This European Standard identifies parameters that affect the fire resistance of ducts for ventilation purposes. It also identifies the factors that need to be considered when deciding whether, or by how much a parameter can be extended either positively or negatively when contemplating the fire resistance on an untested variation in the construction. This European Standard, where applicable, gives guidance on additional tests that are needed to extend the field of application. The European Standard gives the principles behind how a conclusion on the influence of specific parameters/constructional details relating to the relevant criteria (E, I, S) can be achieved. This European Standard only applies to ducts tested to EN 1366-1. Duct sections for use other than in fire resisting heating, ventilation and air conditioning (HVAC) systems are not covered by this European Standard. It does not cover ducts used for smoke control which are tested in accordance with EN 1366-8 or EN 1366-9.