in the case of BP they knew the dangers and took a calculated risk anyway figuring they could handle anything that happened. The shit literally blew up i their face mainly because they purposefully cut so many corners.
the definition of an accident is:
an unforeseen and unplanned event or circumstance...whats unforeseen or unplanned for here? that rigs can blow up? no. that oil can gush uncontrollably from the well in that event? no. They knew all that can happen and they purposefully made the minimum effort to prevent it.
an unfortunate event resulting especially from carelessness or ignorance... they cared about the cost and minimally cared about the safety of the rig. They weren't ignorant of the performance of the safety devices because they falsified performance records and paid off regulators to overlook shit.
lack of intention or necessity..did they intend for people to die and the safety features to fail. no but they made calculated decisions that made those events an even greater possibility. And I'm sure someone there KNEW that.