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The Critical Role of Blowout Preventers in Offshore Operations

The Critical Role of Blowout Preventers in Offshore Operations

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June 3, 2024

April 20 marks the anniversary of the Deepwater Horizon explosion and spill, a disaster that claimed 11 lives and caused the worst accidental oil spill in history. Caused by numerous oversights and decisions on the part of BP, Transocean, and Halliburton, the incident serves as a reminder of the critical importance of safety mechanisms in the high-risk offshore drilling industry—particularly the blowout preventer.

A “blowout” is an uncontrolled release of crude oil or natural gas from a well. Contained in natural reservoirs beneath the earth’s surface, oil and gas are under significant pressure. When we drill into these pressurized zones, oil and gas will naturally escape upward through the wellbore. Drilling operations use various methods to counter blowouts, such as pumping drilling mud into the wellbore. However, if these pressure control systems fail, the well’s natural pressure will overwhelm them, and a blowout will occur.

A blowout preventer, or BOP, is meant to prevent such incidents.

What Is a Blowout Preventer?

Installed at the wellhead, a blowout preventer performs various functions, from monitoring pressure to sealing off the well in the event of an emergency. There are two primary types of BOPs—ram and annular—each with different functions and designs. 

A “BOP stack” typically comprises several individual BOPs, including at least one annular BOP and multiple ram BOPs, each designed to handle specific well control scenarios. Annular BOPs, positioned at the top of the stack, can seal the space around the drill pipe or completely shut off the wellbore when no pipe is present. Ram BOPs can seal around the drill pipe, casing, or tubing, close an open wellbore, or even cut through the drill pipe with steel shearing blades. 

The primary roles of a BOP stack include confining well fluid to the wellbore, adding fluid to the wellbore, and allowing controlled withdrawal of fluid. BOPs also regulate and monitor wellbore pressure, centralize and support the drill string, seal the annulus to shut in the well, prevent additional influx from the reservoir, and, in emergencies, sever the casing or drill pipe to seal the well.

The Deepwater Horizon’s 400-ton BOP stack had 2 annular preventers and 5 sets of metal rams: a blind shear ram that was designed to cut through the drill pipe, a casing shear ram designed to cut through the casing, and 3 sets of pipe rams designed to close off the space around the drill pipe. The BOP could be activated manually, by a remote operated vehicle (ROV), or by an automated “deadman” system. 

On the evening of April 20, 2010, the Deepwater Horizon’s blowout preventer failed.

When Blowout Preventers Fail

According to a Report to the President by the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, a central cause of the Deepwater Horizon blowout was a cement failure at the base of the 18,000-foot-deep well, but the incident involved a series of oversights, maintenance failures, communication blunders, and mechanical errors. Crucially, when the blowout occurred, the BOP failed.

Witness accounts indicate that the crew activated one of the annular preventers at about 9:41 p.m. and a variable bore ram at 9:46 p.m., but these did not successfully seal the well. 

The first explosion occurred at about 9:49 p.m.

The crew then attempted to activate the rig’s emergency disconnect system, which should have closed the blind shear ram to sever the pipe, seal the well, and disconnect the Deepwater Horizon from the BOP—but this failed. 

At this point, the rig’s deadman system, which activates the blind shear ram automatically in the event of a blowout, should have engaged. It didn’t.

At about 9:56 p.m., gas erupted from the wellbore and caught fire, killing 11 platform workers.

Over the next 87 days, 134 million gallons of oil spilled into the ocean before the well was finally capped.

While the Deepwater Horizon incident is the most well-known, it is not the only case where the failure of a BOP has led to serious consequences. Here are a few examples:

• IXTOC I Oil Spill (1979)This spill occurred in the Bay of Campeche off the coast of Mexico. The IXTOC I, an exploratory oil well, suffered a blowout, and its BOP failed to seal the well. This failure led to one of the largest oil spills in history, with an estimated 3 million barrels of oil spilling over approximately 9months before the well was finally capped.

• Montara Oil Spill (2009)Just a year before the Deepwater Horizon disaster, the Montara oil spill in the Timor Sea, off the coast of Western Australia, was another significant incident. The blowout was caused by a wellhead failure, and the blowout preventer did not activate as intended. This spill continued for 74 days, releasing thousands of barrels of oil into the sea and causing extensive environmental damage.

• Mumbai High North (2005)In this incident, the Mumbai High North platform off the coast of Mumbai, India, suffered a massive fire and subsequent sinking after a collision, claiming 22 lives. The BOP reportedly failed to cut the drill pipe and seal the well, contributing to the disaster. Although the primary cause was the collision, the blowout preventer’s failure exacerbated the situation.

Blowout preventers may fail due to a variety of factors, such as mechanical failure, inadequate maintenance, or design flaws. In the case of the Deepwater Horizon, the Commission’s report indicated that post-incident testing revealed low battery charges and defective valves in the rig’s deadman system, which would have prevented it from working if they were present at the time of the blowout.

Accountability for Maintaining BOP Integrity in Offshore Operations

The responsibility for ensuring that blowout preventers work effectively is shared among several parties. This includes oil and gas companies, drilling contractors, manufacturers, and even safety regulators.

The primary responsibility lies with the operators of a drilling project, who are accountable for ensuring that all equipment, including BOPs, is in good working condition, properly maintained, and tested regularly. These companies must adhere to industry standards and regulations in their operations. Oil and gas companies and the entities that own and operate drilling rigs must ensure that their personnel are well-trained and that safety protocols are followed to the letter, without exception.

As evidenced by the Deepwater Horizon disaster, failures to adhere to safety standards will lead to catastrophic equipment failures, lost lives, and environmental catastrophes. The importance of a working blowout preventer—as well as every single piece of equipment on a rig—cannot be understated.


Arnold & Itkin is widely recognized as the nation’s leader in maritime law. The firm’s attorneys represented over one-third of the Deepwater Horizon crew, helping them seek answers and accountability—and life-changing compensation that would help them rebuild and move on. Since 2004, Arnold & Itkin has fought for the rights of the injured and for families who have lost loved ones through no fault of their own, winning more than $15 billion on their behalf. The firm is committed to righting the wrongs caused by corporations’ failures to put their workers, communities, and the environment first.

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