The investigation continues into the fires that caused significant damage to three buildings in Altoona over the weekend. So far no determination has been made as to the cause of the fires at two homes on Lexington Avenue and commercial structure at 18th Street and 13 Avenue. Site investigations set for today could determine if the buildings need to be torn down in the interest of public safety. The first fire, called in around 8:30 Sunday night, destroyed homes at 301 and 303 Lexington Avenue. No residents were injured but a firefighter was treated for heat exhaustion. Crews had the fire under control by 10:30 but 15 minutes later the second blaze at a commercial building at 18th Street and 13th Avenue destroyed at least two antique vehicles.