Shocked staff at estate agent Garside Waddingham were sitting in the ground-floor reception when a girder crashed through three floors.
The Lancashire Evening Post said the 21ft girder is believed to have slipped from a crane during construction of the Premier Inn hotel and a parade of shops on January 16.
Following an investigation by the Health and Safety Executive, it has brought a case against Pocklington Steel Structures Ltd, based in Bridlington, East Yorkshire.
The company is accused of breaching Section three, part one, of the Health and Safety Act 1974 and will appear for a full hearing at Preston Magistrates’ Court, on Wednesday August 18.
The Premier Inn is due to open in January 2011.