NFPA 90A / IMC Section 606.4 / high-rise office Mechanical Specification

NFPA 90A

Flexible duct/air connectors are prohibited from passing through any fire-rated wall, floor, or ceiling assembly regardless of whether a fire damper is installed (NFPA 90A; IMC 603.6 echoes this). A fire damper does not make the penetration compliant. The correct approach is to run rigid sheet metal duct through the wall penetration with a properly installed fire damper, then transition to flex duct (if needed) on the room side only. (NFPA 90A caps flexible air connectors at 14 feet — it sets no 5-foot maximum on flexible duct, so length is not the issue here; the wall penetration is.)

NFPA 90A — Section 6.4 / high-rise office Mechanical Specification

The high-rise office specification requires smoke detector activation to trigger an audio/visual alarm at the control display panel in addition to system shutdown. Without the alarm indicator, building personnel may not know a smoke event occurred, delaying emergency response.

NFPA 90A / ASTM E84

This installation is compliant. NFPA 90A requires that duct insulation materials have a flame spread index of 25 or less and a smoke developed index of 50 or less when tested per ASTM E84 (Standard Test Method for Surface Burning Characteristics of Building Materials). At 20 flame spread and 45 smoke developed, this insulation meets both thresholds. These limits are especially critical in plenum spaces where fire and smoke can spread rapidly through the return air path.

NFPA 90A / NEC 725.3

Duct smoke detector shutdown must be hardwired directly to the AHU disconnect or starter, independent of the BAS. A BAS software command alone is not acceptable for life-safety shutdown because software can fail or be overridden.

NFPA 90A / NEC Article 725.3

Duct smoke detector shutdown must be hardwired directly to the HVAC equipment disconnect, independent of BAS software. A software-only alarm response means the system continues running during a smoke event if the BAS fails or the alarm is dismissed. NFPA 90A requires hardwired shutdown with audio/visual alarm at the control display panel.

NFPA 90A / NEC Article 725.3 / IBC 907.3

HVAC shutdown and smoke damper control on fire alarm must be accomplished through hardwired connections, not through BAS software commands alone. BAS software can supplement but not replace hardwired interlocks. If the BAS network fails, loses power, or has a software error, the life-safety interlock would not function. NFPA 90A requires direct hardwired shutdown independent of any programmable system.