Safety guidelines dictate that clear, solid black ice requires a minimum thickness of four inches to safely support a single human on foot. For group gatherings or small snowmobiles and all-terrain vehicles, a thickness of at least five to seven inches is recommended. When venturing out with heavy passenger vehicles, trucks, or permanent heavy fish houses, ice thickness must measure a minimum of twelve to fifteen inches or more to guarantee structural integrity and prevent breakthroughs into freezing water.