"We believe our efforts at the Texas City refinery to improve process safety performance have been among the most strenuous and comprehensive that the refining industry has ever seen," said Keith Casey, BP's manager of the Texas refinery.
The safety watchdog said BP had committed hundreds of new violations by failing to follow industry controls on pressure-relief safety systems and other precautions.
BP took multiple steps to fix problems found at Texas City in the first three years after the 2005 blast, "but later their commitment waned", said Dean McDaniel, the OSHA regional administrator in Dallas.
Hilda Solis, the US secretary of labour, said: "An $87m fine won't restore those lives, but we can't let this happen again. Workplace safety is more than a slogan. It's the law."
BP said in a statement that most of the alleged violations relate to an ongoing disagreement between OSHA and BP that is already pending before the Occupational Health and Safety Review Commission, a body that is independent of OSHA.
Since the 2005 accident, four additional people have died at the Texas refinery, including one employee and three contractors.
Eva Rowe, whose parents, James and Linda Rowe, were killed in the blast as they worked at the refinery, praised OSHA for "standing up to BP".