The Huntington Fire Department is investigating a vacant building fire as arson. The fire happened about 2 a.m. Thursday at a garage in the 600 block of Fifth Avenue. Firefighters said the building was fully engulfed in flames when they arrived. The building collapsed, and the fire was put out about two hours later. Investigators said information given to them by witnesses lead them to believe the fire was a result of arson. No injuries were reported.