FORT WORTH, Texas — An explosion in the basement of the Sandman Signature Hotel in downtown Fort Worth on Monday blew out windows on the first and second floors of the 20-story hotel, sending debris into the streets. Multiple people were injured, with 21 hospitalized or treated on scene, according to the Fire Department and MedStar. The explosion at the historic Waggoner Building at 810 Houston St. rocked downtown shortly after 3:30 p.m. Debris was scattered hundreds of feet around the front of the building and out the rear toward Throckmorton Street. The Sandman Signature Hotel opened less th…