Ralph Ferraro's Rocking R Bar was heavily damaged by the blast and ensuing fire that destroyed half a city block. He filed the lawsuit in District Court on Wednesday, alleging the utility company and its manager of gas system integrity knew or should have known that pipes in the downtown area were old and susceptible to cracking.

Lab tests on the service line leading into Montana Trails Gallery, where the explosion was triggered, determined that the line was cracked at some point on March 5. But NorthWestern officials have repeatedly said it is unclear whether the crack was a result of the explosion or the cause of it and have denied liability or negligence.

Company spokeswoman Claudia Rapkoch said Thursday she could not comment on pending litigation.

Ferraro is seeking $4 million in damages.