Class A, B, C, D, E



  • fire resistance ratings applied to building components such as doors or windows. class A is an Underwriters' Laboratories classification for a component having a 3-hour fire endurance rating; Class B, a 1 or 1-1/2-hour rating; Class C, a 3/4-hour rating; Class D, a 1-1/2-hour rating; and Class E, a 3/4-hour rating.