Section 4.3.1/Duct Construction and Fire Protection
NFPA 90A Section 4.3 covers fire damper, smoke damper, and duct material requirements at fire-rated and smoke barrier penetrations.
Ducts must be constructed of materials that limit the spread of fire and smoke. Metal ducts are required for most applications. Where ducts penetrate fire-resistance-rated walls, floors, or partitions, fire dampers must be installed to maintain the integrity of the fire barrier. Smoke dampers are required where ducts penetrate smoke barriers. Duct materials within plenums must be limited to those with low flame spread and smoke development indices. Combustible materials (duct liner, insulation) within ducts must meet the flame and smoke requirements of Section 4.3.
Why this section exists
HVAC ductwork connects every room in a building through a continuous air path. Without fire protection measures, a fire in one room can spread through the duct system to every other room in the building. Fire dampers close automatically when exposed to heat, sealing the duct opening in the rated barrier. Smoke dampers close when activated by smoke detectors, preventing smoke from spreading through the duct system to remote areas of the building.
What plan reviewers look for
Plan reviewers check the mechanical drawings for fire damper symbols at every duct penetration through a fire-rated wall, floor, or partition. They verify that smoke dampers are shown at smoke barrier penetrations. They check that duct liner and insulation materials within the duct system meet the flame spread and smoke development ratings required by NFPA 90A.
Common violations
Related NFPA 90A requirements
Section 5.3 covers smoke detector requirements in duct systems. Section 4.1 covers air handling unit construction. NEC Section 300.22 covers wiring in plenum spaces. IBC Section 716 covers opening protectives including fire and smoke dampers.