Plain English:
606.1 controls required
Air distribution systems must have listed/labeled smoke detectors where required.
Duct smoke detectors must comply with UL 268A. Other smoke detectors must comply with UL 268.
606.2 where required
Smoke detectors are required where indicated in 606.2.1 through 606.2.3.
Exception: not required where the air system cannot spread smoke beyond the room or space where smoke starts.
606.2.1 return air systems
Return air systems over 2,000 cfm require smoke detection.
Detectors must be in the return duct or plenum upstream of filters, exhaust air, outdoor air, decontamination equipment, and appliances.
Area smoke detection connected to FA may be used as an exception where compliant with 606.4.
606.2.2 common supply and return systems
Shared supply or return ducts/plenums are evaluated by combined design capacity.
If combined capacity exceeds 2,000 cfm, return smoke detection is required.
Fan-powered terminal units 2,000 cfm or less do not each need individual detectors if they shut down by an approved detection method.
606.2.3 return air risers
Return risers serving two or more stories require detectors at each story where any portion of the return system exceeds 15,000 cfm.
Detectors must be upstream of the riser connection to any ducts or plenums.
606.3 installation
Detectors must be installed per NFPA 72.
They must monitor the entire airflow conveyed by the system.
Access is required for inspection and maintenance.
606.4-606.4.1 controls and supervision
Detector activation must shut down all operational capabilities of the air distribution system.
If part of a smoke control system, the system must switch to smoke control mode.
Where FA is required, duct detectors generally report as supervisory signals, not fire alarm signals.
On Plans: Why it matters
Most IMC 606 redlines are coordination issues: missing cfm thresholds, detector symbols in the wrong location, no shutdown sequence, unclear FA interface, no supervisory signal note, or smoke control systems shown shutting down when they should switch modes.
Code Path: Where to show it
M-001: IMC 606 basis, thresholds, exceptions, and shutdown note
M-101: duct/plenum/riser detector locations
M-501: duct smoke detector installation and access details
M-601: AHU / RTU / fan schedule with cfm and detector requirement
M-603: shutdown sequence and smoke control mode logic
Check: Smoke Detection and Shutdown Summary
M-001 smoke detection summary must list each detector location, the duct served, design CFM, and the fire alarm panel it connects to - with fire alarm drawing cross-reference by sheet number.
Confirm the functional test requirement is stated: detector activation must trigger AHU shutdown and the test is required before occupancy.
Show the AHU shutdown wiring path on the controls sequence and confirm it is included in both the mechanical and fire alarm contract documents.
Review Risk:
AHU shutdown interlock failure at commissioning - detector activates but AHU continues running because interlock wiring was not connected - is the most common 606 commissioning failure.
Duct smoke detectors not included in the commissioning test because the fire alarm contractor was unaware of the mechanical detector locations generate a pre-occupancy hold.
Smoke detectors placed in duct locations with velocities outside the listed range (typically 300-4000 fpm) will not detect reliably - confirm the design duct velocity at the detector location.
Field Tip:
Start with the fan schedule, not the detector symbol.
Flag every system over 2,000 cfm, every shared return path, and every multi-story return riser. Then ask: where is the detector, what does it shut down, how does it report, and does smoke control change the response?
Masterbuild QA Lens
For the 606 summary, the critical close-out check is damper installation verification: confirm the damper access panel location is shown on the as-built floor plan or reflected ceiling plan, each damper has a unique tag that ties to the commissioning test record, and the fire-alarm panel sequence of operations references the mechanical damper reset sequence. Missing damper documentation is a common pre-occupancy hold.
Drawing / Submittal Check
The smoke detection summary on M-001 should list each required detector location, the duct it serves, the CFM, and the fire alarm panel it connects to. Cross-reference the fire alarm drawings by sheet number. The functional test requirement (detector activation shuts down the air handling unit) must be noted on the controls sequence - confirm the interlock is shown on both the mechanical and electrical drawings.
Common Review Risk
The smoke detection and shutdown interlock is the most common AHU commissioning failure. The duct smoke detector activates, the fire alarm panel signals the AHU to shut down, but the AHU continues to run because the interlock wiring was not connected. Confirm the interlock wiring is shown on the electrical drawings and verified during the pre-commissioning inspection.
When To Escalate
Escalate when the smoke detection and AHU shutdown interlock test fails at the final inspection - when the AHU does not shut down when the duct smoke detector activates. The interlock failure is between the fire alarm panel and the BMS or the motor control center. Resolving an interlock failure at final inspection delays the certificate of occupancy and requires coordination between at least three trades.
Duct System Coordination
Duct smoke detector compliance covers placement, sampling tube sizing, shutdown interlock, and reset access. Confirm every detector location is shown on both the mechanical duct drawing and the fire alarm system drawing.
Ventilation Coordination
For smoke detection system closeout (IMC 606): the commissioning protocol must confirm that the smoke detector shuts down the air handling unit and that the AHU restart after the event requires a manual reset. An AHU that automatically restarts after a smoke detector actuation will continue to distribute smoke. Confirm the manual-reset requirement is in the sequence of operation and is tested at commissioning.