For common return systems, where should detectors be installed in relation to openings?

When installing detectors in common return systems, it is crucial to position them properly in relation to openings to ensure effective smoke detection. The correct distance of 12 inches is recommended from any openings, such as doors or return air grilles. This distance provides an optimal balance, allowing the detector to effectively sense smoke and potential threats while minimizing the risk of interference from airflow, which can dilute smoke concentration and delay detection.

Maintaining this 12-inch rule allows detectors to perform optimally in their intended environment, ensuring that they will activate swiftly in the presence of smoke without being prematurely triggered by normal airflow patterns through the openings. It is particularly important in common return systems where the movement of air can significantly influence the behavior of smoke within the space.