UL 10C and UL 10B are two distinct fire-test standards for door assemblies used in the United States. UL 10C applies to positive pressure fire door assemblies, while UL 10B applies to neutral pressure conditions. For most modern commercial buildings, UL 10C is the required standard—and the locks ins

UL 10C is an American standard for positive pressure fire tests of door assemblies, including the locks installed within them. A UL 10C certified door lock has been independently verified to maintain its structural and functional integrity under realistic fire conditions — including the pressurized