Princeton Area Firefighters were dispatched for a structure fire with a possible explosion in the area of Hart Street and Clark Street. The first arriving engine found debris scattered around the house and sections of the house that had collapsed. Light to moderate fire conditions were contained to the second floor of the structure. After the fire was mitigated and the scene was safe, crews began the preliminary investigation. PFT investigators, along with state investigators, determined this was a natural gas explosion. The local gas company was on scene and is conducting its investigation. Two patients were transported with burns to local hospitals. This is an ongoing investigation.