IMC 606 is about one core idea: air distribution systems should not become smoke distribution systems.
Once HVAC equipment can move smoke beyond the room or space where it starts, the drawings need to show the detection location, shutdown logic, fire alarm interface, access, and exception basis clearly.
We'll cover IMC 606 in three parts:
Part 1 (606.1-606.2.3): Where smoke detection is required
Listed duct and area smoke detectors, 2,000 cfm return air threshold, common supply/return systems, fan-powered terminal unit exception, and 15,000 cfm multi-story return riser trigger.
Part 2 (606.3): Installation and detector location
Detector installation, approved sampling methods, location relative to filters, outside air, exhaust air, and access for inspection/testing/maintenance.
Part 3 (606.4-606.4.1): Controls, shutdown, and fire alarm interface
System shutdown on detector activation, fire alarm system connection, supervisory signal, and how the mechanical control sequence needs to match the fire alarm intent.
On Plans: Why it matters
Most IMC 606 comments are coordination comments. The mechanical drawings may show a detector symbol, but the fan schedule does not show cfm, the controls do not show shutdown, the FA sheets do not show the connection, or the detector is not upstream of the right components.
That is how a life-safety item turns into a permit redline.
Code Path: Where to show it
M-001: IMC 606 basis, thresholds, exception criteria, 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 / controls: shutdown sequence and BAS/fire alarm interface
FA / E sheets: fire alarm connection, supervisory signal, remote indicator/test station where required
Check: Smoke Detector Coordination
M-001 must list every duct-mounted smoke detector and cross-reference the fire alarm drawings by sheet number.
Duct smoke detector locations must appear on both the mechanical duct plan and the fire alarm drawings - locations not on both sets will not be included in the commissioning test matrix.
Confirm the AHU shutdown sequence is shown on the mechanical sequence of operations and referenced in the fire alarm drawing notes.
Review Risk:
Duct smoke detectors not cross-referenced on the fire alarm drawings are not included in the commissioning test matrix - an AHU shutdown that was never tested will not be confirmed until occupancy.
AHU shutdown wiring not confirmed between the mechanical controls contractor and the fire alarm contractor is the most common integration gap on HVAC systems.
Duct smoke detectors in inaccessible locations without confirmed access panels generate a pre-occupancy comment - show access panel locations at each detector.
Field Tip:
Start every IMC 606 review with the fan schedule. Flag systems over 2,000 cfm, shared return paths, and multi-story return risers. Then trace the return air path before filters, outside air connections, exhaust air connections, and equipment. The detector location should make sense before the symbol ever hits the plan.
Masterbuild QA Lens
Fire and smoke dampers are life-safety items - wrong placement or missing documentation triggers AHJ holds that cannot be resolved in the field. Before submittal, confirm: every rated assembly penetration is marked on the floor plan with a damper type and UL listing reference, the damper schedule includes access panel location, actuator type, and resetting method, and coordination with the fire-alarm sequence of operations is noted.
Drawing / Submittal Check
M-001 must list every duct-mounted smoke detector on the project and cross-reference the fire alarm drawings. The duct smoke detector locations must appear on the mechanical drawings (reflected ceiling plan or duct plan) and on the fire alarm drawings. Confirm the sampling tube orientation matches the duct airflow direction - a backwards sampling tube is a functional test failure.
Common Review Risk
Duct smoke detectors that are not cross-referenced on the fire alarm drawings are not included in the fire alarm commissioning test. A mechanical smoke detector that is not in the fire alarm test matrix will not be confirmed to shut down the air handler when it activates. Confirm every duct smoke detector is on the fire alarm riser diagram and in the commissioning test sequence before the fire alarm permit is filed.
When To Escalate
Escalate when the duct smoke detector is specified but the fire alarm contractor has not confirmed they will include it in the fire alarm permit and commissioning scope. A duct smoke detector that is installed by the mechanical contractor but not in the fire alarm contractor's scope will not be included in the fire alarm commissioning test. The mechanical contractor installs the device; the fire alarm contractor commissions it - confirm both are aware of their scope.
Duct System Coordination
Smoke detection in duct systems triggers at system airflow thresholds and duct dimension thresholds - both must be checked. Identify which air handlers require duct smoke detectors before routing control wiring.