Spot-type smoke detectors spacing in high air movement areas shall be reduced if the airflow exceeds how many changes per hour?

• A. 5
• B. 7.5
• C. 10
• D. 15

Answer: (B)

Air movement directly influences how fast a spot-type smoke detector can notice smoke. In areas with strong airflow, smoke is swept through the space quickly and can be carried past detectors or diluted, so a fire plume may not linger long enough near a detector to trigger it promptly if detectors are spaced as in low-velocity conditions. To maintain fast detection in such environments, the detector spacing is reduced once airflow becomes sufficiently high. The threshold given—when airflow exceeds 7.5 air changes per hour—tells you to tighten spacing to keep detection timely. Below that rate, standard spacing is usually acceptable because smoke stays in the detector’s vicinity longer, aiding earlier detection. In practice, this means in spaces with airflow above 7.5 ACH you’d place detectors closer together or use more sensitive or additional types of detectors to ensure reliable early warning.