606.2.2 Common supply and return air systems.
MC § 606.2.2
Where multiple air-handling systems share common supply or return air ducts or plenums with a combined design capacity greater than 2,000 cfm (0.9 m 3 /s), the return air system shall be provided with smoke detectors in accordance with Section 606.2.1. Exception: Individual smoke detectors shall not be required for each fan-powered terminal unit, provided that such units do not have an individual design capacity greater than 2,000 cfm (0.9 m 3 /s) and will be shut down by activation of one of the following: 1. Smoke detectors required by Sections 606.2.1 and 606.2.3.
2.An approved area smoke detector system located in the return air plenum serving such units.
3.An area smoke detector system as prescribed in the exception to Section 606.2.1. In all cases, the smoke detectors shall comply with Sections 606.4 and 606.4.1.
