National Air Duct Cleaners Association (NADCA) Practice Test

Materials used in duct access doors are evaluated under fire safety rules specific to HVAC systems. NFPA 90B sets the requirements for installing warm-air heating and air-conditioning systems, including how the materials in ducts and their access doors must be classified for flammability to minimize flame spread and smoke within the ductwork. This standard directly governs what flammability ratings those door materials must have. NFPA 70 addresses electrical safety, which is not about duct material flammability. UL 94 is a flammability test method for plastics, but the formal classification used for duct components in installation standards comes from NFPA 90B. The International Building Code may reference NFPA 90B, but the classification itself is determined by NFPA 90B.