BP, facing billions in penalties over the massive Gulf Coast oil spill, has agreed to pay a record fine of $50.6 million in connection with a previous disaster.

The Occupational Safety and Health Administration said Thursday that BP will pay the biggest fine the agency ever has imposed, for safety violations at the company’s Texas City, Texas, refinery, where a 2005 explosion killed 15 employees and injured 170 more. BP had reached a previous settlement with OSHA but, after the agency found last year that the company still had not made promised safety fixes, it pushed for a stiffer penalty.

As part of the new deal, BP has pledged to take immediate steps to improve safety at the refinery, and will dedicate at least $500 million to the effort. Independent experts will be hired to oversee the safety efforts.

“This agreement achieves our goal of protecting workers at the refinery and ensuring that critical safety upgrades are made as quickly as possible,” Secretary of Labor Hilda L. Solis said in a statement. “The size of the penalty rightly reflects BP’s disregard for workplace safety and shows that we will enforce the law so workers can return home safe at the end of their day.”

In October, the agency sought $56.7 million in fines for the 2009 safety violations leading to Thursday’s settlement, but after duplicate complaints were discovered, the sum was reduced to the $50.6 million.

Still, BP is continuing to contest another $30.7 million in proposed penalties for the 439 new safety violations that OSHA inspectors found last year, The New York Times reports. The company said in a statement that it hoped the agreement would provide a “platform to resolve the remaining citations” but the agency countered that ligitation over those violations “is not impacted” by the $50.6 million settlement.

The biggest fine ever paid previously to OSHA was $21 million — also imposed against BP, in connection with the 2005 explosion.

The company is also facing a lawsuit from the state of Texas, which claims the company continued to operate its Texas City refinery after critical equipment broke down, illegally releasing 500,000 pounds of toxic air pollutants in April and May.

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