Class A (3 hour) – openings in firewalls that divide a single building into fire areas.
Class B (1-1/2 hour) – openings in enclosures of vertical shafts and stairwells through buildings and in 2-hour rated partitions providing horizontal fire separations.
Class C (3/4 hour) – openings in walls or partitions between rooms and corridors having a fire resistance rating of 1 hour or less.
Class D (1-1/2 hour) – openings in exterior walls subject to severe fire exposure from outside the building.
Class E (3/4 hour) – openings in exterior walls subject to light to moderate fire exposure from outside the building.