🧠 Plain-English Highlights
• 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 req'd where indicated in 606.2.1 through 606.2.3.
Exception: detectors are not req'd 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.
Exception: return smoke detection may be omitted where served areas have area smoke detectors connected to the fire alarm and compliant with 606.4.
• 606.2.2 Common Supply and Return Air Systems
- Shared supply or return ducts/plenums must be evaluated by combined design capacity.
- If combined capacity is over 2,000 cfm, return smoke detection is req'd.
- Fan powered terminal units do not each need detectors if they are 2,000 cfm or less and shut down by an approved duct, plenum, or area smoke detection method.
• 606.2.3 Return Air Risers
- Return air risers serving two or more stories require smoke 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.
🏗️ Why it matters
Most IMC 606 comments come from unclear thresholds and detector locations. The plans may show a detector symbol, but not the system cfm, shared return condition, riser condition, upstream location, or FA exception basis.
🗺️ Where to show it
• M-001: IMC 606 basis, thresholds, and exception criteria
• M-101: detector locations in return ducts, plenums, and risers
• M-501: duct smoke detector installation and access details
• M-601: AHU / RTU / fan schedule with design cfm and detector requirement
• M-603 / FA / E: shutdown sequence and device coordination
✅ Do
• Show system cfm so the triggers are clear
• Locate return detectors upstream of filters and air connections
• Evaluate shared returns by combined design capacity
• Coordinate fire alarm interface and shutdown sequence
⛔ Don’t
• Don’t place detectors downstream of filters or outdoor air connections
• Don’t ignore common return plenums serving multiple systems
• Don’t omit riser detection where the 15,000 cfm trigger applies
🔧 Field tip
Start with the fan schedule. Flag systems over 2,000 cfm, shared return paths, and multi-story return risers. Then trace the return path before filters, outside air, exhaust connections, and equipment.
Comment “IMC606” if you want a paste-ready smoke detection systems control checklist + M-001 note set.