Investigators with the Middleton Fire Department say a Wednesday morning explosion in the town of Middleton was apparently caused by an accidental build-up of carbon monoxide. A vehicle had been running in the garage and the blast was set off by some ignition source. Surveillance video shows windows blowing out and a kayak being launched through a window into the yard. No one was injured. Crews from several different departments responded to the call shortly after 8:30 A-M.