The interior floors of the Centennial Mills warehouse are fully collapsed after a Sunday, Aug. 2, fire, putting it at risk of fully collapsing. (Dennis Weis/Portland Fire & Rescue/Courtesy)As investigators work to determine what caused the four-alarm fire that destroyed the historic Centennial Mills warehouse, officials are also preparing for the possibility that the damaged structure could fail. Portland Fire & Rescue said it cannot calculate the likelihood that the 116-year-old waterfront warehouse will collapse. “The odds of the structure collapsing is not an achievable metric we can calculate,” PF&R Public Information Officer Rick Graves said in an email Tuesday. “The most important underlying message is an active investigation,” Graves said.