Occupants of the Garstang Road building reported hearing the loud noise and feeling a 'shock-wave' at around 10.15am.
Two engines from Fulwood and Preston attended the incident and made a search of the area.
A spokesman for the fire service said: "Crews came to check gas pipes and surrounding roads after a loud bang was heard in the area.
"They were unable to find out what it was. It may have been an aeroplane or a a vehicle passing on the A6.
"Unfortunately we were unable to find a source of the noise."
A spokesman for Lancashire Police said: "We received reports of an explosion this morning in the Fulwood Area."