Two days after two city workers in Hays were killed in a trench collapse on Main Street, Hillsboro city workers were continuing their project to replace a sewer line in the alley to the west of Ash Street. Local crews have been trained to use preventive strategies, such as the steel trench box in the foreground. Workers work within the trench box, which prevent soil cave-ins such as the one that occurred in Hays. The Occupational Safety and Health Administration rules require trenches 5 feet deep or greater to have a protective system unless the excavation is made entirely in stable rock. If less than 5 feet deep, a competent person may determine that a protective system is not required.