Flames engulfing a drilling rig in the Gulf of Mexico decreased to a small fire yesterday, as officials worked around the clock to bring the well under control. The rig, called Hercules, is stationed 55 miles off the coast of Louisiana.

Crews were completing the well when they first lost control on Tuesday morning and natural gas started leaking out. The company, Walter Oil and Gas Corp., immediately evacuated all 44 workers on the rig. The methane ignited later that night.

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The incident is reminiscent of the Deepwater Horizon rig fire on on April 20, 2010, which exploded while drilling a well in the Gulf. Eleven men died in the explosion. The resulting oil spill, which continued for 87 days and spilled about 5 million barrels of crude, was the largest in the history of the United States.

There is a piece of equipment implicated in both the Hercules and Deepwater Horizon accidents: the blowout preventer or BOP. These are massive steel devices 25 feet tall, weighing a 100 tons that use sheer force to choke off a well.

The device is the last line of defense when workers lose control of an oil or gas well and fuel is spewing into the air. At that point, the BOP can be activated to seal off the well. It is critical equipment for all wells being drilled, and the Bureau of Safety and Environmental Enforcement (BSEE) requires that companies maintain it very carefully.

When it is not maintained, loss of well control can lead to a blowout or an explosion.

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Companies lost control of their wells three times in the Gulf in 2011, four times in 2012, and five times this year, according to BSEE data. The preventers were brought into action in some of the cases.

BSEE is in the process of updating its requirements for blowout preventers, and industry has been testing a number of new spill caps in recent years.

The increased attention to safety around the world following Deepwater Horizon has made the industry technically safer. But it still has not stopped offshore accidents, which are often caused by human error.

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Here’s a list of some of the latest:

July 23, 2013: Hercules rig blew out off Louisiana and 44 workers were evacuated. BSEE and Walter Oil and Gas Corp. are still bringing it under control.

July 12, 2013: a gas well located off Louisiana owned by Talos Energy LLC, began leaking. The spill was contained with minimal damage, but no one’s life was in danger.

Nov 16, 2012: a Black Elk Energy platform located off Louisiana exploded and caught on fire as workers were welding a pipe. Three men died.

March 26, 2012: the Elgin platform owned by Total SA in the North Sea off Scotland leaked natural gas for 52 days before it was brought under control.

Jan 16, 2012: A Chevron rig blew out off the coast of Nigeria, killing two men. The resulting fire burned for 46 days and the spill was the largest in the nation’s history.

Photo: The Hercules rig on fire. BSEE