An automatic fire sprinkler prevented a warehouse from becoming fully involved after a fire started outside the warehouse early Tuesday morning. Fire dispatchers received a call from a passer-by at 1:40 a.m. that flames were visible on the outside of a warehouse in the alley behind 1510 S. Main St. The alley runs between Wyoming and Utah avenues. When firefighters arrived there was fire on the outside of a large rollup door into the warehouse from the alley. The fire was beginning to burn into the warehouse. When firefighters cut through the rollup door, they found that an automatic fire sprinkler was activated and was preventing the fire from entering the building. Smoke did enter the building and firefighters were able to get it out quickly. The cause of the fire is under investigation. A damage estimate is not available. There were no reported injuries.