If systems share common spaces but not common ducts and capacity exceeds 2,000 cfm, smoke detectors are __________.

In the context of mechanical systems that share common spaces but do not share common ducts and have a capacity exceeding 2,000 cubic feet per minute (cfm), the correct interpretation is that smoke detectors are not required. This is based on codes that specify the conditions under which smoke detection systems must be installed. When systems operate independently in terms of ductwork and do not present a common risk, the requirement for smoke detectors becomes less stringent.

This situation typically applies in scenarios where different mechanical systems, such as heating, ventilation, and air conditioning (HVAC), serve separate areas without interconnecting ducts. The reasoning behind this code stipulation is tied to the concept that if smoke or contaminants arise, they are less likely to spread between systems due to the absence of shared ducting, thus reducing the risk profile that necessitates mandatory smoke detection.

While each situation must be assessed carefully against specific code interpretations and local amendments, understanding that independent systems with separate pathways do not automatically invoke the smoke detector requirement is imperative for compliance and safe practice in building design and operation.