Mt. Pleasant firefighters are investigating a gas line explosion that caused a small fire, Thursday. Firefighters were called to the Lexington Apartments on Deerfield Road just before 2 p.m. Crews saw light smoke coming from the rear of the building and a fire in the crawl space was extinguished quickly. There was some structural damage to the end units of the building. No one was home at the time of the explosion. Mt. Pleasant Fire and Consumers Energy believe the fire started from a damaged gas line.