Here's what we know for sure about the disaster in the Gulf of Mexico: On April 20, the Deepwater Horizon oil rig exploded, killing 11 people onboard; 36 hours later, it sank into the ocean. Investigations are under way to determine the cause of the accident and how it might have been prevented. So far, these have focused on what caused the explosion in the first place (was it a bad cementing job by Halliburton?) and what caused a blowout preventer safety device to fail. But it may be just as important to figure out why the oil rig capsized and sank beneath the waves. This latter event may have turned a manageable disaster into a full-scale catastrophe.
In the first hours after the explosion, most of the spilled oil was burning off in the fire, and the initial damage estimates were small. But when the Deepwater Horizon turned over on its 400-foot pontoons, the mile-long pipe that connected it to the underwater wellhead collapsed like a mess of spaghetti. Now the oil is leaking from this jumbled steel on the ocean floor at two sites where the pipe buckled and broke. If the first rescue crews on the scene had somehow been able to prevent the rig from sinking, they might have disconnected the pipe safely and capped it near the surface.
So what happened? The fireboat crews tried to extinguish the flames as quickly as possible so they might board the oil rig to search for survivors and contain the spill. In the end, though, their efforts to battle the fire may have made the situation worse. By pouring hundreds of thousands of gallons of water and flame-retardant foam onto the rig, it's possible that the fireboats helped sink the Deepwater Horizon.
The oil rig appeared to be floating in the water with a slight list when the initial rescue crews showed up. According to one of the people coordinating the response, Capt. Farhat Imam, the rig did not seem in imminent danger of sinking. (At that point, there was just a "minimal sheen of oil" on the water, he says.) As the fire raged on, the list increased, and then the platform really began to tip over during the six hours before it finally capsized on April 22. Fireboats had continued to pour water and flame-retardant foam onto the rig the whole time.
At the moment, there's no way to know how much the rescue effort contributed to the sinking. It's possible that the blaze was hot enough to melt the steel superstructure of the oil rig, which could have shifted enough weight to make it capsize regardless of the water and foam. But photos of the rig as it was going under show the largest structural members still intact, although the smoke and flames make it difficult to see clearly.
Eventually we may be able to survey the wreckage of the oil rig with submersibles and determine exactly what caused it to sink. But the suggestion that fireboats might be responsible has at least one major historical precedent. When the SS Normandie made her maiden voyage in 1935, she was the largest passenger liner ever built—more than 150 feet longer and 20,000 tons heavier than the RMS Titanic. During World War II, the Normandie was renamed the USS Lafayette, and the U.S. government set about converting her into a troop transport ship in New York Harbor. In February 1942, a spark from a welder's torch started a fire that soon engulfed the entire vessel. Workers rushed to extinguish the blaze, pouring water onto the ship from the adjacent piers and from fireboats in the river.
Much of that water fell on the upper decks, filling compartments and making the ship top-heavy. When the liner began listing to port, the water flowed into compartments on that side, which moved the center of gravity farther away from the centerline of the hull—and the ship capsized into the icy Hudson. Its burned-out carcass blocked one of the largest piers in the harbor for the next 20 months, until it could be righted at last and towed to a scrap yard.
Rescue crews today understand the risk of capsizing a fiery ship. The National Fire Protection Association's guidelines for responding to marine vessel fires explain that "vessels suffer a loss of stability as water utilized in the fire fighting accumulates above the original center of gravity. … If this vulnerability is not properly understood and controlled, the consequences can impact all fire-fighting efforts severely." As a vessel begins to list, the guidelines describe "devastating consequences" in which a "domino effect can quickly compound an already aggravated situation."
These safety considerations have become more important because fireboats now have increased pumping capacity. Most modern fireboats have the capacity to blast more than 10,000 gallons of water per minute. (New York City fireboats can pump up to 50,000 gallons per minute.) Since one gallon of seawater weighs about 8.5 pounds, 10,000 gallons of water weighs more than 42 tons. At that rate, just one fireboat can pump around 2,500 tons of water every hour.
Only a small proportion of that weight would have been brought to bear on the oil rig in the Gulf of Mexico—much of the liquid pumped at a maritime fire ends up boiling off or spilling into the sea. Still, experienced maritime firefighters concede that a significant amount is likely to have collected in the upper decks of the rig.