Residents in a northeast portion of Sioux Center were evacuated from their homes late Friday afternoon after an ammonia leak in the city’s industrial park. Shortly before five o’clock Friday, a cloud of ammonia had formed over a portion of the city. Sioux Center’s fire chief says when he rolled on scene, they started to spray water on the vapor cloud to knock it down. Haz mat crews from Sioux City shut off the valves inside the plant and stopped the ammonia release. The all-clear was given at about 8:15 p.m. The cause of the leak has not been determined.