Baltimore Fire Department officials were investigating a small fire that damaged the interior of a portable classroom at Carver Vocational Technical High School yesterday afternoon. Members of the school's track team had left the building moments earlier after changing out of their uniforms, a spokesman said, and no injuries were reported. Reported at 5:45 p.m., the fire broke out in a one-story, vinyl-covered, 10-classroom portable building near the rear of the school in the 2200 block of Presstman St. It was brought under control in less than 30 minutes by firefighters with about 10 pieces of fire apparatus, said Chief Kevin Cartwright, the spokesman. There was no estimate of damage to the 50-foot-by-120-foot building, Cartwright said.