To determine the fire resistance of ducts (without the aid of fire dampers) passing through or between compartments, the system should normally be tested to EN 1366-1: Fire resistance tests for service installations - Ventilation ducts, and classified in accordance with EN 13501-3 for ventilation ducts or EN 13501-4 for smoke extract ducts. Type A ducts are covered under EN 13501-3, this is the least onerous specification and provides protection from fire outside the duct.