be under control for two days, but on March 19 the previously calm waters turn into five-foot swells, making the underwater wreckage so dangerous and confusing that divers find it impossible to close all the leaks. At 11:40 a.m. on March 20 the platform sinks, landing upside down on the seabed with the bodies of nine firefighters still onboard.
Petrobras immediately formed an inquiry commission to investigate the sinking of their prize oil platform. The commission’s most significant recommendation: Do not build emergency drainage tanks into support columns. Petrobras put this advice to work in their P-40 platform — the first to begin operation after the P-36 sank — which was installed later that year in Brazil’s Marlim Sul oil field. The commission’s investigation, however, was hampered by one critical drawback: The most important piece of accident information, the P-36 itself, will forever lie beyond their reach at the bottom of the Atlantic.