How many stories must a return air riser serve to require smoke detectors on each story?

The requirement for installing smoke detectors in return air risers is tied to the height of the building and the specific risks associated with multi-story structures. When a return air riser extends through three or more stories, it creates a pathway for smoke and heat to travel upwards in the event of a fire. Having smoke detectors on each story in this scenario enhances safety by ensuring that smoke is detected as early as possible, allowing for timely alerts and evacuations.

In buildings served by return air risers extending through multiple stories, the installation of smoke detectors on each floor serves to improve the effectiveness of fire protection measures, making it a crucial safety requirement. This initiative aims to provide early warning in case of a fire emanating from any of those levels. As the number of stories increases, so does the potential for a fire to spread and the necessity to have adequate detection throughout the building.

Therefore, the requirement to install smoke detectors in return air risers is correctly asserted when there are three or more stories affected, as this configuration enhances overall safety and compliance with the applicable building and fire codes.