Classes A, B, and C dams are defined in Section 3.4.b of Title 38 Series 4 of the Coal Related Dam Safety Rule. This is taken from the Department of Environmental Protection Division of Mining and Reclamation:

• 3.4.b.1. Class A Dams: Class A dams are those dams located in rural or agricultural areas where failure may damage non-residential and normally unoccupied buildings, rural or agricultural land, or secondary highways. Failure of Class A dam would cause only a loss of the dam itself and a loss of property use, such as use of related roads, with little additional damage to adjacent property. Any impoundment exceeding twenty-five (25) feet in height measured at the downstream toe or two hundred (200) acre-feet storage volume or having a watershed exceeding five hundred (500) acres should not be class A dam.
• 3.4.b.2. Class B Dams: Class B dams are those dams located in predominantly rural or agricultural areas where failure may damage isolated homes, primary highways, or minor railroads or may cause the interruption of public utility services. Failure of a Class B dam may cause great damage to property and project operations. Loss of human life resulting from failure of a class B dam must be unlikely.
• 3.4.b.3. Class C Dams: Class C dams are those dams located where failure may cause a loss of human life or serious damage to homes, industrial and commercial buildings, important public utilities, primary highways or main haul roads. This classification must be used if failure would cause possible loss of human life.

Mine Safety and Health Administration Hazard Ranking System

• Low Hazard Potential: Facilities in rural areas where failure would cause only slight damage, such as to farm buildings, forest, agricultural land, or minor roads.
• Moderate Hazard Potential: Facilities in predominately rural areas where failure may damage isolated homes or minor railroads, disrupting services or important facilities.
• High Hazard Potential: Facilities whose failure could reasonably be expected to cause loss of human life, serious damage to houses, industrial and commercial buildings, important utilities, highways, and railroads.