Firefighters doused a commercial structure fire early Monday afternoon in the 2900 block of Race Street in northeast Fort Worth.The blaze was reported at 1:27 p.m. The location was northeast of the intersection of North Sylvania Avenue and East Belknap Street.Capt. Tom Crow, fire department spokesman, said the building complex was similar to a strip center, with several units connected. He said the fire started in a unit that was being used to store equipment."Fire crews arrived on scene with heavy smoke and fire showing," he said.They requested a second alarm at 1:40 p.m. More than two dozen units responded, according to fire department records.The fire was under control shortly after 2 p.m., records show."The fire caused heavy damage to two of the four units involved in the fire," Crow said. "The remaining units sustained moderate smoke damage."The cause of the fire was still under investigation Monday afternoon, Crow said. The estimated cost of the damage also was unavailable."This is going to be undetermined for awhile," Crow said. "There was a lot of equipment in there."