Under which condition are smoke detectors not required in air distribution systems?

Smoke detectors are primarily installed in air distribution systems to ensure that any smoke that may be present is detected promptly to enhance safety and facilitate timely evacuation or response. The correct condition under which smoke detectors are not required is when the air distribution system is incapable of spreading smoke.

This situation may arise in systems specifically designed to exhaust air out of a space without having the potential to circulate that air back to other areas, thereby limiting the risk of smoke dissemination. If an air distribution system is effectively sealed or designed in such a way that it does not allow smoke to travel through its components or into the occupied spaces, the necessity for smoke detectors in that system can be waived, as their primary purpose — to detect and alert occupants of smoke presence — is rendered unnecessary.

Other scenarios such as generating low air pressure, smoke production within enclosed walls, or lack of electrical power do not inherently affect the capacity of the system to carry smoke. Therefore, they do not eliminate the need for smoke detectors in air distribution systems that may still transport smoke even under those circumstances.