This part of ISO 6944 specifies a method for determining the fire resistance of vertical and horizontal ventilation ducts under standardized fire conditions. The test examines the behaviour of ducts exposed to fire from the outside (duct A) and fire inside the duct (duct B). It is intended that this part of ISO 6944 be used in conjunction with ISO 834-1. This part of ISO 6944 is not applicable to a) ducts whose fire resistance depends on the fire resistance performance of a ceiling, b) ducts containing fire dampers at points where they pass through fire separations, c) doors of inspection openings, unless included in the duct to be tested, d) two- or three-sided ducts, e) the fixing of suspension devices to floors or walls. NOTE Annex A provides general guidance and gives background information.