The oil giant paid a then-record $21 million fine after the explosion five years ago, while also agreeing to improve safety conditions.
BP fell short of that agreement when inspected last year by the Labor Department's Occupational Safety and Health Administration, leading to the second fine.
In October 2009, OSHA announced $87.4 million in penalties against BP after an inspection of the Texas City plant earlier last year.
During last year's investigation at the Texas City refinery, OSHA found 439 new willful violations and assessed more than $30 million in penalties.
"Safer conditions at this refinery should result from this arrangement, which goes far beyond what can normally be achieved through abatement of problems identified in citations," said David Michaels, assistant secretary of labor for OSHA.